1967 - NASA · 2017-06-27 · ABSTRACT The observations reported herein were made with the University of Iowa Injun IV satellite which was launched on 21 November 1964 into a nearly

~~~ ~

U. of Iowa 67-29

Geomagnetically Trapped Alpha Particles * , -

by --

S. M. Krimigis and J. A. Van Allen

e----

- Depa-t of Physics and Astronomy. /University of Iowa

Iowa City, Iowa _._

July 1967

* Research supported in part by National Aeronautics and Space Administration Grant NsG 233-62 and Contract Nul-2973 with the Langley Research Center and by Office of Naval Research Contract Nonr 1509( 06).

https://ntrs.nasa.gov/search.jsp?R=19670026791 2020-04-19T04:30:17+00:00Z

ABSTRACT

The observations reported herein were made with the

University of Iowa Injun I V s a t e l l i t e which was launched on

21 November 1964 i n t o a near ly polar o r b i t of 81" i nc l ina t ion

with i n i t i a l apogee and perigee a l t i t u d e s of 2502 and 527 k i lo -

meters, respect ively.

depleted s i l i con surface b a r r i e r detector with four e lec t ronic

discrimination leve ls . The two lower l e v e l s a r e sens i t ive t o

protons 0.52 < E < 4.0 MeV and 0.90 < E

The two upper l eve l s a r e sens i t ive only t o nuc le i heavier than

It ca r r i ed a 25 micron th ick , t o t a l l y

< 1.8 MeV, respect ively. - P - - P -

deuterons and, spec i f i ca l ly , a re sens i t ive t o alpha p a r t i c l e s

2.09 5 E,< - 1 5 MeV and 3.89 - < E, - <

Study of the avai lable data up t o 17 April 1965 leads t o the

7 MeV, respect ively.

following conclusions:

(a)

establ ished.

(b) A t constant 1 B 1 z 0.19 gauss the maximum i n t e n s i t y

perpendicular t o B occurs a t L = 3.1.

The presence of geomagnetically trapped alpha p a r t i c l e s i s

4

+ The absolute d i r ec t iona l

i n t ens i ty there i s

2 -1

2 -1

j a (Ea 7 2.09 MeV) = 28 (em sec sr) and

j a (E, > 3.89 MeV) = 4.5 (cm see sr) .

3

( c )

i n t e n s i t i e s of alpha p a r t i c l e s and of protons, both in tegra ted

above the common value ea = 8

A t t h i s outer zone maximum, the r a t i o of the d i rec t iona l

= 0.52 MeV/nucleon, i s P

-4 ja/jp = (2 .3 - + 0.2) x 10 .

(d) A va r i e ty of considerations, no one of which i s decisive,

suggest t h a t the most physical ly s ign i f icant form of the spectra

of alpha p a r t i c l e s and protons may be an exponential one i n terms

of energy/nucleon.

( e ) It appears conceivable that the observed r a t i o j / j

be reconcilable with a solar-wind-source of outer zone protons and

alpha p a r t i c l e s although t h i s r a t i o i s s ign i f i can t ly l e s s than t h a t

pred ic ted from diffusion theory with known loss processes taken

may a P

i n t o account.

( f )

markedly a f t e r the magnetic storm of 18 April 1965 and the i n t e n s i t y

peak moving inward from L = 3.1 t o L = 2.9.

(g )

due t o a d i f f e ren t source than tha t f o r those i n the outer zone.

The d i s t r ibu t ion of outer zone alpha p a r t i c l e s w a s changed

Trapped alpha p a r t i c l e s i n the inner zone a re apparently

4

1. INTRODUCTION AND SUMMARY

Studies over the p a s t several years have shown t h a t the

geomagnetically trapped r ad ia t ion cons i s t s dominantly of protons

and e lec t rons having energies from a few eV t o many MeV. Several

inves t iga tors have searched f o r p a r t i c l e s heavier than protons

using nuclear emulsions. Freden and White [ 19601 i d e n t i f i e d f i v e

t r i t o n t r acks i n the energy range 126 t o 200 MeV and one deuteron

t r a c k in recovered emulsions flown on two rockets through the lower

edge of the inner r ad ia t ion zone. The t o t a l number of proton t r a c k s

i n a comparable energy range w a s 496. In two similar f l i g h t s of

emulsions Heckman and Armstrong [1962] found five deuteron t r acks i n

the energy range 93 t o 133 MeV and no t r i t o n t r acks out of a t o t a l

of 788 t r acks studied, the other 783 t r acks being i d e n t i f i e d as due

t o protons. Neither of these groups reported the presence of helium

nuclei , although t h e i r absence w a s no t considered surpr i s ing , i n

view of the high energy thresholds of the de tec tors f o r alpha

p a r t i c l e s and the l imi t ed s t a t i s t i c a l sample. Heckman and Armstrong

set an upper l i m i t of 1 x for the i n t e n s i t y r a t i o of alpha

p a r t i c l e s t o protons i n the energy i n t e r v a l 125 t o 185 MeV. In

a l a t e r emulsion experiment Naugle and Kniffen [1963] placed an

upper l i m i t of 6 x f o r i n t e n s i t y r a t i o of a l l p a r t i c l e s

heavier than protons t o protons i n the energy i n t e r v a l 12 t o

5

30 MeV/nucleon (Ea > 50 MeV), a t a l t i t udes up t o 2000 km i n the

region 1.45 < L < 1.85.

A l l of the r e s u l t s quoted so f a r were obtained f o r

L < 1.85, i . e . , i n the inner zone. More recent ly Fenton [1967]

has searched fo r alpha p a r t i c l e s i n the region 1.6 < L < 3.3

using a so l id s t a t e de tec tor telescope on OGO-I. On the bas i s of

what he judges t o be an e s sen t i a l ly null r e s u l t , he suggests an

upper l i m i t f o r the alpha p a r t i c l e t o proton i n t e n s i t y r a t i o i n

the in t e rva l 26 t o 85 MeV/nucleon o f 6.7 x

- -

In t h i s paper we report the r e s u l t s of an extensive search

f o r geomagnetically trapped nuclei heavier than deuterons i n the

energy range 0.52 - - < E < 4

roughly two orders of magnitude below the regions previously

invest igated.

reported e a r l i e r [Van Allen and Krimigis, 1965; Krimigis and

Van Allen, 1966; Krimigis, Van Allen, and Armstrong, 19671.

found t h a t ( a ) trapped nuclei heavier than protons a re present

with mewurable i n t e n s i t y i n the e a r t h ' s rad ia t ion zones; ( b ) the

maximum i n t e n s i t y of such pa r t i c l e s occurs a t L - - 3.1; ( c ) the

observed p a r t i c l e s a re most reasonably i d e n t i f i e d a s alpha

p a r t i c l e s ; (d ) the i n t e g r a l i n t ens i ty r a t i o j / j f o r energies

-4 >0.52MeV/nucleon i s - 2 x 10

r e s u l t independent of the respective energy spectra; and ( e ) some

information on the a -pa r t i c l e energy spectrum i s obtained.

MeV/nucleon, an energy region which i s

Preliminary r e su l t s of t h i s experiment were

It i s

a P a t L - - 3.1 and 131 = 0.19 gauss, a

c

6

The significance of these observations l i e s i n the f a c t

t h a t , although the i n t e n s i t y and energy spectrum of trapped protons

E

cosmic r ay albedo neutron hypothesis, protons of energy below

30 MeV and down t o 0.1 MeV o r l e s s cannot possibly be a t t r i b u t e d t o

,> 30 MeV can be reasonably accounted f o r on the bas i s of the P

the albedo-neutron source. Such lower energy protons a re commonly

thought t o be due t o in j ec t ion of solar wind p a r t i c l e s i n t o the

magnetosphere and subsequent accelerat ion and d i f fus ion across

magnetic s h e l l s therein. Other conjectures a t t r i b u t e t h e i r

presence (a) t o the d i r e c t magnetospheric capture of so la r cosmic

rays; (b) t o the decay of neutrons produced i n the polar cap

atmosphere by so lar cosmic rays; and ( c ) t o the i n s i t u accelerat ion

of p a r t i c l e s which a re a component of the e a r t h ' s own exosphere.

Thus, the spec ia l motivation f o r study of trapped nuc le i

--

having Z > 2 i s t o provide a s e t of parameters on one o r more

" t racer" components of the rad ia t ion b e l t s f o r t e s t i n g the v a l i d i t y

-

of hypotheses on t h e i r o r ig in and on the o r ig in of the much more

abundant proton component.

' I

2. DESCRIPTION OF THE DETECTOR

The observations reported hcrcin WE.Y'C obtained with the

Universi ty of Iowa z a t e l l i t e Injun I V . Thc relevant de tec tor i s

a t o t a l l y depleted s i l i c o n one of t h e surface b a r r i e r kind i n t h e

form of a t h i n c i r c u l a r disc, whose thickness i r , 75 micron:; and

whose f r o n t a l a rea i s 1.75 - + 0.2 mm

The de tec tor i s loca ted in s ide a conical coll imator with a f u l l

ver tex angle of 40" and i s otherwise sht-ilded by a minimum of

2 (Nuclear Diodes, Inc . ) .

2 10.2 g/cm

protons (Figure 1). Four e lec t ronic discr iminat ion l e v e l s a r e

provided.

protons and heavier .nuc le i and the l a s t two (channels C and D) a r e

s e n s i t i v e only t o p a r t i c l e s heavier than deuterons (Table 1).

The scheme f o r energy discrimination i s i l l u s t r a t e d i n

Figure 2. The m a x i m u m energy tha t an a x i a l l y inc ident proton

can deposit i n t h e de tec tor i s 1.3 MeV. Since t h e energy needed

t o t r i g g e r channel C i s 1.8 MeV, only p a r t i c l e s t h a t a r e heavier

t han protons are counted i n channel C .

range-energy curves f o r deuterons, t r i t o n s , He , and He shows

t h a t channel C w i l l c l e a r l y count He3 and He4 (as well as nuc le i

having g rea t e r Z), may j u s t barely count t r i t o n s i n a narrow

energy range, bu t w i l l not count deuterons. Similar ly t h e energy

of brass , which corresponds t o the range of 95, MeV

The f i r s t two (channels A and B) a r e s e n s i t i v e t o

An examination of the

3 4

-

a

t h a t must be deposited i n t h e de tec tor t o t r i g g e r channel D i s

3.7 MeV; hence only He , He , and heavier nuc le i can be counted by

t h i s channel.

3 4

The ca l ib ra t ion method used i s i d e n t i c a l t o t h a t described i n

d e t a i l elsewhere f o r similar de tec tors from t h i s labora tory [ Krimigis

and Armstrong, 19661.

t h e Naval Research Laboratory's Van de Graaff acce lera tor (courtesy

of E . Wolicki) i n order t o determine t h e e f f i c i ency of channels C

and D for protons whose t o t a l energy was s u f f i c i e n t t o t r i g g e r

t hese channels, i f f o r some spurious o r unsuspected reason these

protons were able t o deposi t enough energy i n the de tec tor t o

ac tua l ly do so. The de tec tor , connected t o f l i g h t e l ec t ron ic s , was

placed i n a beam of 1.8 MeV protons and the outputs of channels A

( s ens i t i ve t o protons) and C were recorded.

e f f ic iency of channel C f o r counting protons of t he above energy,

given by C/A, w a s 3 x lom4 with an accuracy of 10%.

w a s repeated a t proton energ ies of 1.9, 2.05, and 3.57 MeV.

e f f ic iency remained approximately constant as a funct ion of energy a t

the value of - 3 x 10 . The constancy of the e f f i c i ency with energy

ind ica tes t h a t the counts seen i n channel C may have been due t o s t r ay

alpha p a r t i c l e s o r heavier nuc le i t h a t had en tered the se l ec t ing

magnet i n the acce lera tor with the same momentum/unit charge as the

protons.

I n addition, a spec ia l t e s t run was made on

It w a s found t h a t t he

The experiment

The

-4

I n a t y p i c a l Van de Graaff acce le ra to r , t he "puri ty"

9

3 of' the proton beam i s usua l ly no b e t t e r than 1 p a r t i n 10

[ R . R. Carlson and E. Norbeck, pr ivate communication].

The i n t e r p r e t a t i o n of t h e channel C counts as due t o s t r a y

alpha p a r t i c l e s i s supported by the f a c t t h a t a subsequent experi-

ment using t h e f l i g h t spare u n i t gave an ef f ic iency of - 5 x 10-', near ly a f a c t o r of' t e n less than t h a t found fo r t h e € l i g h t u n i t .

(The two units were accurately similar.) It was es tab l i shed t h a t

during t h e t h r e e months previous t o t h e pcrformance of t h e second

experiment, no helium gas had been used i n t h e Van de Graaff

[E . Wolicki, p r i v a t e communication] so t h a t t h e proton beam was

presumably more pure. The foregoing supports t h e b e l i e f t h a t t he

proton e f f i c i ency of channel C may be considerably l e s s than

3 x nonetheless w e w i l l adopt t h i s number as an

upper l i m i t f o r t h e purposes of t h i s paper.

The proton e f f i c i ency of channel D, measured i n a s imi l a r

manner as t h a t of' C, was found t o be <, 1 x

Knowledge of t h e in - f l i gh t operat ion of t h e de tec tor and t h e

associated e lec t ronics i s obtGned by means of a permanently

mounted Am241 source of a -par t ic les . The source was gold-plated

t o obta in a f a l l i n g spectrum between 0.5 MeV and 3.9 MeV and thus

t o provide an i n - f l i g h t measure of t h e s t a b i l i t y of t h e system and

95

10

i n par t icu lar t h a t of t h e e f f ec t ive discr iminat ion l e v e l s .

example, a 40% increase i n t h e background r a t e of de tec tor C r e s u l t s

from lowering its discr iminat ion l e v e l from 1.8 t o 1 . 4 MeV. Yet no

departure of i t s i n - f l i g h t background r a t e (over t h e polar caps) by

as much as - + 5% has been observed during t h e per iod of t h e observa-

t i o n s on which t h e present paper i s based.

t h e detector and a s t rong developmental e f f o r t on making t h e e n t i r e

system insens i t i ve t o va r i a t ions i n temperature and supply vol tage

contr ibute t o t h e s t a b i l i t y and t rustworthiness of t h e de tec tor .

For

The t o t a l deple t ion of

None of t h e channels A, B, C, and D i s sens i t i ve to g a l a c t i c

cosmic rays.

11

3. DATA ANALYSIS

The Injun I V s a t e l l i t e was launched on 2 1 November 1964 i n t o

a near ly polar o rb i t of 81" incl inat ion, with i n i t i a l apogee

a l t i t u d e of 2502 kilometers and perigee a l t i t u d e of 527 kilometers.

The s a t e l l i t e i s equipped with a permanent magnet and energy-

d i s s ipa t ing hys te res i s rods s o t ha t it w i l l maintain a p a r t i c u l a r

axis continuously aligned with the l o c a l geomagnetic f i e l d vector.

Due t o a l a rge i n i t i a l angular veloci ty at launch and weak damping,

magnetic alignment did not occur u n t i l t h e l a t t e r p a r t of February

1965.

t a ined continuously perpendicular (+lo") - t o t h e l o c a l magnetic f i e l d

vector so t h a t t h e detector was receiving p a r t i c l e s whose p i t c h

angles were 90" - + 30". paper was obtained during t h e period 1 March t o 17 April 1965.

Auxiliary d a t a on angular d i s t r ibu t ions were obtained during t h e

tumbling period i n December 1964 and January-February 1965.

aux i l i a ry observations a re of importance i n es tab l i sh ing t h e

v a l i d i t y of our i n t e rp re t a t ion of detector responses.

Thereafter, t h e axis of the de tec tor coll imator was main-

The primary body of da ta reported i n t h i s

These

A l l telemetered da ta from the s a t e l l i t e are merged with t h e

o r b i t parameters I i n t o subsets spec i f ied by selected ranges of 15 1 and L.

i n t e r v a l used i n t h i s study i s 0.1 and t h e 15 I i n t e r v a l

1 L, and loca l t ime and subsequently sor ted

The L

12

0.02 gauss. For a given L i n t e rva l , the d i rec t iona l i n t e n s i t y

perpendicular to i s p lo t t ed as a ?unction of I ?I I . From a

family o f such p lo ts , a graphical display i s made of constant

i n t ens i ty contours i n + I B I , L space.

13

4 OBSERVATIONS

I n Figure 3, t h e counting ra tes of channels C and D as a

function of L axe shown fo r a constant value of 1 1 . The da ta

a re averaged over t h e time p e r i o d 1 Mach t o 17 April 1965. The

l a t t e r date was chosen as a cutoff da te because a severe magnetic

storm which occurred on t h a t day perturbed t h e d i s t r ibu t ions of

both protons and heavier pa r t i c l e s [Krimigis, 1967a]. The

counting r a t e s due t o t h e in f l igh t source a re indicated by t h e

dashed l i n e s . The e s s e n t i a l features of t h e f igu re may be

summarized as follows:

L = 3.1 - + 0.1 fo r both channels C and D. (b) The counting r a t e s

a re roughly constant from L = 1.3 t o L = 2.6 but r i s e sharply i n

the L i n t e r v a l 2.6 t o 3.1.

m i n i m u m a t t h e point of m a x i m u m counting r a t e and increases

s ign i f i can t ly on e i t h e r side, although it remains constant

(within s t a t i s t i c a l uncertainty) i n the inner zone.

counting r a t e s a re indistinguishable from background fo r

L > 4.3 fo r C and fo r L

r a t e s correspond t o i n t e n s i t i e s of 4.5 (em

1 .5 (em2 see s r ) - l fo r channels C and D, respect ively.

Figure 4 t h e counting r a t e vs L p ro f i l e at a constant

shown fo r channel A, responding t o protons i n t h e energy

(a) The pr inc ipa l maximum occurs a t

(e) The r a t i o C/D has a r e l a t i v e

(d) The

3.9 for D. The threshold counting ry

2 see sr)-l and

I n

15 I i s

14

i n t e rva l 0.52 < E

MeV/nucleon).

i n t ens i ty occurs a t the same L value f o r both A and C, there e x i s t

important d i f fe rences i n the nature of the two p r o f i l e s .

counting r a t e of channel A increases smoothly i n the L i n t e r v a l

< - P - 4 MeV, and f o r channel C (0.52 - < E, - < 4

It i s seen t h a t , although the poin t of maximum

The

1.1 t o 2.6 by a f a c t o r of over lo3, whereas the counting r a t e of

C changes by l e s s than a f a c t o r of two i n the L i n t e r v a l 1 .3 t o

2.6. However, i n t he L range 2.6 t o 4 . 2 the r a t i o A/C i s

approximately constant.

channels C and D may be divided i n t o two d i s t i n c t i v e l y d i f f e r e n t

regions namely L - < 2.6 ( r e f e r r e d t o henceforth as the inner

zone, i n rough analogy t o the usual terminology) and L - > 2.6

( the outer zone).

supported by p l o t s of constant i n t e n s i t y coutours i n 2 , L space (Figures 5 and 6) .

both channels C and D exh ib i t r e l a t i v e maxima a t L - - 2.0.

The pr inc ipa l maxima occur a t L - 3.1.

Thus it appears that the responses of

The v a l i d i t y of t h i s impression i s f u r t h e r

4

It i s seen t h a t a t constant 1 B 1 ,

Thus, t h e data suggest t h a t t h e responses of de tec tors C

and D are due t o d i f f e r e n t causes i n t h e two d i f f e r e n t regions, t h e

inner and outer zones.

It i s important t o note t h a t t h e d i s t r i b u t i o n s of 0.5 MeV

and 0.9 MeV protons obtained from channels A and B of t h e same

detector do not exhib i t such “double-peaked” i n t e n s i t y p r o f i l e s

[Krimigis , 1967bI.

15

The nature of t he responses of C and D i n t h e two d i f f e r e n t

regions i s now examined fur ther i n two ways:

(a) During t h e magnetically aligned period, t h e I B' 1 dependence of t h e counting rates at constant L i s p lo t t ed .

(b) During the per iod before t h e s a t e l l i t e was magnetically

aligned, t he angular dependence of t h e counting r a t e s at constant L

and constant

B and the ax i s of the detector. The a t t i t u d e of the s a t e l l i t e with

respect t o B' i s measured continuously by a system of Schonstedt

+ 1 B I i s plot ted, i . e . , t h e dependence on the angle between -.t

magnetometers.

A. Inner Zone

Figure 7 shows t h e counting r a t e s of channels A (protons

< 4.0 MeV), B (0.90 < E < 1.8 MeV), and C and

1 B 1 f o r L = 1.55 + 0.15.

having 0.52 < E

D as a funct ion of

of C and D decrease monotonically with increasing

genera l ly similar t o t h e counting r a t e s of A and B. The s i m i l a r i t y

i s f u r t h e r enhanced when t h e ne t counting r a t e s a re p l o t t e d

( i . e . , a f t e r subtract ion of t h e appropriate r a t e s of t h e i n - f l i g h t

ca l ib ra t ing source).

- P - - P - 4

The counting r a t e s - + 1 B 1 i n a manner

-

Figure 8 shows t h e angular dependence of t h e counting r a t e of

channel C, averaged over t h e L i n t e rva l 1.3 t o 1.7 and t h e

i n t e r v a l 0.10 t o 0.20.

a x i s of the de tec tor and the l o c a l magnetic f i e l d vector.

i s defined as equal t o zero when the coll imator axis i s p a r a l l e l

1 B' I Symbol cp denotes the angle between the col l imator

This angle

+ the 1 B 1 vector i n the northern hemisphere, i . e . , the de tec tor i s

pointing toward the ea r th . The counting r a t e curve appears t o have

two d i s t i n c t components, one having a maximum a t cp = go", with a f u l l

width a t ha l f maximum of 'jl 60°, and a second having a maximum a t

cp = 0" and probably a l s o a t 180".

i s based was d i s t r i b u t e d more-or-less uniformly over the

specif ied.

the low end of the range and may therefore be somewhat high ( c f .

Figure 7 ) .

Most of the data on which Figure 8 4 1 B 1 range

However, the poilit a t cp = 10" was based mainly on da ta i n

(The counting r a t e of channel D i s t o o low t o permit a

s ign i f icant angular ana lys i s . )

The s ignif icance of Figures 7 and 8 i s developed i n a l a t e r

section.

B. Outer Zone

4

Figure 9 shows t h e 1 B I dependence of t h e counting r a t e s of

detectors A, By Cy and D fo r a constant L at t h e counting r a t e

m a x i m u m i n t h e cu te r zone ( c f . Figures 3 and 4) . funct ional s i m i l a r i t y of t h e four curves i s evident.

shows t h e cp dependence of t h e counting r a t e of channel C at

constant L and 1 B I near t h e outer zone maximum. This curve i s

s imilar t o t h a t of Figure 8 i n t h a t it shows a s t rong maximum at

Again, t h e

Figure 113

4

= 90" but it i s decidedly d i s s imi l a r f o r 'p < 50". Speci f ica l ly ,

t h e r e i s a complete absence o f counts f o r 30" < cp < 0", desp i t e t h e

f a c t t ha t t h i s angular region was sampled repeatedly.

I ,

5. CONSIDERATION OF SPURIOUS EFFECTS

The data shown i n sect ion 4 e s t a b l i s h that the counting r a t e s

of C and D a r e due t o geomagnetically trapped p a r t i c l e s and not t o

g a l a c t i c cosmic rays, f o r example.

A s shown i n Table 1 and discussed i n sect ion 2, channel C

responds idea l ly , only t o t r i t o n s and heavier nuclei , and channel D

only t o He3 and heavier nuclei .

Nonetheless, there a re many physical processes which may con-

ceivably cause counts i n channels C and D and thus inva l ida te a simple

minded in t e rp re t a t ion . After a preliminary s i f t i n g of a l l such pro-

cesses t h a t we have been able t o think o f , we have a r r ived a t the

following l i s t as worthy of de ta i led quant i ta t ive assessment:

(1) Proton pulse pile-up.

(2) Transverse penetrat ion of the de tec tor by high energy

protons ( E > 95 MeV). P -

( 3 ) E l a s t i c sca t te r ing (and hence g rea t e r pa th length i n

de tec tor ) of protons enter ing through the coll imator.

(4) I n e l a s t i c nuclear in te rac t ions of protons i n the de tec tor

and i n o ther mater ia l of the s a t e l l i t e .

( 5 ) E f fec t s of e lec t rons .

The importance of each process v a r i e s with pos i t ion . Thus,

processes (1) and (3) a re more important i n the outer zone than i n

18

the inner zone, whereas processes (2), (4), and ( 5 ) are more

important i n the inner zone. We now consider each of these processes

i n de t a i l .

(1) Proton pulse pile-up.

Whenever two protons, the sum of whose energies deposited

i n the de tec tor exceeds 1.8 MeV, s t r i k e the de tec tor within a s u f f i -

c i en t ly short t i m e i n t e r v a l t h e i r pu lses add up e l e c t r o n i c a l l y so

as t o t r i gge r t he 1.8 MeV discr iminat ion l e v e l (channel C )

(Figure 2) . ("spuriously") t o t h e counting r a t e of C.

a r e both counting protons, we have a continuous knowledge of t h e

Any such acc identa l double coincidences cont r ibu te

Since channels A and B

i n t e n s i t y and t h e spectrum of protons i n t h e r ad ia t ion zones.

Channel B counts protons i n t h e i n t e r v a l 0.90 < E

and we may use i t s counting r a t e t o es t imate t h e expected counting

< 1.8 MeV - P -

ra te of C due t o double coincidences.

Pulses from t h e de tec tor a r e double-delay-line cl ipped and

have a rectangular p r o f i l e whose t i m e width

7 = 0.10 FS.

The r a t e of acc identa l double coincidences

where R1 i s the r a t e of s ing le s and K2 i s a f a c t o r which must

be l e s s than 2.0. I n labora tory t e s t s on a number of u n i t s

s i m i l a r t o t h a t flown on Injun I V , including t h e f l i g h t back-up

u n i t , equation (1) has been found t o be accurately va l id .

both p a r t i c l e s and a laboratory double-pulse generator t h e

value of K2 I- has been determined t o l i e between 0.08 and 0.12 ps.

Using

Hence, we take % = 1.0, T = 0.10 ps and estimate R2 i n f l i g h t by

t h e equation

(2) 2 R2 = 7 R1 .

The highest value of R2 i s expected at t h e outer zone m a x i m u m

of proton i n t e n s i t y (cf . Figure 4 ) .

t h e approximate constancy of t h e counting r a t e ra t ios A / C and

B/C i n t h e range 2.6 < L < 4.2 (Figures 4 and 9) t h a t the r a t e of C i s

- not a quadratic function of t h e r a t e of e i t h e r A or B.

quant i ta t ive estimate of R2 i s as follows.

At L = 3.05, 1s I = 0.19

It i s already evident from

A

A = 800 counts/sec

B = 230

c = 0.2

Since the sum of two pulses l a r g e enough t o t r i g g e r C must come

from s ingle pulses laxge enough t o t r i g g e r B (Figure 2 and

Table l), we ca lcu la te t he spurious r a t e o f C t o be

20

R2 = 5 x IO-’ counts/sec

This i s l e s s by a f ac to r of 40 than t h e observed r a t e of C .

The r a t e of acc identa l t r i p l e coincidences

2 3 R3 = K 3 7 R1 (3)

where K1; i s also of t h e order of un i ty .

obtained by supposing t h a t all pulses l a rge enough t o t r i g g e r A can

combine by th rees t o t r i g g e r C . Using equation (3), t h e estimated

contribution of acc identa l t r i p l e coincidences t o t h e r a t e of C i s

A high est imate of R, i s 1 J

-6 2 3 = (0.i x 10 ) (800)

= 5 x 10 counts/sec, -6 R3

R3

-5 a value much l e s s t han R2, and l e s s t han C by a f a c t o r of 2.5 x 10 . A more rigorous est imate of R 2 can be made as follows.

Channel B responds t o protons i n t h e energy range 0.90 < E - P -

and the maximum stopping power of t h e de tec tor f o r protons i s 1 .3 MeV.

The observed proton energy spectrum at t h e outer zone i n t e n s i t y

m a x i m u m [Krimigis, 1967b] i s

< 1.8 MeV

I *

21

4 - = d j 1.4 x 10 exp (-E/O.30 MeV) counts (see MeV)-l .

Using t h i s spectrum and pa i r ing protons over t h e e n t i r e energy

range ( i . e . , 0.5 MeV with 1.3 MeV, 0.8 MeV with 1.0 MeV, e tc . ,

such t h a t t h e sum of t he pulse height i s always g rea t e r than

1.8 MeV), we find

for t h e accidental double coincidence r a t e of C. Although some-

what l a r g e r than t h e simpler, more d i r e c t estimate given above, t h i s

r a t e i s s t i l l l e s s than t h e observed r a t e of C by a f a c t o r of 27.

F ina l ly w e note t h a t t h e contribution of acc identa l coinci-

dences t o t h e - r a t e of channel D i s a l s o negl ig ib le s ince t r i p l e

coincidences of 1.3 MeV pulses (the l u g e s t possible from s t r a i g h t -

forward penetrat ion of t h e detector) are necessary (and bare ly

adequate) t o produce counts i n D.

We conclude t h a t nowhere i n e i t h e r t h e outer or inner

r ad ia t ion zones can a s ign i f i can t f r a c t i o n of t h e observed counting

r a t e s of e i t h e r C or D be due t o accidental coincidences of proton

pulses .

22

(2) Transverse penetrat ion of the de tec tor by high energy protons.

The s i l i c o n de tec tor i s a th in , approximate1.y c i r c u l a r d i sc

2 of thickness 2.5 x

(350 mg/cm ). The f l a t faces of the d i sc a r e perpendicular t o the

a x i s of the coll imator. The r a t i o of the f r o n t a l t o the pro jec ted

cm (5.83 mg/cm ) and diameter 0.15 cm

2

l a t e r a l a rea i s 4'7.

The design of the brass col l imator i s such t h a t it provides

-2 essen t i a l ly uniform shielding of 10.2 g cm

except w i t h i r i E cmiczll c o x of half-a~gle 29" centered sn i t s a x i s

(Figure 1).

over about 8 s te rad ians

Over the remainder of the s o l i d angle the de tec tor i s

more heavily shielded, both by l o c a l mater ia l and by the s a t e l l i t e

i t s e l f . Thus, only protons whose o r ig ina l energy exceeds 95 MeV

a re able t o reach the de tec tor through the sh ie ld . Such protons a r e

present only i n the inner r ad ia t ion zone and have an angular d i s t r i -

bution which i s sharply peaked a t a p i t c h angle of 90" t o 3. 4

( A proton which t r ave r ses the de tec tor along a diameter can lose a

mximum of 1 5 MeV the re in . ) 3y v i r t u e of the d isc- l ike angular

d i s t r ibu t ion , the contr ibut ion of pene t ra t ing protons i s a maximum

a t cp = 0" and 180" and i s estimated t o be l e s s by a f ac to r of 4 t o 8

a t cp = 90".

kind i n the inner zone ( i n cont ras t t o Figure 10 fo r the outer zone).

Figure 8 suggests the importance of an e f f e c t of t h i s

Figure 11 i l l u s t r a t e s the geometric s i t u a t i o n corre sponding

t o the per iod o f magnetic alignment of the s a t e l l i t e , cp = 90".

The angular nomenclature of t h i s figure w i l l a l s o be used for the

case of cp = 0" or 180"; i n t h i s case B i s p a r a l l e l t o the detector

a x i s and the "d i rec t ion of maximm proton in tens i ty" i s p a r a l l e l

t o the plane of the detector and ro ta t iona l ly symmetric. This

l a t t e r s i t ua t ion i s the one i n which the maximum e f f e c t of penetrat ing

protons i s expected.

+

An estimate of t he magnitude of the e f f e c t a t L - 1 . 5 and

f o r (p = 0" proceeds along the following l i n e s :

(a) Only protons having an o r ig ina l energy exceeding 95 MeV

can reach the detector .

(b ) After penetrat ion of the shield, a proton must have a

r e s idua l energy of a t l e a s t 1.8 MeV ( threshold of channel C ) and - must be moving a t a su f f i c i en t ly small angle t o the plane of the

de t ec to r ' s0 t h a t i t s path through the de tec tor permits it t o

deposit more than 1.8 MeV.

( a

i n order t h a t it t r i g g e r channel C. Protons s t r ik ing the detector

with energies > 1.8 MeV must be incident a t appropriately smaller

angles. The corresponding quant i t ies for channel D a re 3.7 MeV

minimum res idua l energy and 10" maximum angle (aD i n Figure 11).

The maximum value of t h i s angle

i n Figure 11) i s 35" f o r a proton having exac t ly 1.8 MeV C

( c ) For the region of in t e re s t i n t he inner zone ( L - 1.5,

15 1 - 0.18) we adopt a d i f f e r e n t i a l spec t r a l i n t e n s i t y f o r the

o r i g i n a l be a m

2 -1 - - dj - 1.0 (cm sec sr MeV) dE

P

24

i n the v i c i n i t y of E

constant over the energy range which i s pe r t inen t t o t h i s calcula-

= 100 MeV [Freden, 19661 and take it t o be P

t i o n .

( d ) The highest energy which need be considered i s t h a t of

a proton which can j u s t deposit 1.8 MeV ( f o r C ) or 3.7 MeV ( f o r D)

as it t raverses the de tec tor along a diameter--that i s , whose spec i f i c

ionization has f a l l e n t o 5 . 1 MeV cm /g ( f o r C) o r 10.6 MeV cm /g

( f o r D ) . The corresponding values of r e s idua l energy a r e 120 or

2 2

45 MeV and the o r i g i n a l values of energy E

s h i e l d a re 165 o r 110 MeV [ Janni, 19661.

before s t r i k i n g the max

( e ) Since most of the protons i n question have p i t c h angles

wi th in - + 20° of go0, the ava i lab le range of a i n Figure 11 i s not

f u l l y u t i l i zed .

( f ) The pro jec ted geometric a rea of the de tec tor a t angle a

i s 0.0175 ( s i n a + 0.021 cos a ) .

any specified o r i g i n a l energy E i s a function of E as wel l as of a,

The e f f e c t i v e a rea S (E,a) f o r

being approximately equal t o the above value f o r E - 100 MeV and

zero f o r E = E max'

(g) Thus, the counting r a t e of channel C ( o r D) due t o

transverse pene t ra t ions of the de tec tor i s given by:

E 1

Emin 0

RT M dj JrnXdE J S ( E , a ) (41-rda)

Emax

Emin

x (2n) (0.0175) a2 (E) - RT (5 )

Numerical estimates using ( 5 ) give

RT f o r C 2 0.2 counts/sec

RT f o r D 0.04 counts/sec .

These estimates, crude as they are , do show t h a t the cont r i -

butions of side-wall t r ave r sa l s by high energy protons a re indeed

of the same order of magnitude as the observed counting r a t e s of C

and D i n the inner zone when cp - 0" or 180" (Figure 8) .

es t imate gives a plausible explanation f o r the cp - 0" and 180"

(A similar

counting r a t e s of Detectors A and B (cf. Figure 12).) Such "spurious"

contr ibut ions decrease monotonically as cp goes toward 90" and are

l e s s by an estimated f ac to r of 4 t o 8 a t cp - 90".

The d i r e c t experimental evidence supports the b e l i e f t h a t ,

even i n the inner zone, channels C and D a re measuring a t r u e

component of heavy nuclei during the magnetically a l igned period.

F i r s t , there i s the counting r a t e peak a t cp =go" i n Figure 8.

Secondly and more persuasively, there i s a markedly d i f f e ren t

L-dependence of the r a t e s of channel C (and D) and of the penetrat-

ing proton detector SpB (Table 1) a s shown i n Figure 13.

26

I n the outer zone there i s a v i r t u a l l y complete absence of

penetrat ing protons and side-wall t r a v e r s a l s are completely negl i -

g ib l e there ( see a l s o Figure 10).

(3) E l a s t i c s ca t t e r ing of protons en ter - ing through the col l imator .

From th? energy spectrum given by equation ( 4 ) one f inds

2 t h a t there a re - 1600 protons ( c m > 1.8 MeV

perpendicular t o I3 a t the i n t e n s i t y maximum i n the outer zone.

On rare occasions one or these protons i s def lec tcd by e las t ic

sca t te r ing i n the de tec tor or i n the inner w a l l of the col l imator

i n such a way t h a t i t s t o t a l path i n the de tec tor i s increased

s u f f i c i e n t l y t o t r i g g e r channel C and, much more r a re ly ,

channel D. The p robab i l i t y of such sca t t e r ing can be est imated

by means of the Rutherford formula f o r protons:

sec s r ) - l with E P "

-+

2 2

2 Z e

M v dp = n n t ( - ) cot ( e / 2 ) csc ( e / 2 ) de

where dp = probab i l i t y of s c a t t e r i n g i n t o de at angle 8 t o t h e o r i g i n a l d i r ec t ion

n = no. of nuclei per u n i t volume of t h e t a r g e t

t = thickness of t he t a r g e t

Z e = charge o f t a r g e t nucleus

e = charge of incident p a r t i c l e

M = mass of incident p a r t i c l e

v = ve loc i ty of inc ident p z t i c l e

The l e a s t s ca t t e r ing i s required f o r p a r t i c l e s enter ing

t h e de tec tor at t h e maximum angle (20") t o t h e axis of t h e

de tec tor . Specif ical ly , a proton of 1.8 MeV must be def lec ted

by 35" (versus 55" i f incident ax ia l ly) i n order t o lo se i t s

e n t i r e energy i n t h e de tec tor i f the sca t t e r ing occurs at t h e

f ron t face.

g rea t e r angle i n order t o be counted.

po r t iona l t o energy and i s a s teeply f a l l i n g funct ion of increas-

Higher energy pa r t i c l e s must be def lec ted by a

Also dp i s inverse ly pro-

ing 8. Only l a rge angle, s ing le sca t t e r ing need be considered.

Hence, a c l e a r upper l i m i t PmX i s obtained by supposing

t h a t a l l protons E

s c a t t e r i n g throughout t h e detector occurs at t h e f ront face

> 1.8 MeV have E = 1.8 MeV, t h a t a l l P P

and t h a t s ca t t e r ing i s always away from t h e axis of t h e

col l imator . For s impl ic i ty the in tegra t ion i s extended t o 180",

without a f f ec t ing the r e s u l t . Inser t ing t h e appropriate numbers

f o r a 1.8 MeV proton and t h e constants f o r s i l i c o n i n t o equation

(6)

2 180 O -4 180 O

= [dp = 1.22 x 10 cot ( 8 / 2 ) csc ( 8 / 2 ) de pmax e=35 o 3 5 O

iii , I

= 1 .2 x 10 -3 prnax (7)

28

3 2 I n a d i r ec t iona l i n t e n s i t y of 1.6 x 10 (em see sr)-’ Of

5 protons E > 1.8 MeV, (1.6 x 10 ) (6.4 x lo-’) = 10 such p a r t i c l e s

en ter t h e de tec tor pe r second. Thus, an upper l i m i t t o t he P

counting r a t e of channel C by Rutherford-scattered protons i s

-2 = 1.2 x 10 courts/sec.

RS

This rate (a generous upper l i m i t ) i s less by a f ac to r of 17 than

t h e obscrved countin,; r a t e of 0.2 counic/sec. Moreover, t h e

experimentally measured value of t h e proion e f f i c i ency (i .e. , a

-4 value fo r P) f o r channel C was found t o be l e s s than 3 x 10

f o r axial ly- incident protons E = 1.8, 1.9, 2.05, and 3.57 MeV.

(Section 2) P

We conclude t h a t e l a s t i c a l l y sca t t e red protons E

(as well as unscat tered ones of any energy) make a neg l i e ib l e

> 1.8 MeV P -

contr ibut ion t o t h e counting r a t e of channels C and D.

( 4 ) I n e l a s t i c nuclear i n t e rac t ions of protons i n the de tec tor and i n other material of the satel- l i t e . - Tn addi t ion t o e l a s t i c sca t te r ing , one must consider i n e l a s t i c

nuclear in te rac t ions . There a r e severa l reac t ions of poss ib le

importance involving Si28 [Endt and Van der Leun, 19621:

v i z . , S i28 (p ,p’) Si28, Si28 (n,p) AJ?28, and Si28 (n ,a )

Each of these reac t ions has t o be evaluated on the b a s i s of i t s

cross-section and the p robab i l i t y t h a t the outgoing par t ic le may

deposit enough of i t s energy i n the detector t o be counted i n

28 channel C. The reac t ion S i (p ,p ' ) Si28 can contr ibute t o the

counting r a t e i f the proton i s emitted i n such a d i rec t ion t h a t

it deposi ts a t l e a s t 1.8 MeV i n the detector .

sect ions f o r t h i s react ion a re - 165 mi l l ibarns (mb) a t

E

[Yamabe e t al . , 19581.

sect ion i s - 100 mb and (b) a l l i n e l a s t i c a l l y sca t te red protons

with E

of such protons, one f inds t h a t the contr ibut ion t o the r a t e of

channel C i s - 8 x counts/sec. This r a t e i s - 10 times

smaller than the observed r a t e of C.

Typical cross-

- 12 MeV [Conzett, 19571 and - 30 mb/sr a t 4.8 < E P - P

< MeV

Assuming tha t (a ) the average cross

> 1.8 MeV are counted i n C, and using the known i n t e n s i t y P "

4

Trapped protons incident on the skin of the s a t e l l i t e produce

neutrons i n various nuclear reactions and the r e su l t i ng neutrons

can [R. R. Carlson, pr iva te comunication] i n t e r a c t with s i l i con

i n the react ions Si28 (n,p) A J ? , ~ ~ and Si28 (n ,a ) Mg25. The cross

sec t ions f o r both of these reactions a re a s g rea t as 400 mb a t

neutron energies of - 8 MeV, decreasing t o e s s e n t i a l l y zero at

- 5 MeV and at - 20 MeV [Stehn et al., 19641. i n t e n s i t i e s of trapped protons i n t h e region of i n t e r e s t and t h e

s i z e and cons t i tu t ion of t h e s a t e l l i t e , we estimate t h a t t h e

r e su l t i ng counting r a t e of channel C from (n,p) and (n,a) react ions

i s < 10 -6 counts/sec.

From t h e known

r-2

30

Experimental evidence f o r t h e neelect of any such e f f e c t s

(a) During the ca l ib ra t ion runs a t NRL described i s as follows:

i n par t 2, t h e proton beam of severa l microamperes was stopped i n

t h e brass chamber containing the de tec tor and a l a rge number of

neutrons was generated ( the reac t ion threshold f o r protons on Cu

i s 2.165 MeV and proton energies of up t o 3.57 MeV were used), but

no counts a t t r i b u t a b l e t o neutrons were observed.

spare un i t was exposed t o a flux of - 8 x 10

from the University of Iowa Van de Graaff acce lera tor and only one

count was observed i n - 2 hours- Hence t h e observed e f f i c i ency

must be C 10 .

65

(b) The f l i g h t

3 -1 neutrons (em2 sec)

-6 N

I n addi t ion t o t h e above reac t ions one might consider nuclear

stax production due t o high energy ( tens of MeV) protons. The cross

sect ion f o r such processes i s small and t h e r e i s d i r e c t experimental

evidence t h a t t hey could not be a s ign i f i can t source of counts

f o r channel C. The evidence i s shown i n Figure 13, where t h e

counting r a t e s of de tec tor SpB ( sens i t i ve t o protons of E ,> 70 MeV)

and channel C have been p l o t t e d as a funct ion of L. It i s observed

t h a t there i s marked d i s s i m i l a r i t y between these two curves. More-

over, Figure 10 provides d i r e c t evidence aga ins t the importance of

any type of nuclear i n t e rac t ions i n the body of the sa te l l i t e i n the

ou te r zone.

P

(5 ) E f fec t s of e lectrons.

The s m a l l physical s ize of the de tec tor and the 0.10 ps

pulse cl ipping serve t o make it exceedingly in sens i t i ve t o e lec t rons

of any energy. Moreover, the discrimination l e v e l s of channels C

and D (1.8 and 3.7 MeV) a re f a r above the energies of most geo-

magnetically trapped electrons (except f o r the residuum of @-decay

e l ec t rons from the S ta r f i sh nuclear bu r s t of 9 Ju ly 1962 i n the

inner zone).

t o the extrapolated range of only a 60 keV e l ec t ron o r t o a mean

energy loss of about 15 keV f o r a fast e lec t ron . The diameter

corresponds t o the extrapolated range of a 900 keV e lec t ron .

For example, the thickness of the de tec tor corresponds

By p re - f l i gh t laboratory t e s t s w i t h 2 MeV e lec t rons from a

magnetic spectrometer (courtesy L. A. Frank) and by the f l i g h t

da ta from a similar detector on Mariner I V [Krimigis and Armstrong,

19661 it has been es tab l i shed tha t e f f e c t s of e l ec t rons on the

counting r a t e s of any one of the channels A, B, C, o r D a r e

negl ig ib le throughout the magnetosphere. There a re a l s o d i r e c t

Injun I V data on the i n t e n s i t y of e l ec t rons Ee ,> 1.6 MeV (from

another de tec tor ) which have a completely d i f f e ren t L dependence

than do the data from channels C and D ( i n a manner qui te similar

t o the comparison given i n Figure 13) .

6. INTERPRETATION OF COUNTING RATES OF CHANNELS C AND D

On the s t rength of the data and discussion of sect ions 2,

3, 4, and 5, we conclude t h a t the counting r a t e s of channels C and

D during the magnetically a l igned per iod are due almost exclusively

t o the d i r e c t detect ion of geomagnetically trapped nuclei having

Z - > 2. 4 Neither He3 nor nuclei heavier than He can be excluded but

on the b a s i s of t h e i r low r e l a t i v e abundances i n the e a r t h ' s atmosphere,

ir? the slm' 6 atxospl?erej a n d presilmably i n the so la r wind, we w i l l

henceforth regard the responses of channels C and D as due so le ly

t o geomagnetically trapped alpha p a r t i c l e s .

33

7. SPECTRA AND RELATIVE INTENSITIES OF PROTONS AND ALPHA PARTICLES IN THE OUTER ZONE

I n t h e s p i r i t of t h e remarks i n sec t ion 1, it i s des i rab le

t o have a full knowledge of t h e resliective absolute spec t ra and

angular d i s t r ibu t ions of protons and alpha p a r t i c l e s throughout

t h e magnetosphere. The present inves t iga t ion provides a modest

beginning.

It i s noted t h a t t h e energy "pass bands" of our channels A

and C were chosen i n such a way t h a t both t h e i r lower and upper

energy l i m i t s (Table 1) i f expressed i n k i n e t i c energy/nucleon

(8) are i d e n t i c a l f o r protons and alpha p a r t i c l e s , respec t ive ly :

Channel A: 0.52 < e < 4 MeV/nucleon - P - Channel C: 0.52 - <ecz - < 4 MeV/nucleon

The geometric f a c t o r of the de t ec to r i s iden t i ca l , of course,

f o r all four channels. Hence, the r a t i o of counting r a t e s i n

channels C and A ( a f t e r subtract ion of t h e background due t o t h e

i n - f l i g h t c d i b r a t i n z source) provides a d i r e c t and unequivocal

i n t e n s i t y r a t i o j / j

above. This r a t i o character izes a common range of p a r t i c l e

ve loc i ty and i s independent of any assumptions regarding spec t r a l

i n t eg ra t ed over t he common range of t? noted a p

forms. (Further , i f the angular d i s t r ibu t ions of the two

species of p a r t i c l e are i d e n t i c a l and i f the respect ive spectra

34

a re independent of p i t c h angle, the j / j a P

of number dens i t i e s i n the specif ied ve loc i ty range.

these l a t t e r conditions i s known t o be f u l f i l l e d , however.)

r a t i o i s a l s o the r a t i o

Neither of

The most accurate and r e l i a b l e value of the d i r e c t r a t i o

described above i s obtained a t the outer zone i n t e n s i t y maximum

L % 3.1, at the lowest value of

adequate observations a re ava i lab le , and f o r (0 = 90" (Figure 9) .

This value i s :

(0.19 gauss) f o r which

The l a t i t ude parameter I 2 I / I sol decline of both dj/de, and dj /&

given i n (8) i s accura te ly equal t o the more simple r a t i o :

= 18. By v i r t u e of the r ap id

with increasing 8, the r a t i o P

I 1

-4 jahP = (2.3 - + 0.2) x 10 ,

cp - > 0.52 MeV/nucleon. (9)

We regard t h i s value as the most important and trustworthy

r e s u l t of the present inves t iga t ion .

Since the de tec tor has two proton channels ( A and B) and

two alpha p a r t i c l e channels ( C and D) , spec t r a l information of an

approximate nature can a l s o be derived.

s ign i f icant t h e o r e t i c a l guidance, we have f i t two-point spectra

In the absence of

35

t o s i x d i f fe ren t , simple spec t ra l forms--both exponentials and

power laws i n k ine t i c energy, i n k ine t ic energy/nucleon, and i n

magnetic r i g i d i t y . The r e s u l t s of t h i s work a re summarized i n

Table 2 f o r 2.8 < L < 3.3 and It i s

c l e a r t h a t the implications of the various spec t ra l assumptions

a re s t r ik ing ly d i f fe ren t .

expected r a t i o of the in tegra ted i n t e n s i t i e s j / j

k i n e t i c energy or k i n e t i c energy/nucleon labeled on the scale

of abscissa f o r t w o d i f f e ren t exponential spectra f rom Table 2.

= 0.19 - + 0.01 gauss. - -

For example, i n Figure 14 we show the

Q P above the

The value of ( dja/dEQ)/( d j /dE ) 2 0.05 a t E, = E P P P

= 2 MeV i n our or ig ina l report [Van Allen and Krimigis, 19653 was

derived from assumed exponential spectra i n k ine t i c energy.

the r a w observational data available a t t h a t time (though l e s s

complete) were similar t o those reported herein, it i s c l e a r from

Table 2 and Figure 14 t h a t the or ig ina l ly reported spec t r a l r a t i o

should be regarded as an inadequate and perhaps misleading repre-

sen ta t ion of the overa l l s i tua t ion .

Although

From inspection of Figure 14 and Table 2, it i s d i f f i c u l t t o

avoid the impression t h a t j / j

s t rongly increasing) function of increasing energy - o r energy/nucleon

o r magnetic r i g i d i t y and t h i s r e su l t may be one of v a l i d i t y and of

physical significance .

i s an increasing (and perhaps a a P

-

36

I n view of the f a c t t h a t the proton spectrum i n the outer zone

i s best represented by an exponential i n energy [Davis and Williamson,

1963; Hoffman and Bracken, 1965; Armstrong and Krimigis, 19671,

there i s a ce r t a in i n t u i t i v e preference for expressing the alpha

pa r t i c l e spectrum a s an exponential i n energy/nucleon.

i s done the i n t e g r a l j / j

might even be independent of 6.

Figure 14. )

When t h i s

r a t i o i s not a strong funct on of 8 ani a P

(See the uncertainty s t r i p e i n

8. SPECTRA AND FWATIVE INTENSITIES OF PROTONS AND ALPHA PARTICLES

IN THE INNER ZONE

In the inner zone, 1.8 < L < 2.2, = 0.19 + 0.01 gauss, -

= 1.1 x 10 -5’ , Ea, e > 0.52 MeV/nucleon (10)

ja/jp

P -

and the spectra of protons and alpha p a r t i c l e s are given by

and

d j , = 68 e q (-f?/0.41) .

The same u n i t s a re used i n equations (11) and (12) a s i n

Table 2.

9. DISCUSSION

The most widely accepted conjecture f o r the or ig in of

energetic p a r t i c l e s i n the outer zone i s t h a t they have been in-

jec ted from the so la r wind i n t o trapped o r b i t s i n the magnetosphere

and subsequently accelerated and diffused across magnetic s h e l l s

therein by complex electromagnetic processes.

The r a t i o of the nuniber dens i t i e s of alpha p a r t i c l e s and

protons i n the so l a r wind i s 0.01 t o 0 .1 [Neugebauer and Snyder,

1966; Coon, 1965; Wolfe e t a l . , 1966; Gosling e t a l . , 19673.

Tverskoy [ 19651 and Hess [ 19661 have given some considera-

t i o n t o the r e l a t i v e spec t r a l treatment of alpha p a r t i c l e s and

protons i n the framework of the solar-wind-source model. On the

assumption t h a t both protons and alpha p a r t i c l e s a re "thermalized"

t o the same k ine t i c energy i n the t r a n s i t i o n region, Hess f inds t h a t

the spectrum of alpha p a r t i c l e s would a l s o be of exponential form

i n p a r t i c l e energy (s ince the proton spectrum i s known observa-

t i ona l ly t o be of t h i s form) and t h a t the two spectra would have

iden t i ca l values of e-folding energy per p a r t i c l e (not - energy pe r

nucleon) at a given L value f o r L ,> 3. He a l s o p red ic t s t h a t the

r a t i o of spec t ra l i n t e n s i t i e s w i l l be of the same order as t h a t of

the number dens i t i e s i n the so l a r wind ( i . e . , - 0.05).

a t L - - 3.1 appears t o be i n c l e a r disagreement with both o f these

O u r r e s u l t s

39

expectations (Table 2 and Figure 14), though we should note t h a t our

measurements a re made i n a region f a r from the equator

( lq/ l:ol = 18). This l a t t e r f ac t may inva l ida te the comparison,

as noted by Hess, since he has assumed the absence of energy losses

i n h i s preliminary work. Such an assumption i s c l e a r l y l e s s v a l i d

for p a r t i c l e s having mirror points a t low a l t i t u d e s than f o r those

having mirror po in ts near the equator.

ever, t h a t a t t h i s value of I -. B I / may not be important [Krimigis, 1967bI.

There a re indicat ions, how-

1 the e f f e c t of the atmosphere

On the other hand, our r e su l t s a r e not s t rongly inconsis tent

with a r a t i o (dja/dea)/(djp/"eP) which i s independent of energy pe r

nucleon ( i . e . , of ve loc i ty) (lower curve Fig. 14) .

following Tverskoy, t h a t protons and alpha p a r t i c l e s may be

"thermalized" t o the same velocity r a t h e r than t o the same energy

and t h a t i n the trans-L diffusion process the same spec t ra l form i s

maintained i n terms of energy/nucleon.

the Coulomb energy lo s s of p a r t i c l e s t ravers ing the outer atmosphere.

Thus

This suggests,

A fu r the r consideration i s

dE z2 d x v

- - a- 2

i s the r a t e of energy l o s s per u n i t path length x i n the atmosphere

for a non- re l a t iv i s t i c p a r t i c l e having charge Z and ve loc i ty v.

Subs t i tu t ing dx = vdt i n (10) and in tegra t ing ,

where M i s the mass of the p a r t i c l e .

p a r t i c l e s of the same i n i t i a l energy, t h e i r l i f e t imes against

Coulomb energy l o s s a re r e l a t e d by the equation:

Hence, f o r protons and alpha

t = 8 t , P

if the p a r t i c l e s remain f u l l y ionized throughout t h e i r range.

The actual f ac to r i s somewhat less than 8 f o r the energies under

consideration here. For p a r t i c l e s having the same i n i t i a l veloci ty ,

however :

and thus t = t . P a

These considerations i l l u s t r a t e Tverskoy ' s suggestion t h a t spectra

i n terms of energy/nucleon may be more appropriate whenever Coulomb

energy losses i n the atmosphere a re important. Another l o s s process

which may influence proton and alpha p a r t i c l e spectra i n a d i f f e ren t

~y i s charge exchange i n the atmosphere. No treatment of t h i s sub-

j e& f o r alpha p a r t i c l e s i s known t o us. ' I .

'

Tverskoy [1965] makes the following spec i f i c predict ions:

(a)

a t L - 3.2, and t h i s i n t e n s i t y should be - 10

The in t ens i ty maximum f o r 2 MeV a -pa r t i c l e s should be located

3 (em2 see)-' a t the

equator.

t o t a l energy grea te r than 2 MeV should be - Figure 3 we f ind t h a t the loca t ion of the maximum a s wel l as the

(b ) The ja/jp r a t i o a t t h a t point fo r p a r t i c l e s with

Comparing w i t h

41

f l u x a re approximately cor rec t , i f one takes i n t o account the

magnetic coordinates of the observations and assumes t h a t t he

a - p a r t i c l e s a r e evenly d i s t r ibu ted over - 2rr s te rad ians .

h i s po in t (b ) we f i n d from Figure 14 t h a t Tverskoy's r a t i o i s

smaller from t h a t observed by an order of magnitude although, a t a

lower energy ( - TOO keV), h i s pred ic t ion would have been co r rec t .

We note t h a t Tverskoy and Hess have a ce r t a in l e v e l of agreement i n

t h a t Hess p r e d i c t s a r a t i o of 0.05 which i s independent of energy

and does not include any losses and Tverskoy p r e d i c t s a r a t i o of

lo-' which i s a l s o independent of energy but includes Coulomb losses .

The f a c t o r of t en difference i s due t o the Coulomb l o s s e s alone.

Regarding

From the foregoing, it appears conceivable t h a t t he observed

r a t i o j / j

zone protons and alpha p a r t i c l e s , although th i s r a t i o i s s i g n i f i c a n t l y

l e s s than t h a t pred ic ted from diffusion theory with known l o s s

processes taken i n t o account.

may be reconcilable w i t h a solar-wind-source of outer q P

However, the exosphere of the e a r t h a l s o contains a mixture

of hydrogen and helium and it i s not ye t obvious t h a t i n s i t u

acce le ra t ion processes could not y i e l d the observed s i tua t ion ,

wi th atmospheric ions as the source p a r t i c l e s .

a P The j / j r a t i o appears t o be l a r g e r i n t he inner zone

(Section 8) than i n the outer zone.

(Figures 3, 4, 5, and 6) suggests t h a t the source of inner zone

Also the L dependence of J,

42

alpha p a r t i c l e s may be a l toge ther d i f f e ren t than the source of

outer zone alpha pa r t i c l e s . It i s pointed out, however, t h a t

equation (10) represents an average value over the L range 1.8-2.2

where the proton in t ens i ty changes by a f ac to r of 4 (Figure 4 ) .

Thus, although t h i s value i s s ign i f i can t ly d i f f e ren t than t h a t i n

the outer zone, it does not lend i t s e l f t o t h e type of analysis pre-

sented i n the previous section. Specif ic sources of inner zone

alpha-part ic les , which we have not assessed quant i ta t ive ly , a r e

proton-induced nuclear stars i n the atmosphere and radioactive-

decay of miscellaneous f i s s i o n products [ G . F. Pieper, p r iva t e

communication] from several high a l t i t u d e nuclear bu r s t s which have

occurred i n t h i s region.

43

10. REMARKS ON TIME VARIATIONS

The d a t a described so far were taken during t h e per iod before

17 April 1965.

occurred at - 1312 UT and was followed by a magnetic storm with a

main phase depression of t h e horizontal f i e l d o f - 160 y .

d i s t r i b u t i o n of 0.5 MeV protons measured by In jun I V was severely

and durably dis turbed [Krimigis, 1967aI.

p a r t i c l e s for t h e per iod 17 Apri1--31 May i n Figure 1 5 and t h e

previously discussed 1 March--lT’( April d i s t r i b u t i o n has been

included fo r comparison.

increased by - 30% and t h e posi t ion of t h e m a x i m u m moved inward

t o L - 2.9.

d i s t r i b u t i o n of alpha p a r t i c l e s and i t s r e l a t ionsh ip t o t h a t of

protons w i l l provide some addi t ional i n s igh t on t h e dynamics of

both components. Such a study i s underway.

On Apri l 17 a geomagnetic sudden commencement

The

The d i s t r i b u t i o n of a lpha

It i s observed t h a t t h e maximum i n t e n s i t y

We expect t h a t t h e subsequent t ime h i s t o r y of the -

44

11. CONCLUSIONS

( a ) The presence of geomagnetically trapped alpha p a r t i c l e s

i s established.

( b ) A t constant I $ I x 0.19 gauss the maximum i n t e n s i t y 4

prpend icu la r t o B occurs a t L = 3.1.

i n t ens i ty there i s

The absolute d i r ec t iona l

ja (En: > 2.09 MeV) =

5 , : 3.89 WV) = 4,5 (cm se r sr) . 28 (cm2 sec sr)-l and

2 -1

(c) A t t h i s outer zone maximum,the r a t i o of the d i r ec t iona l

l n t e n s i t i e s of alpha p a r t i c l e s and of protons, both in tegra ted above

the common value ea = 8 = 0.52 MeV/nucleon, i s P

-4 ja/jp = (2.3 5 0 . 2 ) x 10 .

( d ) A va r i e ty of considerations, no one of which i s decisive,

suggest t h a t the most physical ly s ign i f icant form of the spectra of

alpha p a r t i c l e s and protons may be an exponential one i n terms of

energy/nucleon.

(e) It appears conceivable t h a t the observed r a t i o j /j a p

may be reconcilable with a solar-wind-source of outer zone protons

and alpha p a r t i c l e s although t h i s r a t i o i s s ign i f i can t ly l e s s than

that predicted from diffusion theory with known l o s s processes taken

i n t o account.

L

45

(f) The d i s t r ibu t ion of outer zone alpha p a r t i c l e s w a s

changed markedly a f t e r the magnetic storm of 18 Apr i l 1965 and the

i n t e n s i t y peak moving inward from L = 3.1 t o L = 2.9.

( g ) Trapped alpha p a r t i c l e s i n the inner zone a r e apparently

due t o a d i f f e ren t source than tha t f o r those i n the outer zone.

1

46

We thank Dr. T. P. Armstrong f o r experimental ass i s tance and

useful discussions regarding t h e r e s u l t s . Messrs. W. A. Whelpley,

F. Zamecnik, J . C, Craven, and K. L . Ackerson have been responsible

f o r the organizat ion and conduct of t h e Injun I V data reduction.

M r . E . Wolicki of t h e Naval Research Laboratory kindly made

f a c i l i t i e s ava i lab le f o r t h e ca l ib ra t ion of t h e de tec tor . Messrs.

D. %emark, E. Strein, B. Randaii, w. Greene, and E. G a i f i S l d

contributed t o t h e e lec t ronic design and experiment t e s t i n g and

ass i s ted with proton ca l ibra t ions at t h e Universi ty of Iowa.

Messrs. A. L. Burns, C. M. T s a i , and J. Bakas a s s i s t ed with t h e

d a t a reduction while L . Shope, B. Brechwald, and P. Dalamaggas

were responsible f o r most of t h e programming e f f o r t .

supervised t h e execution of t h e programs.

Whelpley o f t h e Universi ty of Iowa and C. W. Coffee of Langley

Research Center, as well as many Universi ty of Iowa and LRC

personnel, t oo numerous t o mention by name, who contributed t o

making t h e Injun I V s a t e l l i t e a success.

H. Kiel

We thank Mr. W. A.

Development, construction, and p r e f l i g h t t e s t i n g o f t h e

University of Iowa s a t e l l i t e Injun I V w a s performed under contract

Nul-2973 with t h e National Aeronautics and Space Administration/

47

Langley Research Center. Analysis and publ ica t ion have been per-

formed i n p a r t under National Aeronautics and @ace Administration

grant N s G 233-62 and t h e Office of Naval Research Contract

Nonr 1509(06).

x - . k I @ ? 0"

48

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k 0 -P cd E .rl

u ri .rl rl m 0

cd 0

a, P a, E 5 2 0

-P

0 a, 0 (u 5 *

*n r-

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cn a3 M

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d .ti

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8

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50

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Charged Pa r t i c l e s i n the Inner Van Allen Radiation Belt ,

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Armstrong, T. P. , and S. M. Krimigis, Observations of Protons i n

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Wind and the Distant Geomagnetosphere, pp. 231-255 of

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Publishing Co., Dordrecht-Holland, 1966 (ed. by B. M.

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and I. B. Strong, Measurements of t he Interplanetary S o l a r

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of t he Solar Wind, J. Geophys . Res., - 71, 3329-3335, 1966.

Yamabe, Shotaro, Michiya Kondo, Takashi Yamazaki, and Atsutomo

Toi, Angular Distr ibut ion o f Protons I n e l a s t i c a l l y

Scattered from Si28 and Mg24, 5. Phys. SOC. Japan, - 13,

777-781, 1958

54

FIGURE CAPTIONS

Figure 1. An assembly drawing showing the geometry of the

Injun I V so l id s t a t e de tec tor coll imator.

p a r t i c l e s penetrat ing the sh ie ld t r a v e l approximately the

same path length a t a l l angles of incidence within the

outer hemisphere.

Notice that

Figure 2. hE vs E curves f o r protons and a -pa r t i c l e s incident on -2 a 25 micron s i l i c o n detector with a 0.21 mg cm

foil i n f ront .

n icke l

Figure 3. The L dependence of counting r a t e s of channels C and D

a t constant I $ [ and a t cp = 90".

Figure 4. The L dependence of counting r a t e s of channels A and C

a t constant B and a t cp = 90". I+ I Figure 5. Contours of constant apparent i n t e n s i t y i n lzl - L

space. The labeled values on the several curves a re the

quot ients of the counting r a t e s of channel C by i t s geometric f a c t o r 0.0064 cm sterad. Some of the counts may

be due t o other causes than d i r e c t en t ry of heavy nucle i

through the coll imator. There appear t o be two d i f f e ren t

regimes, divided by the l i n e L = 2.6.

2

Figure 6. S i m i l a r t o Figure 5 , but f o r channel D.

Figure 7. The dependence of the counting r a t e s of channels A, B,

C , and D on B i n the inner zone. 17 Figure 8. The counting r a t e of channel C i n the inner zone as a

function of the angle cp between the coll imator a x i s and

Figure 9. Same a s Figure but for the outer zone.

Figure 10. Same a s Figure 8 but for the outer zone. Mote t h a t

there were no counts between 0" and 30° although these

angles were sampled repeatedly.

Figure 11. Schematic representation of the geometry used i n the

ca lcu la t ion of RT, section 5, paragraph 2, of the t e x t (q .v . ) .

The counting r a t e s of channels A and C i n the inner Figure 12.

zone as a function of cp. Note t h a t the apparent contr ibut ion

t o the counting r a t e of A due by t ransverse penetrat ing p a r t i c l e s

i s - 10 times t h a t of C .

Figure 13. An i l l u s t r a t i o n of the lack of dependence of the counting

r a t e of C as cp = 9" on the i n t e n s i t y of high energy protons.

Figure 14. Dependences of the r a t i o j / j of i n t e n s i t i e s of alpha a P

p a r t i c l e s and protons both in tegra ted from the same lower

l i m i t spec i f ied by the abscissa t o i n f i n i t y . Both E

(upper curve and top scale) and & (lower curve and bottom

sca le ) have a com-on numerical scale of abscissa.

two curves a re derived from Table 2. The cross hatched

region ind ica tes the region of uncertainty due t o

uncer ta in t ies i n spec t ra l f i t s .

The

Figure 15. The d i s t r ibu t ion of trapped a - p a r t i c l e s before ( s o l i d

l i n e ) and a f t e r (dashed l i ne ) the 17 Apri l 1965 magnetic

storm.

INJUN 14I SOLID STATE DETECTOR APERTURE

G67-572

v) W I 0 z I 500 v

i- 0 z W

I 1 ,250

k o

SCALE = 411

. Ih I.'.).

~

I

2 3

4 5 6 7 8 9

IO

DESCR I PT ION MAIN HOUSING MOUNTING SCREW NUCLEAR DIODE SURFACE BARRIER, TOTALLY DEPLETED DETECTOR MICRODOT CABLE MICRODOT DETECTOR MOUNT INNER FOIL HOLDER OUTER FOIL HOLDER LIGHT-TIGHT FOIL ELECTRON BAFFLE APERTURE DEFINING RING

MATERIAL BRASS STAINLESS STEEL

SILVER-NICKEI ALLOY NICKEL BRASS BRASS

Figure 1

n u m

/ Y W 7 0 + 0 ar n

\ \ \

\

I I I I I I l l 1 1 1 1 1 1 I I I I I 1 I I I 1 1 I

0 2- - > - W z W

0 0

G 66 - 876

1 I I I IO J

I .o

n z 0 0 W v) \ 0.1 m I- z 3 0 0

0.01

-00 I

I

I l l INJUN m: I MARCH- 17 APR

d d --

I

I

L 1965

El = 0.19 f 0.01

l l T I I

I I

-28 (CM*-SEC-SR 1 - 1 1

- Ch. C 2.091 E,< 15 MeV -

I / I I h.D 3 .89sE, I 7 MeV

C - t - - C BACKGROUND

2- cc- - D BA

I

KGROUND

.o 2.0 3.0 4.0 5 .O 6 -0

L (EARTH RADII I

FIGURE 3

I I

lo3

2 IO

n 5

a IO'

0 W m LT W

U J + z 3 0 0

0 IO

-I IO

- 2 IO

INJUN IV: I MARCH- 17 A P R I L 1965 E l = 0.19 .01

5 2 7 1.24 X IO (CM SEC SI?)-'

2 28 (CM SEC SRi I

C: 2.09 5 Ea 5 15 Me\ Jy -_-----

I 2 3 4 5 6 7 a L (EARTH RADI I )

FIGURE 4

.30

.25

.20 - cn cn 3

c3 a

tm v

.I 5

.IO

.05

.03

G67-204

l l l j l l l l ~ l l l l j l l l l ~ I I I I ~ I l l l / l l l l

APPARENT I NTENS I TY CONTOURS (CHANNEL C )

1.1 1.5 2 .o 2.5 3.0 3.5 4.0

L (EARTH RADII)

Figure 5

.--.

.25

.20

14 (GAUSS)

.I5

.I 0

( CHANNEL D )

I MARCH - I7 APRIL 1965 - INJUN 1zL -

-

j, IN (CM~SEC-SR? -

-

MAGNETIC EQUATOR - -

1 . 1 1.5 2 .o 2.5 3.0 3.5 4.0 L (EARTH RADII)

F i g u r e 6

h

n Z 0 0 w v, \ v, I- z 3 0 0 W

m a-

I O 0

IO

I .o

t 0 . I L

I , , , , I , ~ , , , , ,

0. IO 0.20 0.30 0.40 1E1 (GAUSS)

Figure 7

0. I

0.01

.A

n Z 0 0 W cn \ v, I- Z 3 0 0 W

n 0-

f7 Z 0 V W m \ m I- Z 3 0 V

IO0

-I 0

G67-306

ANGULARRESPONSE OF CHANNEL C 1.3s L 5 1.7

0.10s 1sil I 0.20 + = ANGLE BETWEEN

DET. AXIS AND E

T I,

IG2

$ (DEGREES) Figure 8

I O 0 0

I O 0

I .o

0.1 0.20 0.30 0.40

Igl (GAUSS)

Figure 9

G 67-316

0. IO

0.05

0.00

ANGULAR RESPONSE OF CHANNEL C

IN OUTER ZONE

2.8 I L L 3.4 0.24

90 60 30 4 (DEGREES)

0

FIGURE LO

G 67- 305

I o2

ANGULAR RESPONSE OF CHANNELS A AND C

1

IO 2L 1.3 I L I 1.7 0.10 I IBI I 0.20

--+

I o1

a Z 0 0 W cn ‘ 0 i? IO Z 3 0 0

IO

4 ANGLE BETWEEN DETECTOR AXIS AND

0 30 60 90 120 150 180 + (DEGREES)

F i g u r e 12

.

G67-454

\ * 2 5 IO 3 0 0

- - I I I I I I 1 COMPARISON OF RESPONSE OF SpB

AND CHANNEL C I MARCH - I7 APRIL, 1965

IEl 0.1 65k 0.005

I oo 1.2 1.4 I .6 1.8 2.0 2.2 2.4 2.6

L (EARTH RAD I I )

n z 0 0 W v, v, F Z 3 0 0

\

c

FIGURE 13

G67-528

IO'

JP

E, KINETIC ENERGY (MeV)

'a! . - VS ENERGY . 'P

2.85 LI 3.3

J P ,

0 I .o 2 .o 3.0 3.5 E , KlNET IC ENERGY/NUCLEON (MeV/NUC)

F i g u r e 14

f 3 2 0 0 W v,

e W Q

I- z 3 0 0

* IO'

lo-*

I 1 I 1

I MARCH - 17 APRIL 1965 17 APRIL - 31 MAY 1965

I -

- -

&--A

A 4 \ I I I

I I :i

- -

I

CHANNEL C

4 ' A

b \

I \ I!\ \ \

I 2 3 4 5 L (EARTH R A D I I )

Figure i 5

~ UNCLASSIFIED Sec uri t v C1 a ss i f ica t ion

I OQlGlNATlN G A C T I V I T Y (Corporate author)

University of Iowa Department of Physics and Astronomy

2 a R E P O R T S E C U R I T Y C L A S S I F I C A T I O N

UNCLASSIFIED - 2 6 G R O U P

8 . DESCRIPTIVE NOTES ( T y p e of report and inclusive dates)

Progress Ju ly 1967

Krimigis, S. M., and Van Allen, J. A. 5 . AUTHOR(S) (Lust name, f irst name. in i t ia l )

j . REP0 RT DATE

J d Y 1967 3a. C O N T R A C T O R G R A N T N O .

Nonr 1509( 06) b. P R O J E C T N O .

7 a . T O T A L N O . O F P A G E 5 7 6 . N O . O F R E F S

70 36 9 a . O R I G I N A T O R ' S R E P O R T NUMBER(S)

U. of Iowa 67-29

C.

81. SUPPLEMENTARY NOTES

NO(.?) ( A n y othernumbers that may be assigned

12. SPONSORING MILITARY ACTIV ITY

Office of Naval Research

d .

0 . A V A I L ABILITY/LIMITATION NOTICES

Distr ibut ion of t h i s document i s unlimited.

I

3. ABSTRACT

The observations reported herein were made with the University of Iowa Injun I V s a t e l l i t e which w a s launched on 2 1 November 1964 i n t o a near ly polar o r b i t of 810 inc l ina t ion with i n i t i a l apogee and perigee a l t i t u d e s of 2502 and 527 kilometers, respect ively. It car r ied a 25 micron thick, t o t a l l y depleted s i l i con surface b a r r i e r detector with four e lec t ronic discrimination leve ls . The two l e v e l s a r e sens i t ive t o protons 0.52 < Ep < 4.2 MeV and 0.90 < E < 2.1 MeV, respectively. The two upper 'sevels a r e sens i t ive only t o nuclei heavier than deuterons and, specif ical ly , a re sens i t ive t o alpha p a r t i c l e s 2.09 < E, < 15 MeV and 3.89 < Ea < 7 MeV, respect ively. Study of t he ava i lab le &ita up t o 17 April 1965-lead; t o the following conclusions:

(a)

(b) occurs a t L = 3.1.

P -

The presence of geomagnetically trapped alpha p a r t i c l e s i s es tabl ished.

A t constant 1; 1 0.19 gauss the maximum i n t e n s i t y perpendicular t o 3 The absolute d i rec t iona l i n t ens i ty there i s

2 -1 ja (Ea > 2.09 MeV) = 28 (cm sec s r ) .and

2 -1 * j, (E, > 3.89 MeV) = 4.5 (cm sec sr) . A t t h i s outer zone maximum, the r a t i o of the d i r ec t iona l i n t e n s i t i e s (c)

of alpha p a r t i c l e s and of protons, both integrated above the common value e = I? = 0.52 MeV/nucleon, i s a P

(continued)

F O R M ID 1 J A N 6 4 1473 UNCLASSIFIED Security Classification

UNCLASSIFIED Security Classification

4. K E Y WORDS

Radiation Belts

Alpha Particles

Geomagnetically Trapped Radiation

INSTRUCTIONS

1. ORIGINATING ACTIVITY Enter t h e name and a d d r e s s of t h e contractor , subcontractor , g ran tee , Deportment of De- f e n s e ac t iv i ty or other organiza t ion (corporate author) i s s u i n g t h e report. 20. R E P O R T S E C U H T Y CLASSIFICATION: E n t e r t h e o v e r all secur i ty Class i f ica t ion of t h e report. “ R e s t r i c t e d D a t a ” is includcd. a n c e wi th appropr ia te secur i ty regula t ions .

26. GROUP: Automatic downgrading is s p e c i f i e d i n DoD Di- r e c t i v e 5200.10 and Armed F o r c e s Indus t r ia l hfanual. E n t e r the group number. Also , when appl icable , show t h a t op t iona l markings h a v e b e e n used for Group 3 and Group 4 ’ a s author- ized .

3. R E P O R T T I T L E : Enter t h e comple te report t i t l e i n all c a p i t a l l e t te rs . Titles in a l l c a s e s should b e unc lass i f ied . If a mesningful t i t l e cannot b e s e l e c t e d without c l a s s i f i c a - t ion. show t i t l e c l a s s i f i c a t i o n i n a l l c a p i t a l s i n p a r e n t h e s i s immediately fol lowing the t i t le .

4. D E S C R I P T I V E XOTES: If appropriate , e n t e r t h e t y p e of re?ort, e.g.. inter im, progress , summary, annual , or final. G i v e the i n c l u s i v e d a t e s when a s p e c i f i c repor t ing per iod is covered.

5. AUTIiOR(S): E n t e r the name(s) of author(s) as shown o n o r i n t h e report. If z i l i t o r y , show rank and branch of service. t h e pr inc ipa l -:rthor is an a b s o l u t e minimum r e q u i r e m e n t

6. Enter t h e d a t e of t h e report a s day , month, year; o r month, year. o n t h e r q o r t , u s e d a t e of publ icat ion. 7a. T O T A L KUMBER OF PAGES: T h e to ta l p a g e c o u n t should fol low normal paginat ion procedures , i.e., e n t e r t h e number of ? a g e s containing information.

76. NUhlBER OF R E F E R E N C E S Enter t h e to ta l number of r e f e r e n c e s c i t e d in t h e report.

8a. C O S T R A C T OS GRANT NUMBER: If appropriate , e n t e r t h e a p p l i c a b l e number of t h e cont rac t or grant under which t h e repor: w a s wri:tea

Ob, &, & Sd. P R O J E C T NUMBER: E n t e r t h e appropr ia te mil i tary department ident i f icat ion, s u c h a s pro jec t number, subpro jec t nunher , sys tem numbers, t a s k number, etc. 9s. ORiGINATOR’S R E P O R T NUMBER(S): Enter t h e offi- c i a l report number b y which the document wi l l b e ident i f ied and cont ro l led by t h e or iginat ing act ivi ty . b e uruque to t h i s report.

96. O T I I E R R E P O R T NUhlBER(S): If t h e report h a s b e e n assigncd any o t h e r report numbers (e i ther b y t h e or ig ina tor or b y t h c sponsor), also e n t e r t h i s number(s).

10. AVAiLABILITY/LI!dITATION K O T I C E S E n t e r a n y lim- i t a t i o n s on fur ther d i sseminat ion of the report , o t h e r t h a n t h o s

I n d i c a t e wiiether Marking is to b e in accord-

Enter. l a s t name, f i r s t name, middle ini t ia l . T h e name of

R E P O R T D A T Z If more t h a n o n e d a t e a p p e a r s

This number m u s t

LINK A

R O L E -

-

W T

LI t

R O L E

B W T

- L l h

R O L E

- C

W T

imposed b y s e c u r i t y c l a s s i f i c a t i o n , u s i n g s t a n d a r d s t a t e m e n t s s u c h as:

(1)

(2)

(3)

“Qual i f ied r e q u e s t e r s may o b t a i n c o p i e s of t h i s report from D D C ” “ F o r e i g n announcement a n d d i s s e m i n a t i o n of t h i s report b y DDC is not a u t h o r i z e d ” “U. S. Government a g e n c i e s may o b t a i n c o p i e s of t h i s report d i r e c t l y from DDC. O t h e r qua l i f ied DDC u s e r s s h a l l r e q u e s t through

I 1

(4) “U. S. mili tary a g e n c i e s may o b t a i n c o p i e s of t h i s report d i rec t ly from D D C O t h e r qua l i f ied u s e r s s h a l l r e q u e s t through

1 1

( 5 ) “All d i s t r ibu t ion of t h i s repor t is c o n t r o l l e d Qual- i f ied DDC u s e r s s h a l l r e q u e s t through

#I

If t h e report h a s b e e p furn ished to t h e O f f i c e of T e c h n i c a l S e r v i c e s , Department of Commerce, for s a l e t o t h e publ ic , indi- c a t e t h i s f a c t a n d e n t e r t h e pr ice , i f known. 11. S U P P L E M E N T A R Y NOTES: U s e for addi t iona l ex2lana- to ry notes . 12. SPONSORING MILITARY A C T I V I T Y E n t e r t h e name of the depar tmenta l p r o j e c t office o r labora tory s p o n s o r i n g (pay- ing for) t h e r e s c a r c h a n d development .

13. ABSTRACT: E n t e r a n a b s t r a c t g iv ing a brief a n d f a c t u a l summary of the document i n d i c a t i v e of t h e report , e v e n though it may a l s o a p p e a r e l s e w h e r e in the body of t h e t e c h n i c a l re - port. be a t t a c h e d .

be u n c l a s s i f i e d . E a c h paragraph of t h e a b s t r a c t s h a l l e n d wi th a n ind ica t ion of t h e mil i tary s e c u r i t y c l a s s i f i c a t i o n of the i n - formation i n t h e paragraph, r e p r e s e n t e d a s (TS). Is). ( C ) , or (V).

T h e r e is n o l imi ta t ion on t h e length of t h e a b s t r a c t . ever , t h e s u g g e s t e d length is from 150 t s 225 words.

14. KEY WORDS: Key w o r d s a r e technica l ly meaningful t e r n s o r s h o r t p h r a s e s t h a t c h a r a c t e r i z e a report a n d may b e u s e d a s i n d e x e n t r i e s for c a t a l o g i n g t h e report. s e l e c t e d S O t h a t n o s e c u r i t y c l a s s i f i c a t i o n is required. I d e n d - f ie rs , s u c h a s equipment model d e s i g n a t i o n , t rade name, m i l i t a r pro jec t c o d e name, geographic loca t ion , may be u s e d a s k e y w o r d s b u t wi l l b e fo l lowed by a n ind ica t ion of t e c h n i c a l c o n - tex t . The a s s i g n m e n t of l i n k s , r a l e s , a n d w e i g h t s is opt iona l .

I n c l u d e address .

If addi t iona l s p a c e is required, a cont inua t ion s h e e t s h a l l

I t is highly d e s i r a b l e t h a t t h e a b s t r a c t of c l a s s i f i e d repor t s

How-

Key words m u s t b e

ID ,5*0% 2473 (BACK) UNC LAS S IF IE D Security Classification

-4 = (2.5 + 0.2) x 10 . jahP - ( d ) A va r i e ty of considerations, no one of which i s Ciecisive,, suggest t h a t the most physical ly s ign i f icant form of the spectra of alpha p a r t i c l e s and protons may be an exponential one i n terms of energy/nucleon.

( e ) reconci lable with a solar-wind-source of ou ter zone protons and alpha p a r t i c l e s although t h i s r a t i o i s s ign i f i can t ly less than t h a t predicted from diffusion theory with known loss processes taken i n t o account.

( f ) markedly a f t e r the magnetic storm of 18 April 1965 and the i n t e n s i t y peak moving inward from L = 3.1 t o L = 2.9. ( g ) Trapped alpha p a r t i c l e s i n the inner zone a re apparently due t o a d i f f e ren t source than t h a t f o r those i n the outer zone.

It appears conceivable t h a t the observed r a t i o ja/jp may be

The d i s t r ibu t ion of ou ter zone alpha p a r t i c l e s w a s changed

Documents

1967 - NASA · 2017-06-27 · ABSTRACT The observations reported herein were made with the University of Iowa Injun IV satellite which was launched on 21 November 1964 into a nearly