Prompt fission neutron (PFN) emission in reaction

Prompt fission neutron (PFN) emission in

reaction

Zeynalov Sh. Sedyshev P., Sidorova O., Shvetsov V.

JINR-Joint Institute for Nuclear Research, Dubna, Russia

),( )( 235252 fnUandSFCf th

Wonder-2018, October 8-12

The mechanism of PFN emission in fission plays important role in nuclear fission theory from the one

hand and the information on PFN is highly demanded by nuclear power industry from the other hand.

Analysis of TKE measured in resonance neutron induced fission of 235U revealed surprising

fluctuation. The recent measurement of PFN multiplicity in 235U resonances demonstrates fluctuations

of PFN multiplicities to.

One of the interesting observation is the increasing from the heavy FF with increase of the

excitation energy of fissioning system still has no clear explanation

In current report we presenting some preliminary results of measurement of PFN emission in thermal

neutron induced fission of 235U reaction as test of apparatus for resonance neutron induced fission of235U measurements foreseen to perform at IREN facility next year

2. Motivation

)(A


Adopted from C. Budtz-Jørgensen and H.-H. Knitter, Nucl. Phys., A490, 307(1988) and modified with digital

pulse processing apparatus

3. Experimental setup and data acquisition system.

),(200 ,),(),( ,),(

),(),()(

00

0

0

dTKEdATKEAYdAdTKETKEAYTKEAdTKETKEAY

dTKETKEAYTKEAA

),(200 ,),(),( ,),(

),(),()(

00

0

0

dTKEdATKEAYdAdTKETKEAYTKEAdATKEAY

dATKEAYTKEATKE


4. Digital Pulse Processing (DPP).

0 1000 2000

0

300

600

900A

mp

litu

de [

arb

. u

nit

s]

Sample No

B Cathode

D Anode 1

E Anode 2

0 500 1000 1500

0,0

2,8

5,6

8,4

Am

plitu

de [

arb

. u

nit

s]

Sample No

Anode 1

Anode 2

Cathode

In our approach we have oversampled FF signals. The oversampling we used to increase the effective number of bits (ENOB)

improving the signal representation. In practice the increase of ENOB realized automatically when signal passed through

second order low pass filter :

Improved signal presentation (left figure) facilitates numerical solution (differentiation) of the integral equation

Solution of the equation is i(t) presented on the right figure for the cathode and two anode signals. In terms of familiar analog

electronics the operation performed equivalent to differential filter on the input of spectroscopy amplifier (SA). To simulate

integrating stage of the SA we implemented integration according to

The last operation, performed with two correlated anode waveforms, provides the pulse heights of FF.

d

tVVd

tVtV outoutinout )

)(exp()( ,)

)(exp()()(

0

12

0

1

t

diConsttV0

)/exp()()(

ditV

t

0

)()(


0 1000 2000 3000 4000 5000 6000

0,010,2

0,4

0,6

0,8

1,0

Av

era

ge

d p

ote

nti

al F

x(y

)

Distance from the cathode (arb.)

Weighting potential for the anode

Grid position

b)

200 400 600 800 1000

4680

5200

5720

Yc

oo

rd.

[arb

]

Xcoord. [arb.]

a)

5. Drift time determination of FF ionization

The concepts of weighting field and weighting potential states that the instantaneous current induced on a given electrode is

equal to , where q is the charge of the carrier, is its velocity, and is called the weighting field. Another way of

stating the same principle is that the induced charge on the electrode is given by the product of the charge on the carrier

multiplied by the difference in the weighting potential from the beginning to the end of the carrier path . The weighting

potential as a function of position was found as the solution of the Laplace equation for the geometry of the detector with

special boundary conditions. Evaluation of the drift time can be done if the weighting potential inside the sensitive volume of the

chamber is calculated as shown in the above graphs. Using explicit functions for weighting potential one can find the following

expression for drift time T for ionization charge density shifting from the origin to the anode:

where the meanings of d, D, ϴ are clear from the sketch of the TBIC, ϭ is the grid inefficiency factor or it is the value of the

average weighting potential at grid location, and X is the center for ionization charge distribution along the FF track. Parameter

T for corresponding anode can be measured using the signal current waveform as follows

0Evqi v0E

qQ

,))cos(1(1

1(2

))cos(1(

D

X

D

d

D

X

W

DT

maxmax

0

0

0

0 )( ,)( where,/

TT

dttiStdttiSSST


6. FFs cos(Θ) evaluation

Cosines calculated from measured drift times T according to formulae above.

50 100 150 200 250

50

100

150

200

250

Drift T

ime

[arb

. un

its]

Pulse height [arb. units]

090

90)cos( TT

TT

)0)(cos(T

)1)(cos(

90

0

T

TT

))cos(1(1

1(2

))cos(1(D

X

D

d

D

X

W

DT

))2

1()1(1/(90 D

d

T

TPP A

C

A


-0.4 -0.2 0.0 0.2 0.40

110000

220000

330000

Co

un

ts

Cos(1)-Cos(2)

Measurement

Gaussian Fit

(a)

0 1 2 3100

120

140

160

Pu

lse h

eig

ht

[arb

]

1/COS()

P1=150.4-4.2/cos()

P2=150.2-8.4/cos()

0,0 0,2 0,4 0,6 0,8 1,0 1,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

(Cos(1)+Cos(2))/2

(Cos(

1)-

Cos(

2))

/2

0,000

75,75

151,5

227,3

303,0

378,8

454,5

530,3

606,0

Color Scale Title

7. FFs pulse height correction for cos(Θ)

50 100 150 200 250

0,0

0,2

0,4

0,6

0,8

1,0

1,2

Pulse height [arb]

CO

S(

)

0,000

60,25

120,5

180,8

241,0

301,3

361,5

421,8

482,0

Color Scale Title

8. PHD correction

90 120 1502,5

3,0

3,5

4,0

4,5

5,0

MASS [amu]

PH

D [

MeV

]

100,0

237,1

562,3

1334

3162

7499

1,778E+04

4,217E+04

1,000E+05

60 90 1202,5

3,0

3,5

4,0

4,5

5,0

Energy [MeV]

PH

D [

MeV

]

200,0

580,0

1682

4877

1,414E+04

4,101E+04

1,189E+05

3,448E+05

1,000E+06

),(* postpost EAPHDPHE

The correction for FF pulse height caused by momentum transfer to working gas

atoms by FF (non ionizing collisions) during its deceleration – is called pulse height

defect (PHD). The PHD depends on the FF mass and kinetic energy and was

corrected in data analysis using parameterization presented above. Figures

demonstrate PHD dependence on mass and kinetic energies of FFs, measured in 235U(nth,ff) reaction investigation.


9. FF mass&energy distributions.

60 80 100 120 140 1600

2

4

6

8

Yie

ld [

%]

MASS [amu]

30 60 90 1200

50000

100000

150000

200000C

ou

nts

Kinetic energy [MeV]

Layer side

Backing side


10. Constant fraction time marking for PFN TOF measurement

0 20 40 60 80 1000

1500

3000

Co

un

ts

TOF [ns]

(b)

0 500 1000 1500 2000

-280

0

280

560A

mp

litu

de

[arb

. u

nit

s]

Sample No

B Cathode Pulse delayed by 400 ns

C Scaled Cathode Pulse (0.2)

D = C-B Waveform

(a)


11. Neutron separation from gamma radiation

The two window algorithm (fast and total light output component) was implemented and resulted function

ND(Fast,Total) was plotted on the upper and middle figs. demonstrates the function ND(Fast,Total) in

rotated according to equation

,where Ω – is axes rotation angle and S>1 – is the scaling factor. Red line in the middle figure is PFN-

PFG separation line . Lower figure demonstrates the TOF distribution before and after PFN separation.

)}cos()sin({),sin()cos( TFSTTFF

50 100 150 200 250

50

100

150

200

250

Fas

t'

Total'

PFN

PFG+background

(a)

200 250 3001

10

100

1000

Co

un

ts

TOF [ns]

Without PFN separation

With PFN separation

62 124 186 248

50

100

150

200

250

Tota

l Lig

ht o

ut [a

rb. u

nits

]

Fast Light out [arb. units]


-1,0 -0,5 0,0 0,5 1,0

1

10

100

1000

10000

Co

un

ts

Cos(CM)

235U(nth,F)

b)

)exp( ,1 y

CM

x

CMyx EEWW

12. PFN angular distribution measurement

C. Budtz-Jorgensen and H.-H. Knitter, Nucl. Phys., A490, 307

(1988) for PFN emission from complementary FF

70 80 90 100 110 120 130 140 150 160 170

0,1

1

10

100

1000

10000

B

MASS [amu]

Complement FF

FF to ND

Correction for FF recoil according to

Nucl. Instrum. and Meth., 115 (1974) 99

Wonder-2018 October 8-12

13. ND efficiency evaluation

0.00 0.05 0.10 0.151

10

100

1000

10000

B

VPFN/C

Measured

Maxwellian, T=1.31 MeV

0.02 0.04 0.06 0.08 0.10 0.12 0.14

0.1

0.2

0.3

0.4

0.5

PF

N_

Eff

icie

nc

y

VPFN/C


0,6 0,8 1,0 1,2

0

1000

2000

3000

4000

5000

6000

Co

un

ts

CosCM()

Unfolded

Measured

0,50 0,75 1,00

0

1000

2000

3000

4000

5000

6000

Cou

nts

CosCM

U-235

0 0

220

140

2

1

0

),(/)(

))cos(()cos(,,,()cos()( dTKETKEAY

VV

VVVVTKEAdTKEddVA

LABLAB

FLABCMLABLAB

14. PFN multiplicity on FF mass evaluation from measured data

(assuming isotropic PFN emission in CM)

FF mass and Energy values were calculated in iterative procedure taking into account FF recoil

after PFN emission according to A. Gavron, Nucl. Instrum. and Meth., 115 (1974) 99

60 80 100 120 140 16010

100

1000

10000

100000

1000000

Co

un

ts

MASS [amu]

With coincidence

Without coincidence

(a)

80 100 120 140 1600

2

4

6

(A

)

MASS [amu]

Measurement

Apalin et al


15. PFN multiplicity on FF TKE evaluation from measured data

(assuming isotropic PFN emission in CM)

dATKEAYVV

VVVVTKEAdAddVTKE

A LABLAB

FLABCMLABLAB

0 0

2

1

0

),(/)(

))cos(())cos(,,,()cos()(

140 160 180 200 22010

100

1000

10000

100000

1000000

Co

un

ts

TKE [MeV]

With coincidence

Without

140 160 180 2000

2

4

6

8

Measurements

(T

KE

)

TKE [MeV]


Adopted from C. Budtz-Jørgensen and H.-H. Knitter, Nucl. Phys., A490, 307(1988) and modified with digital

pulse processing apparatus. The only difference to 235U(nth,f) experiment was increase in sampling frequency

of WFD

16. Experimental setup and data acquisition system in

252Cf(sf) experiment.

),(200 ,),(),( ,),(

),(),()(

00

0

0

dTKEdATKEAYdAdTKETKEAYTKEAdTKETKEAY

dTKETKEAYTKEAA

),(200 ,),(),( ,),(

),(),()(

00

0

0

dTKEdATKEAYdAdTKETKEAYTKEAdATKEAY

dATKEAYTKEATKE


0.00 0.03 0.06 0.09 0.12 0.15

0.01

0.1

ND

_E

ffic

ien

cy

PFN_Velocity/C

0,00 0,03 0,06 0,09 0,12 0,15

100

1k

10k

100k

Cou

nti

ng

ra

te/V

2

PFN_Velocity [m/ns]

Measured

Maxwellian T=1.41 Me

0 2 4 6 8 10 12

0.01

0.1

ND

_E

ffic

ien

cy

PFN_KineticEnergy [Mev]

0 2 4 6 8 10 120.01

0.1

1

10

100

1000

10000

100000

Co

un

tin

g r

ate

/Sq

rt(E

)

PFN_KineticEnergy [MeV]

Measured

Maxwellian

ondistributi Maxwell-)2

exp(~)( where2

2

kT

mVVVM MeV; 1.41kT ,)

2exp()(

2

kT

mVVF

ondistributi Maxwell -)exp(~)( wherekT

EEVM MeV; 1.41kT ,)exp()(

kT

EVF


80 100 120 140 160

0

1

2

3

4

5

6

Nu

Bar [

%]

MASS [amu]

ShZ 2018

B-K 1984

-0,5 0,0 0,5 1,0 1,5

0,0

20,0k

40,0k

60,0k

80,0k

Co

un

ts

CosCM

Measured

Unfolded

Cf-252


80 100 120 140 160

0

1

2

3

4

5

6

Nu

Ba

r [

%]

MASS [amu]

ShZ 2009

ShZ 2018

140 160 180 200 220

0

1

2

3

4

5

6

7

8

9

10

ShZ 2018

ShZ 2009

Nu

Bar [

%]

TKE [MeV]

Inverse slope=13.2

80 100 120 140 1600

1

2

3

4

5

Nu

Ba

r [%

]

MASS [amu]

ShZ 2009

ShZ 2018


The new analysis have taken into account

FF kinetic energy correction due to FF recoil

Due to PFN emission


New experimental facility for PFN investigations in Dubna

For this new facility new Twin chamber was developed and tested.

Thanks to position sensitivity of the chamber the cosine of angle between

Fission axis and PFN can be measured with accuracy better than 0.02

50

100

150

200

250

50

100

150

200

250

X1 [arb]

X2 [

arb

]

0,000

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

100,0

110,0

120,0

Color Scale Title

50

100

150

200

250

50

100

150

200

250

Y1 [arb]

Y2

[a

rb]

0,000

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

100,0

110,0

120,0

Color Scale Title

30 35 40 45 50 55 60

0

12000

24000

36000

CO

UN

TS

Distance [mm]

X1-X2, =0.75 mm

Y1-Y2, =0.45 mm

Prompt fission neutron investigation

Experimental Results with Fission Fragment Detection (precision)


14. Conclusions

1. The digital data acquisition system was developed and tested in experiment.

2. The digital pulse processing algorithms was developed and tested both on-line and off-line.

3. The software for PFN multiplicity analysis was revised and some known bugs were removed

4. The result obtained in this work are differ from the literature and it forces us to revise

5. all stage of new development to verify or improve our recent result.

50 100 150 200 250

50

100

150

200

250

Wide window [arb]

Nar

row

win

do

w [

arb

]

0,000

32,75

65,50

98,25

131,0

163,8

196,5

229,3

262,0

Color Scale Title

50 100 150 200 250

50

100

150

200

250

Wide window [arb]

Nar

row

win

do

w [

arb

]

0,000

221,3

442,5

663,8

885,0

1106

1328

1549

1770

Color Scale Title

50 100 150 200 250

50

100

150

200

250

Wide window[arb]

Nar

row

win

do

w [

arb

]

0,000

37,50

75,00

112,5

150,0

187,5

225,0

262,5

300,0

Color Scale Title

50 100 150 200 250

50

100

150

200

250

Wide window [arb]

Nar

row

win

do

w [

arb

]

0,000

54,75

109,5

164,3

219,0

273,8

328,5

383,3

438,0

Color Scale Title

Cf-252 U-235

Documents

Prompt fission neutron (PFN) emission in reaction