Recommended data on selected gamma-ray and conversion-electron calibration sources

Nuclear Instruments and Methods in Physics Research A297 (1990) 223-229North-Holland

Recommended data on selected gamma-ray and conversion-electroncalibration sourcesW.H. TrzaskaCyclotron Institute, Texas A&M University, College Station, TX 77843, USA, andDepartment of Physics, University ofJyvdskyld, SF-40100 Jyvdskyld, Finland

Received 15 December 1989 and in revised form 18 April 1990

A compilation of experimental energies and relative intensities for gamma-ray and conversion-electron transitions from the decayof 207Bi, 152Eu, 133Ba, 36Co, and 66Ga is presented. In the cases of known transition multipolarities and mixing ratios, calculatedvalues are given for the conversion-electron intensities . Often, these calculated values are more reliable than the measured ones.

1. Introduction

Energy and efficiency calibrations are an indispensa-

ble part of every measurement in nuclear spectroscopy .

They require reliable data on a set of calibration sources

covering a sufficiently wide range of energies. Such data

are usually scattered over many publications and, there-fore, cumbersome to obtain . This is especially true for

conversion-electron data where, unlike gamma-rays, theexperimental information is less complete and less pre-cise. For better results, since the multipolarities and themixing ratios of appropriate transitions are often known,

one can more reliably calculate electron intensities using

the experimental gamma-ray intensities and the tabu-

lated values of the conversion coefficients . This work

includes such calculations based mainly on the tables byRbsel et al . [1] - the most extensive and up-to-date

tables of internal conversion coefficients . These tables

extend up to transition energies of 5 MeV for aK and

cover elements from Z = 30 to 104. For Z < 30 the

tables by Band et al. [2] were used . It is worth mention-

ing that : (i) surprisingly many authors, without an ap-

parent reason for doing so, are still using the older

tabulation [3] by Hager and Seltzer, (ii) for most of the

less demanding applications there are simple computer

codes available, usable even on small programmable

calculators [4].This compilation of the experimental data on en-

ergies and intensities includes some of the commonly

used calibration sources : 207Bi, 152Eu, 133 Ba, 56Co, and

of 66Ga. The choice of the sources as well as the idea of

this compilation result from the needs encountered dur-

ing gamma-ray and electron spectroscopy work done at

the Physics Department at the University of Jyvdskyld

over the past decade . With the exception of the short-

lived 66Ga source, all the listed sources can be readily

purchased . The tables in this publication have been

0168-9002/90/$03 .50 c 1990 - Elsevier Science Publishers B.V. (North-Holland)

223

arranged to aid in the calibration measurements. Forconvenience, the relative intensities for gamma-rays andfor conversion-electrons are normalized to 1000 decays.For 56Co and 66Ga, due to very small values of conver-sion coefficients, the relative electron intensities arenormalized to 106 decays . The half-life information isalso provided [5] .

In the cases where the calculated values of conver-sion-electron intensities differ significantly from the ex-perimental ones, the use of the former is recommendedsince many of the electron measurements in the pastsuffered from possible systematic errors in the effi-ciency determination [6] .

2. M7Bi source

The gamma-ray energies and intensities associated

with the decay of 207Bi are very well known [7] . For

convenience, these values are shown in table 1 (multi-

plied by 9.775 to normalize to 1000 decays [7]). To

calculate the K, L1 , L 2 , and L3 conversion coefficients a

cubic-spline interpolation in a doubly logarithmic scale

to the tabulated values by R6sel, Fries, Adler, and Pauli

[1] was performed . Also electron binding energies were

taken from ref. [1]. For the 569.7 keV transition a pure~ 17.~1E2 was assumed

. The 1003 . ! !RC V LI dliwtlull 10 i11,

M4 with a small admixture of E5 (8 = 0.03(1) [7]) .

Unfortunately, the E5 multipolarity is not covered by

the tabulation . The approximate value can, however, be

extrapolated from the existing numbers. The extrapo-

lated value for the E5 K-conversion coefficient is 3.9 x

10-2 as compared to 9.78 x 10-2 for a pure M4. These

values do not differ much and, therefore, a small admix-

ture of the E5 multipolarity to the dominant M4 has a

negligible effect on the conversion coefficients for this

224 W. H. Trzaska / Gamma-ray and conversion-electron calibration sources

transition energy . The 1770.2 keV transition is a M1 +E2 with the mixing parameter 8 = 0.09(2) [7] .

The calculated electron intensities shown in table 1represent the experimental gamma-ray intensities multi-plied by the calculated conversion coefficients . Intensityvalue for the L peak is a sum of the L1 , - - -, L3 intensi-ties (not resolved with Si(Li) detectors) . The energy ofthe L line was obtained as intensity-weighted average ofthe L l , - - -, L3 energies. The present calculated conver-sion-electron intensities from the decay of 2° 'Bi presenta substantial improvement over the previous calculation[8] : the latest experimental data were used as well as amore recent tabulation of the calculated conversioncoefficients .

The experimental data on the conversion-electronintensities from the decay of 2° 'Bi are only known toreasonable accuracy . The measurements have not beenrepeated since the early 70s. The small experimentalerrors, as shown in table 1, are the result of the evalua-tion of a number of old measurements and not theresult of a single high-precision experiment . A recentpaper by Nemeth [9] provides the best derivation of theintensities extracted from the previously published ex-periments. Unfortunately that paper falls short ofevaluating all of the intensities . Further, the latest issueof the A = 207 Nuclear Data Sheets [7] is not includedin the evaluation, neither is the precision gamma-rayintensity measurement by Yoshizawa et al . [10] . Also,when referring to theoretical values of conversion coef-ficients, the tabulation by Hager and Seltzer [3] isquoted instead of the more recent tabulation by R6se1et al . [1] .

The experimental K intensities in table 1 are derivedfrom the aK 63 = 0.0945(22) and aK9 = 0.0156(3) given

Table 1207Bi source ; Ti/2= 31.8(19) a. Gamma-ray and conversion-electron energies (keV) and relative intensities (normalized to 1000decays)

in ref . [9], and from the gamma-ray intensities from ref.[7] . With these numbers we get : IK9 =15 .25(3) andIK63 = 70.0(16). However, since the aK values in ref. [9]were normalized to another (less recent) theoreticalvalue of the aK

9(E2) the intensities appearing in table 1have been corrected for that by multiplying by 0.01597/0.0156 . Such a correction, of course, does not changethe relative intensities but merely gives a cosmeticchange enabling better comparison with the calculatedvalues . At the same time, the correction does change theabsolute values of conversion coefficients.

The experimental a770 = 0.0030(5) from ref. [11] andquoted in ref. [7] has, as well, to be corrected since itwas calculated relative to a different calculated value ofa569(E2) . The correction factor is this time 0.01597/0.02048 resulting in a clearly underestimated value of0.0023(4) . The author of ref. [11] was aware of possibleerrors in the estimation of this conversion coefficientdue to insufficient thickness of the Si(Li) detector used .For that reason we reject that number. The measure-ment by Allan [12] gives I1770/J1063 = 0.0033(2). Bymultiplying that number by IK63 =71.7(17) one getsIK7° = 0.237(15), as it appears in table 1 .

The experimental L-conversion intensities wereevaluated from experimental K/L ratios . Using thedata from refs . [11,13] and other experimental valuesquoted in ref . [13], one gets the weighted average of:K/L(569) = 3.33(5) and K/L(1069) = 3.75(6) . Both inref . [11] and [13] the Si(Li) detectors used were too thinto measure the 1770 keV transition without an apprecia-ble loss of efficiency . However, the K/L ratios, as arelative intensity of two closely located lines and there-fore less prone to errors from efficiency corrections, canbe used to determine the IL7° . Using the weighted

Egamma Igamma ± Eel Shell Mult. Icalc lexpe569.702 977.5 3.9 481.697 K E2 15 .62 15.62 0.30

553.841 LI 2.30554.502 L2 L .54556.667 L3 0.54554.4 L 4.38 4.69 0.11

1063 .662 740.9 2.4 975 .657 K M4 +E5 72.43 71 .7 1 .71047.801 Ll 14.271048.462 L2 2.811050.627 L3 1.301048 .1 L 18.38 19.12 0.55

1770.237 69.68 0.28 1682.232 K M1 + E2 0.2522 0.237 0.0151754.376 Ll 0.03761755 .037 L2 0.00241757.202 L3 0.00031754.4 L 0.0403 0.038 0.004

3 . 152Eu source

W.H. Trzaska / Gamma-ray and conversion-electron calibration sources

average of the two, one gets K/L(1770) = 6.24(46) . Un-fortunately, ref. [12] did not measure the K/L but onlythe K/(L + M).

To summarize, the adopted experimental conversioncoefficients, normalized to a59 = 0.01597, are: a59 =4.80(11) X 10-3 , aK63 = 9.67(23) X 10-2, aL63 = 2.58(7)x 10-2,

a1770= 3.4(3) x 10 -3 , aï7° = 5.45(63) x 10 -4 .

As one of the most widely used, general-purposecalibration sources, the gamma-ray energies and intensi-ties associated with the decay of 152Eu are very wellknown [14] . The gamma-ray energies shown in table 2are from ref . [14] updated to the recently measured andevaluated values in ref. [15] . For the purpose of mostapplications the differences in gamma-ray energies be-tween refs . [14] and [15] are negligible. However, it isworth pointing out that these differences frequentlyexceed quoted errors . For instance, ref. [14] gives1085.914(3) and, for the same transition, ref. [15] recom-mends 1085.842(4) - a value that is 10 units of error

Table 2152Eu source ; T1/2 =13.542 a . Experimental gamma-ray and conversion-electron energies (keV) and relative1000 decays) ; for the 121 keV transition the calculated conversion coefficients were used

225

smaller (0.072/(0.003 + 0.004)) . In all conflicting casesthe later value [15] was used .

Experimental gamma-ray intensities in table 2 arethe average calculated from the recent measurements byMehta et al . [16] and Iwata et al . [17] . These two mostrecent experiments are in a good agreement with eachother and do not differ significantly from the NuclearData Sheets [14] . The only exception is the intensity ofthe 963.3-964.0 doublet for which the intensity given inref. [14] is by some 10 standard deviations lower thanwhat the authors of refs. [16,17] measured . For conveni-ence, the relative intensities in table 2 are normalized to1000 decays by multiplying by 2.0945 - the averagevalue of 2.104(8) [17] and 2.085(8) [18].

Experimental relative intensities of conversion elec-trons, except for the 121 .8 keV transition, were mea-sured with good accuracy by Colvin and Schreckenbach[19] using the double-focusing iron-core electron spec-trometer BILL [20] . These latest results agree well withprevious measurements [21] only for the electron en-ergies above 400 keV. Below 400 keV the earlier results,measured with a Si(Li) detector, systematically differshowing higher than expected intensities [6] . Such a

intensities (normalized to

Egamma Igamma f Eel Isotope Shell lei ±

121.7825 286 .5 1 .3 74.948 Sm K 193 .8 cale .114.046 Sm L1 18.3 cale .114.471 Sm L2 45.4 cale .115.066 Sm L_, 11 .9 talc .114.6 Sm L 108 .5 cale.

244.6989 75.82 0.46 197.865 Sm K 6 .13 0.20236.962 Sm L 1 0.692 0.024237.387 Sm L2 0.541 0.019237.983 Sm L3 0.424 0.016237.4 Sm L 1.657 0.034

344.281 266.0 1 .2 294.042 Gd K 8.69 0.30335.905 Gd L1 1 .052 0.036336.351 Gd L2 0.569 0.02.0337.038 Gd L3 0.388 0.014336.2 Gd L 2.009 0.044

411.115 22.62 0.13 360.876 Gd K 0.465 0.016

443.965 31.25 0.19 397.131 Sm K 0.205 0.008

586.294 4.59 0.17 536.055 Gd K ÛA09 0.005

615.416 Ell) 565.177 Gd K 0.095 0.003

656.484 1 .49 0.10 609.650 Sm K 0.079 0.003

698.675 8.80 0.08 641.841 Sm K 0.342 0.011

778.903 130.17 0.44 728.664 Gd K 0.230 0.008

867.390 42.60 0.19 820.556 Sm K 0.143 0.005

964.055 147.58 0.44 917.221 Sm K 0.393 0.014

1085.842 100.62 0.31 1039.008 Sm K 0.213 0.008

1089.700 17.38 0.08 1039.461 Gd K 0.0394 0.0016

1112.087 135.81 0.48 1065.253 Sm K 0.277 0.009

1408.022 209.45 0.59 1361.188 Sm K 0.115 0.005

226

different : can be explained if one rejects the commonlyu,ed assumption of a flat detector response to theFiectrons with ranges well below the detector thickness.In a preliminary study [6] it was shown that the ef-ficiency of a 4 mm thick Si(Li) detector drops linearlyby about 140 from 0 to 1 MeV electron energy . Such a

W.H. Traaska / Gamma-ray and conversion-electron calibration sources

Table 3133Ba source ; Ti /2 =10.57 (4) a. Gamma-ray and conversion-electron energies (keV) and relative intensities (normalized to 1000decays)

behavior is in sharp contrast with calculations [22] butagrees well with the intensity data obtained with theBILL spectrometer [19] .

To avoid the controversy over the efficiency calibra-tion of a Si(Li) detector, only the BILL data were usedin table 2. To normalize the results to 1000 decays a

Egamma Igamma f Eel Shell Icalc lexpe f

53.161 21 .99 0.22 17.176 K 108.0 109.0 21 .047.447 Li 13 .2 12.66 0.6947.802 L2 3.048.149 1- 3 2.847 .5 L 18 .9

79.623 26.2 0.6 43.638 K 40.0 36 .8 2.673.909 LI 4.89 4.72 0.4174.264 L~ 0.59 0.57 0.1074.611 L3 0.36 0.37 0.0874.0 L 5.84 5.66 0.43

80.997 340.6 2.7 45 .012 K 497.0 430.0 16.075.283 Lt 60 .5 51 .9 1.375.638 L2 8.5 8.08 0.4875.985 L3 5.9 5 .89 0.3375 .3 L 74.9 65.9 1.4

160.613 6.45 0.08 124.628 K 1.525 1 .427 0.027154.899 Lt 0.167 0.141 0.012155.254 L2 0.074 0.070 0.006155.601 L3 0.069 0.066 0.006155.1 L 0.310 0.278 0.015

223.234 4.50 0.04 187.249 K 0.384 0.324 0.010217.520 Li 0.047217.875 L2 0.003218.222 L3 0.001217.6 L 0.051 0.041 0.006

276.398 71.64 0.22 240.413 K 3.31 3.28 0.35270.684 Li 0.35271.039 L2 0.14271.386 L3 0.12270.9 L 0.61 0.58 0.07

302.853 183.3 0.6 266.868 K 6.98 6.92 0.69297.139 Li 0.850297.494 L, 0.047297.841 L3 0.011297.2 L 0 .909 1 .00 0.13

356.017 620.5 1.9 320.032 K 13.08 13.08 E2350.303 L, 1 .44350.658 L2 0.41351.005 L3 0.33350.5 L 2.18 2.16 0.12

383.851 89 .4 0.3 347.866 K 1 .506 1.54 0.17378.137 Li 0.168378.492 L 2 0.044378.839 L3 0.033378.3 L 0.244 0.255 0.034

factor of 0.15766 was used . This factor comes from themeasured Igamma (per 1000 decays) = 75.82 and acalculated value of OK(E2) = 0.08089 for the 244 keVtransition . The calculation of conversion coefficients forthe 121 and 244 keV E2 transitions was done in thesame way as in the case of 207Bi .

4 . 133Ba source

The experimental gamma-ray energies and intensitiesin table 3 were taken directly from ref. [23] except thatthe present normalization is to 1000 decays. Based onthese intensities and on the experimental mixing ratios8 from ref. [23] the conversion-electron intensities werecalculated ( Icalc). For the calculation a cubic-splineinterpolation in a doubly logarithmic scale to the tabu-lated values [1] was used .

The experimental conversion-electron intensities intable 3 were compiled from the electron measurementsby Hennecke et al . [24], Thun et al. [25], and byTörnkvist et al . [26], and are normalized to the calcu-lated value of 13.08 for the IK

6 .

5 . MCo source

Gamma-ray energies associated with the decay of56Co have recently been measured with good accuracy[27] . The values Egamma and Igamma in table 4 are takenfrom that work . The experimental K-conversion intensi-ties are from the measurements of Pettersson et al. [28]and are normalized to the calculated aK

6(E2) = 2.685 x

Table 456Co source ; TI/2 = 77.35(23) d. Gamma-ray and K-electron energies (keV) and relative intensities (normalized to 103 and 106 decays

W.H. Trzaska / Gamma-ray and conversion-electron calibration sources

227

10 -4 . The gamma-ray intensities in table 4 are normal-ized to 103 decays and the electron intensities are nor-malized to 106 decays. This normalization is apprcxi-mate . For absolute intensities a factor of 0.99935(25)should be used [29] .

Using gamma-ray energy and intensity data fromref. [27] and the mixing ratios 8 and from ref. [29] theK-conversion electron intensities were calculated (IK1C ).The procedure was the same as for

207KBi except that the

tabulation by Band et al . [2] was used . No calculationwas done for the 787 keV transition because 8 is notknown [29]. However, since the aK has been measured[28] to be aKpe = 2.88(31) x 10-4 (normalized to theaK6(E2) = 2.685 x 10-4), one can extract 181 from thecalculated aK7(E2) = 2.303 x 10 -4 and aK7(Ml) _3.249 x 10-4 . This way one gets 0.7 < 181 < 3.0, whereaK = 2.88 x 10 -4 corresponds to 181 = 1.3 .

6 . 66Ga source

The short half-life of 9.49 h makes the 66Ga sourceimpractical to use in laboratories without easily availa-ble accelerator facility . However, there is not muchchoice if energies above 3.5 MeV are of interest [30] . Aconvenient way of producing 66Ga is via the 66Zn(p, n)reaction at EP = 12 MeV [31] ; use of natural Zn ispossible (27.9% of 66Zn). Also the 6sCu( a, 3n) reactionat about E,,, = 40 MeV could be used [32] .

The most recent measurements of gamma-ray en-ergies and intensities from the decay of 66Ga were donein 1971 by Camp et al . [33] and, in 1970, by Phelps et

respectively)

Egamma Igamma EK IKcalc Ixexile

733.516 1.93 0.12 726.402 0.516 0.51 0.10787.742 3.05 0.13 780.628 - 0.88 0.08846.769 1000.0 3 .0 839.655 268.5 268 .5 E2977.368 14.35 0.16 970.254 2.14 2.02 0.061037.842 141.6 0.5 1030.728 18 .7 19.4 0 .41175.097 22.41 0.12 1167.983 2.38 2 .23 0.041238.286 660.6 2 .1 1231.172 71 .6 71.6 0.91360.206 42.65 0.17 1353.092 3.35 3.41 0.721771.344 154 .9 0 .5 1764.230 7.50 7.56 0.221963.714 7.07 0.11 1956.600 0.286 0.29 0.062015.190 30.26 0.14 2008.076 1.19 1 .28 0.062034.769 77.66 0.28 2027.655 2.95 3 .13 0.082598.459 169.6 0 .6 2591.345 4.27 4.67 0.103009.587 10.0 0 .1 3002.473 0.198 0.23 0.063201 .953 30.4 0 .3 3194.839 0.550 0.65 0.033253.428 74 .1 0.7 3246.314 1.33 1 .53 0.063273.006 17.5 0 .2 3265.892 0.305 0.36 0.033451 .148 8 .75 0 .1 3444.034 0.143 0.11 0.02

228 W.H. Trzaska / Gamma-ray and conversion-electron calibration sources

Table 566Ga source ; T1/2 = 9.49(8) h . Gamma-ray and K-electron energies (keV) and intensities normalized to 10 3 decays for gamma-raysand to 10 6 decays for electrons . IT is the total conversion electron intensity

al . [34] . The energies shown in table 5 are the average ofthis two experiments [33] . The relative gamma-ray in-tensities were normalized to 1000 decays by multiplyingby 379(12) [35] but also corrected for the systematicerror. It was pointed out by McCallum et al . [36] thatthe assumption of a linear efficiency drop (in the log-logscale) for Ge(Li) detectors at gamma-ray energies above2.5 MeV, as used in refs . [33,34], is not justified andleads to systematic errors . A correction factor of f(E)=1.053 -0.079E + 0.026E2 for 2 :::_~ E < 5 MeV wassuggested [361 . It is difficult to evaluate the precision ofthe final intensities after the correction is applied. Forthat reason no error bars are quoted in table 5 . Theaccuracy of the original data was claimed to be to about1%, although this is questionable.

The calculated K and total conversion-electron in-tensities were computed using the corrected gamma-rayintensities, as appearing in table 5, and the samenumerica' procedure as for the other sources . The tabu-lated values by Rosel et al . were used [1]. Since, unlikethe aK tabulation that extends up to 5 MeV; the a_ islisted only up to 1.5 MeV, an extrapolation was used forthe IT c . The error of such an extrapolation is probablysmall because the atot/aK ratio remains fairly constantat about 1 .12 (Z = 30, E > 400 keV, for the El, E2 andM1 transitions) [1] . In case of Ml/E2 ambiguity in thetransition multipolarity two corresponding intensitieswere calculated. The intensity normalization for elec-trons in table 5 is to 10 6 decays .

For this source, the experimental conversion-electronintensities are not accurately known . The values listed

in table 5 are from the measurement by Schwarzschildet al . [32] normalized to 1T39 =102.

Acknowledgement

The author wishes to acknowledge fruitful discus-sions with Prof. Juhani Kantele and Prof . Thomas M.Cormier in preparation of this manuscript.

References

[1] F . Rbsel et al ., At . Data Nucl . Data Tables 21 (1978) 91 .[21 I.M. Band et al., At. Data Nucl. Data Tables 18 (1976)

433 .[3] R.S. Hager and E.C. Seltzer, Nucl. Data A4 (1968) 1 .[4] J. Kantele, Nucl. Instr . and Meth . A275 (1989) 149 .[5] K . Debertin and R.G . Helmer, Gamma- and X-ray spec-

trometry with Semiconductor Detectors (North-Holland,1988) .

[61 W.H. Trzaska, Ph.D. Thesis, University of Jyvdskylä,(1989) .

[7l M.R . Schmorak, Nucl . Data Sheets 43 (1984) 383 .[81 L.J. Jardine and C.M . Lederer, Nucl. Instr. and Meth. 120

(1974) 515 .[91 Zs . Nemeth, Nuc!. Instr. and Meth . A267 (1988) 153 .

[10] Y . Yoshizawa et al., Nucl . Instr. and Meth . 174 (1980)109.

[111 F.T. Avignone III, Nucl . Instr . and Meth. 116 (1914) 521 .[121 C.J . Allan, Can . J . Phys . 49 (1971) 157.[131 F . Freund, Z . Phys . 264 (1973) 259 .[141 L.K . Peker . Nucl. Data Sheets 58 (1989) 93 .[151 E.K . Warburton and D.E. Alburger, Nucl . Instr. and

Meth . A235 (1986) 38 .

Egamma [gamma EK Mult. KIcalc IT

calcITexpe

833.65(8) 60.45 824.0 E2 25.2 28 .1 25.5 2 .61039.35(8) 379.0 1029.7 E2, 91.7 102.0 102.0 5 .11333.37(9) 12.36 1323.7 E2 1.72 1 .92 2 .21 0.221418.97(9) 6.37 1409.3 ?1918.66(9) 21.41 1909.0 ? 2.80 0.702190.20(15) 57.31 2180 .5 ? 3 .14 0.352422.50(15) 19.76 2412.8 ? 0.98 0.542752.27(10) 239.1 2742.6 M1 8.38 9.36 11.13 0.893229.35(20) 15.88 3219.7 Ml/El 0.43/0.29 0.48/0.323381 .30(20) 15.31 3371 .6 Ml 0.385 0.4303422.50(20) 8.94 3412.8 ?3791 .56(10) 11.41 3781 .9 Ml 0.240 0.268 0.40 0.144086.45(15) 13.33 4076.8 Ml/El 0.25/0.18 0.28/0.204295.50(20) 41.52 4285.8 Ml 0.724 0.808 0.98 0.234462.10(14) 8.63 4452.4 Ml 0.142 0.1594806.60(20) 18.64 4796.9 Ml 0.276 0.308 0.47 0.12

W.H. Trzaska / Gamma-ray and conversion-electron

[16] D. Mehta et al ., Nucl. Instr. and Meth. A245 (1986) 447.[17] Y. Iwata et al ., Nucl . Instr. and Meth . 219 (1984) 123.[18] K. Debertin, Nucl . Instr. and Meth. 158 (1979) 479.[19] G.C . Colvin and K. Schreckenbach, Nucl. Instr. and Meth.

228 (1985) 365.[20] W. Mampe et al ., Nucl . Instr. and Meth . 159 (1978) 243.[21] J. Deslauriers and S.K . Mark, Nucl . Instr. and Meth. 159

(1979) 243.[22] M.J. Berger et al., Nucl. Instr . and Meth . 69 (1969) 181.[23] Yu.V . Sergeenkov and V.M. Sigalow, Nucl . Data Sheets

49 (1986) 639.[241 H.J. Hennecke et al ., Phys . Rev. 159 (1967) 955.[25] J.E. Thun et al ., Nucl . Phys . 88 (1966) 289.[26] S. T6rnkvist °t al ., Nucl . Phys. A142 (1970) 238.[27] G. Wang, E.K . Warburton and D.E. Alburger, Nucl.

Instr. and Meth . A272 (1988) 791.

calibration sources

229

[28] H. Petterson et al ., Ark. for Fys. 29 (1965) 423.[29] H. Junde et al ., Nucl. Data Sheets 51 (1987) 1 .[30] R.G . Helmer et al ., At . Data Nucl . Data Tables 24 (1979)

39 .[31] F. Szelecsenyi et al ., ATOMKI 1988 Ann. Rep. (1989) p.

3.[32] A. Schwarzschild and L. Grodzins, Phys . Rev. 119 (1960)

276.[33] D.C . Camp and G.L. Meredith, Nucl . Phys . A166 (1971)

349.[3=}] M.E . Phelps, D.G . Sarantities and W.G. Winn, Nucl .

Phys. A149 (1970) 647.[35] N.J . Ward and F. Kearns, Nucl . Data Sheets 39 (1983) 1 .[36] G.J . McCallum and G.E . Coote, Nucl. Instr . and Meth .

124 (1975) 309.