Appl. Radial. hf. Vol. 41, No. 3, pp. 333-334, 1990 hr. J. Radiat. Appl. Instrum. Part A !C Pergamon Press plc 1990. Printed in Great Britain 0883-2889/90 $3.00 + 0.00

K-Electron Capture Probability to the 136 keV Level in the Decay of “Co

KULWANT SINGH, T. S. GILL and K. SINGH

Department of Physics, Guru Nanak Dev University, Amritsar-143005. India

(Receired 12 September 1988; in recisedform 25 May 1989)

The K-electron capture probability to 136 keV in the decay of “Co has been determined by K x-ray-y-ray sum peaks observed in single HPGe (28.27 mm’ x 5.5 mm) detector. The results are independent of fluorescence yields and detector efficiencies.

1. Introduction

The probability of orbital electron capture from any shell or subshell can be determined from the intensities of x-rays, y-rays or conversion electrons. Bambynek et al. (1977) have reviewed experimental data on electron capture proba- bilities. There are several methods from which the K-capture probability to a level can be determined. In all these methods, the knowledge of the absolute efficiency for K x-rays is needed, the measurement of which requires an identical geometrical configuration.

In the present paper, the K-capture probability has been measured from the sum peaks observed with a HPGe detector. The same method was also used by Singh and Sahota (1983) for Cs. In this measurement the fluorescence yield and absolute detector efficiency for K x-rays are practically cancelled.

2. Experimental Set-up and Results

The standard source of strength 1.1 x lo4 Bq was placed at a distance of 3 mm from the window of the HPGe detector. The energy resolution of the detector was 165 eV for the 5.9 keV line of Fe. The sum spectrum was recorded with a 4096-channel analyser; the relevant portion of the spectrum is shown in Fig. 1. Details of the method are given in our earlier paper (Singh and Sahota, 1983). The nuclide s7Co decays by electron capture (Fig. 2) to excited states of “Fe. Since the 136 keV y-ray is in coincidence with the K x-ray arising after K-capture to the 136 keV level, the area under the sum peak (136 + K,) can be written as:

I N 1X+ K, = M’K

K, ------c,,Pk(136)N,16 I& + It+

(1)

where ~a is the K-shell fluorescence yield in Fe, Ik, and IKg are the relative intensities of K, and K, x-rays. tk, is the absolute photopeak efficiency for K, x-rays. N,,, denotes the area under the 136 keV peak, corrected for summing.

Similarly, the area under the sum peak (122 + K,) can be written as:

N 122+iG = WK N,,,. (2)

105 7 136 4 ,; “..

:

1q4 E 4

I

‘.*, 136cK,

“_.;.:,. ,: ,. :,_

. :-‘.;>- .,.,. _ -:- -,), .;-.:.y:,-’ ‘5_

z? 1..,,. . . ..,.

E

z I I I I I

2690 2740 2790 2640 2690 2940

: 1:’

*e/” / ; ‘...,,

4 122+ K,

.T. i...___

‘.

-‘~ZLX..._,.__ :..a

.c ‘.

,. 103- ‘.,,

5'-

<. "%.'_....,

, I / I I

2410 2460 2510 2560 2610 2660

Channel no.

Fig. 1. Relevant portion of the sum spectrum

It is apparent from the decay scheme that both the 136 and 122 keV lines depopulate the same level. By division, the values of ~2~ and ck, can be eliminated.

N 136+K, f’~(136) N,,, _._ N (3)

1*Z+K, P,(,36)+ A_ N ‘E

1 +r’? 1

The values of conversion coefficients (x,(14) = 7.35 + 0.19 and c(r(14) = 8.18 + 0.11 were taken from Hansen (1985). The typical values of the areas obtained for one set of measurement for N,Z2r Niz2 + x,, N,,, and N,,, + k,, were 63,323O rfr 2580,41,987 f 280,627,688 & 810 and 2190 _t 77 respectively.

The values of Pk(136) obtained for two independent measurements along with other experimental and theoretical values are shown in Table 1. The contributions to 136 and 136 + K, due to the summing effect of 122 + 14 and

7/Z- (270 d)

5’CCl 5,2_ 136 / 131 1’2

1/2-

57Fe

Fig. 2. Decay scheme of s7Co.

334 Technical Note

Table I. Emerimental and theoretml K-electron-caoture arobabilities

Experimental P, values

Level ~ Theoretical energy Rubinson and Mukery and P, value

(keW Present Gopinath (1968) Bosch PI <I/. (1969) Chm (1973) (Present)

136 0.891 * 0.054 0.885 _t 0.009 0.87 _t 0 02 0.92 2 0.010 0.901 0.895 k 0.060 Wt av. value

= 0.893 + 0.040

122 + I4 + K, are apparently negligible in this experiment. The present relative value of P, (136) has also been compared with the theoretical value calculated using the expression given by Behrens et al. (1969)

In the above expression. Behrens er ~1. (1969) have taken into account the effects of the finite size of the nucleus, the screening of the nuclear electromagnetic field by the orbital electrons and electron exchange.

E,. B,, and B,, are the electron binding energies in the daughter atom and have been taken from Lederer and Shirley (I 978). while [I,. /IL,, P,_ , and &,, , . the amplitudes of radial wave functions have been taken from Bambynek <‘I ul. (1977).

Our experimental value of P, 1s in agreement with the values determined by Rubinson and Gopinath (1968), Bosch c/ cl/. (1969) and with the theoretical value. The value of P,( 136) determined by Mukerji and Chin (1973) is higher than all other values.

The present method is advantageous over the earlier ones because this method does not involve M‘~ and absolute x-ray efficiency, the measurement of which requires a separate geometry vvhich is difficult to achieve.

.4c,~no,l,/~~d~mlent~~The authors are grateful to CSIR. Go\- ernment of India. for a research project for carrymg out this work.

References

Bambynek W.. Behrens H.. Chen M. H.. Craseman B.. Fitzpatrick M. L.. Ledingham K. W. D., Genz H.. Mutterer M. and Intemann R. L. (1977) Orbital electron capture by the nucleus. &I,. .v&. P/I~s. 49, 77.

Behrens H.. Jenecke J. and Landolt-Bomstein (1969) ~Y~mrcric~ul &r/u Furwrionul Relutionship m .‘Qienw urld Twhnolog~~. Xumeric~rrl Tuhlr.t ./or /3 -dwuy und Electron Cup/urr. New Series Group, pp. I, 4. Springer-Verlag. Berlin.

Bosch H. E.. Fariolli N. A., Martin N. and Simon M. C. (1969) X-ray spectroscopy related to the determi- nation of electron capture ratios. Nucl. Insrum. Mrthodv 73, 313.

Hansen H. H. (198.5) European appl. res. rept. Nut,/. .%i. T~hnol. 6, 777.

Lederer C. M. and Shirley V. S. (1978) T&e of /coro~<,.~. 7th edn. Wiley, New York.

Mukerji A. and Chin L. (1973) Prwrrdings of /hr Inr. Corzf: on Inner Sht~ll loni.wriotl Phcnomcwon and Futuw App’pliccrtions.

Rubinson W. and Gopmath K. P. (1968) Convertion co- efficient of the “Fe l4.4-keV transition, the K-capture fraction in “Co e -capture, and the K-fluorescence yield of Fe. Phy.v. Ret,. 170, 969.

Singh K. and Sahota H. S. (1983) A new approach to K-electron-capture probabilities to the 437 and 384 keV levels in the decay of “‘Ba. J. Phys. G. ,Vuc/. PIIW. 9, 1565.