Note on the methods of determining the subshell photoelectric cross sections

NUCLEAR

INSTRUMENTS

AND METHODS

81

(1970)

205-206;

© NORTH-HOLLAND

PUBLISHING

CO.

N O T E O N THE M E T H O D S OF D E T E R M I N I N G THE SUBSHELL PHOTOELECTRIC CROSS SECTIONS K. P A R T H A S A R A D H I

The Laboratories Jbr Nuclear Research, Andhra University, Waltair, India Received 31 October 1969 The available methods for the determination of the subshell photoelectric cross sections of g a m m a rays are discussed. A few results on the subshell cross sections obtained by multiplying the total photoelectric cross sections by the subshell to total ratios,

are presented. It has been concluded that this method of obtaining the subshell photoelectric cross sections is not only simple but also better than a direct measurement in general.

Subshell photoelectric cross sections of g a m m a rays can be determined either by directly measuring the subshell photoelectron intensity for a known incident g a m m a flux on a foil, or by multiplying the total experimental photoelectric cross sections with the experimental ratio, subshell to total. The first method involves not only high resolution experimental setup but also various experimental difficulties in measuring the total photoelectron subshell intensities in view of the characteristic angular distribution. However, in the second method if the ratio is known, the subshell cross section can be determined. The total photoelectric cross section can be determined accurately either by direc0) or by indirect method2). Moreover, in an investigation 3) it has been shown, energy independence

of these ratios within the experimental accuracy, even in uranium. Hence the second method becomes more simple. As far as K-shell cross sections are concerned results using both the methods are available 4-7). However, photoelectron subshell cross section measurement for L and higher shells is rather difficult in view of the high resolution and low intensity measurements. Hence no direct attempts seem to have been made on the total subshell photoelectric cross sections. As has already been mentioned the second method is simpler, using the ratios reported by Hultberg3), Davisson 8) and Bergkvist 9) the L and M + N + O + . . . subshell photoelectric cross sections are estimated from the total experimental photoelectric cross sections which 2) are

TABLE 1 Subshell photoelectric cross sections of g a m m a rays in barns per atom. Element

Energy (keV)

K-shell U Pb

1332 662 280 662

Au Sn

662 280

L-shell U

5.4 12.8 94.0 10.2 10.8 1.9 14.0

± 0.3 ± 0.7 ~ 3.0 -~_ 0.3 ~ 0.7 ~- 0.3 ~ 0.4

2620 1332 662 50 412 50

Au M+N+O+ U

Method I

Ref.

Method 11

6)

4.7 11.9 97.7 9.8

4) 4) 5) 4) 4) ~)

± ~ ± ~-

0.2 0.2 3.0 0.2*

1.27 ± 0.07* 13.0 ~z 0.50 0.28 0.86 3.60 2945.00 5.40 1710.00

~ j~~J: -k

Ref.

Theory

v) 7) 7) ~)

4.8 12.2 98.9 10.4

1t) 7)

1.4 13.30

40~ 6~ 5 ~o 4 ~o 10% 8~o

0.29 0.87 3.7 3050.00 5.2 1640.00

1.42 ~ 4 0 ~ 4310.00 _~ 1 0 ~

1.19 3920.00

... 662 30

... ...

* These values are obtained by multiplying the total by the ratio K to total.

205

206

K. PARTHASARADHI

estimated by subtracting the other partial theoretical cross sections from the total. All these values, along with the theoretical values reported by Schmickley and Pratt 1°) are given in table 1. It can be noted from the table that the errors in het L and M + N + O . . . cross sections, are quite reasonable. It can be seen from the table that the second m e t h o d n o t only gives equally good values b u t also these are in better agreement with the recent theoretical values of Schmickley a n d Pratt, and Hultberg et al.a o). Moreover, it can be seen that even though both methods are useful for the d e t e r m i n a t i o n of K-shell cross sections, the second m e t h o d is more useful especially for L a n d higher subshell cross section measurements. Thus it can be concluded that the second method is n o t only simple but also more suitable in general a n d it can be applied for the m e a s u r e m e n t of the cross section at any energy when once the ratio is measured at a convenient energy.

References ~) W. F. Titus, Phys. Rev. 115 (1959) 351.

2) K. Parthasaradhi and S. Ramamurty, Nuovo Cimento, in press. 3) S. Hultberg, Arkiv Fysik 15 (1959) 307. 4) B. S. Ghuman, S. Anand and B. S. Sood, Indian J. Pure Appl. Phys. 5 (1967) 70. s) M. A. Di Lazzaro and G. Missoni, lstituto Superiore Di Sanita ISS 65/11 (1965). 6) S. Hultberg and R. Stockandal, Arkiv Fysik 15 (1959) 355. 7) B. V. Narasimha Rao and K. Parthasaradhi, J. Appl. Phys. (Sept. 1969). 8) C. Davission, Alpha-, beta- and gamma-ray spectroscopy 1 (ed. K. Siegbahn; North-Holland Publ. Co., Amsterdam, 1965). 9) K. E. Bergkvist, Arkiv Fysik 27 (1964) 483. 1o) R. D. Schmickley and R. M. Pratt, Tables of calculated photoelectric cross-sections for energies 10 to 3000 keV, LMSC 5-10-67-11 (Lockheed Research Laboratories, (Lockheed Missiles and Space Company, Palo Alto, 1967); S. Hultberg, B. Nagel and P. Olsson, Arkiv Fysik 38 (1968) 1. 1~) K. Parthasaradhi, V. Lakshminarayana and S. Jnanananda, Indian J. Pure Appl. Phys. 2 (1964) 280.