Internal conversion electron measurements following the decay of 152Eu

N U C L E A R I N S T R U M E N T S AND METHODS 159 (1979)

243-244 ; ©

N O R T H - H O L L A N D PUBLISHING CO.

INTERNAL CONVERSION ELECTRON MEASUREMENTS FOLLOWING THE DECAY OF ISZEu J. DESLAURIERS and S. K. MARK

Foster Radiation Laboratmy, McGill University, Montreal, Canada* Received 28 September 1978 Relative intensities of internal conversion electron lines from the decay of I52Eu are measured accurately with a Si(Li) detector. The results thus obtained are presented, clarifying many discrepancies of previous works.

In nuclear spectroscopy work, it is often required to measure the internal conversion electrons associated with the transitions between nuclear states. To carry out such measurements, it is convenient to use a known source which emits conversion electron lines spanning over a wide range of energy to calibrate the relative efficiency of the instruments employed. This is particularly true when a magnetic device of large momentum acceptance is used to measure the electrons. We found that ~52Eu is a suitable source for this purpose. ~52Eu is one of those nuclides which decays by (/3 + +EC) as well as by /3- emission, leading to two different isobars; it decays to states in 52Gd by /3- emission and to states in ~S2Sm mostly by electron capture. Its half-life is relatively long (13 y) and it emits many intense electron lines with energies ranging from about 75 keV to about 1.4 MeV, making it convenient to be used as a standard efficiency calibration source. The conversion electron lines observed in the decay of 152Eu have been studied previously by different research groups ~-3) and their results are shown in table 1. A glance of these results leads to the following observations: discrepancies between the different measurements for the strong lines at low energy frequently lie outside the quoted experimental errors; the intensity values for the higher energy lines are often differed by as much as a factor of two or more. In view of the lack of consistency between these different works, a study of the conversion electron lines following the decay of m E u was carried out. A Si(Li) detector housed inside a vacuum chamber was used to perform the measurements. The detector has a surface area of 300 mm 2 and a deWork supported by the National Research Council of Canada.

pletion layer of 3 mm; it gives a resolution of 2.5 keV for the 976 keV conversion electron line of 2°7Bi. A depletion layer of 3 mm of silicon corresponds to the range of 1.2 MeV electrons; the efficiency of the detector is thus expected to drop slowly for electrons with energies above 1 MeV. In order to determine the exact shape of the efficiency curve, a tuBa and a 2°7Bi source was used. The decay of 133Ba to 133Cs and of 2°7Bi to 2°7pb have been studied previously by several workers and the relative intensities of the conversion electron lines associated with their decays are well known and may be obtained from refs. 4 and 5. Each source was counted in turn for several hours and the relative efficiency for the detection of different TABLE 1 Relative intensities of conversion electron lines from the decay of 152F4a. Numerals in parentheses indicate uncertainties in the last digit(s). Transition (keV) 121.8 K L 244.7 K L 344.3 K L 411.1K 444.0K 586.2 K 615.4 K 656.5 K 688.7 K 778.9K 867.3 K 964.0 K 1085.0K Il12.0K 1408.0 K

Ref. 1

2930 1570 81 24.0 100 29.1 4.5 3.5 4.1 3.6 3.5 7.9 2.7 1.6 4.6 2.9 3.6 1.7

Ref. 2

Ref. 3

(150) 2930 (300) 2180 (80) (80) 1690 (170) 1700 (80) (4) 76 (8) 74 (3) (12) 24.0 (24) 18.3 (13) 100 100 (15) 25.0 (25) 24.0 (20) (3) 5.0 (5) 4.9 (4) (4) 3.0 (3) 1.67(14) (4) 1.5 (3) (5) 0.80(8) 1.11(15) (5) 1.20(12) 0.82(15) (12) 5.3 (5) 3.6 (3) (4) 3.8 (4) 2.6 (3) (2) 0.90(10) 1.39(14) ('7) 3.9 (4) 4.0 (3) (4) 1.3 (2) 2.4 (3) (5) 2.7 (3) 2.8 (3) (3) 1.00(10) 1.14(8)

Present work 2450 (120) 1440 (70) 79 (4) 19.7 (10) 100 21.8 (11) 5.1 (3) 2.14(11) 0.99(10) 0.90(9) 0.82(8) 3.3 (2) 2.22(11) 1.36(8) 3.7 (2) 2.36(14) 2.51(15) 1.14(7)

244

J

DESLAURIERS

a ~

S. K. M A R K

302,851 and 356.005 keV) in ~33Cs and the K, L and ( M + N + . . . ) lines of the three strong transitions (569.7, 1063.6 and 1770.2 keV) in 2°Tpb were used to construct a relative efficiency curve for the detection system. A thin source of L52Eu ( - 5 0 / , t g / c m 2) was prepared and counted for about 9 h. The conversion electron spectrum obtained is displayed in fig. 1. The relative intensities of the conversion electron lines corrected for detection efficiency are listed in table 1. Grossly speaking, our results are consistent with those of Malmsten et al. 3) and disagree frequently with those of Mukherjee et al. 2) and Schneider]). However, there are four conversion electron lines (121.8 K, 121.8 L, 444.0 K and 586.2 K) for which our results differ from those of Malmsten et al. by more than the experimental errors. We have checked our results by using them to calibrate our magnetic filter conversion electron spectrometer and reproduced accurately the previously known internal conversion coefficients for the transitions in 1 3 3 C s and 2°TPb. Finally, our results for the high energy conversion lines are more precise than those of the previous works.

ii ° ~':'

AND

g

\+°

Z 0

<; 1 o4_

I 0 3-

~o

i

0 500 'OOO

CHANNEL

NUMBER

500 1000 1500

Fig. 1. Internal conversion electron spectrum from the decay

of 152Eu. Electron lines associated with the decay are labelled by their transition energies in keV followed by the conversion atomic shells. The three channel number labels on the abscissa are for the three portions of the spectrum, respectively. electron lines were evaluated. The K lines of the strong transitions (79.62+80.997, 160.60, 276.397,

References J) w. Schneider, Nucl. Phys. 21 (1960) 55. 2) p. N. Mukherjee, I. DULL,A. K. Sen Gupta and R. L. Bhattacharyya, Physica 26 (1960) 179. 3) G. Malmsten, O. Nilsson and 1. Andersson, Ark. Fysik 33 (1966) 361. 4) E. A. Henry, Nucl. Data Sheets !1 (1974) 495. ~) M. R. Schmorak, Nucl. Data Sheets 22 (1977) 487.