MLOrbital-Electron-Capture Ratio inAr37Decay and the Fraction of

J.P. Renier

¹

,

H. Genz

²

,

K.W.D. Ledingham

³

et al.

Abstract

The ratio of M-to Z,-orbital electron capture in the decay of 35-day Ar 37 has been measured in a singlewire proportional counter containing the gaseous source. This counter was operated with variable paralysis times, 2.0 and 3,8 msec being used in the present experiments to minimize the contribution from afterpulses. Recent investigations of the pulse-height distribution from proportional counters due to single-and multipleelectron events make it possible to measure single-electron spectra down to essentially zero energy with much greater accuracy than heretofore. The experiment was undertaken because of the considerable disagreement between experimental and theoretical M/L capture ratios, particularly in the low-Z region. A survey of all experimental work on M capture is included for comparison with available theoretical results. In the decay of Ar 37 the experimental value for the M/L capture ratio is PM/PL = 0.104_O.OO3 +0006 , where the error limits have been subjected to careful detailed analysis. From this result, a value of ^a = 0.980±0.015 for chlorine was determined, where k a is the fraction of K a x rays in the K series of chlorine. The theoretical predictions of Bahcall for PM/PL lie about 23% above the experimental point, for a theory with exchange correction. The older theoretical value due to Wapstra et al. is in no better agreement with experiment, even if a correction for exhange is applied. An intensive effort is reported to measure the L/K capture ratio in the decay of 53.5-day Be 7 , as gaseous ^He^Be 7 in the single-wire proportional counter, but owing to the low energy of the iT-capture events (55 eV) and very low counting statistics, this measurement appears to be beyond the present state of the proportional-counter art.

Orbital electron capture by the nucleus

“…periments to measure the PL/P ratio of Be have been unsuccessful due to experimental limitations (Renier et al, 1968).…”

“…Most recent advances in low-energy proportional counter technique are related to the electronic system (Dougan et al, 1962a;Renier et al, 1968;Genz et al, 1971a). Proportional-counter spectrometry of radiation below %500 eV is affected by certain problems that are less important or negligible at higher energies: (1)After pulses from primary ionizing events can occur (Dougan et al, 1962a;Renier et al°, 1968;Genz et al, 1971a;Campion, 1968Campion, , 1973; (2) degradation tails from peaks of higher energy can appear (Renier et al, 1968;Genz et al, 1971a;Heuer, 1966;Vaninbroukx and Spernol, 1965;Spernol, 1967); (3) small pulses can be mutually induced between ring and center counters in multiwire detectors (Genz et al, 1971a;Drever et a., 1957); (4) the anticoincidence gate may cause front-and back edge clipping of large pulses, producing smaller pulses (Dougan et al, 1962a;Renier et al, 1968;Genz et al, 1971a); (5) large deadtime may arise when radiation of higher energy is present in high intensity (Dougan et al, 1962a;Renier et al, 1968;Genz et al, 1971a). The electronic system shown in Fig.…”

“…These improvements were attained with more sophisticated low-noise electronics and through an understanding of the degradation spectrum (Genz et al, 1971a) and of after-pulses . Single-and few-electron peaks have been resolved on the basis of their spectral shape (Renier et al, 1968) or by fitting a Poisson distribution (Genz et al, 1971aPengra et al, 1972).…”

“…The techniques of single-electron spectrometry have been applied by Renier et al (1968) in a precision measurement of the M/L capture…”

Accurate determination of the pKωK value and the fluorescence yield ωK of Sr after electron capture decay of88Y

“…Pul/PLI ratios were derived from the g~h/gL, ratios as given by Renier et al [21]. Allowance was made for the energy dependence (qgJqL1) 2, but no correction was applied for exchange and overlap.…”