Test of internal-conversion theory with measurements in ${}^{134}\mathrm{Cs}$ and ${}^{137}\mathrm{Ba}$

We have measured the ratio of $K$-shell internal conversion coefficients, ${\alpha }_K$, for the 127.5-keV $E3$ transition in ${}^{134}\mathrm{Cs}$ and the 661.7-keV $M4$ transition in ${}^{137}\mathrm{Ba}$. Previous measurements of these ${\alpha }_K$ values led to a ratio that differed from calculated internal conversion coefficients. Our measured result, 30.01(15), disagrees with, but is a factor of three more precise than, the previous average of all experimental results. Our new result is consistent with calculations.

Figure 1

Decay scheme for the decay of the 2.9-h isomeric state in ${}^{134}\mathrm{Cs}$. The information is taken from Ref. [13]. Note that the strong transitions are shown with heavy arrows. The weak 139-keV transition accounts for ∼0.5% of decay from the isomer (including the effects of internal conversion).

Figure 2

Decay scheme for the β decay of ${}^{137}\mathrm{Cs}$. The information is taken from Ref. [13]. The strong transition is shown with a heavy arrow.

Figure 3

Spectra for the four energy regions of interest in the determination of the ${\alpha }_K$ ratio: (a) the cesium x rays from the decay of ${}^{134}\mathrm{Cs}$${}^m$; (b) the 127.5-keV γ ray from the same decay; (c) the barium x rays from ${}^{137}\mathrm{Ba}$, the β-decay daughter of ${}^{137}\mathrm{Cs}$; and (d) the 661.7-keV γ ray also from ${}^{137}\mathrm{Ba}$.

Figure 4

A portion of the γ-ray energy spectrum $T2.1$, measured soon after the activation of source $T2$. Peaks are identified by their β-decay parent, with “SE” designating a single-escape peak.

Figure 5

The top panel shows an expanded region of the HPGe spectrum at the base of the barium $K_{\alpha }$ x-ray peak. The solid squares are the measured data from the ${}^{137}\mathrm{Cs}$ source; the curve is the result of a Monte Carlo simulation. The bottom panel gives the same region of the ${}^{137}\mathrm{Cs}$ spectrum as measured with a Si(Li) detector; the ordinate scale has been adjusted so that both panels display approximately the same fraction of the total $K$ x-ray peak area.