Accurate ft-value measurements for ^22Mg and ^34Ar
Abstract
We have studied the decays of ^22Mg and ^34Ar as part of our program to refine the test of CKM unitarity via superallowed 0^+-to-0^+ β-decays. In each case, we bombarded an LN-cooled hydrogen gas target with a heavy-ion beam, and separated the recoil products in the MARS spectrometer. A pure beam of the isotope of interest exited the vacuum system, was degraded, collected for about 2 half-lives and the activity moved by a fast tape-transport system to a shielded detection location. The primary beam was turned off during the counting period. For branching-ratio measurements, β-γ coincidences were recorded with a well-calibrated HPGe detector; for half-life measurements, the emitted β's were recorded for up to 20 half-lives with a 4-π proportional gas counter. The required precision (about 0.1% for the superallowed transition) demanded careful attention to possible systematic errors; thus, the experiment was subdivided into numerous runs, each with different settings for critical parameters. For ^22Mg, we measured the superallowed branching ratio and half-life to be 0.5315(12) and 3.8755(12) s; for ^34Ar, we obtained 847.0(37) ms for the half-life, and a preliminary branching ratio consistent with, but more precise than the previously known value.
- Publication:
-
APS Division of Nuclear Physics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..DNP.BF002I