Precise Measurement of the Half-life of ^22Mg
Abstract
As part of a program to test CKM unitarity via superallowed β-decay, we have measured the half-life of ^22Mg with high precision. The ^1H(^23Na, 2n)^22Mg reaction was used to produce a pure ^22Mg beam from the MARS recoil spectrograph. The beam was collected for 8 s on a fast tape-transport system, and the sample (>99.9% pure) moved into the center of a 4π proportional gas counter located in a low background region 1 m away. The counter signals were then multi-scaled for a period of 80 s, and then the whole cycle was repeated. A pulse synthesizer accurate to 5 ppm provided the time-stamp, and a gate generator with non-extendable dead time defined a dominant fixed dead time. A total of 30 million ^22Mg decays were recorded in more than 30 separate runs. To test for possible systematic errors, from one run to another we changed the critical settings of the acquisition chain: the discriminator threshold, the detector bias and the dominant dead time. Two fitting procedures were applied to extract the half-life: (i) a maximum-likelihood fit of the sum of all dead-time corrected decay spectra and (ii) a global fit of individual cycles, with common half-life but with amplitudes and dead-time correctly matched to each cycle. The second procedure gives the ultimate precision, as it contains no approximation. Our preliminary result is t_1/2 = 3.8782(9) s.
- Publication:
-
APS April Meeting Abstracts
- Pub Date:
- April 2001
- Bibcode:
- 2001APS..APRB15008I