Precise half-life measurement of the superallowed β+ emitter 10C
The half-life of '°C has been measured to be 19.310(4) s, a result with 0.02% precision, which is a factor of three improvement over the best previous result. Since 10 C is the lightest superallowed 0 + → 0 + β + emitter, its ft value has the greatest weight in setting an upper limit on the possible presence of scalar currents.
New approach to precisely measure γ-ray intensities for long-lived fission products, with results for the decay of 95Zr
Abstract For many fission products, the γ rays emitted following β decay provide an easily-detectable signature that can be used to identify their quantities and distributions in a sample. As a result, γ -ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the γ -ray intensity is available. However, in many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. To address this need, we have developed a new experimental method that is well suited to precisely measure absolute γ -ray intensities in the β decay of long-lived fission products. The approach involves the production of a radiopure sample by implantation of a mass-separated ion beam from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility on a thin carbon foil. The emitted β -decay radiation is detected with a 4 π gas proportional counter and a meticulously efficiency-calibrated high-purity germanium (HPGe) detector. As a first measurement to demonstrate the approach, we studied the absolute γ -ray intensities of the strongest transitions following the β decay of 95 Zr and its decay-daughter 95 Nb, and determined them to fractional precisions of better than 1-2%. In addition, with a larger sample of activity produced through neutron irradiation of an isotopically-enriched Zr foil, we performed a high-precision measurement of the relative γ -ray intensities following the decay of 95 Zr with just the HPGe detector. The sample-production method at CARIBU and the coincidence detection approach demonstrated here can be applied to study fission products with half-lives longer than a day, which includes isotopes important not only for nuclear-energy and national-security applications, but also for medical-isotope research and environmental monitoring.
TRANSITION RATES IN $sup 29$P.
Lifetimes of three of the low-lying excited states in 29P, populated in the 28Si(p,γ) reaction, have been determined using the Doppler shift attenuation method. The mean lifetimes of states at 4.085, 1.956, and 1.385 MeV were found to be 15 ± 4, 370 ± 80, and 200 ± 60 fs.Angular distribution measurements have also been performed on gamma rays resulting from the decay of the 4.085 MeV resonance level. The decay was found to go via states at 3.107 MeV (3%), 1.956 MeV (54%), and 1.385 MeV (43%). The spin of the resonance level was uniquely assigned as 7/2 and the multipole mixing ratios of the 2.129 and 1.385 MeV transitions as + 0.17 ± 0.05 and + 0.303 ± 0.050 respectively. The consequent transition rates indicate that the parity of the resonance level is positive.