The TIGRESS Integrated Plunger device (TIP) has been developed for recoil distance method (RDM) lifetime measurements using the TIGRESS array of HPGe γ-ray detectors at TRIUMF’s ISAC-II facility. A ...commissioning experiment was conducted utilizing a 250 MeV 84Kr beam at ≈2×108 particles per second. The 84Kr beam was Coulomb excited to the 21+ state on a movable 27Al target. A thin Cu foil fixed downstream from the target was used as a degrader. Excited nuclei emerged from the target and decayed by γ-ray emission at a distance determined by their velocity and the lifetime of the 21+ state. The ratio of decays which occur between the target and degrader to those occurring after traversing the degrader changes as a function of the target–degrader separation distance. Gamma-ray spectra at 13 target–degrader separation distances were measured and compared to simulated lineshapes to extract the lifetime. The result of τ=5.541±0.013(stat.)±0.063(sys.) ps is shorter than the literature value of 5.84±0.18 ps with a reduction in uncertainty by a factor of approximately two. The TIP plunger device, experimental technique, analysis tools, and result are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The
β
-decay half lives of nuclei near the
r
-process path are critical information required for abundance calculations, especially those near neutron number
N
= 82. Specifically, the nuclei below ...doubly-magic
132
Sn are key, and play an important role in the formation and shape of the second
r
-process abundance peak. The half lives in this region are challenging to measure due to the significant
β
-delayed neutron decay branches and the population of isomeric states with half lives comparable to the ground states. However, by measuring the time distribution of γ rays, these complications can be eliminated. This requires, however, a very effcient γ-ray spectrometer since the production of isotopes in this region is very limited. The new GRIFFIN array at TRIUMF-ISAC provides the high effciency required for these measurements. Recent improvements in the quality of the beams produced at TRIUMF, employing the IG-LIS device, are outlined, as well as the current status of the ARIEL facility. The GRIFFIN spectrometer and its use are briefly described. The experiment to measure the half lives of
128-130
Cd is outlined and the results given, and some examples of the power of GRIFFIN to expand decay schemes, specifically for the decay of
128
Cd to
128
In, are given.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Excited states of \(^{129}\)In populated following the \(\beta\)-decay of \(^{129}\)Cd were experimentally studied with the GRIFFIN spectrometer at the ISAC facility of TRIUMF, Canada. A 480-MeV ...proton beam was impinged on a uranium carbide target and \(^{129}\)Cd was extracted using the Ion Guide Laser Ion Source (IG-LIS). \(\beta\)- and \(\gamma\)-rays following the decay of \(^{129}\)Cd were detected with the GRIFFIN spectrometer comprising the plastic scintillator SCEPTAR and 16 high-purity germanium (HPGe) clover-type detectors. %, along with the \(\beta\)-particles were detected with SCEPTAR. From the \(\beta\)-\(\gamma\)-\(\gamma\) coincidence analysis, 32 new transitions and 7 new excited states were established, expanding the previously known level scheme of \(^{129}\)In. The \(\log ft\) values deduced from the \(\beta\)-feeding intensities suggest that some of the high-lying states were populated by the \(\nu 0 g_{7/2} \rightarrow \pi 0 g_{9/2}\) allowed Gamow-Teller (GT) transition, which indicates that the allowed GT transition is more dominant in the \(^{129}\)Cd decay than previously reported. Observation of fragmented Gamow-Teller strengths is consistent with theoretical calculations.
The "Island of Inversion" for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modelling of shell evolution with isospin. In this ...context, the structure of the transitional nucleus 29Mg is critical. The first quantitative measurements of the single particle structure of 29Mg are reported, using data from the d(28Mg,p gamma)29Mg reaction. Two key states carrying significant ell=3 (f-wave) strength were identified at 2.40 +/- 0.10 (Jpi = 5/2-) and 4.28 +/- 0.04 MeV (7/2-). New state-of-the-art shell model calculations have been performed and the predictions are compared in detail with the experimental results. Whilst the two lowest 7/2- levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2- and 5/2- levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell model calculations.
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