Half-life systematics across the N=126 shell closure: role of first-forbidden transitions in the ß decay of heavy neutron-rich nuclei.

This Letter reports on a systematic study of ß-decay half-lives of neutron-rich nuclei around doubly magic (208)Pb. The lifetimes of the 126-neutron shell isotone (204)Pt and the neighboring (200-202)Ir, (203)Pt, (204)Au are presented together with other 19 half-lives measured during the "stopped beam" campaign of the rare isotope investigations at GSI collaboration. The results constrain the main nuclear theories used in calculations of r-process nucleosynthesis. Predictions based on a statistical macroscopic description of the first-forbidden ß strength reveal significant deviations for most of the nuclei with N<126. In contrast, theories including a fully microscopic treatment of allowed and first-forbidden transitions reproduce more satisfactorily the trend in the measured half-lives for the nuclei in this region, where the r-process pathway passes through during ß decay back to stability.

Coulomb excitation of 104Sn and the strength of the 100Sn shell closure.

A measurement of the reduced transition probability for the excitation of the ground state to the first 2+ state in 104Sn has been performed using relativistic Coulomb excitation at GSI. 104Sn is the lightest isotope in the Sn chain for which this quantity has been measured. The result is a key point in the discussion of the evolution of nuclear structure in the proximity of the doubly magic nucleus 100Sn. The value B(E2; 0+ → 2+) = 0.10(4) e2b2 is significantly lower than earlier results for 106Sn and heavier isotopes. The result is well reproduced by shell model predictions and therefore indicates a robust N = Z = 50 shell closure.

Microscope cover-slip glass for TLD applications.

As a result of the various evolving needs, thermoluminescence dosimetry is constantly under development, with applications intended in environmental and personal radiation monitoring through to the sensing of radiotherapy and radiation processing doses. In radiotherapy dosimetry challenges include small-field profile evaluation, encompassing the fine beams of radiosurgery, evaluations confronting the steep dose gradients of electronic brachytherapy and the high dose rates of FLASH radiotherapy. Current work concerns the thermoluminescent dosimetric properties of commercial low-cost borosilicate glass in the form of thin (sub-mm to a few mm) plates, use being made of microscope cover-slips irradiated using clinical external-beam radiotherapy facilities as well as through use of 60Co gamma irradiators. In using megavoltage photons and MeV electrons, characterization of the dosimetric response has been made for cover-slips of thicknesses up to 4 mm. Reproducibility to within +/5% has been obtained. In particular, for doses up to 10 Gy, the borosilicate cover-slips have been demonstrated to have considerable potential for use in high spatial resolution radiotherapy dosimetry, down to 0.13 mm in present work, with a coefficient of determination in respect of linearity of >0.99 for the thinner cover-slips. Results are also presented for 0.13- and 1.00-mm thick cover slips irradiated to 60Co gamma-ray doses, initially in the range 5- to 25 Gy, subsequently extended to 5 kGy-25 kGy, again providing linear response.

Observation of isomeric decays in the r-process waiting-point nucleus 130Cd82.

The gamma decay of excited states in the waiting-point nucleus (130)Cd(82) has been observed for the first time. An 8(+) two-quasiparticle isomer has been populated both in the fragmentation of a (136)Xe beam as well as in projectile fission of 238U, making (130)Cd the most neutron-rich N = 82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N = 82 shell quenching at Z = 48. They allow us to follow nuclear isomerism throughout a full major neutron shell from (98)Cd(50) to (130)Cd(82) and reveal, in comparison with (76)Ni(48) one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.

Coulomb energy differences in t = 1 mirror rotational bands in (50)Fe and (50)Cr.

Gamma rays from the N = Z-2 nucleus (50)Fe have been observed, establishing the rotational ground state band up to the state J(pi) = 11+ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror (50)Cr, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the pf model space.