Gamow-Teller beta decay of the very neutron-deficientN=50 nuclide98Cd

For the first time, detailed decay-spectroscopic investigations were performed for the very neutron-deficientN=50 nuclide⁹⁸Cd. The⁹⁸Cd activity was produced in spallation reactions between 600 MeV protons and a natural tin target, yielding a⁹⁸Cd beam intensity of 10 to 60 atoms/s at the collector of the ISOLDE massseparator. By means of-ray and conversion-electron spectroscopy, 19 transitions were found to follow the ⁺/EC decay⁹⁸Cd⁹⁸Ag. The transitions at 61 and 107 keV were shown to beM1(+E2) andE2, respectively, and the⁹⁸Cd half-life was measured as 9.2±0.3 s. TheQ _EC value of⁹⁸Cd is determined semiempirically and is compared to model predictions together with the measuredQ _EC values of the neighbouring cadmium isotopes^100,102Cd and theN=50 isotones⁹²Mo,⁹⁴Ru, and⁹⁶Pd, taken from the literature. The newly established decay scheme of⁹⁸Cd includes 9 excited states of⁹⁸Ag. Four states at 1691, 1861, 2164, and 2544 keV are directly fed by 0⁺ 1⁺ Gamow-Teller beta transitions with a summed strength of 3.5 _–0.7 ^+0.8 . This value corresponds to 25±5% of the strength predicted for the GT transformation of a g_9/2 proton (in⁹⁸Cd) into a g_7/2 neutron (in⁹⁸Ag) by the extreme single-particle shell model. The GT-strength splitting and quenching, observed for⁹⁸Cd, are compared with the corresponding data for lighter even-even N=50 isotones, and are discussed with reference to the predictions of more sophisticated nuclear models. We find that only in some cases it is possible to explain qualitatively the observed GT strength distribution and its total magnitude without renormalizing the free-neutron value of the axial-vector coupling constant.Dedicated to Prof. P. Armbruster on the occasion of his 60th birthday     

Distributions of i132 transfer strength in (τ, α)-induced population of odd-a platinum isotopes

The odd-A platinum isotopes ₇₈^{191, 193, 195, 197}pt have been populated by means of the (τ, α) reaction at E_τ = 50 MeV. Spectra covering a range of 4 MeV of excitation energy were obtained. Angular distributions for levels in this excitation range have been deduced. Only a few $\text{13}\text{2}{}^{\mathrm{+}}$ states are strongly populated in each isotope, the actual number being 1, 2, 3, and 2 for A = 191, 193, 195 and 197 respectively. The spacing between these peaks exhibits an interesting variation with neutron number. The data are compared with predictions of current quasiparticle-core coupling models.     

The variation in γ-ray multiplicity with nuclear temperature studied in 160Dy

A novel method of obtaining detailed infromation on the level density far above the yrast line is described. The γ-ray multiplicity as a function of excitation energy in ¹⁶⁰Dy is studied by means of the ${}^{161}\text{Dy}\text{(}{}^3\text{He}\text{, α)}{}^{160}\text{Dy}$ reaction.     

Nuclear spectroscopy at 133Sn

It is described how the measurement of nγ-coincidences can be used to identify single-particle states in ¹³³Sn. This method, in combination with the improved yields at ISOLDE, has facilitated firm determination of three excited single-particle states in ¹³³Sn: p_3/2, h_9/2 and f_5/2. The i_13/2 state is not observed in this experiment and probably unbound, and the data did not allow a firm identification of the p_1/2 state. The results are well reproduced in a Woods–Saxon calculation based on the data from the ²⁰⁸Pb region and taking into account the distance from β-stability of the ¹³²Sn region. This revised version was published online in July 2006 with corrections to the Cover Date.     

New neutron-rich isotopes of astatine and bismuth

Neutron-rich isotopes of astatine have been produced through spallation reactions with 600 MeV protons on a²³²Th target and identified by spectroscopic techniques combined with one-line mass separation at the ISOLDE facility. The half-lives of²¹⁸At and²¹⁹At have been remeasured to be 1.5(3) s and 57(4) s, respectively. Four new isotopes of astatine,^220?223At, have been observed for the first time, and their half-lives were found to be 3.73(13) min, 2.3(2) min, 54(10) s, and 50(7) s, respectively. Another nuclide,²¹⁶Bi, has been observed for the first time as the daughter product of the²²⁰At alpha decay, and its half-life has been measured to be 6.6(21) min.     

The nuclear structure of 225Ra

The level structure of ²²⁵Ra has been studied using the (d, t) reaction with both unpolarised and polarised deuterons and the β^? decay of ²²⁵Fr. Cross sections and excitation energies have been measured for 41 levels below 1800 keV in the (d, t) reaction, and levels up to 724 keV have been established from the β^? decay measurements. The level structure is interpreted in terms of the Nilsson model.