G. D. Jones

The GREAT spectrometer

Abstract The GREAT spectrometer is designed to measure the decay properties of reaction products transported to the focal plane of a recoil separator. GREAT comprises a system of silicon, germanium and gas detectors optimised for detecting the arrival of the reaction products and correlating with any subsequent radioactive decay involving the emission of protons, α particles, β particles, γ rays, X-rays or conversion electrons. GREAT can either be employed as a sensitive stand-alone device for decay measurements at the focal plane, or used to provide a selective tag for prompt conversion electrons or γ rays measured with arrays of detectors deployed at the target position. A new concept of triggerless data acquisition (total data readout) has also been developed as part of the GREAT project, which circumvents the problems and limitations of common dead time in conventional data acquisition systems.

Calibration of the new composite “clover” detector as a Compton polarimeter for the EUROGAM array

Abstract The application of a composite Ge detector to the measurement of the linear polarisation of γ-rays has been investigated. The polarisation sensitivity of this device has been determined over the energy range 197–1368 keV. Comparison to a previous design of a similar detector has been made.

A study of the 16O(d, p)17O reaction

Abstract Angular distributions and excitation functions have been obtained for the 16O(d, p)17O reaction and the elastic scattering of deuterons on 16O and protons on 17O. An optical model analysis has been made of the elastic scattering results. A vector spin-orbit term was needed in order to fit the back-angle deuteron data. The optical model parameters have been used in distorted wave calculations for the stripping reactions leading to the bound and virtual single-particle states of 17O. The significance of the spectroscopic factors obtained is discussed in detail.

Spectroscopy of Rn, Ra and Th isotopes using multi-nucleon transfer reactions

Abstract High-spin spectroscopy of Rn, Ra and Th isotopes has been performed. The nuclei have been populated using multi-nucleon transfer reactions involving a 232 Th target and a 136 Xe projectile. This type of reaction offers the only mechanism for populating high-spin states in many of these nuclei. Interleaving bands with opposite parities have been observed to high spin ( ∼28 h ) in 218,220,222 Rn, 222,224,226,228 Ra and 228,230,234 Th. A systematic study of the rotational alignment properties of octupole bands in radon, radium and thorium isotopes reveals information concerning the role of the octupole phonon and the onset of stable octupole deformation with increasing rotational frequency. Measurement of the magnitude of the intrinsic electric dipole moment, D 0 , provides additional information concerning the strength of octupole interactions in these nuclei.

The DWBA and spin-orbit effects in the 46,48Ti, 50,52Cr(d,p) reactions

Abstract Differential cross sections have been measured in the 46,48Ti, 50Cr(d,p)47,49Ti, 51Cr reactions at a deuteron bombarding energy of 9.15 MeV. The angular distributions for l=1 states at large angles differ for 2 p 3 2 and 2 p 1 2 single particle states. Differences in the angular distributions with l=3 are observed and attributed to the final state being either 1 f 7 2 or 1 f 5 2 . DWBA calculations with spin-orbit terms in the deuteron, proton and neutron channels and finite range and non-local corrections are made in an attempt to reproduce the observed j-dependence. Deuteron optical model parameters including the spin-orbit terms are derived by making best fits to the relevant elastic scattering data. It is found that the DWBA calculations produce a j-effect for 2 p 3 2 and 2 p 1 2 configurations that is qualitatively the same as that observed experimentally but does not have the correct magnitude. The calculated differences between states with 1 f 7 2 and 1 f 5 2 configurations is opposite to that suggested experimentally. The difficulties in selecting a unique deuteron potential are not resolved by the inclusion of spin-orbit terms in the DWBA.

Detection of long-lived isomers in super-heavy elements

Abstract Electromagnetic decay of long-lived isomers, in super-heavy elements (SHE), is invariably accompanied by the emission of internal conversion electrons. The possibility of detecting a pulse of electrons from such a process appears to have been overlooked in experiments designed to search for SHE.

Electron spectroscopy using a multi-detector array

A description is given of the novel electron spectrometer SACRED, which uses a multi-element Si array to detect cascades of conversion electrons. Its application to the study of deformed structures in 222Th is described.

Further measurements and zero-range DWBA calculations for the 52Cr(d, p)53Cr reaction

Abstract An analysis of angular distributions in the 52Cr(d, p)53Cr reaction is made with zero-range DBWA calculations without spin-orbit terms. The variation of the predicted spectroscopic factors with incident deuteron energy, set of deuteron optical parameters used, cut-off and neutron wave function is examined.

Sub-Coulomb neutron transfers from 17O onto 40Ca, 44Ca and 48Ca

Abstract The reactions 48 Ca( 17 O, 16 O) 49 Ca, 44 Ca( 17 0, 16 O) 45 Ca and 40 Ca( 17 O, 16 O) 41 Ca have been observed at bombarding energies of 27,27 and 28.5 MeV, respectively. The cross sections for transitions to levels in the final nuclei with predominantly 2p 3 2 configurations were measured over the angular range 100–170°. The results have been analysed using a DWBA theory with Coulomb wave functions describing the entrance and exit channels. For a chosen wave function for the 17 O ground state, the analysis yields the rms radii of the 2p 3 2 single-particle orbits in the odd Ca isotopes. With the use of a simple potential model the rms radii of the 1f 7 2 orbits are determined within reasonable limits and the sizes obtained compared with the rms radii of the neutron excesses in the Ca isotopes as calculated from Coulomb energy differences. The latter estimates are significantly lower than the values suggested by the present experiments.

Observation of unexpectedly small E1 moments in 224Ra

Abstract The α-decay of 228Th and the reaction 226Ra(58Ni, 60Ni)224Ra have been employed to populate states in 224Ra up to Iπ=12+. Values of the intrinsic electric dipole moment |Q1| have been deduced from the observed of B(E1)/B(E2) braching ratios. These values are ≲0.1e fm for spins up to Iπ=9−, and are thus smaller than those in 218,220Ra or 226Ra. The behavior of Q1 suggests that shell effects are important in this mass region, although theoretical calculations which include these effects do not reproduce the observed pattern.