Optimising resistive charge-division strip detectors for low energy charged-particle spectroscopy

Two novel approaches to improving the signal-to-background ratio (SBR) for silicon resistive charge-division strip detectors (RSDs), when performing low energy charged-particle spectroscopy, are presented. Firstly, the normally-unutilized rear contact of the detector was used to veto events where the charge collected by this rear face did not match the sum of the charges collected by the strips on the front. Secondly, leading edge discriminator time walk was used to determine complementary information about the hit position along a strip. Using this alongside the position extracted from the charge division allowed clearer identification of true events over background, leading to an improved SBR. These methods were tested by measuring radiation from a triple-α source and then the 12C(4He,α)ααα breakup reaction at 40 MeV beam energy. The first method was found to improve the SBR by a factor of 4.0(2). The second method gave a SBR improve- ment of factor of 3.7(4). When both methods are applied together, a total improvement by a factor of 5.7(3) was measured

Experimental study of high-lying states in ²⁸Mg using the resonant elastic scattering of α particles

International audienceThe excitation function of Mg28 above the α-decay threshold has been measured for the first time using the resonant scattering of α particles with the technique of a thick target in inverse kinematics. Thirteen new states are reported between Ex=15.5 and Ex=20.5 MeV, and suggestions for spin-parity assignments are given for two of these. Calculations of the branching ratio to α decay for these states as well as comparison of the measured cross sections to calculations suggest that α+Neg.s.24 clustering is not dominant in this energy regime

Analysis of states in ¹³C populated in ⁹Be + ⁴He resonant scattering

Measurements of 9Be+α resonant scattering have been performed using the thick-target approach with a 4He gas volume and a large area silicon strip detector. 9Be beam energies in the range 12 to 21.4 MeV were used to measure the 13C excitation energy spectrum between 13.2 and 16.2 MeV. An R-matrix analysis has been performed to characterize the spins and widths of 13C resonances, some of which have been proposed to be associated with a 3α+n molecular band

Shape evolution in the neutron-rich osmium isotopes:Prompt γ-ray spectroscopy of Os 196

The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich 196Os nucleus through in-beam γ-ray spectroscopy using a two-proton transfer reaction from a 198Pt target to a 82Se beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident γ rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of 196Os were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even 188-198Os isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect γ-unstable/triaxial rotor yrast band is predicted for 196Os which is in agreement with the experimentally measured excited state