β Decay Of The Proton-rich Nuclei ²⁹S And ²⁸P And Their Isospin Symmetry Breaking

The continuous developments in radioactive beam facilities have enabled the production of nuclei far from the β stability line.The study of the nuclear structure of these exotic nuclei has become the leading frontier in current nuclear physics.β-decay spectroscopic study has proved to be a powerful tool to study nuclear structure,especially for nuclei far away from the β stability line.When moving from the β stability line to the drip line,the decay energy becomes dramatically large,which turns the decay mode from β decay to β-delayed particle emission,such as deexciting by emitting protons,a particles in the proton-rich side.The decay properties of sd shell nuclei and isospin symmetry breaking have attracted great attention.The experiment was performed at the Heavy Ion Research Facility of Lanzhou(HIRFL),with the help of the Radioactive Ion Beam Line(RIBLL1),aiming to study the β-decay properties of proton-rich nuclei 29S and 28P,and their isospin symmetry breaking.The secondary radioactive ions were produced via the projectile fragmentation reaction of the primary beam 80.6 MeV/nucleon 32S16+at an intensity of 46 enA impinging on 1581μm-thick 9Be target.By adjusting the setting of RIBLL1,the secondary beam was optimized for selecting and purifying 29S and 28P.In the run time,the average intensity and purity of 29S and 28P were 16.5 pps and 1.35%,23.5 pps and 1.92%,respectively.The particle identification was achieved by the ΔE-ToF method.The ΔE was obtained by measuring the energy loss of two silicon detectors,while the ToF(Time of Flight)with respect to the T1 and T2 chamber was given by two plastic scintillators.Under the continuous-beam mode and implantation-decay correlation method,the β-decay spectroscopy of proton-rich nuclei 29S and 28P were studied using a detector array consisting of three double-sided silicon strip detectors(DSSDs)with different thickness surrounded by five clover type high-purity germanium(HPGe)detectors.Using the three different thickness DSSDs,the charged particles were measured with high detection efficiency and good energy resolution.The y-rays emitted in the decay process were measured simultaneously by five clover-type HPGe detectors.The temporal-spatial correlation between the implantation event and subsequent decay event was established on an event-by-event basis.For 29S,in this work,the most precise half-life of 29S was obtained to be 183(4)ms.Also,it’s the first time to apply β-γ coincidence and four y-rays were observed,which determine the β-feeding intensities to proton-bound states.Twenty-six proton peaks were observed.The initial and final state of proton transitions were determined by applying the proton-y-ray coincidence analysis.An updated decay scheme of 29S was constructed,and a wrong assignment was corrected.Seven y-rays were observed in studying the β-decay of 28P.Six levels of 28Si populated in 28P β-decay were reconstructed.Based on experimental results,the isospin symmetry breaking in the mirror decay process 29S→29P/29Al→29Si and 28P/28Al→28Si were studied.The small values of mirror asymmetry parameters indicate that the isospin symmetry breaking is small.