Experimental Research On β Delayed Proton Decay Of ²⁵Si

In the past few decades,the structure of nuclei far from stable lines has been one of the hot topics in nuclear physics.Study on decay spectra of nuclei near the drip-line can help ones to locate the proton and neutron drip-lines of unstable nuclei,to understand the properties of nuclear forces,as well as to test and improve nuclear models.the production of nuclei far from theβstability line may face some difficulties:low cross section,large contaminators in the same reaction,and very short half-life of target nucleus.However,as the experimental technology on detection efficiency is gradually improved,decay modes even with very small energies and branching ratios can be found in the experiments,which better expand our understandings on the nucleus.²⁵Si is the first discovered nucleus withβp decay mode.It has been well studied,and its knownβp andβγare used as the internal source for the calibration.After a detailed review on the literatures,we found that the study on theβp decay of²⁵Si still has some shortcomings,for example:some transitions have not been clearly specified,and some transitions were not found in all experiments.²⁵Si is selected for study in this work,because:on the one hand,we hope to establish a perfect research method ofβdecay spectrum,and on the other hand,we hope to determine some key physical quantities of²⁵Si decay with higher statistics,such as half-life,branch ratio,etc.to establish a detailed decay schemeand and lay a solid foundation on the study ofβdecay spectroscopy for nuclei far from theβstability line.Besides,the isospin asymmetry of mirror nuclei is also investigated.The experiment was carried out on the radioactive beam line of Lanzhou,Institute of Modern Physics,Chinese Academy of Sciences in November 2017,to study theβdecay prop-erties of the proton rich nuclide²⁵Si.By bombarding the primary target of⁹Be with the primary beam³²S¹⁶⁺with 80.6 Me V/u energy and 87 en A current intensity,the target nu-cleus²⁵Si,one product of fragmentation reaction,was selected and separated by achromatic magnetic rigidity–energy loss–magnetic rigidity by the spectrometer,and transmitted to the target chamber where the detector array was placed.In this experiment,we used two scintillator detectors and two quadrant silicon detectors（QSDs）to identify beam particles,three double-sided silicon strip detectors（DSSDs）with different thickness to measure the implanted²⁵Si and its subsequentβdelayed protons,three installed downstream to detectβparticles and to reject the contaminators of light ions in the beam,five high-purity Ger-manium（HPGe）detectors and three lanthanum bromide（La Br₃）detectors to measure theβdelayedγrays.The half-life of²⁵Si has been determined as 218（1）ms,which is the most precise one in the existing experimental data.Theβdelayed proton spectrum of²⁵Si has been obtained.Total of 25 peaks of delayed protons have been found,which agrees with the previous experimental data.A suspectedβdelayed proton peak（1682 ke V）,which was also found but failed to be assigned by previous experiments,has been identified.Compared with the decay of mirror nucleus²⁵Na,the asymmetry parameter is very small and no isospin breaking is found.Combined with the observed²⁵Siβdecay data,we calculated the mass excess of the ground state and itsβdecay Q value,as well as the corresponding branch ratios,GT transition intensities and logft values feeding to the different excited states of the daughter nucleus²⁵Al.Base on the obtainedβdecay information,the detailed decay scheme of²⁵Si is constructed.It is in good agreement with the previous experimental results,which confirms the feasibility of our experimental method and the reliability of the data processing program.