Mass Measurements Of A=2Z+3 Proton-rich Nuclides

The nuclear mass is one of fundamental properties of nucleus.High-accuracy mass values for atoms play an very important role in nuclear physics and nuclear astrophysics.So high-precision measurement of nuclear mass has always been one of the most important topics in these research areas.Isochronous Mass Spectrometry(IMS)in heavy-ion storage rings is an excellent experimental method for precision mass measurements of exotic nuclei,and the experiments of accurate mass measure-ment of A=2Z+3 short-lived proton-rich nuclei has been performed by using IMS in 2016.The short-lived nuclei of interest were produced in projectile fragmentation reaction of 112Sn primary beams at a relativistic energy on a beryllium-9 target with a thickness of 10 mm.At these energies,the produced fragments are fully ionized.The fragments were selected and analyzed by RIBLL2.A cocktail beam was injected into the CSRe.To measure the revolution times of stored ions,a high performance time-of-flight detector(TOF)was applied.In the first half of this paper,we introduce the history,principle and experi-mental setup of the nuclear mass measurement.In the latter part,we have proposed some specific solutions in the data analysis,discussed the results obtained from the experiments,and analyzed the related physics.Main topics and results are listed as follows:(1)A new particle identification method was developed to distinguish ions on the measured revolution time spectrum for each injection.Based on this method,the shifts of the revolution time due to instable dipole magnet fields can be corrected and the isomeric states of 101In and 95Pd have been observed for the first time.(2)We investigated the effects of the momentum distribution,the yt curve and the momentum acceptance of CSRe on the mass resolving power.Besides,the effects of HIRFL-CSRe magnets on the yt curve have been discussed.In order to achieve a higher mass resolving power,the ring aperture was reduced by applying a mechanical slit system at the dispersive straight section.The momentum acceptance was reduced as well as better isochronous conditions were achieved.The results showed a significant improvement of the mass resolving power reaching 5.2 × 105,though at the cost of about 40%ion loss.(3)We compared the mass results obtained from this experiment with AME'16,and it is proved that the mass results obtained from this experiment basically con-sistent with the mass value given by other laboratories in the error range,thus demonstrated the reliability of our mass results.(4)The evolution of the energy difference between the ground and isomeric states in the chain of Z=49 isotopes have been interpreted as the effects of configu-ration blending?Theoretical calculations indicate that the nucleus above the v199/2 oribit occupies the v197/2 and v2d5/2 orbits simultaneously.Furthermore,we per-form the first calculation for 95Pd by using the JUN45 interaction in the fpg model space including the monopole correction.The calculation agrees excellently with experimentally-observed 1/2-level in 95Pd by using a monopole correction with the strength of 200 keV.Thus the importance of the monopole correction in the shell-model calculation is demonstrated.