Mass Measurements Of Proton-rich Nuclei In Fp Shell Using The Bρ-defined Isochronous Mass Spectrometry

Mass is a fundamental property of atomic nuclei.Precision mass measurements of short-lived nuclei play an important role in nuclear structure and nuclear astrophysics researches.In this thesis,mass measurements of the proton-rich f p-shell nuclides are reported and relevant physics is discussed.The experiment was performed using a novel isochronous mass spectrometry(IMS),termed as "Bp-defined IMS(Bp-IMS)",at the experimental cooler storage ring CSRe in Lanzhou.The Bp-IMS relies on simultaneous determinations of the revolution time and velocity for every stored ion using two time-of-flight(TOF)detectors installed in one of the straight sections of the storage ring.To measure the velocity of the stored ions accurately,we developed several innovative methods such as the reduction of the background noise,the passing time extraction from the signals,the consideration of influences of ions’ Betatron oscillations and the combined fitting of signals from the two TOF detectors.The relative precision of the velocity determination was improved to the level of 10-5.The single-ion sensitivity,fast measurement,and background-free characteristics of the Bp-IMS are ideally suited to address nuclides with very short lifetimes and tiny productions.In this work,the "Bp-IMS" was applied to measure mass-unknown nuclides for the first time.The masses of 57Zn,60Ga,62Ge,64As,66Se and 70Kr were measured for the first time,and the mass of 58Zn,61Ga,63Ge,65As,67Se,71Kr and 75Sr were re-determined with improved accuracy.It is striking that only 2 ions of the short-lived 57Zn were detected,which corresponds to about 1 ion per week.Using the new masses,the coefficients of the Isobaric Multiplet Mass Equation(IMME)were studied for the series of T=1/2,T=1,T=3/2 isobaric multiplets.In T=1 isobaric multiplets,the isobaric tensors were derived up to A=70,revealing a discrepancy in the mass of 70Br.By comparing the experimental and theoretical results of Coulomb displacement energies,a new mass value was recommended for 70Br.The new masses allowed us to derive residual proton-neutron interactions ΔVpn in the Tz=0 nuclei up to Z=37.The ΔVpn values beyond Z=28 were found to decrease/increase with increasing mass A for even-even/odd-odd nuclei.This bifurcation of ΔVpn cannot be reproduced by the available mass models.We performed ab initio calculations with a chiral three-nucleon force(3NF)included,which indicated the enhancement of the T=1 pn pairing over the T=0 pn pairing in this mass region,leading to the opposite evolving trends of ΔVpn in even-even and odd-odd nuclei.With the new mass data,all relevant separation energies around the 64Ge waiting point in the rapid proton capture nucleosynthesis process(rp-process)were precisely determined.The five new masses of 64As,66Se,63Ge,65 As and 67Se were used as inputs for X-ray burst model calculations.An important conclusion was that the slowed-down matter flow through 64Ge preserves hydrogen fuel for later burning.We obtained the X-ray burst light curve to constrain the neutron star compactness,and suggested that the distance to the X-ray burster GS 1826-24 from the earth needs to be increased by about 6.5%to match astronomical observation.