Design And Test Of High-resolution Beam-line Systems&Mass Measurements Of N=Z Nuclei

Since 2007,Radioactive Ion beam factory(RIBF),at RIKEN Nishina center in Japan,one of the new generation facilities,has been in operation to enhance RI beam intensities for advancing experimental studies on the nuclear chart as well as to explore nuclear astrophysical processes.The RIBF accelerator complex,consisting of linacs and cyclotrons,can accelerate various kinds of heavy ions(from proton to uranium)up to 345 MeV/nucleon,and the goal beam intensity is as high as 1 p??,corresponding to 6.24×1012 particles/s.Strong interest in fast,high-accuracy and high-precision mass measurements for exotic nuclides due to their importance in nuclear astrophysics and nuclear structure studies,has triggered the development of a various of techniques for mass measurement around the world.An isochronous mass spectrometry(IMS)using a newly constructed storage ring named the 'Rare-RI ring'(R3)has been implemented at the RIKEN Nishina Center to determine the masses of short-lived rare nuclei with a relative precision of the order of 10-6.Firstly,we design a high-resolution ion optics for the beam-line and then the isochronous optical design for the R3 considering of dispersion matching condition of the beam-line and the storage ring.Based on the high-resolution ion-optical design,we develop a fast response matrix method for beam tuning with the measurements of matrix elements at each focus with the beam-line position-sensitive detectors.We also develop and test a scheme of high-resolution particle identification and selection of the secondary beams.The scheme is based two stage methods:B?-?E-Bp and B?-?E-TOF,at the high-resolution beam-line BigRIPS-HA/OEDO-SHARAQ-IL-R3.With the estab-lishment of the scheme of high-resolution separation,identification and selection of secondary RIs at the BigRIPS-HA beam-line,we could individually inj ect the ions of interest with a limited rate of 100 Hz to the R3 which has a relative momentum ac-ceptance± 0.3%for IMS mass measurements.Meanwhile,some of the nuclei which are not injected into R3 but accepted by the high-resolution BigRIPS-HA/OEDO beam-line within a relative momentum acceptance ± 0.5%are also of interest,and the reachable ones will be measured simultaneously via the B?-TOF method.The high-resolution identification of secondary RIs will also benefit the subsequent data analysis processes for mass deduction.Especially,the identification of N=Z nuclei with very close m/q values,which can not be realized by other in-ring TOF techniques for mass measurements developed at CSRe/IMP and ESR/GSI,couldbe easily carried out with the scheme.We have successfully tested the fast tuning method with the dedicatedly designed optics,achieved high resolution particle iden-tification resolutions of the A/Z and Z of each ion,transported the ions into R3 individually during injection,checked storage of ions in R3 and extraction of them.Simulation studies of beam tracking,high-resolution particle identification and selection of the secondary beams at RIBF for two complementary TOF mass mea-surements methods have been carried out.Projectile fragmentations from primary beam of 48Ca and 124Xe have been studied with several different ion-optical designs.The results show that the revolution time of all the N=Z nuclei are independent of momentum dispersion in the storage ring when we set one species of N=Z nucleus in isochronous condition.Based on the machine studies,the developments of the new techniques and to take advantages of specific characteristic of N=Z nuclei verified via simulation,we propose the experiment aimed at measuring the masses of neutron-deficient nuclei in the mass region near A = 78-100 N=Z line,using two complementary direct time-of-flight methods for mass measurements:magnetic-rigidity-time-of-flight(B?-TOF)and Isochronous storage ring TOF Mass Spectrometer(IMS),i.e.7,BigRIPS in conjunction with the OEDO beam-line for B?-TOF method and the R3 for IMS method at RIKEN.This novel technique is ideally suited for mass measurements experiments,as one can reach isotopes very far from stability and get access to a large district of the chart of the nuclides in a single experimental run.The two measurements techniques will be performed simultaneously,in which we believe to be a good approach to make full use of limited beam-time resources at radioactive ion(RI)beam facilities.The importance of nuclear mass data along the heavy neutron-deficient N = Z nuclei up to 100Sn and its neighbors for nuclear astrophysics and nuclear structure studies have been discussed,especially for the doubly-magic nuclei 100Sn.Nuclear mass data of these nuclei is crucial for the investigation of the rp-(rapid-proton capture)and the vp-(rapid-neutrino capture)processes.In addition,access to nuclei on(or more proton-rich than)the N = Z line will be greatly enhanced to solve key questions relating to many open questions of nuclear structure:The origin of the Wigner energy,or of the T = 0 pairing condensate,isospin symmetry,and the location of the proton drip-line,deformation and the evolution of shell-closures,test of mass models,constrainment of the B(GT)values of beta-decay along N=Z and the test of the CVC hypothesis.Meanwhile,we outlined the design and development of a new type of MCP detector at next-generation facility HAIF,including its operating principles,design and specifications,characteristics and performance via simulation.The MCP detec-tor equipped with a thin foil is segmented to two parts dedicated for position and timing measurements separately.The momentum distribution and position disper-sions of the SEs ejected from the conversion foil during their transmission to the front surface of the MCP are counteracted by the electrostatic lenses to maintain their position information.With the specifications of low energy loss and energy straggling by detection of SEs induced from the conversion foil,a large effective area to cover a large beam size,good timing and position resolution at the same time,and a high rate capability,the applications of the detector have been discussed and demonstrated in detail.This type of detector is a versatile instrument which can be used on the beam-line HFRS for two-dimensional position measurement to recon-struct beam trajectory for beam tuning,high-resolution PID,beam-line momentum measurements of heavy ions for velocity reconstruction,and for beam-line TOF measurements between two foci to ensure the high-resolution PID and to deduce the velocity of each RI.Meanwhile,it could be used for position monitoring and revolution time measurement turn by turn inside the storage ring SRing for mass measurements directly.A new scheme of mass-measurement technique,in which two complementary methods:IMS and B?-TOF would be performed simultaneously in one experimental setting with the usage of this type of detectors,has been proposed for HIAF.A single in-ring TOF detector with good position-sensitivity to deduce the Bp of circulating RIs for IMS mass measurements,which has the equivalent advantage of Double-TOF method but with less energy loss of the RIs during their passage,has also been proposed in this thesis.Besides,several promising MCP detectors developed in other heavy-ion facilities have been designed and simulated for the employment at the HIAF facility.The methods to reconstruct the in-ring Betatron function and to measure the dispersion function have been proposed,and corresponding simulations have been carried out to validate these methods.