High Spin States Of¹¹³In,¹²⁸La And¹⁶⁰Ho Nuclei

This thesis consists of two parts:experimental investigation of high spin states of113In,128La and160Ho nuclei.Part1:experimental investigation of high spin states of113InIn recent years, much effort has been made in the identification and theoretical interpretation of rotational bands in the A-110mass region, which exhibit electric rotation coexisting with magnetic rotation. Electric rotational bands in well-deformed nuclei, consisting of strong electric quadrupole transitions, are commonly interpreted as arising from the collective rotation of many nucleons along the nuclear rotation axis (perpendicular to the symmetry axis). In contrast, the magnetic rotation bands have very strong magnetic dipole (M1) transitions and very weak or absent crossover quadrupole (E2) transitions, and exhibit smaller dynamical moments of inertia and almost no signature splitting. They represent a novel rotational mechanism called "shears mechanism", and the angular momentum is increased by gradual alignment of the proton and neutron angular momentum along the total angular momentum, which is not along any of the principal axes of the nucleus. These bands have been successfully described by the tilted axis cranking (TAC) modelTo pursue above investigation, the Z=49Indium nuclei are expected to be a good candidate for the observation of these phenomena. Recently, several experiments have been performed in Indium isotopes. In the odd-A In isotopes, the△I=1bands based on the high-Ω g9/2proton hole and low-Ω h11/2, g7/2/d5/2neutrons have already been reported in105-121In nuclei. In total, five bands in107,111,113In have been suggested to be shears bands, whereas in the even-A In isotopes, the shears mechanism has been observed in the light indium isotopes106-114In.Furthermore, intruder structures were found in odd-mass113-119Sb and109-125I nuclei, which were interpreted as the h112or g72valence protons coupling the underlying core. Recently, the interest has been turned to the nuclei below the Z=50shell closure and several experiments have been performed in Ag, Cd, and In isotopes. However, the πh112intruder bands which were only found in two nuclei'111,113In have not been linked to any known states in the level schemes. Hence their spins and parities were assignedIn the present study, high-spin states in113In were populated through the10Pd(7Li,4n)113In reaction at a beam energy of50MeV. The7Li beam was provided by the HI-13tandem accelerator at CIAE in Beijing. The110Pd target, with an enrichment of97.2%and a thickness of2.4mg/cm2, was rolled onto an Au backing, y-y coincidence measurements were performed using the detecting system consisting of12Compton-suppressed HPGe detectors and two planar HPGe detectors. In our array, the Ge detectors were placed at900,±37,±300and±600relative to the beam direction. Energy and efficiency calibrations of the detectors were performed by standard sources of60Co and152Eu. A total of1.9x108two fold coincidence events were collected. A symmetrized coincidence matrix and a asymmetric DCO (directional correlation ratios of oriented states) matrix were constructed for off-line analysis. The DCO matrix was created by sorting the detectors at37" on one axis and the detectors at900on the other. In our array geometry, if one gates on a quadrupole transition, the expected RDCO value is close to1.0for stretched E2transitions and close to0.6for stretched dipole transitions. Similarly, with a dipole gating transition, the RDCO value is close to1.7and1.0for quadrupole and dipole transitions, respectively.For new bands are established for the first time. Wherein the△I=2band based on proton excitation has been assigned to πg9/2-2(?)vh11/22d5/2configuration. Besides, the backbending associated with the additional aligned h112neutron pair has been found in the negative parity yrast band. The experimental results are compared with self-consistent tilted axis cranking relativistic mean field calculations. Several decay paths of the πh112intruder band have been established, by which the level energies and spins of the7h11/2intruder band have been determined. The bandcrossing delay of the7h11/2intruder bands around the Z=50shell and the dynamic moment of inertia of the πg9/2-1(?)vh11/22bands in113,115,117,119In have been studied systematically.Part2:experimental investigation of high spin states of128LaTheoretical calculation shows that the nuclei in A-130mass region are characterized with a γ-soft deformed core and the orbitals occupied by the protons and the neutrons with competing shaped driving tendency. The proton Fermi level lies near the low-Ω h11/2obitals, prolate driving, whereas the neutron Fermi level lies above the mid-Ω h11/2obitals, oblate driving. A number of interesting phenomena have been exhibited in this region, such as the competition of alignment of protons and neutrons, shape coexistence and hyperdeformation etc. The part one of this thesis is about the expermental sturdy of the high spin states, and the new experimental results will help to get better understanding on the below topics:1. octupole correlation;2. signature splitting;3. chirality.Chiral doublet bands were predicted to appear in odd-odd nuclei in the A-130mass region fourteen years ago, and since then candidates of chiral doublet bands based on πh11/2(?)vh11/2configuration have been reported in more than ten odd-odd nuclei in this mass region. For a deeper understanding of the systematically appeared chiral doublet bands in this mass region, it is important to try to experimentally define the boundaries of the Z, N region where chiral candidate doublet bands appear in this mass region. For this purpose, the present work will try to extend the study of candidate chiral doublet bands to128La.In the present study, high-spin states in128La were populated through the118Sn(14N,3n)128La reaction at a beam energy of69MeV. The14N beam was provided by the HI-13tandem accelerator at CIAE in Beijing. The118Sn target, with an enrichment of92.8%and a thickness of2.4mg/cm2, was rolled onto a lead backing. y-y coincidence measurements were performed using the detecting system consisting of fourteen Compton-suppressed HPGe detectors and two planar HPGe detectors. The γ-γ coincidence matrix and DCO matrix have been constructed and a total of3.6×106coincidence events were collected.The separation energy between the states in the side band and the yrast band at the same spin I, AE(I)=E(I)side-E(I)yrast, is a important quantity for the interpretation of the side band. Level energies of the side band and the yrast band of128La are shown in Fig.-4together with those of130La,132La and134La for comparison. Fig.-4exhibits the separation energies of the states in the side bands and the yrast bands for these isotopes. Similar to the cases of130La and132La, AE(I) in128La stays roughly constant within a wide range of spin, and AE(I) of128La is about500keV which is～100keV higher than those of130La and132La. A possible interpretation of the side band is that it may result from the coupling between the unfavoured signature of the πh11/2orbital and the two signatures of the vh11/2orbital. The difference between the lowest πh11/2quasiparticle Routhian had been calculated to be700-800keV, as shown in Fig.-8of Godfrey(1989), and this is consistent with the observed properties of the h11/2bands in the neighboring odd-Z nuclei.700-800keV is much larger than the separation energy AE(I)-500keV between the side and the yrast band in128La, and thus the interpretation of the quasiparticle excitation can be ruled out. An interpretation of y-vibration coupled to the yrast band is also unlikely because the vibration energy are larger than600keV in this mass region. The exclusion of the interpretations of quasiparticle excitation and y-vibration provides the possibility to interpret the side band as the chiral partner band of the yrast band, and thus the side band and the yrast band form the candidate of the near degenerate chiral doublet bands.Previous to the present study, three isolated rotational bands with tentative spin assignments had been reported in the literature and the authors estimated that, to meet the predicted alignments, the spin of these band have to be increased by4-5h. Based on the configuration assignments, the Iπ assignment of5+for the bandhead of the yrast band proposed by T. Hayakawa et al. and the DCO ratios of linking transitions of the present work, the spins of levels in the πh11/2(?)vh11/2,πh11/2(?)vd5/2and πh11/2(?)(h11/2)3band are reassigned, and as results, the spins of the levels in these three bands have been increased by3,1and4h respectively comparing to the previous tentative spin assignments of Godfrey (1989,1989). The alignments of bands in128La deduced from the present new spin assignments are consistent with the alignments of relevant bands observed in neighbouring odd-A nuclei127La,127Ba and131La. Additionally, a new band with tentative configuration assignment πh11/2(?)vd3/2is reported.Part3:experimental investigation of high spin states of HoHigh-spin states of odd-odd nucleu160Ho have been populated through fusion-evaporation154Sm(11B,5n)160Ho at a beam energy of62MeV, and the intensity of incident beam was about4.5nA. The target consisted of a1.4mg/cm2foil of isotopically enriched (99.5%)154Sm backed with10mg/cm2of Pb. The experiment is performed at the HI-13Tandem Accelerator in the China Institure of Atomic Energy (CIAE). The detecting array consists of12HPGe detectors, each of which was equipped with a BGO Compton suppression shield. A total of160million of two-fold events were collected. The energy and efficiency of each detector are calibrated with standard radioactive source152Eu. After unfolding, the y-y coincidence events were sorted off-line into a symmetric two-dimentional Eγ-Eγ matrix and a asymmetric DCO ratio matrix.The level scheme of16Ho suggensted from the present experiment. Comparing to the level scheme proposed by S. Drissi et al., a great number of new transitions were observed and the level scheme of160Ho was much improved. The band2and band3was extended to higher spin with14and8additional levels repectively. The high-K rotational band namely band4was extended to higher spin with8additional levels.Considering the possible connections with the yrast band, large experimental alignments, band crossing frequency (-0.31MeV), population intensity of band3and systematic comparison of the πg7/2(?)vi13/2bands in Ho and162Tm, band3was believed to built on πg7/2(?)vi13/2. Thus, this band in160Ho make it realistic to study the systematic features of πg7/2(?)vi13/2rotational band in doubly odd Ho isotopes.