Pn Gamma Research Articles

High-spin states in doubly odd 112I

High-spin states have been identified in doubly odd 112I, up to a spin approaching 30h(cross), using the 58Ni(58Ni,3pn gamma ) reaction. Gamma-ray coincidence data were collected with the Eurogam spectrometer coupled to the Daresbury recoil separator. The results represent the lightest doubly odd iodine isotope for which gamma -ray transitions have been identified.

Band termination in doubly odd 116I

The 92Mo(27Al,2pn gamma ) reaction has been used to populate high-spin states in doubly odd 116I. Evidence for a termination of the collective rotational states is observed at spin Ipi =(23-). Total Routhian surface calculations have been performed in order to interpret the structure of this non-collective state which is found to be closely related to termination states seen in several neighbouring odd-A iodine isotopes.

111Ag utilizing the (3He, pn gamma ) reaction: A rotational nucleus with intermediate deformation.

The structure of $^{111}\mathrm{Ag}$ was studied using the $^{110}\mathrm{Pd}$${(}^{3}$He, pn\ensuremath{\gamma}) $^{111}\mathrm{Ag}$ reaction, which has populated an essentially complete set of low-energy states. The proton exit channel was isolated from competing reaction channels by operating \ensuremath{\gamma}-ray detectors in coincidence with a large-solid-angle proton detector. The experiments included \ensuremath{\gamma}-ray excitation functions, \ensuremath{\gamma}-ray angular distributions, and \ensuremath{\gamma}-\ensuremath{\gamma} coincidences. Four rotational bands have been identified. A symmetric particle-rotor model has been used to interpret these bands, and the model has identified other rotational features as well. A tentative interpretation of several nonrotational states is presented, suggesting that the mixing between rotational and nonrotational states is minimal.

Gamma-ray studies of62Zn

The reaction 58Ni(6Li,pn gamma )62Zn was used to populate levels in 62Zn at bombarding energies between 15 and 24 MeV. Gamma-gamma and neutron-gamma coincidence measurements at beam energies of 20 and 24 MeV were used to establish a decay scheme up to 7.4 MeV in excitation. Spins and parities of the levels together with branching and mixing ratios of the gamma-ray transitions have been deduced from angular distribution and linear polarisation measurements. Mean lifetimes of many levels have been measured using the doppler-shift attenuation method and the recoil-distance method. Comparisons are made with the shell model and the interacting boson approximation model.

High-spin states in55Fe and56Fe

The reactions 46Ti(13C,2p2n gamma )55Fe and 46Ti(13C,2pn gamma )56Fe were used to populate high-spin states in 55Fe and 56Fe at bombarding energies of 55 and 49 MeV. gamma - gamma coincidences, angular distributions and the excitation function were measured with a Ge(Li)-Na(I) anti-Compton spectrometer. New high-spin states are observed in 55,56Fe and 51Cr.

Gamma-ray studies on the neutron-deficient isotope70Se

The level structure of 70Se has been studied with the aid of the 58Ni(14N, pn gamma )70Se and 60Ni(12C, 2n gamma )70Se reactions. A decay scheme has been established from results of gamma-gamma and neutron-gamma coincidence experiments. Spin and parity assignments of 2+ (945 keV), 2(+) (1600 keV), 4+ (2039 keV) and 6+ (3003 keV) have been deduced from the results of gamma-ray angular distributions and linear polarisation measurements. Spin restrictions have also been placed on two levels: 3, 5 (3524 keV) and 5, 7 (3915 keV). Comparisons are made with the structure of neighbouring even-even isotopes and their energy level systematics.

A study of the neutron-deficient isotope66Ge

The neutron-deficient isotope 66Ge has been studied using gamma-ray spectroscopy techniques. States in 66Ge were populated using the 58Ni(10B,pn gamma )66Ge reaction at bombarding energies of 28.5, 29 and 30 MeV. A decay scheme has been established from the results of gamma-gamma and neutron-gamma coincidence experiments performed at a beam energy of 28.5 MeV. Angular distributions were measured at beam energies of 28.5, 29 and 30 MeV, and linear polarisations were measured at 28.5 MeV. The analysis of these data yields spin-parity assignments of 1694 keV (2+), 2175 keV (4+), 3686 keV (4+,5-), 4208 keV (6+,7-) and a probable 6+ assignment to the 3657 keV level. Spin restrictions are also placed on several other levels. The lifetimes of the 958, 1694 and 4208 keV levels are deduced from a recoil-distance-method experiment, performed at a beam energy of 29 MeV, to be 5.3+or-1.0 ps, 6.5+or-2.5 ps and 295+or-40 ps respectively. A limit of less than 3 ps has also been placed on the lifetime of the 2175 keV level.

Gamma-ray spectroscopy in63Zn and63Cu

Electromagnetic decay transitions in 63Zn and 63Cu have been studied using the 60Ni( alpha ,n gamma )63Zn and 60Ni( alpha ,p gamma )63Cu reactions at incident beam energies of 9.5-19.0 MeV, the 54Fe(11B,np gamma )63Zn and 54Fe(11B,2p gamma )63Cu reactions at EB=30.0 MeV, and the 58Ni(7Li,pn gamma )63Zn reaction at ELi=20.0 MeV. Gamma-gamma coincidence measurements have been used to determine the decay schemes. Spins and parities of the levels together with branching and mixing ratios of the gamma -ray transitions have been deduced from angular distribution and linear polarisation measurements. Mean lifetimes of the 193, 248, 1704 and 2585 keV levels in 63Zn have been obtained using the recoil-distance method (RDM). Lifetimes of many levels in 63Zn and 63Cu have been deduced from the Doppler-shift attenuation method (DSAM). The results are discussed in terms of the shell model and the intermediate coupling model.

Gamma-ray spectroscopy on48Cr

High-spin states in 48Cr have been investigated with the 36Ar(14N,pn gamma )48Cr and 40Ca(10B,pn gamma )48Cr reactions. Mean lifetimes or limits have been obtained for the following levels: 0.75 MeV (10.6+or-1.1 ps), 1.86 MeV (1.9+or-0.5 ps), 3.45 MeV (<1.0 ps), 3.53 MeV (3.6+or-1.0 ns), 4.06 MeV (40+or-10 ps) and 5.19 MeV (<1.2 ps). New spin-parity assignments have been made for the last four levels: 6+, 5(-), 6(-), and (8)+, respectively. Comparisons are made with simple shell-model calculations.

Experimental evidence for low-lying intruder states in54Mn

High-spin states in 54Mn were populated in the 52Cr( alpha ,pn gamma ) reaction. Using angular distribution, linear polarisation and gamma - gamma coincidence measurements, the following unambiguous spin and parity assignments were obtained: Ex, Jpi ; 1073 keV, 6+; 1784 keV, 7+; 1925 keV, 7+; 2857 keV, 8+; and 3244, (9)+. In addition a new level was observed at an excitation energy of 3939 keV. The experimental data show evidence for low-lying intruder states as predicted by a recent shell-model calculation.

Gamma-ray spectroscopy of high-spin levels in67Ga

Reactions 64Zn( alpha ,p gamma )67Ga and 53Cr(16O, pn gamma )67Ga populated the levels in 67Ga. Gamma-gamma coincidence experiments were carried out at Ealpha =13 and 15 MeV with the ( alpha ,p gamma ) reaction and E(16)O=42 MeV with the heavy-ion reaction. The Doppler-shift attenuation method was used with the ( alpha ,p gamma ) reaction to deduce mean lifetimes (or limits) for certain levels, along with the recoil-distance method utilised both in singles and gamma - gamma coincidence with the heavy-ion reaction. A mean lifetime of tau m=60+or-30 ns for the first excited state at 167 keV was measured using the delayed coincidence method. Gamma-ray angular distributions and linear polarisations were measured at Ealpha =13.5 MeV using a Ge(Li)-NaI(Tl) escape-suppressed spectrometer and a three-Ge(Li) Compton polarimeter and analysis resulted in spin and parity assignments. Transition strengths were calculated and the results are discussed in terms of the particle-cluster-vibrational-core coupling model.

Quasi-band structure in64Zn

The reactions 61Ni( alpha ,n gamma )64Zn and 56Fe(11B,2pn gamma )64Zn have been used to make spin assignments of Jpi =6+,6+ and 7- to the levels in 64Zn at 3994, 4237 and 4636 keV respectively. Lifetime measurements of 175+or-50 fs and 190+or-60 fs for the two Jpi =6+ levels yield E2 transition strengths of 23+or-5 Wu for the 61+ to 41+ transition and 37-9+17 Wu for the 62+ to 42+ transition. These results indicate the presence of two quasi-bands in 64Zn.

The γdecay of low-lying states in44Sc (populated in44Ca(p,nγ),41K( α ,nγ) and28Si(18O,pn γ) reaction)

Levels in 44Sc have been studied using the reactions 44Ca(p,n gamma )44Sc, 41K( alpha ,n gamma )44Sc and 28Si(18O,pn gamma )44Sc. The level scheme up to 1.5 MeV has been established. Lifetimes have been measured using the Doppler shift attenuation method and the recoil distance method. gamma ray angular distributions were measured near threshold in the (p,n) reaction and these results together with the lifetimes and branching ratios allow spin assignments to be made for the most of the states. The low-lying negative parity states are interpreted as deformed bands, co-existing with the spherical positive parity states predicted by the shell model.