A M Al-Naser

Gamma-ray spectroscopy experiments for levels in 39K below 8.4 MeV excitation

The gamma-ray spectroscopy of sixty excited states in 39K below an excitation energy of 8.4 MeV has been studied. The data were obtained mainly from the 36Ar+ alpha reaction at beam energies between 7.5 and 16.0 MeV, the remaining data coming from the 24Mg+18O and 28Si+16O reactions, both at beam energies of 42 MeV. 13 new levels were established in 39K and several previously unobserved branches were revealed between the previously known levels. Spins, parities, mixing ratios and gamma-ray branching ratios were determined from angular distribution and linear polarisation measurements using the 36Ar+ alpha reaction at several different beam energies. Mean lifetimes were deduced using both the Doppler-shift attenuation method (with the 36Ar+ alpha reaction) and the recoil-distance method (with the 28Si+16O reaction). The results have allowed transition strengths to be calculated for the decays between many of the levels. The results are discussed in terms of both the shell model and the simple weak coupling model.

The structure of levels in 67Ga below 2.5 MeV excitation

The reaction 64Zn( alpha ,p gamma )67Ga was used to populate levels of 67Ga. Excitation energies, mean lifetimes, gamma -ray branching ratios, angular distributions and linear polarisations have been measured for levels below Ex=2.5 MeV. Gamma ray spectra at bombarding energies in the range Ex=7-16 MeV and gamma - gamma coincidence data at Ealpha =13.0 and 15.0 MeV were used to determine the decay scheme.

Gamma-ray spectroscopy of high-spin levels in 67Ga

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.

The structure of high-spin positive-parity states in 43Ca

Abstract The 40Ar(α, nγ)43Ca reaction has been used to study high-spin states in 43Ca. The γ-ray decays of levels at 3505 and 4186 keV are established in γ-γ coincidence measurements and new decays are observed from levels at 3944 and 4591 keV. Solid Ar targets enable the Doppler shift attenuation method to be used to measure mean lifetimes for the following levels E x ( keV )(τ m )J π : 2951(>5 ps ) 11 2 + ; 3371(>5 ps ) 13 2 + ; 3505 (105±35 fs ) 13 2 + ; 3944 (1.1±0.3 ps ) 15 2 + ; 4186 (180±70 fs ) 15 2 + and 4591 (300±75 fs ) ( 13 2 + , 17 2 + ) . The structure of these levels is discussed in terms of a deformed K π = 3 2 + band and shell model configurations of the type ( f 7 2 ) 7 + 4 ⊗(d 3 2 ) −1 .

Spin-alignment attenuation factors in mass 61–67 nuclei populated by (α, n) and (α, p) reactions

Gamma-ray angular distributions for 39 E2 transitions in A = 61–67 nuclei, excited in ( α , n) or ( α , p) reactions, are collected from the literature and reduced to spin-alignment attenuation factors α 2 and α 4 . The validity of the prediction for α 2 from statistical compound nucleus reaction theory is investigated. Also the sensitivity of this prediction to the optical-model parameters is examined. The present data support the rule 0 ⩽ α 4 ⩽ α 2 , but contradict the assumption of a Gaussian shape for the population of magnetic substates.

Angular distribution and linear polarisation measurements of gamma rays in 41Ca

The use of the38Ar( alpha ,n gamma )41Ca reaction on a frozen target, together with high-precision gamma-ray measurements, has allowed many rigorous spin and parity measurements to be made on states in 41Ca. Several restrictions of spin and parity were possible and many multipole mixing ratios were deduced. Simple phenomenological models are used to give a first-order description of most states of both positive and negative parity up to 4 MeV in excitation. Collective core excitations are found to have a strong influence on the properties of many states.

A comprehensive study of the γ-ray spectroscopy of 43Ca

The reaction 40Ar( alpha ,n gamma )43Ca was used to populate the levels in 43Ca at bombarding energies between 5.5 and 19 MeV, gamma - gamma coincidence measurements at Ealpha =8.5, 15 and 16 MeV being used to establish the decay scheme of 53 levels. Several new levels and new decays of levels with high angular momentum were established. The Doppler-shift attenuation method was used with solid Ar targets to deduce the mean lifetimes for most of these levels. A Ge(Li)-Na(Tl) escape-suppressed spectrometer and a three-Ge(Li) Compton polarimeter were used to measure the angular distribution and linear polarisation of gamma rays at alpha bombarding energies of 7.0, 14.5 and 17 MeV.

Decay scheme of excited states in 67Ge

Excited states in 67Ge were studied using the reaction 64Zn( alpha ,n gamma ). Excitation functions for the production of 67Ge determined the Q value for this reaction to be -8993+or-5 keV. Neutron-gamma coincidences at Ealpha =15 MeV and gamma - gamma coincidences at Ealpha =13 and 15 MeV helped in the placing of 25 gamma rays into a decay scheme of 14 levels in 67Ge. The first excited state was placed at 18.3 keV and the 734 keV gamma ray has been identified as a decay from a level at 751.8 keV to the 18.3 keV level. The mean lifetimes of the isomeric states at 18.3 keV ( tau m=21.0+or-0.3 mu s) and 751.8 keV ( tau m=160+or-2 ns) have been determined by pulsed-beam techniques, the decay of the 18.3 keV state being detected by X-ray detection. The mean lifetime of the level at 751.8 keV (Jpi =9/2+) and the angular distribution and linear polarisation measured for the 734 keV gamma ray have limited the spin of the level at 1803 keV to 5/2 with a proposed negative parity.

Properties of levels in 41K below 3.3 MeV

The reaction 38Ar( alpha ,p gamma )41K was used to populate levels up to 3.3 MeV excitation in 41K. Solid 38Ar targets were used. Gamma-ray angular distributions and linear polarisations were measured at alpha-particle energies of 9.50 and 10.75 MeV. Analysis of these data yielded spin and parity assignments of Jpi =3/2+, 3/2-, 7/2+, 5/2+, 5/2-, 9/2+, 7/2+, 11/2+, 11/2- and 13/2+ for levels at 1560, 1582, 1677, 1698, 2317, 2495, 2509, 2528, 2761 and 2774 keV. Gamma-ray multipole mixing ratios were deduced for many transitions and several branching ratios were measured. A simple shell-model calculation was carried out in an attempt to clarify the structure of positive-parity states.

High-spin states in 43K

The nucleus 43K has been studied via the 40Ar( alpha ,p gamma )43K reaction, using solid targets of natural argon. A gamma - gamma coincidence experiment established five new levels at excitation energies of 1850, 2048, 2509, 3115 and 3139 keV. Gamma-ray angular distributions and linear polarisations were measured at an alpha-particle energy of 17.0 MeV. The analysis of these data yielded spin and parity assignments of Jpi =7-/2, 7+/2, 11-/2 and 15-/2 for the levels at 738, 1510, 1850 and 3115 keV respectively. Mean lifetimes were measured for four levels using the DSAM: 1510 keV, 8.2+or-2.1 ps; 2048 keV, 2.4+or-0.8 ps; 1850 keV, 6.7+or-1.7 ps; 3115 keV, 5.0+or-1.5 ps. A lower limit of 7 ps was obtained for the lifetimes of the levels at 1207 keV and 2509 keV.