A J Brown

Decay modes and level lifetimes in 41Ca and 41K

Levels in 41Ca and 41K were populated using the reactions 38Ar( alpha ,n)41Ca and 38Ar( alpha ,p)41K. Solid 38Ar targets were produced using a 4He refrigerator system at a mean temperature of 14K. Gamma-gamma coincidence data were collected at Ealpha =10.50, 11.50 and 15.00 MeV to study principal decay modes. In 41Ca new gamma decays from levels at 3975 and 4519 keV were found. Mean lifetimes were measured using the Doppler-shift attenuation method at several beam energies. Data were obtained for 36 levels in 41Ca and 21 levels in 41K.

High spin states in 39K

The reaction 36Ar( alpha , p gamma )39K has been used to measure angular distributions, linear polarizations, mixing ratios, branching ratios and mean lifetimes for a number of high spin states in 39K. The results give the following unambiguous spin and parity assignments: ExJpi ; 2814 keV 7/2-; 3597 keV 9/2-; 3944 keV 11/2-; 5718 keV 9/2- and 6475 keV 11/2+. Using a solid 36Ar target and the Doppler shift attenuation method a mean lifetime of 250+or-65 fs has been measured for the 5718 keV level. There are several discrepancies between the present results and the results of previous work, particularly the heavy ion data published by the Brookhaven group.

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.

Electromagnetic and angular momentum properties of states in 25Mg below 6.05 MeV in excitation

The reaction 22Ne ( alpha ,n)25Mg was used to populate levels in 25Mg at alpha -particle energies of 8.00 and 9.15 MeV. The analysis of angular distributions and linear polarizations gave unique spin and parity assignments of 1/2-, 9/2+, 1/2-, 13/2+, 11/2+, 9/2+ and 7/2+ to the levels at 4277, 4712, 5116, 5461, 5533, 5971 and 5977 keV and strongly favoured values of 11/2- and 11/2+ for the levels at 5793 and 6041 keV respectively. Also, gamma -ray multipole mixing ratios were accurately determined for many transitions from states below 6.05 MeV in excitation. The experimental measurements are discussed in terms of rotational model structure built on both single particle and 2 particle-1 hole excitations. The properties of the positive parity states are compared with predictions of existing shell model calculations, and are found to be well reproduced by a model calculation which used the full 2s-1d space.

Properties of 37Ar II. Levels above 3.8 MeV excitation energy (populated in 34S(α,n γ)37Ar)

For pt. I, see abstr. A12157 of 1974. Excitation energies, mean lifetimes, gamma ray branching ratios, angular distributions and linear polarizations have been measured for levels in 37Ar above 3.8 MeV excitation energy. The states were populated using the 34S( alpha , n gamma )37Ar reaction at beam energies between 10.5 MeV and 16.0 MeV. Gamma-gamma coincidence measurements at beam energies of 11.5 MeV and 16.0 MeV were used to determine the decay scheme. The results of an intermediate coupling vibrational model calculation for the negative parity states are presented.

Levels in 37Cl between 4 and 9 MeV in excitation

The 34S( alpha ,p gamma )37Cl reaction has been used to study levels in 37Cl between 4 and 9 MeV in excitation. A decay scheme was determined for 21 levels by detecting proton-gamma ray coincidences, the majority of these levels being previously unreported. Angular distribution measurements were possible for ten of these levels. The Doppler-shift attenuation method was used to measure mean lifetimes as follows: 4461 keV, 60+or-45 fs; 4921 keV, 80+or-45 fs; 5379 keV, 150+or-55 fs; 6050 keV, >2 ps; 6197 keV, 320+or-80 fs; 7020 keV, >2 ps. Combining the measured mixing ratios, mean lifetimes and the results of previous work leads to the following spin and parity restrictions: 4270 keV, 3/2+; 4461 keV, 9/2; 5379 keV, (5/2-,9/2).

Gamma ray spectroscopy studies in the nuclei 36Ar and 36Cl

Excitation energies, mean lifetimes, mixing ratios, branching ratios, angular distributions and linear polarizations have been measured for levels in 36Ar and 36Cl. The states were populated using the reactions 33S( alpha ,n gamma )36Ar and 33S( alpha ,p gamma )36Cl at beam energies up to 14 MeV. The decay schemes were determined with the help of a gamma-gamma coincidence experiment carried out at a beam energy of 14 MeV. New spin assignments were made for four levels in 36Cl: 2518 keV, 5-; 2810 keV, 4-; 3102 keV, 4-; 3723 keV, 4-. Mean lifetimes were measured for four levels in the two nuclei using the recoil distance method. Two new levels were found in 36Cl at excitation energies of 4291 keV and 5311 keV, both being candidates for high spin. The results are discussed in terms of recent shell-model calculations which reproduce very well the three new 4- states in 36Cl.

The properties of low-lying levels in 37Cl (populated in 34S(α,pγ) reaction)

Excitation energies, mean lifetimes, gamma-ray branching ratios, angular correlations and linear polarizations have been measured for levels below 5.3 MeV in 37Cl. The states were populated using the 34S( alpha ,p gamma )37Cl reaction at bombarding energies between 9.0 MeV and 12.2 MeV. A gamma-gamma coincidence experiment was performed at 11.5 MeV to obtain the decay scheme. New measurements were made for the following levels: Ex( tau m)Jpi ; 3087 keV (<40 fs) 5/2+; 3105 keV (48+or-5 ps) 7/2-; 3626 keV (40+or-20 fs) 3/2, 5/2, 7/2+; 3708 keV (<25 fs) 3/2+, 5/2-; 3740 keV (<20 fs) 5/2-; 4011 keV (31+or-3 ps) 9/2-; 4547 keV (2.7+or-0.6 ps) 11/2- and 5271 keV (2.7+or-0.4 ps) 13/2-. The results are compared with the properties of high-spin negative-parity states in neighbouring nuclei and are discussed in terms of recent shell-model calculations.