W.F. Davidson

In-beam study of prompt γ-rays emitted in the 66Zn(p, nγ)66Ga reaction

Abstract The level structure of the nucleus 66 Ga has been studied by means of the 66 Zn(p, nγ) 66 Ga reaction ( Q = −5.957 MeV). Levels in 66 Ga up to 730 keV in excitation were selectively populated by varying the proton bombarding energy in the range of 6.00 to 6.82 MeV. The γ-rays associated with these levels were identified both in singles spectra, from a study of their threshold behaviour, and inγγ-coincidence measurements. Altogether 24 levels in 66 Ga were identified, of which 10 are known from previous studies of the β + decay of 66 Ge to 66 Ga, and the remaining 14 are reported here for the first time. Gamma-ray branching ratios for these new levels have been determined and a decay scheme comprising 68 γ-transitions is presented. Angular distributions of de-excitation γ-rays have been measured at proton bombarding energies close to threshold for the levels studied. Comparison of these distributions with the theoretical predictions of the compound nucleus statistical model has led to spin and parity assignments for the levels studied.

Experimental study of low-lying levels and decay structure in the nucleus 62Cu

Abstract The reaction 62 Ni(p, nγ) 62 Cu has been used to investigate the low-lying levels of 62 Cu and their γ-decay. Gamma-ray angular distributions were carried out using incident proton energies close to threshold for the states under investigation and comparison of these results were made with the predictions of the compound nucleus statistical model. In addition to levels seen in the β + /EC decay of 62 Zn, namely the ground state (1 + ), 40.84 keV (2 + ), 243.43 keV (2 + ), 287.86 keV (2 + ), 548.25 keV (1 + ) and 637.20 (1 + ), other levels were found at 389.9 keV, 426.1 keV, 644.9 keV, 675.1 keV, 698.3 keV, 727.5 keV, 756.3 keV and 915.5 keV. The 426.1 keV, 675.1 keV and 727.5 keV states are assigned to be 3 + , 3 + and 2 (+) respectively, and possible spin values for the remaining levels are advanced. Gamma-ray branching ratios were obtained, and a decay scheme for 62 Cu comprising 30 transitions is presented.

Angular distributions of gamma rays following the 64Ni(p, nγ)64Cu reaction

Abstract Gamma-ray angular distributions in the reaction 64Ni(p, nγ)64Cu were measured under conditions where the incident proton energies were close to the neutron threshold for the levels of interest. Using the theoretical predictions of the compound nucleus statistical model, unique spin assignments were obtained for the 159 keV (2+), 278 keV (2+) and 609 keV (2+) levels in 64Cu, and the most probable spins for the other levels were found to be 344 keV (1+), 362 keV (3+), 663 keV (1+), 739 keV (2+ or 3 +), 746 keV (3+), 878 keV (1+ or 2 +), 895 keV (3+) and 927 keV (1+). Multipole mixing ratios of the γ-rays observed were also obtained.

The reaction 23Na(p, p) in the range 8.0–12.0 MeV: (I). Analysis of average elastic cross sections

Abstract Absolute differential cross sections have been measured for the elastic scattering of protons from 23 Na. Excitation functions were measured in 20 keV steps for incident proton energies from 8.0 to 12.0 MeV and at 23 different angles. Average angular distributions every 0.5 MeV were obtained from smooth fits to the excitation functions; these were analysed using the optical-model and Hauser-Feshbach theories. The variations with energy of the optical-model potentials, the compound-nucleus reduction factor and the amount of compound nucleus and direct reaction cross sections have been investigated. There is some evidence for the presence of intermediate structure in the compoind nucleus 24 Mg.

Compound and direct processes in proton elastic scattering from 31P and 62Ni

Abstract Absolute differential cross sections have been measured for the elastic scattering of protons from 31 P and from 62 Ni. For 31 P the measurements were taken in 10 keV steps from 8.00 to 8.20 MeV and at 27 angles. For 62 Ni six angular distributions were measured between 8.00 and 8.05 MeV. The averaged angular distributions have been analysed using the optical model and Hauser-Feshbach theories. The effect of reducing the Hauser-Feshbach contribution to allow for direct interaction competition has been investigated.

Spins of levels in 70Ga

Abstract The level structure of the nucleus 70 Ga has been studied by means of the 70 Zn(p, nγ) 70 Ga reaction ( Q = − 1.435 MeV). Levels in 70 Ga up to 1633 keV in excitation were selectively populated by varying the proton bombarding energy in the range of 1.7 to 3.2 MeV. The γ-rays associated with these levels were identified in singles spectra from their energies and their threshold behaviour. Gamma-ray branching ratios were obtained and a decay scheme for 70 Ga comprising 58 transitions is presented. Angular distributions of de-exciting γ-rays have been measured at proton bombarding energies close to threshold for the levels studied. Comparison of these distributions with the theoretical predictions of the compound nucleus statistical model has led to spin and parity assignments for the levels studied.

Note on the cross section of the 25Mg(τ, γ)28Si reaction

Abstract The differential cross section for the 25 Mg(τ, γ) 28 Si reaction has been measured at Eτ = 4.44, 6.08, 6.15 and 8.26 MeV, with a large NaI crystal spectrometer. The smallness of the observed cross section suggests that 3p-3h states play an insignificant role in explaining the “intermediate” structure observed above the 28 Si giant resonance in a recent study of the 28 Si(γ, n) 27 Si reaction.

Lifetime and γ-ray angular distribution measurements for low-lying levels in 45Ti

Abstract The decay modes, lifetimes and spins of low-lying levels in 45 Ti have been investigated via the 45 Sc(p, nγ) 45 Ti reaction. The mean lifetimes of the 1353, 1468 and 1521 keV levels were found to be 146±24, 670 +164 −120 and 79±13 fs respectively, by the technique of attenuated Doppler shifts. Lower limits of 1000 fs were set for the levels at 330, 744 and 1226 keV. Angular distributions of de-excitation γ-rays have been measured and compared with theoretical predictions of the compound nucleus statistical model to give spin assignments. From data obtained here and in previous experiments spins and parities were deduced for levels at 40 ( 7 2 − , 9 2 − ), 1353 ( 9 2 − ) and 1468 ( 11 2 − ) keV .

The reaction 23Na(p, p) in the range 8.0 TO 12.0 MeV: (II). Evidence for and interpretation of intermediate structure

Abstract The selective occurrence of intermediate structure in the compound nucleus 24 Mg observed in the excitation functions for decay through different exit channels is interpreted on the basis of the statistical model of intermediate structure of Moldauer and the compound nucleus theory of Hauser and Feshbach.

A study of the reaction 11B(3He, γ0)14N in the energy range E3He = 0.9–2.6 MeV

Abstract Excitation functions for the reaction 11 B( 3 He, γ 0 ) 14 N have been measured, at 0° and 90° in 25 keV steps for 3 He energies between 0.9 and 2.6 MeV. The γ-ray detector used was a 23.8 × 25.4 cm NaI(Tl) crystal. When the yield from the reaction is divided by the barrier penetration factor a broad resonance is seen at both angles, which peaks at a 3 He energy of 1.4 MeV, corresponding to an excitation energy in 14 N of 21.8 MeV. The ( 3 He, γ) excitation functions are compared with other reaction channels leading to the same excitation region in 14 N. Angular distributions were measured at six 3 He energies and were found to be approximately isotropic. Possible spin assignments are discussed.