A.B. McDonald

Thick target neutron yields and spectral distributions from the 7Li(pd, n) and 9Be(pd, n) reactions

Abstract Neutron yields and spectral distributions of neutrons produced by bombarding thick 7 Li and 9 Be targets with protons and deuterons of energies 14.8, 18 and 23 MeV were measured at five angles between 0° and 40°. Time-of-flight spectra of neutrons with energies greater than 0.3 MeV were obtained with a 13.2 cm 3 stilbene detector using (n, γ) discrimination. Background was measured by blocking the direct path of neutrons to the detector.

Magnetic moments and half-lives of isomeric states in polonium isotopes

Abstract We have observed small violations of the additivity rule for isomeric two-proton states in 202, 208–210Po. The g-factors of the 110 ns 8+ state in 202Po and of the 24 ns 13 2 − state in 209Po were measured for the first time. The accuracy of relative g-factors which were previously measured has been considerably improved. The static quadrupole moment of 209Bi g.s. is deduced from three E2 transition probabilities in 210Po. The absolute value of Q is ≈ 15% larger than obtained by optical spectroscopy and possible reasons for the discrepancy are discussed.

Knight shifts and absolute magnetic moments of (h9/2) n proton states in trans-bismuth nuclei

The Knight shiftsK(FrT1) andK(RaPb) have been measured in connection with a systematic study on magnetic moments of (h9/2)n proton states. The Knight shifts were obtained directly by a comparison of precession frequencies and, indirectly, from relaxation times involving the Korringa relation. Good agreement is found among the results from the different methods; the average values areK(FrT1)=(0.89±0.09)% andK(RaPb)=(1.05±0.15)%.

A measurement of the radiative width of the 8+ 11.948 MeV level of 20Ne

Abstract With the 4He(16O,γ)20Ne capture reaction, the 8+, 11.948 MeV level in 20Ne was observed as a resonance in the yield of γ-rays corresponding to the 8+→ 6+ transition. A strength, ωγ = 104 ± 35 MeV was obtained for the resonance which gives 7.5 ± 2.5 W.u. for the 8 + → 6 + transition probability establishing the 11.948 MeV level as the 8+ member of the ground state band. The experimental E 2 transition probabilities in the ground state band of 20Ne deviate strongly from those of the pure rotational model, but agree reasonably well with the predictions of the SU3 shell model.

High spin states in 20Ne from 16O(α, α) scattering

Unbound levels in 20Ne have been studied by 16O(α,α) elastic scattering at energies between Eα = 5–11 MeV with an experimental resolution of 3–5 keV. Four resonances have been observed with a width equal to the experimental resolution. From a phase-shift analysis of these resonances the following 20Ne excitation energies, spin-parity assignments and α-decay widths have been derived: 8775 ± 3 keV (Jπ = 6+, Γc.m. = 110 ± 25 eV); 11,925 ± 5 keV (Jπ = 4+, Γc.m. = 440 ± 150 eV); 11,948 ± 5 keV (Jπ = 8+; Γc.m. = 35 ± 10 eV); 13,333 ± 6 keV (Jπ = 7−, Γc.m = 80 ± 30 eV). The Jπ = 6+, 8+ and 7− levels are likely members of the lowest quasi-rotational bands with Kπ = 0+ and Kπ = 2−. The known reduced widths in both bands are small (θ2 < 0.1) indicating that the bands should be adequately described by the spherical shell model. The reduced widths within each band are found to decrease sharply with increasing spin.

Gamma-decay properties of 20Ne levels below 12 MeV

Abstract Nine levels in 20 Ne below 12 MeV excitation were studied using the 12 C( 12 C, αγ) 20 Ne reaction. Doppler-shift attenuation measurements on de-excitation γ-rays in three Ge(Li) detectors at 0°, 90° and 125° yielded mean lifetimes (in ps) of levels at 1.633 MeV (1.15 ± 0.20), 4.246 MeV (0.093 ± 0.009), 5.618 MeV (0.20 ± 0.05), 7.004 MeV (0.47 ± 0.09), 9.950 MeV ( − ) and the 4.966 (2 − ) MeV levels, and of (4.5 ± 1.2) % between the 10.609 (6 − ) and 8.446 (5 − ) MeV levels were observed. These branches firmly establish these levels as members of the negative parity K = 2 band based on the 4.966 MeV level. Particle-gamma angular correlation measurements, with six NaI(T1) detectors yielded the main decay modes of levels at 9.950, 10.920 and 11.528 MeV. The presently known electromagnetic matrix elements are compared with nuclear model predictions. The 5.618 → g.s. E3 transition probability is considerably larger than that predicted by a shell model with four valence particles.

Coulomb reorientation of 2+ states in 32S and 112Cd

Abstract The static quadrupole moments of the first excited states in 32 S and 112 Cd have been measured using a 100 MeV 32 S beam. The results are interpreted in terms of the reorientation effect in Coulomb excitation and yield Q( 32 S , 2232 keV ) = −0.175 ± 0.050 b and Q( 112 Cd , 617 keV ) = −0.40 +0.13 −0.20 b provided the signs of E2 matrix elements are chosen according to an anharmonic model. The B (E2)(0 + → 2 + ) values were measured to be 0.0284 ± 0.0020 e 2 · b 2 and 0.52±0.02 e 2 · b 2 , respectively. The results indicate that 32 S deviates strongly from a purely vibrational nucleus.

Nuclear polarizability of 7Li from Coulomb excitation

Abstract Excitation of the first excited state in 7Li in the Coulomb and nuclei fields of 208Pb was studied. Below E( 7 Li) = 24 MeV the polarizability of 7Li was deduced to be α = 0.32 ± 0.07 fm3. At higher energies a large backward cross section for α-particle production was observed reflecting the prominent α-t cluster structure of 7Li.

Precise magnetic moments of (h92)n proton states

Abstract The induced microscopic magnetic fields (Knight shifts) for Fr and Ra recoils in metallic hosts have been determined by several independent methods. The observed accurate g-factors of ( h 9 2 ) n proton states and the magnetic moments of single-particle states are difficult to explain by a consistent theoretical approach.

E1 polarization in coulomb excitation of 7Li

Abstract Coulomb excitation of the 0.478 MeV J π = 1 2 − state of 7Li has been studied by a partiele-γ coincidence technique. From the dependence of the excitation probabilities on bombarding energy and scattering angle a sizeable interference contribution from E1 excitation of continuum states has been determined. General expressions for the size of the E1 polarization effect in Coulomb excitation are given and the observed magnitudes in 6,7Li are compared with schematic model calculations.