E.D. Earle

Gamma-Ray Strength Functions

The study of the energy dependence of multipole transition probabilities is a broad subject in which certain subfields have progressed much more rapidly than others. Thus for gamma rays ≲2 MeV, E1, M1, and E2 transition probabilities have been well studied (Per 66, SHR 66, SG 65), and at higher energies, ≳10 MeV, the absorption cross section and other properties of the E1 giant resonance are well known (Fir 70), but between these energies there are large gaps in our knowledge. In the present review we are concerned with the distribution of reduced radiation width, particularly for E1 and M1 radiation, in the less well-known “tail region” well below the peak of the E1 giant resonance. We will concentrate on elements with mass number A≳ 90, where a statistical description of radiative processes is appropriate, and on γ-ray energies above ~2 MeV.

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.

Resonance neutron capture in 198,199,201Hg

Abstract Partial radiation widths of γ-rays of energies E γ > 4.1 MeV following capture of neutrons with E n 199 Hg, 200 Hg and 202 Hg. Gamma-ray tables and decay schemes are given. Gamma-ray strength functions and level density distributions are derived. Departures from statistical behaviour are observed in 199 Hg. It is found that the energy dependence of the level density below 3 MeV differs in functional form in the three isotopes.

The 115In(n,γ)116In reaction

Abstract High-energy γ-rays following neutron capture at thermal energies and at the 1.46, 3.86, 9.12, 12.1, 23.0, 39.9 and (46.3+48.6) eV resonances in natural In are examined. Details of the level structure of 116 In are deduced and the partial radiation widths of primary transitions determined. The neutron separation energy is found to be 6781±3 keV. Strength functions are derived E1 and M1 transitions. The E1 strength is found to remain constant and the M1 strength to decrease with γ-ray energy from 5.2 to 6.7 MeV.

Doubly radiative thermal neutron capture in 2H and 16O: Experiment and theory

Abstract Measurements and calculations are presented for the cross sections for two-photon emission following thermal neutron capture in 2H and 16O. Upper limits for σ2γ were measured in both cases. For 2H, σ2λ = 8 ± 15 μb, for γ-rays in the energy region 700

Gamma rays following μ− capture in heavy elements

Abstract The spectra of γ-rays > 0.6 MeV following the capture of μ − mesons in Bi, 208 Pb(NO 3 ) 2 , radiogenic Pb, Au, Ag and Zr targets are measured with a large NaI detector and the intensity and energy distributions are deduced. The spectra are distinguished by a few resolved lines at low energies and, for Bi, radiogenic Pb and Au, by a distinct group of γ-rays centered at 4.2 MeV. In gross shape, the spectra resemble those following inelastic neutron scattering. There is no prominent γ-ray anomaly near 5.5 MeV similar to that in the spectra following neutron transfer reactions in the same mass region. The average number of γ-rays per σ-capture and mean excitation energy prior to γ-emission are estimated.

The 205Tl γ-ray strength function below 7.5 MeV

Abstract The 205 Tl γ-ray strength function below 7.5 MeV is derived from a measurement with 3% energy resolution of the 205 Tl(γ, γ) 205 Tl cross section between 3.5 and 7.5 MeV. This strength function is found to be similar to those extracted from (n, γ) data in the neighbouring Tl isotopes. The structure observed in the Tl strength function below 7.5 MeV is consistent with that predicted from recent particle-hole calculations for 208 Pb.

An experiment to measure parity violation in the 2H(γ,n)H reaction

An experiment to measure parity violation in the photodisintegration of deuterium near threshold is in preparation. The sensitivity to parity violation in the np system is similar to the sensitivity in the measurement of Lobashov et al. who reported a γ‐ray circular polarization value of −(1.3±0.45)×10−6 for the 1H(n,γ)2H reaction at thermal energies. This value is much larger than theoretical calculations (∼5×10−8). Details of the planned (γ,d) experiment are discussed and the present status indicated.