Influence of Giant Nuclear-spin Polarisation on Resonant Gamma-ray Absorption and Emission

We propose a new scheme of gamma-quanta amplification without inversion. Laser pumping of electron states creates giant nuclear-spin polarisation via the hyperfine interaction. This results in extreme cooling of the ground-state nuclear spin in a projection which does not absorb both laser pump and gamma-quanta according to selection rules for these transitions. Induced emission from the nuclear excited state is not influenced by the pump. Therefore gamma-quanta travelling inside the pump beam have an opportunity to induce stimulated emission without subsequent quenching by ground state nuclei.

Lifetimes of 7/2− States in 35Cl, 37Cl, and 39K

Nuclear excited state lifetimes have been determined by direct timing, using a pulsed beam and a Ge(Li) detector in singles. Results are 35Cl (3163 keV), 46 ± 6 ps; 37Cl (3103 keV), 16 ± 9 ps; 39K (2813 keV), 71 ± 5 ps; 39K (3598 keV), 91 ± 27 ps. M2 and E3 transition strengths of the transitions in 35Cl and 37Cl are compared with previous theoretical calculations.

On a Symmetry Property of the Inelastic Scattering Amplitude in the Adiabatic Approximation

A symmetry property of the exact T matrix for the inelastic scattering of particles with arbitrary spin is derived, in the adiabatic limit, using time reversal invariance properties of the elastic scattering amplitude and neglecting interaction terms that involve spins or velocities of the target nucleons. The symmetry property is used to show the equality of the generalized polarization and asymmetry tensors for inelastic scattering and to derive the symmetry properties, with respect to the adiabatic recoil axis, of the angular correlation function and the circular polarization of the deexcitation gamma rays. It is also shown that the nuclear excited state is aligned along the axis normal to the scattering plane. A brief discussion of the symmetry properties of the adiabatic DWBA amplitude is given. When interaction terms involving spins or velocities of the target nucleons are taken into account, it is shown that the inelastic scattering T matrix can be divided into two parts; one that satisfies the above-mentioned symmetry relation, and a second part which has a different symmetry.