G. S'heeren

Quadrupole moments of isomeric states in 212Ra, 213Ra and 214Ra

Abstract The static-quadrupole-interaction frequency of the 8 + isomers in 212 Ra and 214 Ra and of the case17 2 − isomer in 213 Ra has been measured with the level-mixing-spectroscopy (LEMS) method. Measurements have been performed both at low and high target temperatures (10 and 420 K) and on polycrystalline as well as single-crystalline targets. Shell-model calculations have been performed to demonstrate the influence of configuration mixing on the B (E2, 8 + → 6 + ) values and the quadrupole moments of N = 126 isotones.

NUCLEAR ORIENTATION IN A TWO-STEP LASER IONIZATION PROCESS

Abstract In this paper a method is proposed to obtain a pure beam of oriented exotic nuclei by using the element selective laser-ionization process followed by on-line mass-separation. A two-step resonance photo-ionization process is not only very element-selective and efficient, it also provides an easy way of obtaining polarized nuclei if the resonant excitation is performed with a circularly polarized laser beam. Polarizations of the order of 10 to 20% can be expected. We give some examples and we discuss the conditions needed to maintain the orientation during the subsequent mass-separation.

Hyperfine Coupling of B-12 in Noble-metals and Al - Enhancement of the Conduction-electron Spin Susceptibility By E-e Exchange

We have remeasured the Korringa contributionT1e to the nuclear spin lattice relaxation time of the interstitial12B in nobel metals and in Al. TheT1eT times the squared Knight shiftK of12B taken from the literature, that is the Korringa product of12B, shows that the conduction-electron spin susceptibility is exchange enhanced similarly to that sensed by the matrix nucleus. The enhancement factors are equal within the experimental errors for both interstitial and matrix positions in Cu and Ag. The enhancement factors at the boron and at the matrix position are different in Au and Al.

Identification of Cross-relaxation Resonances of B-12 Implanted in Sc Aluminum

Polarized12B nuclei were produced andrecoil implanted in single crystals of fcc aluminum. The boron decay asymmetry andrelaxation times were measured as a function of external magnetic field values andat different orientation angles of the crystal. To identify the resonances at certain field values in the12B depolarization in Al, a consistent theory based on the principle of a multi-spin system and Nuclear level-crossing has been developed. A unique identification of the resonances, based on the resonant interaction between boron andparticular pairs of aluminum neighbours, is perfectly possible. The strong dissipative coupling of the Al nuclei with the electron bath of the lattice hinders a straightforward interpretation of the resonance width anddepth.

Quantum interferences in nuclear decay

At nuclear level mixing condition, interferences between different transition amplitudes can occur. In a narrow frequency range, absorption can be hindered while not the emission. This feature offers interesting applications on the design of a graser and of a resonant scatterer for γ-rays.

Measurements of quadrupole interaction frequencies of long-lived isomers with the level mixing spectroscopy (LEMS) method

The level mixing spectroscopy (LEMS) method has proven to be a very useful method to determine the quadrupole interaction frequency of an isomer in a solid host. Especially in the “difficult” cases, e.g. when the isomeric lifetime is very long or its spin is very high, the method yields valuable information which is not accessible with other methods (such as TDPAD). Since the development of the method some years ago, many experiments have been performed on high spin isomers in the lead region. The static quadrupole moment of isomers with lifetimes ranging from 20 ns up to 13 ms andspins up to 65/2ħ have been determined in neutron deficient isotopes of Bi, At, Fr andRa.