Lifetimes and Gj factors in excited states of chromium. Hyperfine structure of Cr53

Electronic and nuclear properties of excited chromium isotopes using level crossing and double resonance spectroscopy technique

Astrophysical Reaction Rates for 10^{10}B(p,α\alpha)7^{7}Be and 11^{11}B(p,α\alpha)8^{8}Be From a Direct Model

The reactions $^{10}$B(p,$\alpha$)$^{7}$Be and $^{11}$B(p,$\alpha$)$^{8}$Be are studied at thermonuclear energies using DWBA calculations. For both reactions, transitions to the ground states and first excited states are investigated. In the case of $^{10}$B(p,$\alpha$)$^{7}$Be, a resonance at $E_{Res}=10$ keV can be consistently described in the potential model, thereby allowing the extension of the astrophysical $S$-factor data to very low energies. Strong interference with a resonance at about $E_{Res}=550$ keV require a Breit-Wigner description of that resonance and the introduction of an interference term for the reaction $^{10}$B(p,$\alpha_1$)$^{7}$Be$^*$. Two isospin $T=1$ resonances (at $E_{Res1}=149$ keV and $E_{Res2}=619$ keV) observed in the $^{11}$B+p reactions necessitate Breit-Wigner resonance and interference terms to fit the data of the $^{11}$B(p,$\alpha$)$^{8}$Be reaction. $S$-factors and thermonuclear reaction rates are given for each reaction. The present calculation is the first consistent parametrization for the transition to the ground states and first excited states at low energies.Comment: 27 pages, 5 Postscript figures, uses RevTex and aps.sty; preprint also available at http://quasar.physik.unibas.ch/ Phys. Rev. C, in pres

INTRODUCTORY PAPER ON HANLE EFFECT, LEVEL CROSSING AND DOUBLE RESONANCE EXPERIMENTS

L'auteur passe en revue un certain nombre de techniques expérimentales qui utilisent les propriétés de la diffusion de la lumière par des atomes libres au voisinage d'une fréquence de résonance pour étudier des niveaux atomiques excités : - L'effet Hanle et ses divers développements récents (effet Hanle moléculaire, effet Hanle en présence d'un champ électrostatique, effet Hanle de niveaux excités par échelons, effet Hanle par fluorescence sensibilisée). - La double résonance et ses variantes (effets de « battements lumineux », excitation en lumière modulée...). - Les croisements et anticroisements de niveaux (y compris l'étude de l'effet Stark par croisements de niveaux).The author reviews experimental techniques which use the properties of the scattering of light by free atoms in the neighborhood of a resonant frequency for investigation of excited atomic energy levels : - Hanle effect and its recent developments : (Hanle effect in an electrostatic field, molecular Hanle effect, Hanle effect of stepwise excited levels, sensitized fluorescence Hanle effect). - Double resonance experiments and its variations (« light beats »), excitation with modulated light...). - Level crossings and anticrossings (including of the study Stark effect by level crossings)

Aspects of time in radiation scattering processes

It is investigated for which radiation processes the time evaluation of the process can be connected with possibilities for experimental measurements. In the case of resonance reactions the time of retardation for observing the signal of scattered radiation is connected with the lifetime of the metastable system while for energies far outside of resonances the average retardation time has no simple meaning. If several energy states of the system contribute coherently to the interaction process the time dependence is determined by the perturbation, which causes the coherent superposition of the transition amplitudes. In the case of multistep compound nuclear reactions the average retardation time is connected with the complexity of the reaction process due to the contribution of several interaction steps