J. Morgenstern

Étude de la capture radiative des neutrons de résonance dans le platine

Resume The statistical properties of the partial radiation widths in 196 Pt have been studied with the Saclay linear accelerator using the time-of-flight method and a Ge(Li) detector. The spectra for 22 resonances with spin and parity 1 − were analysed, and a sample of 66 transitions was obtained. The result of such a study confirms the validity of the Porter-Thomas distribution for these widths; the data agree with a χ 2 -distribution with one degree of freedom and are clearly inconsistent with the exponential law. Several statistical analysis methods have been used. From the number of 1 − resonances, it is possible to calculate the average relative intensity of some transitions and to compare them with values calculated from theoretical estimates. In addition a new level scheme of doubly even 196 Pt nuclei has been obtained and is compared with previous results and theoretical predictions; 40 levels have been found. This scheme is confirmed by thermal neutron capture and by 196 Au radioactive decay. A partial scheme is obtained for some odd isotopes of platinum ( 193 Pt, 197 Pt and 199 Pt).

Capture radiative partielle des neutrons de résonance dans quelques isotopes de l'étain

Abstract Gamma-ray spectra of radiative neutron capture have been studied in several tin isotopes with the Saclay linear accelerator using the time-of-flight method and a Ge(Li) detector. The intensity of 13 E1 transitions and 12 M1 transitions has been evaluated. This study has shown that strong M1 transitions are on the average only five times less intense than E1 transitions. We have also obtained some indications of the level schemes of four odd-mass nuclei and two even-mass nuclei.

Analyse des paramètres des résonances du cobalt pour les neutrons d'énergie inférieure à 30 keV

Abstract The total neutron cross-section of 59Co has been measured with a resolution of 0.8 ns/m up to an energy of 60 keV. The parameters of the resonances below 30 keV have been determined by means of the single-level Breit-Wigner formula using a shape analysis. The value of the s wave neutron strength function Λ n 0 D is found to be (6.7±3.3)×10 −4 eV − 1 2 for the state J=3 and (3.3±1.4)×10 −4 eV − 1 2 for the state J=4 . The value of the potential scattering length is found to be 4.9±0.5 fm for the state J=3 and 5.8±0.5 fm for the state J=4.

Variation de la fonction densité (strength function) avec la valeur du spin

Abstract The total neutron cross section has been investigated for natural bromine from 100 eV up to 200 eV. Resonance parameters and spin valies are given for many levels. As in neighbouring nuclei (As75, Ga) the strength function for the spin value J = 2 is twice that for J = 1. This strength function dependence is discussed for different nuclei investigated at Saclay and the significant results are summarized in table 4.

Détermination du spin et des paramètres des résonances pour 197Au+n DE 1000 eV à 2100 eV

Resume Experiments on gold have been performed with the Saclay linear accelerator using the time-of-flight method. Resonance parameters are given for 63 resonances in the energy range 10–1000 eV. Spin assignment methods are described and discussed. The J value is found for 40 resonances in combining total capture and transmission experiments. A convenient relation is used to take into account interference effects between resonances of the same spin. The strength function value is dependent upon the spin value S0(J=2)=2.2 S0(J=1). The total radiation width Γγ is practically constant from resonance to resonance within experimental errors. Statistical properties of levels are considered and correlation coefficients are calculated.

Détermination des fonctions densité (strength functions) S0 et S1 dans Nb par identification de la nature des résonances de neutrons

Abstract Experiments on niobium have been performed with the Saclay linear accelerator using the time-of-flight method. The resonance parameters were investigated in the energy range from 30 to 4000 eV. Transmission experiments allowed identification of the p wave neutron resonances above a few hundred eV, and for the low-energy range, identification was performed by neutron capture gamma ray experiments. It is possible to determine a value of S1 from individual resonance parameters at low energy (S1=(5.05±1)·10−4). The S0 value is (0.35±0.06)· 10−4 and confirms the low values of S0 in the neighbourhood of mass number 100. The total radiation widths are found to depend on the nature of the resonance: Г γ = 140 meV for “s” levels, Г γ = 230 meV for the “p” levels.

Traitement sur ordinateur des spectres de rayons γ de capture obtenus a l'aide d'un cristal central associe a un cristal annulaire

Abstract The correct knowledge of the detector response is the main difficulty for analyzing experimental data. A simple shape is obtained with an annular cristal operating in coincidence or anti-coincidence with a central cristal 4″ × 6″. Merits of this detector are discussed and results are presented. A program is described to find intensities of different gamma-ray lines in complex spectra. The check of this analysis has been made in fitting many thermal neutron capture gamma-ray spectra.

Intermediate structure in the 59Co neutron total cross section between 0 and 500 keV

Abstract The neutron strength function of cobalt has been measured for neutron energies between 0 and 500 keV. Intermediate structure in the form of oscillators with widths of about 40 keV is observed.