G. Lamoureux

Calculated relative efficiency for coaxial and planar Ge(Li) detectors

Abstract With the aid of a Monte Carlo computer program, the relative efficiency to monoenergetic γ-rays of coaxial and planar Ge(Li) detectors has been calculated. Considering a point source, placed on the extended axis of the detector, at a fixed distance, radiations of different energies are generated within the solid angle subtended by the crystal. The gamma-rays impinging on the detector are followed until a fraction whatsoever of their energy escapes from the active region of the crystal. If the γ-ray releases all its energy in the active region, a photopeak is counted and then its efficiency is calculated. At the end of the program the efficiency for the double-escape peak is also obtained. Following this procedure the photopeak efficiency was calculated for three Ge(Li) detectors, having volumes of: 2.0 cm 3 (planar), 5.3 cm 3 and 30 cm 3 (coaxial) from ≈ 100 keV up to 4000 keV. By means of these calculated efficiency curves, the well measured gamma-ray relative intensities in sources as 22 Na, 88 Y, 207 Bi, 133 Ba and ThC″ could be reproduced to within 1%–3%.

Measurement of the static quadrupole moments of the first 2+ states in 76Se, 78Se, 80Se and 82Se☆

Abstract The reorientation effect in Coulomb excitation was employed to measure the static quadrupole moments of the first 2 + excited states in 76 Se, 78 Se, 80 Se, and 82 Se. Beams of 4 He and 16 O were used on thin highly enriched targets and the resulting spectra of the well resolved backward elastic and inelastic scattered particles were detected by four surface-barrier detectors. For constructive interference via the second 2 + excited states the determined quadrupole moments are: −0.34±0.07 e· b for 76 Se ; −0.26±0.09 e· b for 78 Se ; −0.31±0.07 e· b for 80 Se ; −0.22±0.07 e· b for 82 Se .

Geometrical correction factors for angular correlation measurements with Ge(Li) detectors

Abstract A computer program calculation for the determination of the finite solid-angle corrections, for truly coaxial Ge(Li) detectors, is presented. The basis of these calculations is an exact knowledge of the differential efficiency of the detectors, i.e. the efficiency versus the position of irradiation on the detector surface. In order to calculate the differential efficiency of the Ge(Li) detectors two approaches were employed. The first is based on the probability of a direct photoelectric interaction of the γ-ray impinging on the crystal whereas the second is a Monte-Carlo simulation method. These calculations were carried out on four truly coaxial Ge(Li) detectors, which are currently employed in this laboratory. These counters have active volume of 5.3, 32, 36 and 45 cm3, respectively. The finite solid-angle corrections were calculated for source-detector distances of 3.0, 5.0, 7.0, 10.0 and 14.0 cm and for an energy range from 60 keV to 2.0 MeV.

Level properties of 96Mo investigated via multiple coulomb excitation, Ge(Li)Ge(Li) directional correlations and the decay of 96Nb and 96m, gTc

Abstract Oxygen-16 ions with energies of 35 to 44.8 MeV have been used to Coulomb excite levels of the even molybdenum isotope 96 Mo. The de-excitation γ-radiations from the Coulomb excited states at 778.22(2 + ), 1148.0(0 + ), 1497.70(2 + ), 1625.8(2 + ), 1628.10(4 + ), 1869.51(4 + ) and 2234.5 keV (3 − ) have been observed with a 45 cm 3 Ge(Li) detector having 2.0 keV resolution for the 60 Co lines. The reduced electromagnetic transition values for most of the observed transitions were calculated using the general formulation of the semi-classical theory to first and second order. It is shown that this treatment is quite adequate to extract reliable results from the simple and double E2 Coulomb excitation process in the 96 Mo nucleus. In addition, Ge(Li)Ge(Li) directional correlation measurements were performed on cascades from the decays of 96 Nb and 96g Tc. These experiments showed that the 719.55 keV γ-ray de-exciting the 2 + ′ state at 1497.70 keV to the 2 + level at 778.22 keV is mostly an M1 transition ( δ = −0.42 +0.20 −0.27 ) and that the 2440.64 and 2755.0 keV levels have, most probably, a spin-parity value of 6 + . Furthermore, a reinvestigation of the disintegration of 96 Nb and the 96m, g Tc isomeric pair, performed with the 45 cm 3 Ge(Li) detector, revealed the existence of several new γ-transitions and levels in the structure of 96 Mo.

E2/M1 ratios in the 427.90 and 635.90 keV transitions of 125Te

Abstract γγ directional correlation measurements, performed with two Ge(Li) detectors have been carried out on the (635.90-35.46), (606.68-35.46), (600.56-35.46) and (427.90-35.46) keV cascades in the decay of 2.7 y 125 Sb. The result from the composite (606.68; 600.56-35.46) keV cascade was used to normalize the other two correlations. The angular correlation measurements on the other two cascades lead to mixing ratio values of: σ (427.90) = 30.50±0.13 or 33.9 −2.9 1.2 and σ (635.90) = 0.34±0.05 or = 1.66±0.17. For both cascades only the first value of δ is consistent with the mixing ratios obtained in nuclear orientation measurements.

A rotating target holder for low melting point nuclear targets

Abstract Using a ferromagnetic feedthrough a simple rotating target holder has been constructed for an Ortec 600 series scattering chamber. In actual measurements we obtained significant improvement in the maximum beam current, which a selenium target could tolerate.