M. Barrette

Precision measurements of gamma-ray intensities and energies in the decay of 152g, 154Eu, 56Co, 110mAg and 125Sb

Abstract With the aid of a computarized program the relative intensities of the prominent transitions present in the decay of 152g, 154Eu, 56Co, 110mAg and 125Sb have been calculated with very high precision. The energy values of the same transitions in the 152g, 154Eu, 110mAg and 125Sb decays were also determined, very precisely, so that each of these sources, could be employed both for energy calibration measurements, and for linearity calibration of multichannel analysers. The measurements were performed with two Ge(Li) coaxial detectors with active volume of 5.3 cm3 and 30 cm3, respectively. It is shown that with the aid of these radioactive sources, one can construct a very precise efficiency curve for any other Ge(Li) detector from 100 keV to 3500 keV and reproduce to within 2%–3% the well measured gamma ray relative intensities in sources as 22Na, 207Bi, 88Y, 133Ba and ThC″. For these latter measurements a third Ge(Li) coaxial detector, with active volume of 32 cm3, was employed.

Coulomb excitation of the even-mass selenium nuclei

Abstract The properties of the low-lying states of the doubly even selenium nuclei have been investigated via multiple Coulomb excitation effected with 39.2 MeV oxygen projectiles. The excitation probabilities of the first 2 + states of 76 Se, 78 Se and 80 Se have been determined directly by resolving inelastically and elastically scattered 4 He projectiles on thin targets. These measurements yielded values of B (E2; 0 + → 2 + ) equal to 0.421 ± 0.009 ( 76 Se ), 0.321 ± 0.009 ( 78 Se ) and 0.248 ± 0.005 ( 80 Se ) e 2 · b 2 . The multiple Coulomb excitation experiments enabled us to detect 2 + and 4 + levels in all isotopes studied up to 2.1 MeV. Moreover the double Coulomb excitation of 0 + states at 854.1 keV ( 74 Se), 1498.5 keV ( 78 Se), and 1478.3 keV ( 80 Se) was also observed. The enhancement of the E2 transition between these 0 + levels and the first 2 + states decreases rapidly with the increase of the neutron number, i.e., B( E 2; 0 + ′ → 2 + )/B( E 2; 2 + → 0 + ) = 2.04 ± 0.08 ( 74 Se ), 0.91 ± 0.08 ( 78 Se), and 0.28 ± 0.04 ( 80 Se ) . States interpreted as the result of direct E3 Coulomb excitation have been observed at 2350.2, 2429.2, 2507.6, and 2717.6 keV in 74 Se, 76 Se, 78 Se and 80 Se, respectively. Their B (E3; 0 + → 3 − ) values are 2.1 ± 0.5 ( 74 Se ), 4.0 ± 0.5 ( 76 Se ), 2.7±0.3 ( 78 Se ) and 0.9 ± 0.2 ( × 10 −2 e 2 · b 3 which represent enhancements of 9.2 ± 2.2, 16.6 ± 2.1, 10.8 ± 1.2 and 3.2 ± 0.7 respectively. Furthermore, angular distribution measurements of γ-rays following Coulomb excitation with 42 MeV 16 O ions in 78 Se and 80 Se have been performed. The E2 content of the 2 + → 2 + transition in these two nuclei is 87.9 % ( 78 Se), and 96.2 % or 33.5 % ( 80 Se).

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 .

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)ue5f8Ge(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.