S. Monaro

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.

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%.

Automatic data acquisition and on-line analysis of trace element concentration in serum samples

Abstract A completely automated system has been developed to determine the trace element concentration in biological samples by measuring charged particle induced X-rays. A CDC-3100 computer with ADC and CAMAC interface is employed to control the data collection apparatus, acquire data and perform simultaneously the analysis. The experimental set-up consists of a large square plexiglass chamber in which a commercially available 750H Kodak Carousel is suitably arranged as a computer controlled sample changer. A method of extracting trace element concentrations using reference spectra is presented and an on-line program has been developed to easily and conveniently obtain final results at the end of each run.

Gamma-ray spectroscopy of 126Ba

Abstract States of 126Ba up to spin 36+ were populated in the reaction 96Zr(34S, 4n)126Ba at 155 MeV and up to spin 20+ in the reaction 116Sn(13C, 3n)126Ba at 56 MeV. Gamma-ray spectroscopy was performed with the 8π spectrometer, an instrument comprising 20 Campton-suppressed HPGe detectors and 71 BGO ball elements. A level scheme organized into fifteen rotational bands is proposed on the basis on the γγ-coincidence and γ-ray angular correlation data. The competing π h 11 2 and v h 11 2 band crossings are investigated and interpreted in terms of cranked shell model and total routhian surface calculations. Amongst the topics discussed are (i) a comparison of DCO and spin orientation techniques for determining spins and multipolarities. (ii) the addivity property of quasiparticle energies or routhians, and (iii) analysis of B(M1)/B(E2, ratios between signature partner bands. The possibility of couplings between vibrational and aligned quasiparticle structures is explored.

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 .

Alignment processes and shape variations in 184Pt

Abstract High-spin states in the transitional nucleus 184Pt were populated via the reactions 154Sm(34S, 4n)184Pt and 172Yb(16O, 4n)184Pt. The yrast band was extended up to I = 28 ħ and six new side bands built on both neutron and proton quasiparticle configurations were observed. Shell correction-type calculations indicate variations of the nuclear shape in different bands, especially as a result of band crossings due to the process of angular momentum alignment. Comparison of the band characteristics are made between 184Pt and eight adjacent nuclei. The pattern of band crossings in these nine nuclei is considered from the viewpoint of blocking comparisons and of theoretical calculations. The competition between low-frequency vi 13 2 and πh 9 2 band crossings is discussed.

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.

Characterization of Trace Elemental Pollutants in Urban Snow Using Proton Induced X-ray Emission and Instrumental Neutron Activation Analysis

Abstract Proton-induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA) methods have been employed to determine trace elemental pollutants in urban snow collected mostly from the island of Montreal and some from Toronto. The use of small pore filters, 0.40μm, enabled a distinction to be made between soluble and insoluble particulate fractions. Results for those elements, including heavy metals, that filtered through the 0.40 /an pore filters gave an indication of their bioavailability and potentially toxic actions. A total of twenty-five trace elements (Na, Mg, Al, P, S, CI, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Mo, Cd and Pb) were obtained in the soluble snow portion with detection limits between 0.2ng/g and 147ng/g. Twenty-eight elements (Na, Mg, Al, P, S, CI, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Cd, Sb, La, Sm and Pb) were analyzed with detection limits between 3 μg/g and 720 μ/g in the insoluble particulate matter. INAA pro...

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.

Rotational bands and shape changes in 124Ba

Abstract High-spin states in 124 Ba were populated via the 94 Zr( 34 S, 4n) 124 Ba and 110 Cd( 16 O, 2n) 124 Ba reactions at 145 MeV and 60 MeV, respectively. The yrast band has been extended to 34 ħ and seven side bands have been observed. Gamma-ray angular distributions with respect to the nuclear spin axis have been used along with directional correlation (DCO) ratios to establish spins and multipolarities. The competing π h 11 2 and ν h 11 2 crossings in this region are investigated and an interpretation of the observed crossings is proposed within the framework of the cranked shell model (CSM) and total routhian surface (TRS) calculations.