State selective fragmentation of doubly ionized sulphur dioxide

Using multi-electron–ion coincidence measurements combined with high level calculations, we show that double ionisation of SO2 at 40.81 eV can be state selective. It leads to high energy products, in good yield, via a newly identified mechanism, which is likely to apply widely to multiple ionisation by almost all impact processes.

State-selection by an Unconventional Mechanism in Dissociative Double Ionization of Sulphur Dioxide

Using multi-electron-ion coincidence measurements combined with high level calculations, we show that double ionization of SO2 at 40.81 eV can be state selective. It leads to high energy products, in good yield, via a newly identified mechanim, which is likely to apply widely to multiple ionization by almost all impact processes.

Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material

Within the EC-funded CHANCE project several non-destructive techniques are being considered for the assay of waste bearing drums. Such techniques include calorimetry, gamma-ray spectrometry and neutron coincidence counting. The aim is to quantify uncertainties on the inventory of radionuclides, and how these are potentially reduced by combining the signatures from different techniques in the data analysis. In this framework, neutron coincidence measurements were carried out with two slab counters based on 3He detectors coupled to shift register electronics. Such a system consists of two identical slabs with 6 detectors each, and is transportable, rather compact and flexible in terms of sizes and geometries that can be measured. With this system three 200 L drums containing certified reference nuclear material and different filling materials were measured. The certified nuclear material was in the form of 21 pellets of mixed oxide of U and Pu with a total mass of about 10.5 g; in addition, a single pellet of about 10.05 g was also available. The pellets could be placed in predefined positions within the drum in a reproducible way. The geometry and composition of the three drums was well characterized and consisted of Ethafoam, a mixture of Ethafoam, stainless steel and PVC, and mortar with an inner core of extruded polystyrene. The measurement setup was arranged such that the drum was placed between the two slab counters. The positions of the slab counters relative to the drum were accurately measured before each measurement, and a dedicated system was used to minimize the uncertainty on the detector positioning. The measurement data were first analysed by applying the point model of Hage and the mass of nuclear material in the drum was determined from the rate of totals and reals and the radionuclide composition. Due to the fact that not all the point model conditions were met, we found that the point model overestimates the mass up to about 50%. In addition, a Monte Carlo model of the measurement geometry was developed using the MCNP code. The model was used to determine a calibration factor between the reals rate and the mass of the sample. Measurements with a calibrated 252Cf source were used to verify the model. With a Monte Carlo based approach the mass of the mixed oxide pellets is within a few percent from the nominal values, except for strongly asymmetrical configurations where the deviation is up to about 20%. The results reveal the importance of an accurate background correction and of accounting for surrounding materials of the building such as walls, floor and ceiling in the Monte Carlo model.

HIGH SPIN STRUCTURE OF 173Os

High-spin states in 173Os have been studied by γ-γ coincidence measurements following the 146Nd(32S,5n)173Os reaction. Four main sequences have been identified as the two signature branches of the bands built an the [642]5/2+ and [523]5/2- Nilsson states. Multi-polarity assignements have been derived utilizing the directional correlation (DCO) ratios aa well as the anisotropies of the γ-rays. B(M1)/B(E2) ratios have also been extracted to deduce farther information an the detailed structure of the bands

High spin structure of 155Dy

High spin states in 155Dy have been studied by γ-γ coincidence measurements via the 124Sn(36S, 5n)155Dy reaction at a beam energy of 155 MeV. Eight rotational bands have been populated and observed up to high spin (I<91/2).The band features have been analysed within the framework of the cranked shell model. The Ì13/2 neutron alignments and the h11/2 proton alignments are discussed. B(M1)/B(E2) ratios have also been extracted for the strongly coupled bands to deduce further information on the detailed structure of these bands. For the highest states (above spin 30) of the negative parity bands an irregularity in y-ray energies appears which is discussed in terms of band termination.

Decay properties of high spin states in Mn

The electromagnetic decay properties of high spin states in 52Mn have been studied through various experiments with the GASP and EUROBALL arrays plus the ISIS charged-particle detector, the Neutron-Wall and the Recoil Filter Detector. From 7-7-particles coincidence measurements, spins and parities of these states have been determined and using the Doppler-shift attenuation method the mean life of some of these states have been determined. These results are compared with large scale shell-model calculations in the full fp shell.