Results 1 - 10 of 19
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[en] Tobacco is a Weapon of Mass Destruction. It is arguable that, as smoking is by far the major cause of cancer, the most effective action in the fight against it would be to prosecute the chief executives of the major tobacco companies with charges of genocide, mass extermination and crimes against humanity. But there are also other cancers which are not related to addiction. These deserve our best technical and scientific skills to detect and treat. This talk will detail recent advances in the use of nuclear and radiation technologies to both detect and to treat cancer and other malignancies. The examples given will mostly be from current clinical practice in our iThemba LABS near Cape Town, South Africa and from plans we are currently promoting for new facilities
[en] Although four decades ago it had been conclusively shown that the first excited 02+ state in 15666Dy90 was a pairing isomer, the lessons of this identification has taken a long time to connect with the Nuclear Structure Community. The 02+ states that can be populated significantly with two particle neutron transfer, all have large enough cross-sections to demonstrate that simple monopole pairing in theoretical descriptions will be insufficient. The conclusion that these states cannot be associated with time-dependent β vibrations of the nuclear shape is also supported by their very weak excitation in inelastic scattering processes such as (d,d'). Blocking of the coupling of the single particle neutrons in odd nuclei to the 02+ states near N=90 have shown that a major part of their configurations is a pair of neutrons in the 11/2- Nilsson orbit. This high-K orbit is extruded from the h11/2 shell to the Fermi surface by the increasing deformation caused by adding neutrons outside the N=82 core. These data confirm the separation of prolate-prolate and oblate-oblate pairing. At iThemba LABS we have used conventional γ-ray spectroscopy to investigate structures in the pairing gaps of even-even nuclei in the ranges Z=62-70 and N=88-92, in particular to study the systematics of the excited Kπ = 02+2 and 2γ+ positive parity bands. We find that the 02+ bands all have moments-of-inertia that are greater than those of the ground state 01+1 bands, in complete contradiction to the predictions of all Interacting Boson Models (IBM). The larger moments-of-inertia for 02+ bands are consistent with reduced pairing due to the low density of oblate (high-W) orbitals near the Fermi surface. The odd spin members of the γ bands all track the ground state bands while the even spin members can mix with the 01+ and 02+ bands. Indeed the γ bands and 02+ bands cross and interact strongly affecting the signature splittings S(I) observed in the γ bands. The systematic data will be discussed in terms of the Triaxial Projected Shell Model (TPSM) and the 5-Dimensional Collective Model (5-DCM). This document is composed of an abstract and the slides of the presentation. (author)
[en] New and original gamma ray spectrometers recently designed and built in the United Kingdom have provided significantly improved resolution and sensitivity and led to renewed interest in nuclear spectroscopy. Many significant discoveries have been made, including the observation of superdeformed nuclear shapes in discrete quantum states while using the new arrays of bismuth germinate (BGO) detectors and escape-suppressed spectrometer (ESS). The next generation of spectrometers, a European collaboration called EUROGAM, aims to offer sensitivity improved by a factor of 100. French and British scientists will use this European Gamma-Ray Microscope to search for hyperdeformed nuclei at very high spins and their vibrational modes, excitation energies and spins. (UK)
[en] The physics of intrinsic states, within the pairing gap of deformed nuclei with N∼90 neutrons, is discussed in the light of the recent realization that the first excited 02+ states in these nuclei are not β-vibrations but four quasi-neutron states. The properties of γ-vibration Kπ = 2+ bands is discussed. A method of measuring two proton transfer in high resolution using the (3He,n) reaction is proposed.
[en] The g-factor of the K=I=25 isomer in 182Os has been measured by observing the angular precession of the decay γ-ray angular distribution in an external magnetic field as g=+0.425(8). This result is compared with predictions based on experimental g-factors of single-particle Nilsson orbitals in this mass region. (orig.)
[en] The high spin normally deformed and superdeformed states of 194Hg have been populated in an exit channel of the 16O + 186W reaction at 110 MeV. The Doppler shift analysis of the energies of the γ transitions de-exciting both normal and super-deformed states in this nucleus indicates a lower recoil velocity of the 196Hg nucleus compared to that of 196Pb obtained form the 6n exit channel of the complete fusion compound nucleus. This suggests that incomplete fusion plays the main role in the population of these states in 194Hg. The recoil velocities (β = v/c) for different residual nuclei are: 0.87% for 195,196Pb, 0.41% for 190Pb, 0.24% for 186-188Os and 0.37% for 193,194Hg. The value obtained for 196Pb is in fair agreement with the value obtained for a complete fusion of 16O but, the values obtained for Os, Pt and Hg agree with a kinematic calculations of incomplete fusion where the 'spectator' fragment of 12C, 8Be, 4He continues its trajectory along the beam axis with the velocity of the last one. This analysis indicates already that the incomplete fusion plays probably a crucial role in populating the superdeformed nucleus 194Hg. The study of the angular and energy distributions of the α particles in coincidence with this nucleus is presently under way
[en] Negative-parity bands in the vicinity of 156Gd and 160Yb have been suggested as candidates for the rotation of tetrahedral nuclei. We report the observation of the odd and even-spin members of the lowest energy negative-parity bands in 160Yb and 154Gd. The properties of these bands are similar to the proposed tetrahedral band of 156Gd and its even-spin partner. Band-mixing calculations are performed and absolute and relative quadrupole moments deduced for 160Yb and 154Gd. The values are inconsistent with zero, as required for tetrahedral shape, and the bands are interpreted as octupole vibrational bands. The failure to observe the in-band E2 transitions of the bands at low spins can be understood using the measured B(E1) and B(E2) values.
[en] When a left-handed and a right-handed nuclear system form in angular momentum space, a pair of nearly degenerate rotational bands is observed. To identify chiral symmetry most important is to establish near-degeneracy not only in excitation energies of the partner bands, but also in their intra-band and inter-band B(M1) and B(E2) transition probabilities. This needs dedicated lifetime measurements. Such measurements were performed for four bands of "1"9"4Tl. Two of these have very close near-degeneracy and form a prime candidate for best chiral pair. The lifetime measurements confirm the excellent near-degeneracy in this chiral pair. (paper)