Browsing by Author "Allen, BJ"

Now showing 1 - 13 of 13
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    Compilation of keV neutron capture gamma rays in the mass range a=40-70
    (Australian Atomic Energy Commission, 1969-10) Allen, BJ; Bird, JR; Kenny, MJ
    keV neutron capture gamma ray spectra have been measured for eleven elements in the mass range A=40 to 70 using lithium drifted germanium detectors. Averaged or resolved resonance spectra were obtained for neutrons in the energy range 5 - 100 keV, produced by a pulsed Van de Graaff accelerator. A compilation of the results for each element is given together with thermal capture and (d,p) data. Gamma ray spectra are presented and major features of thermal capture and keV results are shown in decay schemes.
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    keV neutron capture in zinc
    (Australian Atomic Energy Commission, 1970-11) Allen, BJ; Musgrove, ARD
    Averaged gamma ray transition strengths in 65Zn and 67Zn have been measured after neutron capture in the keV energy region. These results have been compared with calculations based on resonance parameters and a statistical neutron capture mechanism. Evidence for d-wave capture in excess of that expected is given. However because of the substantial deviation from statistical behaviour of the averaged transition strengths, it is apparent that configuration effects play a major role in the determination of partial capture cross sections.
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    keV neutron capture in zirconium-91
    (Australian Atomic Energy Commission., 1975-01) Allen, BJ; Musgrove, ARD; Macklin, RL
    The neutron capture cross section of 91Zr has been measured with high resolution (∆E/E ~ 0.2 per cent) between 3 and 30 keV. Values of the gгnгγ/г for 119 resonances in this energy range have been obtained. The average capture cross section is consistent with values of <гγs> = <гγp> = 200.
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    keV neutron resonance capture in barium-135
    (Australian Atomic Energy Commission, 1974-12) Musgrove, ARD; Allen, BJ; Macklin, RL
    The neutron capture cross section of 135Ba has been measured with high resolution at the Oak Ridge Linear Accelerator in the energy range 3 to 100 keV. From over ninety observed resonances in the 3 to 6 keV energy range, the average resonance parameters obtained were: <гγ> = 150 ± 20 meV; = 39.3 ± 4 eV and l0 4S = 0.8 ± 0.2. The quoted radiation width and p-wave strength function also have a normalisation error of ± 20 per cent. The method of separation of в- and p-wave populations by statistical methods is described.
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    Monte Carlo calculation of microbeam radiation in a tissue/lung/tissue phantom
    (Australian Institute of Nuclear Science and Engineering, 1994-11-16) Company, FZ; Allen, BJ; Miskelly, P
    Recent advances in synchrotron generated X-ray beams with high fluence rate, small divergence and sharply defined microbeam margins permit investigation of the application of an array of closely spaced, parallel or converging microbeams in radiotherapy. The proposed technique takes advantage of the hypothesis repair mechanism of capillary cells between alternate microbeam zones, which regenerates the lethally irradiated capillaries. Unlike a pencil beam, more accurate dose calculation, beam width and spacing are essential to minimise radiation damage to normal tissue cells outside the target. The absorbed dose between microbeam zones should be kept below the threshold for radiation damage. Thus the peak-to-valley ratio for the dose distribution should be optimized. The absorbed dose profile depends on the energy of the incident beam and the composition and density of the medium. In this study, using Monte Carlo computations, the radial absorbed dose of single 24 x 24 μm2 cross-section X-ray beams of 100 and 300 keV in a tissue/lung/tissue phantom are investigated. Two parallel, 100 keV, 24 x 24 μm2 cross-section beams, using 200 μm center-to-center spacing, give similar peak-to-valley ratio in both media at the same depth. These results indicate that at 100 KeV, closely spaced microbeam therapy can be applied to the lung as well as the tissue. It is found that in the 300 keV region the peak-to-valley ratio decreases 200 times compared with 100 KeV. At the center of a bundle of a 1 x 1 cm2 cross-section, 200 μm center-to-center microbeams, the ratio approaches unity, indicating the unsuitability of this energy region when using closely spaced microbeam therapy. In the 33 KeV region the peak-to-valley ratio is similar to the 100 KeV. The relatively high surface absorbed dose of 33 KeV microbeam rules out its possible application in the deep microbeam therapy.
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    Neutron capture by the chromium isotopes
    (Australian Atomic Energy Commission, 1977-01) Kenny, MJ; Allen, BJ; Musgrove, ARD; Macklin, RL; Halperin, J
    Capture cross sections of the chromium isotopes have been measured at neutron energies up to 350 keV using the capture cross section facility at the 40 m station of the Oak Ridge Electron Linear Accelerator. Parameters have been derived for 180 resonances. A moderate correlation [p(г0n,гγ) - 0.45] is observed between reduced neutron widths n y and radiative widths for s-wave resonances. Calculations of valence widths show that valence capture can only account for the correlated component of the observed radiative widths. An additional mechanism such as a 2p-lh doorway state must therefore be occurring to explain the uncorrelated component.
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    Neutron capture mechanisms in the threshold region
    (University of Wollongong, 1978) Allen, BJ
    Neutron capture mechanisms in the threshold region are investigated through the measurement of high resolution y-ray spectra and resonance capture cross sections. Initial and final state width correlations are observed for many nuclides across the periodic table, and are indicative of dominant valence and doorway interactions. A detailed investigation of resonant capture in the isotopes of iron provides strong evidence for these effects. Estimates of the magnitude of the doorway component are obtained for the 3s region when valence and statistical contributions are compared with the average s- and p-wave radiative widths.
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    Non-statistical effects in the radioactive capture cross sections of the neodymium isotopes
    (Australian Atomic Energy Commission, 1977-01) Musgrove, ARD; Allen, BJ; Boldeman, JW; Macklin, RL
    The neutron capture cross sections of the stable neodymium isotopes have been measured with high energy resolution in the keV region at the 40 m station of ORELA. Average resonance parameters are extracted for s-wave resonances. Significant positive correlations are found between T0n and Tγ all isotopes. The magnitude of the observed correlation coefficient, particularly for 142Nd (p = 0.9), cannot be explained in terms of valence neutron capture and additional mechanisms are discussed. The average s-wave radiative widths for the odd-A isotopes are markedly greater than for the even-A isotopes, while the p-wave radiative width for 142Nd is considerably less than the s-wave width.
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    Resonance neutron capture in the isotopes of titanium
    (Australian Atomic Energy Commission, 1977-06) Allen, BJ; Boldeman, JW; Musgrove, ARD; Macklin, RL
    The neutron capture cross sections of 46,47,48,49,50Ti have been measured from 2.75 to 300 keV with ~0.2 per cent energy resolution. The reduced neutron and radiative widths of the s-wave resonances exhibit correlations which, with the exception of 47Ti, are consistent with the calculated magnitudes of the valence component, assuming that the radiative widths contain an additional uncorrelated part. In 47Ti, a significant correlation is observed for J=3- resonances, although the calculated valence component is small.
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    Response functions of a germanium-sodium iodide detector system
    (Australian Atomic Energy Commission, 1967-04) Allen, BJ; Bird, JR; Engstrom, S
    A gamma ray spectrometer is described which uses a lithium drifted germanium diode or sodium iodide crystal as a central detector in conjunction with an annular segmented sodium iodide assembly. The system can operate as a total absorption, anticoincidence, or pair spectrometer and individual detectors may be used separately. Thus, the requirements of high resolution or high efficiency gamma ray spectroscopy can be met by suitable choice of mode of operation. The various modes of operation are compared and typical results given to illustrate their performance at a variety of gamma ray energies. A detailed analysis is given of the response of 30 cm3 Ge(Li) detector for gamma rays up to 17.6 MeV.
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    Review of gamma-ray transitions from keV neutron captur.
    (Australian Atomic Energy Commission, 1970-09) Allen, BJ
    The study of gamma rays from neutron capture in the keV energy region provides information on the properties of individual resonances with keV spacing in light nuclei or nuclei near closed shells, and on the average behaviour of resonances in heavy nuclei. The effects of p and d-wave capture can be investigated across the periodic table, as can the neutron capture mechanisms. A variety of techniques are applicable in this energy range and these, with the results obtained, are reviewed in this paper.
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    Towards epithermal boron neutron capture therapy for cancer
    (The Institution of Engineers Australia, 1994-05-01) Allen, BJ
    Progress in the treatment of local disseminating cancer such as high grade brain tumours is poor, and the ability to kill individual cancer cells in the midst of normal cells has not been achieved. Binary therapies hold the most promise of this, and of these Boron Neutron Capture Therapy is the most advanced. Epithermal neutron beams are essential for outpatient treatment of high grade brain tumours and these are now installed and being characterised in Europe and the USA, and are at the design stage in Australia. These beams would allow the bilateral irradiation of the entire brain, and as such are ideally suited for the prophylactic therapy of subclinical metastases. When coupled with appropriate cancer affined boron compounds, therapeutic ratios of 2-3 should be achieved. At present the only source of an epithermal neutron beam is a nuclear reactor. The Euratom reactor at Petten and the Brookhaven Medical Reactor have been retrofitted with filters to produce an epithermal neutron beam. These beams have been characterised and used in dose escalation studies with dogs to study normal tissue tolerance using borocaptate (BSH). Another beam is available at the MIT medical research reactor. Clinical trials at Petten for glioblastoma with BSH and at MIT using boronophenylalanine for melanoma metastases to the extremities are expected to commence this year. The state of the art of reactor based BNCT is reviewed and the potential for a major change in the prognosis of local control of disseminating cancer is explored.
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    Valence neutron capture in iron 54Fe
    (Australian Atomic Energy Commission, 1977-02) Allen, BJ; Musgrove, ARD; Boldeman, JW; Macklin, RL
    The neutron capture cross section of S4Fe has been measured with 0.2 per cent energy resolution from 2.5 to 500 keV. A large and significant correlation is observed between the s-wave reduced neutron widths and the corresponding total radiative widths. The valence model readily accounts for this correlation as well as a large fraction of the s-wave radiative widths.