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DA Bradley

Publications and source records attributed to DA Bradley.

7 recordsLinked to original sources
PubMed2000

Energy behaviour of neutrons generated by Witch-type distributed axi-symmetrical deuteron beams accelerated onto plane tritium targets

This paper is an analytical study of the spatial dependency of the d-T neutron energy in the vicinity of a homogeneous tritium-occluded plane target. Close to the target, and along the path of incidence of axially symmetric deuteron beams, the transverse density of accelerated deuterons is assumed to be governed by a law approximated by the 'Witch' function. In particular circumstances, the elementary neutron emission process in non-dispersive media can be considered to be omni-directional (due consideration being paid to collision kinetics, depending upon mass and kinetic energy of particles involved in the nuclear collision, nuclear reaction energy, etc.). Consequently, analytical expressions can be considerably simplified. By applying the classical kinetic energy and momentum conservation laws to nuclear processes, a theoretical description is obtained, taking into account the exoergic character of d-T fusion reaction. A number of expressions for energetic prediction of the fast neutron field are proposed. The associated relations, involving elementary functions, can be investigated using a desk-top computer. Computationally tractable tools are of importance in the study of diverse situations such as induced reactions and activation analysis using 14 MeV neutron generators, investigations in health-physics, radiation dose measurements, nuclear medicine, damage effects, and simulation studies.

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PubMed2000

On the low order approximation of radiation fields generated by some hollow-cylindrical ion beams accelerated to produce exoergic nuclear reactions

Increasing interest is being shown in obtaining accurate predictions concerning radiation fields produced by hollow-cylindrical ion beams impinging on homogeneous plane targets, the net effect of this process being exoergic nuclear reactions. Previous theoretical studies by the authors have focused on radiation fields generated by homogeneous plane ring-shaped sources, based on a unified treatment of the radiation field distribution developed by Hubbell and co-workers. In the case of an equivalent homogeneous source anisotropically emitting in nondispersive media, the Legendre polynomial series expansion method for emissivity function can be successfully applied when conditions for the convergence of the approximating series are satisfied. We have developed an analytical expression for the radiation field distribution around a homogeneous plane target bombarded by hollow-cylindrical ion beams whose elementary areas anisotropically emit in non-dispersive media. The expression includes summation of four terms in a cos-type approximation, yielding a low order approximation of the angular distribution of source emissivity. The resulting expression is a linear combination of common and elliptic functions. Particular interest focuses upon the evolution of the shape of the curves close to the source and to the discontinuity at the source boundary. Results of this investigation can be extended to experimental situations in which the assumption of an omni-directional distribution of nuclear reaction emissivity over the accelerator target surface or other kinds of axi-symmetric plane sources of radiation, is no longer valid.

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PubMed2000

Measurement of the viscosity of irradiated silicone using a differential viscometer

High-energy electron (2.0 MV) and gamma irradiation (60Co) has been used to modify polymeric silicone fluids of initial viscosities in the range, 90-700 cSt. Doses of electron and gamma radiation were delivered at rates of 0.246 kGy s(-1) and 15 kGy h(-1), respectively, exposure times being adjusted to ensure energy deposition in the range 30-360 kGy. Measurements were made using a differential viscometer based on a Bose Institute design. In line with expectation, samples of greater initial molecular weight (and hence greater viscosity), were observed to be more susceptible to radiation induced cross-linking than those of lower molecular weight. The role of dose rate and oxygen diffusion in determining the extent of change is discussed.

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PubMed2000

Modification of some properties of polyamide-6 by electron beam induced grafting

Electron irradiation, applied on its own or in combination with other physical and chemical treatments, can result in radiation damage to materials. One category of such pursuits is electron beam radiation processing technologies, the intent being to produce favourable modification of materials. Study has been made herein of the use of accelerator-generated electron beams for the induced grafting of acrylic and methacrylic acids and acrylamide onto polyamide-6, the latter being popularly used in the textiles industry. Samples of polyamide-6, in the form of rectangular sheets of dimension, 10 cm x 10 cm or granules, have been irradiated using a 3 GHz travelling wave electron accelerator of energy 6.5 MeV. Results show that the degree of grafting is dependent upon radiation dose and extent of monomers dilution. Modifications have been observed in the melting temperature of the crystalline phase, glass transition temperature, mechanical parameters and the reticulation of polyamide.

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