The presence of defects and their influence on the performance of CVD diamond as an alpha-particle radiation sensing element.

Three types of diamonds produced by chemical vapor deposition (CVD) and broadly classified as detector grade, optical grade and single crystal were evaluated in terms of their response to alpha-particle radiation when used as detection elements. It is well known that the presence of defects in diamond, including CVD specimens, not only dictates but also affects the response of diamond to radiation in different ways. In this investigation, tools such as electron spin resonance (ESR), thermo-luminescence (TL), Raman spectroscopy and ultraviolet (UV) spectroscopy were used to probe each of the samples, which were then graded on their performance as alpha-particle radiation detectors. The presentation discusses the presence of defects identifiable by the techniques used and correlates the radiation performances of the three types of crystals to their presence.

Radiation doses from low energy X-ray beams measured with synthetic diamond compared with calculated values obtained from the PENELOPE Monte Carlo code.

The utilization of a probe with synthetic diamond as the sensing material developed to measure radiation doses from mammography X-ray beams is described. The computer code system PENELOPE was used, with a geometry model simulating the experimental conditions, to compute the doses from the mammography X-ray beams to the diamond sensing material. The orientation of the diamond sensor to provide maximum absorption of the incident X-ray beam during exposure was also investigated using the PENELOPE code. The results from the theoretical model and experimental measurements are compared.

A synthetic diamond probe for low-energy X-ray dose measurements.

The desirable physical properties of diamond have made the mineral a choice material in radiation measurements. Diamond detectors are currently used extensively in high-energy physics. Their use for low-energy beams such as, for example, in mammography X-ray beams however, has not been fully investigated. This paper describes a diamond probe which has been constructed for the evaluation, as the radiation sensing material, of polycrystalline synthetic diamonds produced by chemical vapour deposition (CVD). The specimens were fabricated in wafer form and so the exposure orientation geometry of the diamond wafers, to give optimum absorption of the incident X-ray beam, was also investigated both experimentally and theoretically. The samples were characterized to obtain information regarding the elemental impurity levels, especially nitrogen, and consequently to establish the material quality. Nitrogen impurities and concentration levels in the diamond lattice have been shown to have a profound effect on the radiation detection properties of diamond. The probe described has the diamond surfaces metallized with titanium, platinum and gold to provide ohmic contacts. The probe was connected independently to both Wellhöfer Dosimetrie (model CU 500) and PTW Unidos E commercial electrometers. In all of the measurements, the incident radiation beam was normal to the edge of the diamond wafer to optimize absorption of the X-ray beam after establishing that this orientation was the optimum geometry. The results of the study are presented in both tabular and graphical forms.

Comparison of mammography radiation dose values obtained from direct incident air kerma measurements with values from measured X-ray spectral data.

The application of X-rays and ionising radiations for diagnostic radiology requires that the procedure is justified and optimised and that the exposure to the patient is kept as low as possible, without compromising image information. X-ray mammography is considered to be the most sensitive technique currently available for early detection of breast cancer. The magnitude of the absorbed radiation dose to the breast from mammography X-ray beams forms an important part of the quality control of the mammographic examination since it gives an indication of the performance of the mammographic imaging system as well as an estimated risk to the patient. In this work mean glandular dose (MGD) values were obtained at various tube potentials and tube loadings (TL) using direct measurements of the incident air kerma (ESAK) at the surface of a standard breast phantom and also from spectral measurements acquired with a solid-state detector. Comparisons of the MGD values thus derived are presented and the relationship between MGD, phantom thickness, image quality and tube operating parameters is discussed.

Effect of air cavities on the dose delivered to the lung during high-dose brachytherapy.

In the treatment of lung cancer using the radiotherapy technique of intracavitary brachytherapy with an 192Ir source, the lung is normally assumed to be entirely composed of a homogeneous mass of soft tissue. The aim of this study is to investigate whether there is the possibility that the air cavities in the lung influence the dose delivered to the lung at a prescribed distance from the source. The Monte Carlo code MCNP-4A was used to model the dose delivered by both 192Ir and 198Au as a function of treatment medium, density and composition, photon energy, and distance from the source. The suitability of MCNP-4A for this study was tested by producing depth-dose profiles for photons in water and comparing these to calculated profiles produced using well-documented methods.

Synthetic diamonds as in vivo radiation detectors.

Synthetic diamonds with controlled amounts of impurity atoms can be manufactured so that, as thermoluminescent dosimeters, they can be made to have sensitivities at least as good as presently available commercial thermoluminescent dosimeters. They also exhibit, for radiations normally found in therapy situations, a linearity of response that extends from less than 0.01 Gy (1 rad) to over 10 Gy (1000 rad). Their physical size and form, crystals which can have volumes of less than 1 mm3, make them ideal candidates for in vivo monitoring of radiation fields, particularly electron fields where high-resolution measurements are essential for accurate isodose line determinations. Aspects of dose response from gamma-ray beams in relation to the type and concentrations of the impurity atoms within the diamond are discussed, and some experimental values for gamma, x-ray, and electron beams are presented.

Synthetic diamonds as ionisation chamber radiation detectors in biological environments.

Synthetic diamonds with nitrogen concentrations higher than previously reported in the literature are found to operate very effectively as alpha-particle detectors, as well as detectors for gamma radiation, when operated as ionisation chambers. Certain of the specimens exhibited extensive linear response characteristics when subjected to either alpha particles or gamma radiation of various dose rates. For alpha particles, the response of the detectors at constant particle flux was also found to increase linearly with increasing alpha-particle energy. Unlike previously reported investigations, however, the variation in the response of the synthetic stones to gamma radiation as a function of time was found to be not only more rapid but also to be virtually unaffected by illumination with intense white light.

Negative development xeroradiography of the breast: doses and clinical indications.

Negative-mode xeroradiography is discussed in relation to the clinical indications and the radiation doses in the breast per exposure. The radiation doses have been obtained using a computer algorithm specially designed to calculate breast volumes by constructing a three-dimensional body from the two dimensional cranio-caudal and medio-lateral images. A mathematical integration procedure is then applied throughout the volume to obtain the absorbed dose.

Radiation exposure in xeroradiography of the breast.

A survey of the radiation exposure during xeroradiography of the breast for normal clinical exposures is presented. Average values obtained from the measurements made on a number of patients are presented and compared with measurements made by other workers. An estimate of the radiation dose received by the breast during the clinical exposures is also made and the parameters affecting the doses are discussed.