Sudhakar J. Supe

Radiation dose to the breast during mammography: a comprehensive, realistic Monte Carlo calculation

Certain assumptions have been made regarding the composition of the breast in different age groups: these are believed to be more realistic than existing assumptions and have been used in comprehensive Monte Carlo calculations of radiation dose to the breast and of appropriate indicators of risk as follows: (i) Mean dose to the sensitive tissues in an average breast. This may be used to compare risk in different mammographic techniques, and has been calculated for a wide variety of techniques, including some not previously explicitly studied. (ii) Integral dose to the sensitive tissues in a breast, which is a good indicator of risk in an individual case, has been calculated for two commonly used mammographic techniques and for four different breast compositions and thicknesses. The results have been compared with results obtained using other approaches.

Glow curve behaviour of CaSO4: Dy thermoluminescent phosphor in high dose region

Abstract The influence of 60 Co gamma exposure on the shape and peak temperature of the glow curve for CaSO 4 : Dy, in the region between 10 R and 10 8 R, was studied. With increase in exposure, initially, the glow peak shifts towards higher temperatures and later it shifts towards lower temperatures. The process of peak shift with exposure is accompanied by an unusual change in the shape of the glow peak. The wide variation in the shape of the glow peak has been found to be due to unusual changes in TL kinetics.

Photothermoluminescence and the behaviour of high-temperature glow peaks in Li2B4O7:Mn and CaSO4:Dy phosphors

Li2B4O7:Mn exhibits a high-temperature glow peak (at ∼ 370°C) in addition to its dosimetric glow peak (at ∼ 210°C) for exposures greater than 105R of 60Co γ-rays. No γ-ray induced sensitization has been observed in the presence of the high-temperature glow peak. Also, this high-temperature glow peak does not exhibit photo-transer in Li2B4O7:Mn. However, CaSo4:Dy, like other phosphors, exhibits γ-ray induced sensitization and photo-transfer in the presence of a high-temperature glow peak. The u.v. sensitivity in Li2B4O7 Mn has been ascribed to the creation of new centres associated with the high-temperature glow peak.

Effect of residual thermoluminescence on the radiation induced sensitization of some TL phosphors

Abstract The effect of the high temperature residual TL (RTL) peak on the sensitization of the dosimetric peak in CaSO 4 : Dy, CaSO 4 : Tm and CaF 2 : Dy phorphors was studied and it was found that the sensitization factor ( S / S 0 ) is dependent on the intensity of the RTL peak. On bleaching the RTL peak intensity by a factor of ∼16 by means of intense UV irradiation (253.7 nm), it was possible to bring down the sensitization factor for CaSO 4 : Dy from a value of 2.6 to 1.0. A similar effect has also been observed in CaSO 4 : Tm and CaF 2 : Dy phosphors. The shape and also the position of the main dosimetric peak is dependent on the intensity of the RTL peak.

Stability of CaSO4: Dy thermoluminescent phosphor in high dose region

Abstract The thermoluminescent fading of CaSO4 :Dy phosphor was studied under the laboratory conditions in the high gamma exposure region between 10 R and 108 R. With increase in exposure, beyond 100 R, initially the phosphor shows an improvement in the stability and later above 103 R exposure region the stability of the phosphor deteriorates, reaching its original value at 6 × 104 R corresponding to that at exposures less than 100 R. With further increase in exposure the phosphor shows a continuous deterioration in TL stability. This increase and decrease in the TL stability of the phosphor has been attributed to shifting of glow peak and appearance and disappearance of additional peaks.

Effect of radiation quality on thermoluminescence fading of CaSO4:Dy in the high dose region

Abstract The loss of thermoluminescence (TL) response during the storage of CaSO 4 :Dy TL dosimeters under laboratory conditions has been investigated for various radiation qualities and quantities (i.e., LET and dose). For a given radiation field, the TL stability first increases, reaching a maximum followed by its gradual decrease, depending on the quality (LET i.e., linear energy transfer) of the radiation. The dose dependent variation of TL stability is maximum for low LET radiation, decreases with increases in LET and remains least or negligible for high LET radiation. Such a TL fading phenomenon, referred to as “anomalous TL fading”, has been explained by the characteristic (nonlinear) glow curve behaviour of CaSO 4 :Dy.

Photo-transfer thermoluminescence in CaSO4:Dy

CaSO4:Dy irradiated to doses above 102 Gy, annealed partially, and exposed to UV, exhibits strong photo-transfer thermoluminescence (PTTL) due to transfer of charge carriers from filled deep traps to shallower traps. The PTTL below 280 degrees C is up to two times the reduction in the residual thermoluminescence. The UV irradiation does not appear to produce the free charge carriers from the filled deep traps for the transfer.

High level γ-dosimetry using CaSO4: Dy phosphor with high dy-concentration

Abstract It has been observed that the thermoluminescent traps in CaSO 4 :Dy phosphor with a high concentration of activator (2.0 mol% Dy) compared to that of normal samples (containing 0.05 mol% Dy) show a better stability and a lesser tendency towards saturation to γ -radiation. This effect has been observed for the main dosimetric peak (∼225°C) as well as for the high temperature peak (∼390°C). Thus by using 390°C TL peak in CaSO 4 :Dy (2.0 mol%) we were able to make high level γ dose measurements in the range from 2 × 10 2 to 3 × 10 6 Gy. The 390°C TL peak in CaSO 4 :Dy (2.0 mol%) samples increases non-linearly with dose and does not show any tendency towards saturation at least up to 3 × 10 6 Gy— the dose level studied. However, the corresponding high temperature peak in the normal samples (0.05 mol% Dy) shows saturation in its TL response above a γ -dose of 1.18 × 10 6 Gy. In addition, a high temperature TL peak at 572°C which is only observed for the high activator concentration sample (as reported in our earlier work (11) increases non-linearly with dose and does not show saturation up to the γ -dose of 3 × 10 6 Gy. Investigations on photo-transferred TL of high temperature peaks as a function of γ -dose were also carried out for both the types of samples.

X-rays scattered from a tissue equivalent phantom

Abstract The effective energy and intensity of X-rays scattered from a mix-D phantom have been assessed around the phantom at distances of 1 m and at angles of 0, 45, 90 and 135° from the central axis of the primary beam. The measurements were carried out using the dual phosphor TL technique to assess, simultaneously, the quality and quantity of scattered X-rays in relation to primary X-ray beams from 60 kV to 250 kV.

Dosimetry for irregular shaped fields of beta rays

The feasibility of using various shapes and sizes of field limiting devices and collimators with beta-ray eye applicators has necessitated the study of dosimetry for these fields. A method of calculating surface and depth doses for any shaped field from the data for circular fields is presented. The depth dose evaluation is based on a measured dose function which is defined as the dose rate at a particular depth for a particular circular field. The evaluated values for the surface and depth dose were compared with experimentally obtained values for three non-circular fields. The good agreement in these data indicates the practicability of the method suggested.