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1-4 of 4

K. S. Sharada

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Journal Articles

Journal:
Radiation Research

*Radiation Research*(1993) 136 (3): 335–340.

Published: 01 December 1993

Abstract

For some calculations, the proton stopping power in tissue must be known accurately. The composition of tissue was assumed to be constituted of 11 elements; the proton stopping powers were available for hydrogen, carbon, nitrogen, and oxygen. Those for the remaining 7 elements for the energy range 0.5 to 10 MeV at intervals of 0.5 MeV are evaluated and presented in this paper. Corrections such as the Barkas effect correction, Bloch's correction, and shell correction are evaluated and used in the calculation of proton stopping powers. Corrections for the Bethe formula for heavy ions were suggested by Barkas et al. (Phys. Rev. Lett. 11, 26, 1963) when they observed that the stopping powers for positive ions were larger than those for the negative ions with identical velocities. They suggested that a charge-dependent correction term be incorporated in the Bethe formula. Theoretical estimates of this correction derived by Ashley et al. (Phys. Rev. 85, 2392-2397, 1972) were used in the calculation of the Barkas effect. The Barkas effect correction depends on projectile velocity and Z. It decreases with energy. To account for the discrepancy between the classical and the quantum mechanical treatment of the Bethe formula, Bloch (Ann. Phys. 285, Chap. 18, 1933) suggested a correction to the stopping-power formula; this correction is also evaluated in this paper. Bloch's correction also decreases with energy. The shell correction needed for the binding of the electrons in the target atom is also calculated using Walske's asymptotic formula taking into account the screening effect of the atomic electrons of the K and L shells of the target atom. A computer program was written to calculate the stopping powers of protons with all these corrections for seven low-Z elements which are part of the tissue composition. These values are compared with those of other authors, and fairly good agreement is found. The lack of sufficient experimental information and uncertainty in the mean excitation energy values and shell corrections area are some of the causes for the differences in the evaluation of stopping power by the different authors.

Journal Articles

Journal:
Radiation Research

*Radiation Research*(1984) 97 (2): 424–433.

Published: 01 February 1984

Abstract

The general expression given by Dr. Sternheimer is used to calculate the density effect correction in the stopping power values for electrons in calcium and sulfur for energies 0.75 to 10 MeV to study the linearity of the electron energy response of <tex-math>${\rm CaSO}_{4}\colon {\rm Dy}$</tex-math> Teflon disk dosimeters toward higher energies. It is found that up to 10 MeV the stopping power values versus electron energy above 2 MeV tend to be a constant which predicts the linearity of the electron energy response of the dosimeter toward the high-energy region so that it can be used for dose measurements of high-energy machines with no loss of accuracy. The various constants entering into the general expression for density effect correction are calculated and tabulated. The density effect correction is computed and tabulated. The stopping power for electrons in <tex-math>${\rm CaSO}_{4}\colon {\rm Dy}$</tex-math> Teflon TLD disk dosimeter is computed and presented. The electron energy response of this material for the energy range 10 keV to 10 MeV is also computed and presented. The stopping power values for electrons in calcium and sulfur with density effect correction are computed and tabulated.

Journal Articles

Journal:
Radiation Research

*Radiation Research*(1983) 93 (1): 33–39.

Published: 01 January 1983

Abstract

The photon energy response of CaSO 4 : Dy teflon disk dosimeters used widely in radiation dosimetry is computed using the energy absorption coefficient values for calcium, sulfur, oxygen, and carbon taken from J. H. Hubbell's tables. For fluorine, the energy absorption coefficients were obtained from the values given by F. H. Attix for CaF 2 and Ca. The energy response of the radiation-monitoring disk for the range of 10 keV to 10 MeV, relative to air, is computed and plotted. The response is maximum between 20 and 30 keV and then gradually falls to a constant at 200 keV to 10 MeV. This computed response for different energies is compared with the experimental TL response of the dosimeter. The electron energy response of these TLD disks is computed using the stopping-power values for the different component elements. The electron stopping power for sulfur and calcium from 10 keV to 10 MeV is computed using the Bethe-Bloch formula. Those for oxygen and carbon are taken from the tables give by M. J. Berger and S. M. Seltzer. For fluorine, the values are computed from those for Li and LiF given in the same tables. This calculated response is compared with the experimental β response of the TL dosimeter.

Journal Articles

Journal:
Radiation Research

*Radiation Research*(1982) 89 (1): 1–10.

Published: 01 January 1982

Abstract

Accurate knowledge of energy absorption coefficients is needed to calculate the absorbed dose in any material. The photon kerma for LiF relative to air and soft tissue is computed using energy absorption coefficient values for Li, F, air, and tissue. Values of energy absorption coefficients for air are already available in J. H. Hubbell's (Photon Cross-Sections, Attenuation Coefficients and Energy Absorption Coefficients from 10 KeV to 100 GeV. National Standard Reference Data System-National Bureau of Standards Report No. 29, Washington, D. C., 1969) tables. Those for tissue are obtained by adding the weighted average of the energy absorption coefficients of the different elements constituting the tissue. For fluorine, they are computed from the values given by F. H. Attix and W. C. Roesch (Eds, Radiation Dosimetry, Vol. I, Fundamentals. Academic Press, New York/London, 1968) for CaF 2 and Ca. The values for lithium have been computed taking into consideration the photoelectric effect, Compton process, and pair production. Corrections for radiative energy losses, fluorescence yields, screening of electrons, etc., are appropriately applied. The energy absorption coefficients due to photoeffect, Compton scattering, and pair production are added to get the total. The energy absorption cross-section data for photon energies from 0.01 to 10 MeV are tabulated for each interaction.