Nonradiative Effects Research Articles

Recent Results of the German Thorotrast Study - Statistical Evaluation of Animal Experiments With Regard to the Nonradiation Effects in Human Thorotrastosis

Our first long-term animal experiment made use of 1920 female Wistar rats divided into 20 groups of 96 animals each. These were injected at 12 weeks of age with different volumes and different dosages of Thorotrast which was enriched with 230Th to enhance the alpha-energy emission rate. The purpose of the study was to evaluate the effects due to the colloidal substance and the radiation. In the main experiment, 12 groups of rats were injected intravenously with 60, 120 and 300 μl Thorotrast. 230Th was added to some Thorotrast preparations so that the total alpha-energy emission rate varied by factors of 1, 2, 5 and 10 relative to normal Thorotrast. Two groups were injected with 12 and 60 μl of 50-fold enriched Thorotrast. One group was given 600 μl of normal Thorotrast. In addition, we had 5 control groups, 1 NaCl and 4 Dextrin groups. The latter were injected with 60, 120, 300 or 600 μl of Dextrin. The first animals died 8 months after injection, and the last 11 animals were killed 41 months after starting the experiment. The number of animals that developed a hepatic or splenic tumor increased by a factor of 10 in the highest dose-rate groups compared to controls. Our results demonstrated a ….

Recent Results of the German Thorotrast Study-statistical Evaluation of Animal Experiments With Regard to the Nonradiation Effects in Human Thorotrastosis

Our first long-term animal experiment made use of 1920 female Wistar rats divided into 20 groups of 96 animals each. These were injected at 12 weeks of age with different volumes and different dosages of Thorotrast which was enriched with 230Th to enhance the alpha-energy emission rate. The purpose of the study was to evaluate the effects due to the colloidal substance and the radiation. In the main experiment, 12 groups of rats were injected intravenously with 60, 120 and 300 microliters Thorotrast. 230Th was added to some Thorotrast preparations so that the total alpha-energy emission rate varied by factors of 1, 2, 5 and 10 relative to normal Thorotrast. Two groups were injected with 12 and 60 microliters of 50-fold enriched Thorotrast. One group was given 600 microliters of normal Thorotrast. In addition, we had 5 control groups, 1 NaCl and 4 Dextrin groups. The latter were injected with 60, 120, 300 or 600 microliters of Dextrin. The first animals died 8 months after injection, and the last 11 animals were killed 41 months after starting the experiment. The number of animals that developed a hepatic or splenic tumor increased by a factor of 10 in the highest dose-rate groups compared to controls. Our results demonstrated a linear correlation between the dose-rate and the number of primary hepatic and splenic tumors. It appeared that the volume of injected Thorotrast, by itself, had little influence on the number of tumors. However, at a constant dose-rate of 10, a 50-fold increase in the volume of Thorotrast (12-600 microliters) decreased the minimal tumor-appearance time by about 250 days.

Recent Results of the German Thorotrast Study - Statistical Evaluation of Animal Experiments With Regard to the Nonradiation Effects in Human Thorotrastosis

Recent Results of the German Thorotrast Study - Statistical Evaluation of Animal Experiments With Regard to the Nonradiation Effects in Human Thorotrastosis

A theoretical study of resonance Raman scattering from molecules

An expression for the resonance Raman scattering (RRS) cross section from large molecules is derived by means of a time independent Green function method. This expression is obtained in the adiabatic basis set, and both the radiative and nonradiative damping effects are explicitly considered, assuming the statistical limit in the excited vibronic states. Expanding the nuclear coordinate dependence of the transition moment, an analytical expression for the RRS cross section is derived for a displaced potential energy surface model. The expression obtained is applicable to the resonance Raman scattering not only in the weak coupling but also in the strong coupling case, and consists of the sum of the nth order vibrational transitions. It is shown that in the weak coupling case, the fundamental cross section may be explained as a succession of the absorption to the lowest level in the excited electronic state followed by the emission from it. Multimode effect on the RRS cross section which has not been reported before is studied and the analytical expression for the RRS cross section including this effect is obtained. The dimensionless displacement Δ dependence on the excitation energy profile is calculated. The effect of the nonadiabatic coupling (or the Born–Oppenheimer coupling) on the RRS cross section is also investigated. It is shown that using the adiabatic basis set, the BO coupling appears only in the high order approximations in most cases.

Lifetimes of Bound Excitons in CdS

Weakly bound excitons in CdS have giant oscillator strengths which lead to exceedingly fast radiative lifetimes. We have been able to measure the lifetime of the ${I}_{2}$ line, an exciton bound to a neutral donor, and the lifetime of the ${I}_{1}$ line, an exciton bound to a neutral acceptor. We find ${\ensuremath{\tau}}_{{I}_{2}}=0.5\ifmmode\pm\else\textpm\fi{}0.1$ nsec and ${\ensuremath{\tau}}_{{I}_{1}}=1.03\ifmmode\pm\else\textpm\fi{}0.1$ nsec. The measurements were made at 1.6\ifmmode^\circ\else\textdegree\fi{}K. The lifetimes are measured by exciting the luminescence with an argon laser modulated at 100 Mc/sec, and measuring the time delay of the luminescence with a 100-Mc/sec phase-sensitive detector. Previous calculations by Rashba and Guygenishvili predicted radiative lifetimes which were an order of magnitude shorter than our measured values. They used an incorrect value for the exciton mass. When corrected, their theory gives ${\ensuremath{\tau}}_{{I}_{2}}=0.56$ nsec and ${\ensuremath{\tau}}_{{I}_{1}}=1.86$ nsec, in reasonably good agreement with our measurements. Thomas and Hopfield measured the absorption oscillator strength of the ${I}_{2}$ line. Their measurements predict a radiative lifetime for the ${I}_{2}$ line of 0.4\ifmmode\pm\else\textpm\fi{}0.1 nsec. This is very close to our measured value and shows that the ${I}_{2}$ line decays radiatively. We conclude that the nonradiative Auger effect is negligible for the ${I}_{2}$ line and either negligible or small for the ${I}_{1}$ line. We also calculate the lifetime for donor-acceptor pair recombination to be 2.2 nsec as the pair separation goes to zero. This agrees with Colbow's experimental value of 2.5\ifmmode\pm\else\textpm\fi{}1 nsec. Using the same method, we calculate the lifetime of the Te isoelectronic trap to be 27 nsec. This agrees poorly with Cuthbert and Thomas's measured value of 300 nsec.

Lifetimes of bound excitons in CdS

Weakly bound excitons in CdS have giant oscillator strengths, which lead to exceedingly fast radiative lifetimes. We have been able to measure the lifetime of the I2 line, an exciton bound to a neutral donor, and the lifetime of the I1 line, an exciton bound to a neutral acceptor. We find τI2 = 0.5 ± 0.1 nsec and τI1 = 1.03 ± 0.1 nsec. The measurements were made at 1.6°K. The lifetimes are measured by exciting the luminescence with an argon laser, modulated at 100 mc, and measuring the time delay of the luminescence with a 100 mc phase sensitive detector. Previous calculations of Rashba and Gurgenishvili predicted radiative lifetimes which were an order of magnitude shorter than our measured values. They used an incorrect value for the exciton mass. When corrected, their theory gives τI2 = 0.56 nsec and τI1 = 1.85 nsec in reasonably good agreement with our measurements. Thomas and Hopfield measured the absorption oscillator strength of the I2 line. Their measurements predict a radiative lifetime for the I2 line of 0.4 ± 0.1 nsec. This is very close to our measured value and shows that the I2 line decays radiatively. We conclude that the nonradiative Auger effect is negligible for the I2 line and either negligible or small for the I1 line.