On the quasi-equilibrium problem in thermally stimulated luminescence and conductivity.

Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption used in the derivation of the analytical expressions of thermoluminescence (TL). So far there is no established method available to check if QE actually prevails during the emission of an experimental TL signal. The present study shows that the level of QE changes with a change in the heating rate beta. The change in the level of QE in its turn gets reflected in a change in peak shape when the system turns to a non-QE condition. This property is used as the first ever experimental method to test whether or not the emission of a given glow peak occurs under the QE condition. An essential condition for holding the QE condition is found to be T(R)/taum> or = 10(-3) where T(R) and taum are the glow peak recording duration and the maximum value of the free carrier lifetime, respectively. This relation between T(R) and taum is useful in finding the approximate value of taum. The value of taum being a function of the concentration and cross section of the TL related centres, one may be able to assess these basic parameters from the study of TL glow curves. The theoretical results are discussed in the perspective of LiF (TLD-100).

A sensitive method for the determination of Th in body fluids.

A method involving neutron activation followed by simple radiochemical separation was developed and applied to determine the concentrations of Th in blood serum and urine. The method is sufficiently sensitive to detect 0.025 ng of 232Th. The average concentration of Th found in the blood serum and urine of subjects from normal environments is 7.9 ng L-1 and 2.7 ng L-1, respectively.

A geochemical basis for endomyocardial fibrosis.

Analysis of hearts of patients dying from endomyocardial fibrosis showed a significantly greater concentration of cerium, a lanthanide present in leafy vegetables and root tubers, than in control hearts. This may be important in the pathogenesis of the disease and provides a geographical basis for the prevalence of the disease in the tropics.

Daily intake of thorium by an Indian urban population.

Thorium intake by an urban group (Bombay) has been estimated using neutron activation followed by simple chemical separation. Daily intake of thorium via all the three sources: food, water and air, is reported in this paper. The major contribution of thorium to intake is through food (2.0 micrograms), followed by water (0.02 microgram) and air (0.02 microgram). The individual food ingredients such as cereals, pulses, vegetables, milk, etc. were also analysed for their thorium content. The cereals were found to contribute most to the daily intake.

A geochemical basis for endomyocardial fibrosis.

In a search for geochemical factors that could play a role in the pathogenesis of tropical endomyocardial fibrosis, endomyocardial tissue samples obtained from patients at necropsy or operation were analysed for major elements present in laterite and monazite, which are important soil constituents of Kerala State of India. Atomic absorption spectrophotometry was used for detecting iron, silicon, aluminium, zinc, magnesium, calcium, sodium, potassium, and manganese and neutron activation analysis for thorium. Compared with control samples from victims of fatal accidents, an excess of thorium, sodium, and calcium and a deficiency of magnesium were present in samples from patients. It has been shown earlier that the staple diets of people in Kerala have high concentrations of thorium, and these data show that thorium can become concentrated in cardiac tissues. It is speculated that thorium excess in conjunction with magnesium deficiency may play a role in the causation of tropical endomyocardial fibrosis.