ESTIMATION OF THORIUM IN GAS MANTLES TO ASCERTAIN REGULATORY COMPLIANCE

In India, stipulated limits for the use of thorium in gas mantles are 600 mg for less than 400 ed rating and 800 mg for greater than 400 ed rating. Although measurements of radioactivity are easily done there a re uncertainties in assessing the mass of thorium present because of t he age of the thorium, and hence the degree of radioactive disequilibr ium in the sample, is unknown. This paper describes the detailed non-d estructive gamma spectrometric measurements performed on mantle sample s from 18 different manufacturers and verification by neutron activati on analysis and presents estimates of thorium in them. Five of these s amples were also subjected to gravimetric analysis and good agreement was obtained. All of the mantles contained thorium in amounts well wit hin the prescribed limits. The results show that about lis by weight o f the mantle accounts for the mass of thorium. This factor may be used for a rapid preliminary estimation of thorium in gas mantles in the I ndian context.