Additivity of alpha and gamma response in Li2B4O7:Mn

It is well known because of supralinear response of TL material that equal TL outputs are not obtained for equal increments of exposure. Thus for most phosphors additivity does not hold for gamma exposure. However, earlier investigation on thermal neutron response of Li2B4O7:Mn showed that additivity holds for thermal neutron and gamma exposures. The phenomenon was explained on the basis that the high LET radiation from 10B(n,α)7Li reaction and the low LET gamma radiation interact independently. Another study was undertaken to support this with alpha and gamma rays. A curium alpha disc source with a surface dose rate of 2.9 k rad/min was used for alpha exposures. Li2B4O7:Mn of grain size, 105-106 micron was chosen for the study. Results of TL measurements indicated that additivity holds between these two radiations and further TL output remained same irrespective of the alpha exposure was given first or later to gamma exposure. Because of the existence of supralinear region beyond 102R of gamma rays, one would expect higher TL output for (α+γ) exposure on the basis of individual calibration plots. As this was not observed, it was concluded that the space taken up by alpha interaction is negligibly small and does not interfere with gamma exposure resulting in additivity. No memory effect was observed upto the alpha exposure of 3 x 106 rads studied. (author)