Particle size effects on the dosimetry characteristics of K3Na(SO4)2:Eu TLD micro- and nanophosphors

Abstract

K3Na(SO4)2:Eu is a highly sensitive TLD material in its microcrystalline form. It has been found that the material in its nanocrystalline form could also be used for very high dose measurements (of the order of 100 kGy) of high-energy radiations, like γ rays. However, it is not known whether the nanoparticle prepared by different methods of preparation, i.e., prepared using chemical coprecipitation method (by bottom up approach) and by ball milling (top down approach) behave in a similar manner. In the present paper, the TLD material was prepared by the standard solid state diffusion method, crushed and sieved/ball milled for different time periods to get particles of different sizes ranging from micro- to nanosize ranges. TL dosimetry characteristics of the material were studied and compared with our earlier results on the nanoparticles prepared by chemical coprecipitation method. It has been found that the K3Na(SO4)2:Eu powder sample in the particle size range 75–106 µm show the highest sensitivity and could be used up to 10 kGy dose of γ radiation. It has also been found that the nanoparticles prepared by two different approaches behave differently, i.e., the nanoparticles prepared by chemical coprecipitation method though are less sensitive than the microcrystalline but they do not saturate even up to very high doses (∼100 kGy, whereas the nanoparticles prepared by ball milling are equally sensitive to that of prepared by solution coprecipitation method but saturate early (at lower doses). It has been concluded that the surface defects might be playing an important role. The effect of high energy γ radiation on its repeated use as TLD phosphor for high doses (radiation hardening) was also studied and found that another TL peak at high temperature appears and its intensity varies on repeated use but the dosimetry peak remains invariant making the phosphor reusable for several times.