Dear friend Sansar Chand

In thermoluminescence dosimetry, the behavior of the TL glow curve shape is closely related to the type and energy of the incident radiation, as well as the dose and dose rate. At low doses, the TL glow curve is usually composed of several peaks corresponding to different trap depths and activation energies. As the dose increases, some of the lower temperature peaks may disappear or become less prominent, while other peaks may merge into a single broad peak. This behavior can be attributed to the fact that the higher energy radiation produces more ionization in the material, leading to a greater number of electrons being trapped in the deeper traps and fewer in the shallower ones.

Several studies have investigated the effect of dose on the TL glow curve of various materials. For example, in a study by Meftah et al. (2016), the TL response of a calcium fluoride dosimeter was analyzed at different doses of gamma radiation. The results showed that at low doses, the TL glow curve was composed of several peaks, while at higher doses, the peaks merged into a single broad peak. A similar effect was observed in a study by Pagonis et al. (2014), where the TL response of a lithium fluoride dosimeter was analyzed at different doses of gamma radiation. The results showed that as the dose increased, the TL glow curve shifted towards higher temperatures and the lower temperature peaks disappeared.

References:

Meftah, A., Bedja, M., & Benkhouja, K. (2016). Study of the thermoluminescence response of calcium fluoride (CaF2: Mn) dosimeter under gamma irradiation. Journal of Radiation Research and Applied Sciences, 9(1), 1-10.

Pagonis, V., Fountos, G., & Kitis, G. (2014). Thermoluminescence dosimetry for retrospective assessment of doses from high dose-rate exposures. Radiation Measurements, 68, 54-61.

Thanks Kaushik for your reply. But the references you suggested, I could not find their full text. Kindly send the full text of these, if possible.

Dear friend Sansar Chand

Please contact your librarians

Although Dr. Kaushik Shandilya; has already explained the reason in detail. Following points may be of further help-

1.Type of trap (activation energy & its concentration/m^3) will give height and position of TL peak if keeping all other exp. parameters same for simplicity. N1, E1; N2, E2 & N3, E3 have role, if E2>E1 and N2> N1 & N2> N3; You get 3 peaks with middle peak having high intensity. Depending upon value of N (trap conc), filling will occur further depending upon which active and passive competing traps get saturated.

2. Presence of re-trapping during heating is also important, which slows the fall of glow curve and widens it also possibly.

3. There are N no. of traps may be active and passive and competation is always there (few out of competition., when fully filled), TL response of some curves may increase (more output/dose at higher doses than at low doses-supralinearity)

4. Shift of position of peak with dose (non-first order kinetics),

All this leads to some complex glow curve at higher doses, not for all phosphors but may be for majority of them & may be in different dose ranges

5. Additionally, see track interaction model of supralinearity, tracke more close at higher doses so .....

6. There is distribution of trap depths, not single traps but close by traps-

all this leads to some complex glow curves (may be beyond explanation based on simple TL kinetics).

7. Distribution of electrons in traps (shallow, deep, deepest, other inactive traps, and their luminescence behaviour in different regions of dose)

8. shift or no shift of peak positions with changing dose

further given glow curve arise from localised recombination or delocalised recombination or combination of both and so on...

so merging of multiple peaks ......

These are few reasons, but actual situation is very very complex,

Thanks @ Dr.

@Manish Kumar

Welcome Sansar Chand ji. Just adding one more point that, some low Temp. peaks do not survive/not stable for not more than 5-10 days particularly those whose Tm is below 120 C or so. If u r making measurements after 2 weeks of irradiation, they will disappear. Additionally typical temperature gradient of 20C or so may occur as we generally record Temp of planchet and not of phosphor/disc/crystal, so generally Tm in recording always higher than actual values, more the heating rate , more is €temp gradient. So always maintain single layer of phosphor grains or use thin discs/crystals preferably below 0.4 mm or so to minimise the Temp. gradients.