Thermoluminescence studies in LiF dosimeter irradiated at 77K and their implications on theoretical models

Abstract

In LiF:Mg, Ti dosimeters, gamma -irradiation at low temperature (77K) reduces the TL intensities of peaks 7 (260 degrees C) and 10 (450 degrees C) drastically whereas the TL intensity of peak 5 (200 degrees C) remains nearly the same as that after irradiation at room temperature (RT). This implies that during irradiation, interstitial migration is involved in the formation of traps giving rise to peaks 7 and 10. The generic nature of peaks 7 (Z2) and 10 (Z3) traps and their (Z2 to or from Z3) trap conversion are further demonstrated. Since diffusion processes are inhibited, F and Z centres are not formed efficiently in LiF dosimeters irradiated at 77K. Studies on supralinearity, sensitisation, thermal history, optical absorption, optical bleaching, phototransfer and LET dependence following irradiation at RT and at 77K imply that four different processes (competing nonluminescent centre, track interaction during read-out, Z centre and mobile interstitial) are operating simultaneously to varying extents during the trapping/luminescent stage of different TL glow peaks. The photon emission mechanisms of these peaks are discussed. The claim that supralinearity of peak 5 is related to Z3 production is disproved. Further studies on Z centre identification in LiF:Mg, Ti are indicated.

5.5 eV optical absorption, supralinearity, and sensitization of thermoluminescence in LiF TLD-100

“…Studies by many authors e.g., Refs,8,17,22,23,27,28 have indicated that the 5.5 eV band is thermally stable up to 400 °C whereupon its thermal destruction appears to correlate with the appearance of TL peak 10. Studies by many authors e.g., Refs,8,17,22,23,27,28 have indicated that the 5.5 eV band is thermally stable up to 400 °C whereupon its thermal destruction appears to correlate with the appearance of TL peak 10.…”

On the thermoluminescence of LiF from 83 to 320 K

“…14 However, absorption bands at 380, 310, and 280 nm become visible, mainly above 252 K, in addition to the bands at 250 and 200 nm. It is interesting to note that the F band which appears in the optical absorption spectra obtained at 252 and 273 K presents a lower relative intensity, when these spectra are compared with that determined with a room temperature irradiated TLD-100 single crystal, see Lakshmanan et al, 3 Da Rosa and Caldas. 15 For room temperature irradiated samples, the F band is the most prominent one.…”

“…Based upon results from Nepomnyashchikh and Radzhabov, 16 F centers are not easily formed when LiF samples are irradiated at temperatures near 77 K. It should be mentioned that the band at 280 nm does not appear clearly in the optical spectrum determined with a room temperature irradiated TLD-100 single crystal. 3,15 …”

“…As in other alkali halides, they suggested that the TL process in the material irradiated at room temperature is caused by the recombination with vacancy centers (F,Z 2 ) of interstitial halogen atoms thermally released from traps. According to Lakshmanan et al, 3 Mayhugh's electron-hole model has some bearing only on the process of LiF:Mg, Ti TL glow peaks below 473 K. The TL process of peaks above this temperature is better explained by the model of Sagastibelza and Alvarez Rivas.…”

Thermoluminescence of alkali halides doped with alkaline earth impurities

“…Even if one assumes that only some Mg ÷ centres change to Mg ° centres, then the peak 10 (correlated with 225 nm OA) TL in virgin LiF TLD-100 should have been considerably greater than that for the 140°C preirradiation annealed sample, because peak 5 (correlated with 310 nm OA) TL traps and hence the electrons released from them are a factor of 20 to 30 times higher in the former sample than in the latter one. But experiments show no appreciable difference in peak 10 TL between the two samples (Lakshmanan et al 1985). (4) In § 4.1 of paper I, it is also mentioned that ESR measurements by Watterich et al (1980) show that in LiF:Mg, the 0 value is 2.006 for the F band and 2-029 for the 225 nm band suggesting that the latter is not a Za band.…”