The Effect of Thermally Stimulated Photoconversion of Oxygen Centres on the Sensitivity of TLD-500 Dosimetric Crystals

Abstract

The influence of UV radiation at a high temperature on the luminescent properties of oxygen-deficient corundum was studied. Efficient photoconversion, F- => F+-centres, which leads to appearance of the 3.76 eV F+-centre emission in the main dosimetric TL peak and the 5.91 eV band in luminescence excitation spectra of this centre, was found. Correlation between the integral intensity of the TL peak in the 3.76 eV emission band and the intensity of the 5.91 eV excitation band was established. Probable mechanisms of the thermostimulated photoconversion and TL in the F+-centre emission band are discussed.

Dosimetric application of green luminescence in irradiated TLD-500 detectors

“…Note that after the photothermal treatment, the intensity of the 3.7 eV band increases by a factor of 13 and becomes dominant, as observed earlier (McKeever et al, 1999;Weinstein et al, 2002). This effect arises due to the growing concentration of the F þ -centers resulting from the UV-induced F / F þ -conversion.…”

“…However, after the UV treatment of the sample (see Fig. 1b), a contribution of the 335 nm emission band (3.7 eV) at T max ¼ 470 AE 3 K, caused by the F þ -centers, is added to the TL signal (McKeever et al, 1999;Weinstein et al, 2002). At the same time, in a green spectral region, the 515 nm (E max ¼ 2.4 eV) luminescence at T max ¼ 470 AE 3 K is observed, with a relatively weak intensity that is thought to be related to the F 2 -or Al þ i -centers, as specified above in the Introduction.…”

“…First, the measurements were performed for sample 1 in the initial state. Next, the crystal was subjected to a photothermal treatment with unfiltered UV irradiation from a DRT-230 Hg lamp for 30 min at 623 K. It is known that as a result of such an impact, the deep traps are filled due to the active photoconversion of the F-and F þ -centers, and the TL yield of the TLD-500 detectors in different luminescence bands increases (Weinstein et al, 2002;Vokhmintsev, 2009). Then, TL measurements at different emission wavelengths were performed for the UV-irradiated sample 1.…”

Luminescent and dosimetric properties of nanostructured ceramics based on aluminum oxide

“…In particular, the TL intensity of the main peak at 475 K after UV irradia tion for 4 min is eight times higher than the TL inten sity after irradiation from the beta source with a dose of 32 mGy. It is known [19,20] that UV radiation effectively ionizes F centers in aluminum oxide, and, as a result of photoconversion, they transform into F + centers. Free electrons generated in this case are cap tured by traps.…”

Specific features of 3.8‐eV emission in TL spectra of oxygen‐deficient corundum

“…It was shown earlier [3,4] that the luminescence at 3.8 eV considerably increases after UV and thermal treatment, which leads to the F⇒F + conversion and a growth of the concentration of one-electron F + -centers in crystals. In this case, deep traps, which are responsible for TL peaks at ≈730 K and ≈880 K, are filled [3,5].…”