S. P. Kathuria

Effect of impurities on scintillation - optical and thermoluminescent properties of NaI(Tl)

Abstract The effect of the presence of impurities usually present in the starting material for growth of a NaI(Tl) crystal on its scintillation output is investigated. To comprehend the role of impurities optical and thermoluminescent (TL) measurements have been carried out. The effect of impurities on crystal transparency at 420 nm is not correlated with their effect on scintillation. The TL output in the presence of cationic impurities is enhanced while an opposite effect for anionic impurities is observed. The results suggest that both types of impurities adversely affect the scintillation but in a different manner.

Thermoluminescence of coloured alkali halide crystals after plastic deformation

Abstract Changes in the thermoluminescence (TL) intensity and the glow profile are found due to the plastic deformation caused by the application of the periodic uniaxial pressure in X-irradiated KBr, KC1, KI, LiF-TLD-100 and NaCl crystals. Trap destruction and trap competition models are discussed for the decrease in the TL intensity of the crystals. The increase in the TL intensity of some of the glow peaks is possible by the creation of new defects which act as traps, which are intrinsic in the crystal. If during the plastic deformation some of the interstitial atoms are released from one trap and are trapped again in some other trap, then the TL intensity corresponding to the first trap may decrease and the TL intensity corresponding to the other trap may increase. If the deformation of a crystal creates some traps which are different in energy than the intrinsic traps, then a new glow peak may appear.

On the mechanism of phototransfer thermoluminescence in LiF TLD-100

LiF TLD-100 exposed to 25.8 C kg-1 and then annealed at 350 degrees C for 15 minutes contains defects responsible for the 225 nm optical absorption band and peak XII. Other defects have not been identified in this sample. Consequently, phototransfer thermoluminescence (PTTL) has been assumed to originate from peak XII. Results are presented that show that PTTL is not as simple a process as the transfer of charges from peak XII traps to the traps corresponding to peaks at lower temperatures. The mechanism is much more involved and the defects responsible for absorption at 225 nm play only a catalytic role in PTTL.

A low temperature study of the glow peaks of LiF TLD-100 single crystals after alpha irradiation

Abstract In addition to 5 well known glow peaks between room temperature (RT) and 500 K, 8 glow peaks are observed between liquid nitrogen temperature (LNT) and room temperature (RT) after alpha irradiation of LiF TLD-100 single crystal. Intensity of the glow peak observed at 131 K is about 120 times higher than that of dosimetry peak 5 (481 K). Activation energyE was determined for glow peaks of 131 K, 144 K and 256 K using (i) Initial rise and (ii) Peak shape methods. The average values of trapping parametersE and s are 0.36 eV and 4.4 × 1012 sec -1; 0.3 2 eV and 7.0 × 109 sec -1; 0.74 eV and 1013 sec -1 for these glow peaks respectively.

Thermoluminescence in gamma-irradiated NaI(Tl) crystal

Abstract Thermoluminescence (TL) in NaI(Tl) single crystals has been studied in the temperature range 25–265°C. Four glow peaks around 70, 120, 160 and 195°C are observed in the glow curves recorded for the crystals containing 1.5 – 5 millimolar (mM) activator fraction. However, for crystals containing a high activator concentration of 15 mM fraction, two strong peaks around 110 and 215°C are obtained. The normalized total TL output follows a complex dependence on activator concentration. In the optical absorption spectra recorded at room temperature, distinct changes are seen on increasing the activator concentration from lower values to 15 mM fraction. The results suggest that the Tl + dimers and higher order centers present in the lattice affect the TL output differently at higher doping concentration.