Activation Energy and Orderof Kinetics for 200°C THERMOLUMINESCNECE  Dosimetry Peak in NaCl:Tb(T)

The paper provides a detailed calculation of the activation energy and the order of kinetics of the 200°C thermoluminescence dosimetric peak in NaCl:Tb(T)material. The TLD-grade NaCl:Tb(T) phosphor was prepared  by crystallization from aqueous solution and its subsequent annealing at 750°C for two hours followed by a quenching. The activation energy was estimated by two different methods namely, the peak shape method and the initial rise method. Both the  methods are found to give a value around 1.3 eV, The isothermal decay and peak shape methods gave the order of the kinetics followed  by the peak is 1.4 .

EXPERIMENTAL METHOD

The polycrystalline specimen of NaCl:Tb(1000 ppm) was prepared by the method of crystallization from aqueous solution.  The specimen thus obtained was annealed at   750 oC  for two hours and subsequently quenched to room temperature in air. After irradiation with gamma dose of 800 rad, the specimen was heated at  167 oC  with the heating rate of 200 oC/min. The radiation source used for excitation is  Co60  gamma. .[6-7]

Fig-1show typical glow curves of thermally treated and annealed and quenched NaCl:Tb (1000 ppm ) specimen. The specimen is exposed to gamma radiation .It is seen that from fig-1 that thermally treated specimen exhibits a single well defined peak at 200 oC. Initial portion at the 200 oC glow peak was recorded for the purpose of determining the activation energy.[8] The Arrhenious plot for initial rising part of 200 oC peak is presented in Fig-2. The activation energy calculated using above data was found to be aroun1.3 eV. Fig-3 and 4  represent the data used for determining the order of kinetics using isothermal decay at 200oC glow peak. In present case the thermo luminescence process found to be of second order.
The appearance of well resolved 200 oC peak in the glow curve clearly indicates that the trap is single valued and that a large number of them are involved in the generation of the peak 200 oC .  The well defined intense peak satisfied the basic requirement of high TL efficiency for a TLD material. The thermal activation energy for 200oC peak is around 1.3 eV. The energy value is a definite indication of the stability of the glow peak. Thus the high stability is found to have been satisfied in the present material. The isothermal decay and peak shape methods gave the order of the kinetics followed by the peak is 1.4. These experimental facts suggested low fading and high stability of the 200oC  glow peak

The value of activation energy and order of kinetic of 200oC peak for NaCl:Tb(T) phosphor suggest low fading and high stability. Thus the basic consideration have been satisfied in  NaCl:Tb(T)  TLD material.

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