Christodoulides [1] developed some expressions for the determination of the activation energy, E, of a first order peak, vising the widths or half-widths of the peaks. These widths correspond to temperatures at which the signal level is 1/4, 1/2 or 3/4 of the peak height, on both sides of the peak temperature at the maximum, T _M . Fig.3 shows the various temperatures previously defined.

Fig. 3: A glow-peak and the various temperatures used in the method.

The expressions are valid in the region of E/kT _M values between 10 and 100. Using the first-order kinetics equation giving the variation of light intensity with temperature, and inserting in it the equation of the maximum for a constant heating rate, one gets the following expression in terms of the variable ?=E/kT and its value at the peak maximum, ? _M =E/kT _M:

(1)

The integral in Eq.(1) can be expressed in terms of the second exponential integral

(2)

So that Eq.(1) becomes

(3)

which has a maximum value, for ?= ? _M equal to

(4)

and finally

(5)

which gives the signal output I as a function of ? for a TL peak of given I _M and ? _M . For a given value of ? _M , the ratio I/I _M depends only on ?. An iteration procedure is needed to solve Eq.(5) because one must...