الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
The effect of storage time and annealing on the properties of CR-39 (poly allyl diglycol carbonate) (PADC) solid state nuclear track detector (SSNTD) with molecular composition C12H18O7 has been investigated.
Samples from CR-39 SSNTD are classified into two groups. The first group is storage samples since 25 years at 4ºC, this group is divided into two sets; the first one is irradiated with 6.1MeV α- particles from 252Cf source and the second set is irradiated with 5.5 MeV α- particles from 241Am source. The behaviors of the relations between the alpha track diameter and the fission fragment track diameter against etching time of storage samples at 4˚C were as that of new samples. The bulk etching rate of the storage samples at 4˚C is ≈1.2 μm/hr and this value agrees with the results in previous work [Ahmed M. Ahmed, 1987]. The sensitivity of these samples have the same behavior as in previous work [Ahmed M. Ahmed, 1987] also the relation between the track density and the etching time agrees with previous work [Ahmed M. Ahmed, 1987].
The second group is storage samples since 17 years at room temperature. For these samples we investigated the following:
The maximum track diameter of unetched storage samples at room temperature is shifted down from the range between 15and 30 μm to range between 5and 20 μm. The damage in surface of storage samples at room temperature shows an increase with increasing the etching time in etchant solution (6.25N NaOH). The results show the bulk etching rate of these samples is 1.52 μm/hr by using NaOH as etchant solution where it is 2.15 μm/hr for them using KOH as an etchant solution and the relation between the removal thickness percentage and etching time is direct relation that using 6.25N NaOH also using 6.25N KOH. The dependence of the bulk etching rate (Vb) on the etchant concentration (C) was studied and it is found in accord with the equation:
where T is the temperature in K, C is the concentration of the etchant in the unit of normality, k is the Boltzman’s constant and constants FB, nB and ε are obtained from fitting procedures.
The annealing effect was studied for the second group of samples where, the damage and cracks in sample surface increased at annealing temperature 200˚C for annealing time more than 5 hours. The bulk etching rate increases with increasing the annealing time and in case of isothermal and isochronal annealing the bulk etching rate behaves the same against annealing temperature. The value of maximum track diameter frequency decreases with increasing annealing temperature that may be due to thermal degradation in sample. By increasing the annealing temperature, the track density decreases and the times needed to completely fade all latent tracks annealed at 100, 120, 160 and 200°C are 16.70, 16, 13.38 and 11.92 hours respectively, which that means, the time required for completely fading latent tracks decreases by increasing the annealing temperature.
Two new samples were compared while one of them was not- annealed and the other one was annealed at 200ºC for 11.92 hours. The results show that,the new sample annealed at 200°C for 11.92 hours can not register any new track where other new sample (un- annealed) has track density 97.143 track/mm2. By comparing the damage in surface of two new samples one of them annealed and the other un- annealed, it is found that the surface of annealed one is completely damaged.
The annealing effect on the crystallinity was studied by using XRD, where the crystallinity decreases by increasing the annealing temperature and its behavior agrees with this for the bulk etching rate except at 200°C. The high crystallinity at 200°C may be attributed to change in the crystal structure of polymeric sample. TGA and FTIR analysis show the stable chemical structure of CR-39 where the TGA analysis clear a weight loss at 200°C with value 2.7% of sample weight, which may be the reason for increasing the bulk etching rate value at 200°C although there is increasing in crystallinity at this temperature or we can say that the increase in the bulk etching rate may be related to the thermal degradation at this temperature.