الفهرس 
ِAcknowledgementOnly 14 pages are availabe for public view
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Abstract
Plastic detectors have been shown to be very sensitive for measuring ionizing particles. They have been increasingly used for studies in fields of radiation dosimetry and particle identification because they posses many advantages over the other detectors. In some cases, the detectors are exposed to certain environmental conditions, which may affect the etching rates. The irradiation chamber was designed for measure the alpha energy under different environmental conditions such as temperature, pressure, humidity and gases. A study of these effects could be useful for the interpretation of the results in a particular experiment.
The chamber consists of ajar from iron rectangular in shape with the dimensions of 16.7 cm width, 19.8 cm length and 19.2 cm height. The chamber has a cover from Perspex of 1.2-cm thickness, through a rubber to ensure a good vacuum inside the chamber.
Inside the chamber there are two circular rotating discs of diameter 15.6 cm rotated from outside the chamber through co-axial axes. The lower disc made of stainless steel, has a hole and twelve positions to be used as a holder for the detectors. The upper disc made of Perspex has one only hole to use as a shutter to irradiate only one detector and prevent the radiation from the others. The α-particles source is supported on the lower end of the holder source, where its position can be change up and down from outside the chamber. The chamber can be under vacuum by connected it with a diffusion pump where the vacuum is controlled by a needle valve and vacuum gauge. Also, there is a heater and thermocouple to vary the temperature inside the chamber. The temperature inside the chamber is changed, read and controlled with an accuracy 1 °C using a variac and temperature controller.
This work divided mainly into four parts:
In the first part, the bulk etch rate VB of CR-39/PATRAS has been measured in various concentrations of NaOH (in the range 5 N to 8 N) at temperatures from 50-80 °C. VB is determined by using two different methods: (1) the fission fragment method and, (2) the mass decrement method. It is found that a dependence of the VB on both the etchant concentration and temperature. Values of the VB for the fission fragment and mass decrement methods under the used optimum etching conditions (7.25 N, 70 °C and 6 hr) are 1.59 ± 0.05 and 1.57 ± 0.04 µm/hr, and the values of the activation energy (Eb) are 0.73 ± 0.02 and 0.752 ±0.011 eV, respectively.
In the second part, the effect of temperature of detector material during irradiation is investigated. For this purpose, the samples of CR-39 have been exposed to 5.48 MeV α-particles in the irradiation chamber and the temperature of the detector have been varied from 30-70 °C. It is found that the responses of the detector become better with the decrease of detector temperature during irradiation.
In the third part, a study of the effects of ultraviolet (UV) radiation on the damaged tracks of α-particles m CR-39 is reported. Two different UV irradiation schemes were used, pre-exposed (UV+α) and post-exposed (α+UV) for different exposure times from 2-8 hr. Results indicate that the track diameter increases with increasing the exposure time (for both pre-and post-exposed) and tends to saturate after about 4 h. The increase in track diameter for post-exposed is larger than that for pre-exposed.
In the last part, the effect of pre-and post-gamma irradiation on the α-particle track response of CR-39 is investigated. The γ-source was 60CO with dose rate 10 kGy/h. The bulk etch rate VB and track etch rate VT have been found out for different γ-doses from 30-200 kGy. The results indicate that both the track diameter and track etch rate increases with increasing the γ-dose in both the experimental schedules (pre-and post-gamma irradiation) but this increasing is small up to about 70 kGy. The increasing in track diameter and track etch rate for post-γ irradiation is larger than that of pre-γ irradiation. Also, the bulk etch rate and normalized bulk etch rate increases linearly with increasing γ-dose. Within such range of γ-dose (0-30 kGy) the bulk and normalized etch rate was not linear which reflected the difficulty of using such detector as γ-dosimeter in 0-30 kGy. The decrease in sensitivity of the detector with increasing gamma doses was observed.