GAMMA IRRADIATION EFFECTS ON THE THERMAL, OPTICAL AND STRUCTURAL PROPERTIES OF  CR-39 NUCLEAR TRACK DETECTOR * NOUH, S.A.(1), SAID, A.F.(2), ATTA, M.R.(3), EL-MELLEEGY, W.M.(3) and EL-MENIAWI, S.(3) (1) Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt, (2) Radiation Physics Department, Nuclear Materials Authority, Cairo, Egypt and (3) Physics Department, Faculty of Science, Al-Azhar University, Girls Branch, Egypt. Key words: Gamma rays, Thermal properties, Refractive index,  X-ray diffraction, SSNTD. تأثير أشعة جاما على الخواص الحرارية والضوئية والتركيبية للكاشف النووى سى ار-39 سمير احمد نوح و عبد الغنى فاوى سعيد و مرفت رجب عطا و وفاء المليجى و سلوى المنياوى خلاصـــة تم تشعيع عينات من كاشف الجوامد النووى سى ار-39 بجرعات مختلفة من أشعة جاما تتراوح بين 20  -300 كيلوجراى وتم دراسة تأثير هذه الأشعة على الخواص الحرارية. تم تعيين درجات الحرارة الانتقالية وكذلك طاقة التنشيط الحرارى اللازمة لكسر الروابط فى الكاشف كما تم دراسة الخواص الضوئية والتركيبية له من خلال قياس معامل الانكسار وحيود الأشعة السينية وقد تم ربط الثبات الحرارى للعينات بتكون الشقوق الحرة نتيجة التأثير الأيونى لأشعة جاما. ABSTRACT A study of the effect of gamma irradiation on the thermal, optical and structural properties of CR-39 diglycol carbonate solid state nuclear track detector (SSNTD) has been carried out. Samples from CR-39 polymer were irradiated with gamma doses at levels between 20 and 300 KGy. Non-isothermal studies were carried out using thermo-gravimetry (TG), differential thermo-gravimetry (DTG) and differential thermal analysis (DTA) to obtain the activation energy of decomposition and the transition temperatures for the non-irradiated and irradiated CR-39 samples. In addition, optical and structural property studies were performed on non-irradiated and irradiated CR-39 samples using refractive index and X-ray diffraction measurements. The variation of onset temperature of decomposition (To) thermal activation energy of decomposition (Ea) melting temperature (Tm) refractive index (n) and the mass fraction of the amorphous phase with the gamma dose were studied. It was found that many changes in the thermal, optical and structural properties of the CR-39 polymer could be produced by gamma irradiation via the degradation and cross linking mechanisms. Also, the gamma dose gave an advantage for increasing the correlation between the thermal stability of CR-39 polymer and the bond formation created by the ionizing effect of gamma radiation.   Accepted January 2006.