DISCUSSION AND CONCLUSIONS

It was observed that the dose vs TL intensity curves of 220°C peak in the H2O2- and FIF-treated sand samples do not show saturation up to 6 kGy. Therefore, they can be used as in situ TL dosimeters for radiation hygienisation of sewage sludge. The dose normally given to sludge is about 3-4 kGy. The 370°C TL peak in the FIF-treated samples does not saturate even up to the studied dose of 10 kGy.

Therefore, the dose response of 370°C TL peak can also be used for estimating the dose given during radiation disinfection of sewage sludge in addition to the 220°C TL peak. Use of such in situ TL dosimeters (separated from the irradiated sludge) has many advantages over other external dosimeters

as explained earlier. Using these dosimeters, the estimated dose rate for the sludge irradiator facility was found to be 0.49 ± 0.02 kGy per hour (see Table I). In order to minimise uncertainties introduced due to batch-to-batch variations in TL sensitivity, it is recommended that a separate calibration be drawn for each batch. This is done by taking sludge samples at the inlet of the irradiator facility as well as at the outlet on completion of the irradiation. Since both the types of samples (H202- and HF-treated) show room-light-induced as well as sunlight-induced TL fading, care should be taken to protect the sand samples from exposure to room-light or sunlight during collection of sludge samples at the inlet as well as at the outlet of the irradiator, and also during cleaning, irradiation and TL readout of the sand samples.

REFERENCES

[1] BENNY, P.O., SHAH, M.R., "Problems in dosimetry at Sludge Hygienisation Research Irradiator (SHRI), Baroda", Nuclear Energy Programme - Achievements and Prospects in Medicine, Industry and Agriculture (Proc. Symp. Indian Nuclear Society', Bombay, 1992), pp. 119-121.

[2] BENNY, P.O., BHATT, B.C., Investigation of TL properties of Sand collected from Sewage Sludge as an 'In-Situ' dosimeter in Radiation Disinfection, Appl. Radiat. Isotopes 47 (1996) 115-121.

IAEA-SM-365/60 ULTRAVIOLET AND INFRARED SPECTRAL ANALYSIS OF

POLY(VTNYL)BUTYRAL FILMS: CORRELATION AND POSSIBLE APPLICATION FOR HIGH-DOSE RADIATION DOSIMETRY S. EBRAHEEM, M. EL-KELANY, W. BESfflR, A.A. ABDEL-FATTAH National Centre for Radiation Research and Technology,

Cairo, Egypt Abstract

A detailed study was performed to develop the dosimetric characteristics of poly(vinyl)butyral film (PVB), to be used as a film dosimeter for high-dose gamma radiation dosimetry. The useful dose range of this polymeric film extends up to 350 kGy. Correlations were established between the absorbed dose of gamma radiation and the radiation-induced changes in PVB measured by means of ultraviolet (UV) and Fourier Transform Infrared (FTIR) spectrophotometry. The results showed a significant dependence of the response on the selected readout tool of measurements whether FTIR (at 1738 and 3400 cm"1) or UV (at 275 and 230 nm), as well as on the quantity used for calculation. The effect of relative humidity during irradiation on dosimeter performance as well as the post-irradiation stability at different storage conditions are also discussed.

1. INTRODUCTION

According to extensive studies of the radiation effects on polymers [1,2], irradiation of polymer film in air induces the oxidation of the polymer and the production of carbonyl groups. The magnitude of the oxidation process depends not only on the structure of polymer but also on the type of ionizing radiation; more specifically, the dose rate. Hence, it would be expected that oxidation processes predominate for irradiation with gamma rays which are characterized by their slow rate. On the contrary, for irradiation with accelerated electrons, which are known to have very high dose rates, processes other than oxidation, such as inter-molecular and disproportion reactions would predominate.

In the polymeric film dosimeters, the radiation-induced signal depends on the absorbed dose of ionizing radiation by the dosimeter and may also depend on the dose rate or fractionation of dose [3], on the temperature during the irradiation and handling, on the presence or absence of oxygen in the surrounding atmosphere or in the dosimeter [3], and on the ambient humidity or rather on the amount of water in the dosimeter [4,5].

2. EXPERIMENTAL

The film used in this investigation was prepared using poly(vinylbutyral) (PVB), (Pioloform BM18, average molecular weight of about 36,000, product of Wacker Co., USA). 5g of PVB was dissolved in 100 mL of n-butanol at about 50 °C and kept well stirred at that temperature for about 24 h. 30 mL, of this solution, poured onto a 15x15 cm glass plate and dried at room temperature for about 48 h. After drying, the film was stripped from the glass plate, then cut into 1x1 cm pieces and stored for different investigations. The thickness of the obtained film was found to be 50±5 mm (Is).

A Uvikon 860 spectrophotometer was used for scanning the absorption spectra and measuring the optical density at l^x. of the different film dosimeters. Also, Mattson 1000 Fourier Transform Infrared (FTIR) spectrometer (Unicam) was used for measuring and scanning the infrared absorption spectra at resolution of 4 cm"1. High signal-to-noise spectra were obtained by collection of hundred scans for each sample. The resultant digitilized spectra were stored for further data processing. Irradiation was carried out in the ^Co gamma chamber 4000 A (product of Bhabha Atomic Research Center, India). Dose rate of ( 2.17 ) kGy/h was used as checked by Fricke dosimetry [5],

4.00

Dose. kGv

= 0.0 2 = 50 3 = 100 4 = 150 5 = 250 6 = 350

180 235 290 345 400 WAVELENGTH

FIG. 1. UV-absorption spectra of PVB films, unirradiated and irradiated to different absorbed doses.

Dose, kGv 1 = 100 2 = 200 3 = 300

4000 3500 3000 2500 2000 Wavenumbers

1500 1000 ⁵⁰⁰

FIG. 2. FTIR-difference spectrum of PVB films irradiated to different absorbed doses.

3. RESULTS AND DISCUSSION