LNF:Technology: Difference between revisions

LNF:Technology (view source)

Revision as of 13:16, 30 October 2015

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→‎NAYADE Co-60 irradiation facility

Garciacortes

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 Main irradiation characteristics:
 *Type of source: 12 Co-60 cylindrical sources (15 mm diam. x 135 mm long) are distributed in a circle to provide an inner cylindrical irradiation volume.
-*Two distributions are available: High flux; ≤ 8.3 103Gy/h within a 60mm diam. x 100 mm high volume. Low flux; ≤ 1.2x102 Gy/h within a 200 mm diam. x 100 mm high volume (in the low flux configuration the sources can be rotated along an outer circle for uniform dose).
+*Two distributions are available: High flux; ≤ 8.3 10<sup>3</sup>Gy/h within a 60mm diam. x 100 mm high volume. Low flux; ≤ 1.2x10<sup>2</sup> Gy/h within a 200 mm diam. x 100 mm high volume (in the low flux configuration the sources can be rotated along an outer circle for uniform dose).
 *Irradiation at controlled temperatures and atmospheres, together with in-situ testing of electrical properties, is also possible.
-*Irradiation can be carried out at controlled temperature up to 300ºC. Gas flow (such as dry air or nitrogen) can be used during irradiation to minimize humidity. The uncertainty in the dose rate is better than 20% for a volume of about 283 cm3.
+*Irradiation can be carried out at controlled temperature up to 300ºC. Gas flow (such as dry air or nitrogen) can be used during irradiation to minimize humidity. The uncertainty in the dose rate is better than 20% for a volume of about 283 cm<sup>3</sup>.
 Irradiation rigs to perform in-situ measurements at different dose rates and under different conditions are routinely fabricated at Ciemat workshops. Sensors, cabling, laboratory equipment, feedthroughs, and environmental monitors (temperature, pressure, humidity, radiation) are available.
 *Dosimetry system
-Routine gamma dosimetry is performed using commercially available Red Perspex™ 4034 Harwell dosimeters. These are widely used polymethylmethacrylate (PMMA) dosimeters. When exposed to ionising doses that exceed 1 kGy, the Red 4034 polymer starts to darken due to the formation of a new absorption band extending from 600 nm to beyond 700 nm (it peaks at 615 nm). The absorbed dose is therefore determined by measuring radiation-induced absorbance in the 630nm-650 nm range where post-irradiation fading is minimal. For this the 640 nm wavelength is used as measurement wavelength. The absorbance per unit thickness, expressed in cm−1, is the dose-dependent quantity measured against air as reference. These dosimeters has been shown to be valid in the range of 5 to 50 kGy and their accuracy is better than 10 per cent. The Red 4034 dosimeters are pre-conditioned in a fixed humidity environment and hermetically sealed in polyester/aluminium foil/polyethylene laminate pouches, as absorbed water concentration was identified as a parameter which could influence the spectrophotometric response and hence the dose readout. Keeping the dosimeter in its packaging is mandatory to use the calibration curves (absorbance at 640nm (cm-1) related to dose) supplied by the manufacturer. The temperature sensitivity of the dosimeter is the most important environmental dependence. From a practical point of view, the Red 4034 dosimeters are temperature-independent up to 40ºC, provided that measurements are made as soon as possible after ending an irradiation
+Routine gamma dosimetry is performed using commercially available Red Perspex™ 4034 Harwell dosimeters. These are widely used polymethylmethacrylate (PMMA) dosimeters. When exposed to ionising doses that exceed 1 kGy, the Red 4034 polymer starts to darken due to the formation of a new absorption band extending from 600 nm to beyond 700 nm (it peaks at 615 nm). The absorbed dose is therefore determined by measuring radiation-induced absorbance in the 630nm-650 nm range where post-irradiation fading is minimal. For this the 640 nm wavelength is used as measurement wavelength. The absorbance per unit thickness, expressed in cm<sup>-1</sup>, is the dose-dependent quantity measured against air as reference. These dosimeters has been shown to be valid in the range of 5 to 50 kGy and their accuracy is better than 10 per cent. The Red 4034 dosimeters are pre-conditioned in a fixed humidity environment and hermetically sealed in polyester/aluminium foil/polyethylene laminate pouches, as absorbed water concentration was identified as a parameter which could influence the spectrophotometric response and hence the dose readout. Keeping the dosimeter in its packaging is mandatory to use the calibration curves (absorbance at 640nm (cm-1) related to dose) supplied by the manufacturer. The temperature sensitivity of the dosimeter is the most important environmental dependence. From a practical point of view, the Red 4034 dosimeters are temperature-independent up to 40ºC, provided that measurements are made as soon as possible after ending an irradiation
 These dosimeters have been also used to measure gamma dose in BR1 graphite-moderated, air-cooled nuclear reactor (SCK·CEN MOL), in mixed gamma neutron fields at a temperature below 40º.
 A gamma dosimetry before starting an irradiation test is always carried out.