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LNF:Technology: Difference between revisions
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→NAYADE Co-60 irradiation facility
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*Dosimetry system | *Dosimetry system | ||
The routine gamma dosimetry is performed using the commercially available Red Perspex™ 4034 Harwell dosimeters, they are polymethylmethacrylate (PMMA) dosimeters that have become widely used in routine high-dose rate dosimetry in the field of the industrial radiation processing. When exposed to ionising doses in excess of 1 kGy, the Red 4034 polymer starts to darken due to the formation of a new absorption band peaking at 615 nm and extending from 600 nm to beyond 700 nm. The absorbed dose is therefore determined by measuring its radiation-induced absorbance in the | The routine gamma dosimetry is performed using the commercially available Red Perspex™ 4034 Harwell dosimeters, they are polymethylmethacrylate (PMMA) dosimeters that have become widely used in routine high-dose rate dosimetry in the field of the industrial radiation processing. When exposed to ionising doses in excess of 1 kGy, the Red 4034 polymer starts to darken due to the formation of a new absorption band peaking at 615 nm and extending from 600 nm to beyond 700 nm. The absorbed dose is therefore determined by measuring its radiation-induced absorbance in the 630nm-650 nm range where post-irradiation fading is minimal. 640 nm wavelength is used as read-out 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 its 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 dependance. From a practical point of view, the Red 4034 dosimeters are temperature-independent up to 40 ºC, provided that the measurements are made shortly after the end of the 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 to start the irradiation test is always carried out. | |||
==Material Characterization Facilities== | ==Material Characterization Facilities== | ||