NRSL-INER employed cobalt-60 gamma ray source and air cavity ionization chamber to establish the air kerma rate calibration system. The measurement principle is based on the definition of air kerma and the Bragg-Gray cavity theory. Measured ionizing charge is generated from Co-60 gamma ray in the air cavity, and then converted to energy imparted according to the W value (33.97 eV / i.p.). Referred to ISO 4037 and IEC 60731 , the air-kerma rate at the reference point in the calibration field is determined and that value adopts appropriate corrections based on the environment measurement and perturbation evaluation.
1.2 Cs-137 air kerma rate calibration system
NRSL-INER employed cesium-137 gamma source and air cavity ionization chamber to establish the air kerma rate calibration system. The measurement principle is based on the definition of air kerma and the Bragg-Gray cavity theory. Measured ionizing charge is generated from Cs-137 gamma ray in the air cavity, and then converted to the energy imparted according to the W value (33.97 eV / i.p.). Referred to ISO 4037 and IEC 60731 , the air-kerma rate at the reference point in the calibration field is determined and that value adopts appropriate corrections based on the environment measurement and perturbation evaluation.
2. Absorbed Dose Rate to Water Standard
Cobalt-60 absorbed dose rate to water calibration system
( 1 ) Ionization chamber method :
NRSL-INER employed cobalt-60 gamma ray source and air cavity ionization chamber to establish the absorbed dose rate to water calibration system. The measurement principle is based on the definition of absorbed dose rate to water and the Bragg-Gray cavity theory. Measured ionizing charge is generated from Co-60 gamma ray in the air cavity, and then converted to energy imparted according to the W value (33.97 eV / i.p.). Under 5 cm depth below the water surface, the air-kerma rate at the reference point in the calibration field is determined with appropriate corrections based on the environment measurement and perturbation evaluation.
( 2 ) Calorimetry method :
The graphite calorimeter system is used to evaluate the very slight temperature change caused by radiation to determine absorbed dose rate to water of the reference point in the calibration field. With constant-temperature operating mode, the measured value also considers the conversion factor of graphite-water ratio and perturbation corrections.
3. X-ray air kerma rate standard
3.1 medium energy X-ray air kerma rate calibration system
The X-ray is produced by using the medium energy X-ray machine with tungsten target , and then the X-ray filter is adjusted to produce appropriate X-ray spectrum. The measuring principle is based on the definition of air-kerma , measure the charge of the free air chamber generated by the ionization of medium energy X-ray, and then the charge is converted to the amount of energy according to the W value (33.97 eV / i.p.). Making appropriate corrections based on the measurement of the environment, radiation attenuation and other perturbations to determine the air-kerma rate at the reference point in the calibration field.
3.2 low energy X-ray air-kerma rate calibration system
X-ray is produced by X-ray machine with tungsten target, molybdenum target or rhodium target, and then X-ray filter is adjusted to produce appropriate X-ray energy spectrum. The measuring principle is based on the definition of air-kerma , measure the charge of the free air chamber generated by the ionization of low energy X-ray, and then the charge is converted to the amount of energy according to the W value (33.97 eV / i.p.). Making appropriate corrections based on the measurement of the environment, radiation attenuation and other perturbations to determine the air-kerma rate at the reference point in the calibration field.
4. X-ray tube voltage standard
Standard establishment of X-ray tube voltage is that the tube voltage is divided to below one thousandth of the original voltage of X-ray high-voltage generator through the high voltage divider, and then use the precision meter to measure the divided voltage value. Instruments will be placed on the rack, and then irradiated with X-ray to compare the difference between the standard value and measured value, and get the calibration factor.
5. Reference air kerma rate (RAKR) calibration system for high dose rate Ir-192 brachytherapy sources
Ir-192 sources are popular used in brachytherapy and around seven thousand man-times uses the high dose rate (HDR) Ir-192 brachytherapy source per year in Taiwan. To establish the primary measurement stand of reference air kerma rate for the HDR Ir-192 brachytherapy sources in Taiwan, the Institute of Nuclear Energy Research (INER) fabricated a dual spherical graphite-walled cavity ionization chambers system to direct measure the reference air kerma rate (RAKR) of the Ir-192 brachytherapy source.
In this system, the ion-charge were accumulated by the two cavity ionization chamber and made appropriate. The reference air kerma rate of the Ir-192 source was obtained in the ambient conditions of 22 ℃ and one atmosphere. The measurement uncertainty of this system is within 1% in 95% confidence level (k=2.0).
6. Neutron dose rate calibration system
The neutron emission rate of Cf-252 source and Am-Be source was calibrated by NIST in the United States and NPL in the United Kingdom, respectively. This neutron ambient dose equivalent calibration system was based on ISO 8529 standard, we used shadow cone method to calibrate neutron detector. The measurement uncertainty was about 2.3%. The neutron personal dose equivalent rate was based on the recommendations of the HPS N13.11 specifications. The measurement uncertainty was about was 4.6%.
7. Beta dose rate standard
INER established a tissue-equivalent extrapolation chamber as a primary standard system for the dosimetry and calibration of beta radiation sources and detectors. Using the extrapolation chamber, and in accordance with the Bragg-Gray cavity theory and polyethylene terephthalate absorption plate attenuation experiments, the absorbed dose rate to tissue for Beta Radiation is determined from the ionization density in a small air gap, the extrapolation chamber volume, embedded in tissue equivalent material (PMMA). The standardized procedures were adopted to determine absorbed dose rate to tissue for depths of 0.07 mm that are recommended by ISO 6980.
8. Radioactive liquid gamma source activity calibration system
( 1 ) Radionuclide specific activity calibration：
Specific activity is the activity per quantity of a radionuclide and is a physical property of that radionuclide. We measured the specific activity by using the properties that the radionuclide released the gamma radiation, such as Cs-137, Re-188, F-18, Ga-67.
( 2 ) Radionuclide gross activity and dose calibrator calibration：
Activity is a quantity related to radioactivity. We measured the gross activity and dose calibrator calibration by using the properties that the radionuclide released the gamma radiation, such as Cs-137, Re-188, F-18, Ga-67.
9. Radionuclide particle emission rate calibration system
The system provide α or β particle emission rate calibration for the large area source, this kind of the source is mainly applied for detection efficiency calibration of survey meter to ensure the radiation safety in our environment.