Energy dependent response of plastic scintillation detectors to photon radiation of low to medium energy

• Published in: Medical physics (Lancaster) Vol. 43; no. 8; pp. 4598 - 4606
• Main Authors: Ebenau, Melanie, Radeck, Désirée, Bambynek, Markus, Sommer, Holger, Flühs, Dirk, Spaan, Bernhard, Eichmann, Marion
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-08-2016
• Subjects: 60 APPLIED LIFE SCIENCES; AIR; BC400; Calibrating of instruments or apparatus; CALIBRATION; COBALT 60; Cobalt Radioisotopes; Computer Simulation; COMPUTERIZED SIMULATION; dosimetry; Electromagnetic radiation detectors; Electrons; ENERGY ABSORPTION; ENERGY DEPENDENCE; Energy Transfer; Error analysis; KERMA; Measurement of nuclear or x‐radiation; Models, Theoretical; MONTE CARLO METHOD; Monte Carlo methods; Phantoms, Imaging; PHOTONS; plastic scintillation detector; PLASTIC SCINTILLATION DETECTORS; PLASTIC SCINTILLATORS; Plastics; Plates or blocks in which tracks of nuclear particles are made visible by after‐treatment, e.g. using photographic emulsion, using mica; Polyvinyls; Position sensitive detectors; QUENCHING; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; RADIATION QUALITY; radiation therapy; Radiometry - instrumentation; Radiometry - methods; Scintigraphy; Scintillation Counting - instrumentation; Scintillation Counting - methods; Scintillation detectors; Secondary emission; solid scintillation detectors; Standards and calibration; Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00; the detector being a crystal; the detector being a liquid; the detector being made of plastics; Toluene; Tubes for determining the presence, intensity, density or energy of radiation or particles; Uncertainty; WATER; Water vapor; with semiconductor detectors; x‐ray; BC400; dosimetry; x-ray; energy dependence; plastic scintillation detector
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4957348

Purpose:
Plastic scintillation detectors are promising candidates for the dosimetry of low- to medium-energy photons but quantitative knowledge of their energy response is a prerequisite for their correct use. The purpose of this study was to characterize the energy dependent response of small scintillation detectors (active volume <1 mm3) made from the commonly used plastic scintillator BC400.
Methods:
Different detectors made from BC400 were calibrated at a number of radiation qualities ranging from 10 to 280 kV and at a 60Co beam. All calibrations were performed at the Physikalisch-Technische Bundesanstalt, the National Metrology Institute of Germany. The energy response in terms of air kerma, dose to water, and dose to the scintillator was determined. Conversion factors from air kerma to dose to water and to dose to the scintillator were derived from Monte Carlo simulations. In order to quantitatively describe the energy dependence, a semiempirical model known as unimolecular quenching or Birks’ formula was fitted to the data and from this the response to secondary electrons generated within the scintillator material BC400 was derived.
Results:
The detector energy response in terms of air kerma differs for different scintillator sizes and different detector casings. It is therefore necessary to take attenuation within the scintillator and in the casing into account when deriving the response in terms of dose to water from a calibration in terms of air kerma. The measured energy response in terms of dose to water for BC400 cannot be reproduced by the ratio of mean mass energy-absorption coefficients for polyvinyl toluene to water but shows evidence of quenching. The quenching parameter kB in Birks’ formula was determined to be kB = (12.3 ± 0.9) mg MeV−1 cm−2.
Conclusions:
The energy response was quantified relative to the response to 60Co which is the common radiation quality for the calibration of therapy dosemeters. The observed energy dependence could be well explained with the assumption of ionization quenching as described by Birks’ formula. Plastic scintillation detectors should be calibrated at the same radiation quality that they will be used at and changes of the spectrum within the application need to be considered. The authors results can be used to evaluate the range of validity of a given calibration.