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The neutron component of two high-energy photon reference fields
S Röttger1, K Schäler, R Behrens
1Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany. stefan.roettger@PTB.de
Radiation Protection Dosimetry
|August 7, 2007
Summary
The 4.4 MeV photon reference field is contaminated by neutrons, impacting dosemeter calibration. A mixed photon/neutron field was generated for calibrating tissue-equivalent proportional counters (TEPCs).
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Nuclear Physics
Background:
- The ISO 4037 standard 4.4 MeV photon reference field is produced using a carbon-12 target and a proton beam.
- This field is unintentionally contaminated by neutrons from carbon-13 (13C) due to its natural abundance.
- The neutron contamination contributes significantly to the ambient dose equivalent, comparable to the photons themselves.
Purpose of the Study:
- To characterize the neutron spectral fluence in the 4.4 MeV photon reference field.
- To develop a mixed photon/neutron radiation field for calibrating radiation detection instruments.
- To enable accurate calibration of tissue-equivalent proportional counters (TEPCs) using a well-defined mixed field.
Main Methods:
- Production of the 4.4 MeV photon field using the (12)C(p,p')(12)C reaction with a 5.7 MeV proton beam on a thick carbon target.
- Identification and quantification of neutron contamination from the (13)C(p,n)(13)N reaction.
- Generation of a mixed photon/neutron field using a thin CaF(2) + (nat)C target and a 5.7 MeV proton beam at the PTB accelerator facility.
Main Results:
- The neutron component in the 4.4 MeV photon reference field has an ambient dose equivalent of the same order of magnitude as the photon component.
- A mixed photon/neutron field was successfully produced with a high-linear energy transfer (LET) component from neutrons and a low-LET component from photons up to 7 MeV.
- The spectral fluence distribution of the contaminating neutrons was determined, crucial for accurate dosemeter calibration.
Conclusions:
- The neutron contamination in the standard 4.4 MeV photon field necessitates detailed spectral characterization for precise dosemeter calibration.
- The generated mixed photon/neutron field is suitable for calibrating TEPCs, particularly for assessing their response to mixed radiation fields.
- Accurate calibration of radiation detection equipment in mixed fields is essential for reliable radiation protection and measurement.
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