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Secondary charged particle equilibrium in 137Cs and 60Co reference radiation fields
R Behrens1, M Kowatari, O Hupe
1Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany. Rolf.Behrens@PTB.de
Radiation Protection Dosimetry
|September 17, 2009
Summary
To ensure accurate dosemeter calibration, a build-up plate (BUP) must be placed directly in front of the dosemeter. Standard ISO geometries often fail to achieve secondary charged particle equilibrium, impacting radiation measurements.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Radiological Physics
Background:
- Photon irradiation of dosemeters at energies above a few hundred keV often lacks secondary charged particle equilibrium due to small beam radii.
- The International Organization for Standardization (ISO) recommends using a polymethyl methacrylate build-up plate (BUP) to address this issue in calibration procedures (ISO 4037-3).
Purpose of the Study:
- To investigate the impact of build-up plate (BUP) thickness and distance from the dosemeter on secondary charged particle equilibrium.
- To evaluate the effectiveness of the geometrical arrangement recommended by ISO 4037-3 for dosemeter calibration.
Main Methods:
- Experimental measurements were conducted to assess the influence of BUP parameters.
- Monte Carlo simulations were employed to calculate particle interactions and equilibrium conditions.
Main Results:
- The study found that the ISO-recommended geometrical arrangement for BUP placement frequently fails to establish secondary charged particle equilibrium.
- Variations in BUP thickness and distance significantly affect equilibrium, particularly at larger source-to-detector distances.
Conclusions:
- The current ISO recommendations for dosemeter calibration may not consistently ensure secondary charged particle equilibrium.
- Optimal placement of the BUP directly in front of the dosemeter is crucial for accurate radiation measurements and calibration.
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