Argon/propane ionization-chamber dosimetry for mixed x-ray/neutron fields.

Area of Science:

• Medical Physics
• Radiation Oncology
• Health Physics

Background:

• High-energy X-ray machines generate photoneutrons that can bypass typical radiation shielding.
• Measuring neutron dose in the presence of X-rays is challenging due to a lack of standardized methods.
• Photoneutrons can penetrate maze structures and lead-lined doors, posing a radiation hazard.

Purpose of the Study:

• To develop a method for separating X-ray dose from neutron dose.
• To accurately measure neutron dose equivalent in a mixed radiation field.
• To inform the design of effective radiation shielding for high-energy X-ray facilities.

Main Methods:

• Utilized an ionization chamber filled alternately with argon or propane to distinguish between X-ray and neutron radiation.
• Characterized the response of the ionization chamber to both X-rays and neutrons.
• Calculated the neutron spectrum to determine quality factors for dose equivalent estimation.

Main Results:

• Successfully differentiated between X-ray and neutron contributions to the total dose.
• Established a method for measuring neutron dose equivalent in mixed radiation fields.
• The measurements indicated the need for enhanced shielding against photoneutrons.

Conclusions:

• A novel ionization chamber technique effectively separates X-ray and neutron doses.
• The findings support the implementation of additional shielding to mitigate photoneutron exposure.
• A 10-inch polyethylene door was added to a 25-MV linear accelerator treatment room entrance based on these results.