Efficiency as a function of MEQ-CWT for large area germanium detectors using LLNL phantom

Area of Science:

• Nuclear physics
• Occupational health
• Radiation detection

Background:

• Occupational workers exposed to transuranics require accurate lung deposition monitoring.
• Existing lung counting systems need precise efficiency calibration for effective transuranic estimation.
• Germanium detector arrays are crucial for in-vivo low-energy photon detection.

Purpose of the Study:

• To calibrate the efficiency of a germanium detector array for estimating lung-deposited transuranics.
• To investigate the impact of muscle equivalent chest wall thickness (MEQ-CWT) on detector efficiency.
• To determine the optimal energy response for transuranic detection in occupational workers.

Main Methods:

• Efficiency calibration using ²⁴¹Am and ²³²Th lung phantom sets.
• Derivation of MEQ-CWT for varying adipose mass ratios at 59.5, 75.95, and 238.9 keV.
• Calculation of individual and array detector efficiency as a function of MEQ-CWT.

Main Results:

• MEQ-CWT variations (16-40 mm) caused ~40% efficiency change across all energies.
• Array efficiencies ranged from 1.1×10⁻³ to 3.3×10⁻³ depending on energy and MEQ-CWT.
• Maximum detector efficiency was observed at 75.95 keV.

Conclusions:

• Chest wall thickness significantly impacts lung counting system efficiency.
• The germanium detector array shows energy-dependent efficiency, peaking at 75.95 keV.
• Accurate MEQ-CWT assessment is vital for reliable transuranic deposition estimations in occupational health surveillance.