Experimental HPGe coaxial detector response and efficiency compared to Monte Carlo simulations

Area of Science:

• Nuclear Physics
• Radiation Detection and Measurement

Background:

• High-purity germanium (HPGe) detectors are crucial for precise gamma-ray spectroscopy.
• Accurate efficiency calibration is essential for quantitative analysis in nuclear physics applications.

Purpose of the Study:

• To experimentally map the peak efficiency of an n-type HPGe coaxial detector for photons between 31 and 383 keV.
• To validate Monte Carlo simulations (using PENELOPE) against experimental data for detector efficiency.
• To investigate the impact of dead-layer variations and collimation on detector response.

Main Methods:

• Experimental efficiency mapping using a (133)Ba source with acutely collimated beams.
• Monte Carlo simulations with the PENELOPE code, incorporating detector dimensions and varying dead-layer thicknesses.
• Spectral analysis of (137)Cs source measurements with and without a broad angle collimator, shielded from background radiation.

Main Results:

• Monte Carlo simulations accurately fitted experimental results within the detector bulk but showed deviations near the rim.
• Simulated spectra, using fitted dead-layer thicknesses, underestimated the continuum and overestimated peak efficiency by <10% with a broad angle collimator.
• Simulated results demonstrated sensitivity to photon attenuation coefficients.

Conclusions:

• Accurate modeling of detector geometry, particularly near the rim, is critical for precise simulation of HPGe detector efficiency.
• Monte Carlo simulations provide a valuable tool for efficiency mapping, but require careful validation and consideration of subtle physical effects.
• Photon attenuation is a significant factor influencing simulation accuracy in HPGe detector response modeling.