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

The peak efficiency for photons hitting the frontal surface of a medium volume n-type HPGe coaxial detector is mapped using acutely collimated beams of energies between 31 and 383 keV from a ¹³³Ba radioactive source. Simulated values obtained with the Monte Carlo radiation transport code PENELOPE, using a model that respected actual detector dimensions and physical constants while varying dead-layer thicknesses, allowed us to fit the experimental results in the detector bulk but not near its rim. The spectra of a ¹³⁷Cs source were measured using the detector shielded from the natural background radiation, with and without a broad angle collimator. The corresponding simulated spectra, using the fitted dead-layer thicknesses, underestimate the continuum component of the spectra and overestimate the peak efficiency, by less than ten percent in the broad angle collimator arrangement. The simulated results are sensitive to the photon attenuation coefficients. - Highlights: • Comparison between experiments and Monte Carlo simulations of a HPGe detector. • Peak efficiency for photons hitting the detector edge are not well simulated. • Any dead layer used is not able to reproduce experimental spectrum. • Experiment-simulation agreement changes with modifications Compton cross section. • Better agreement when HPGe is irradiated with off-centered broad angle collimator.