Nonproportionality in the scintillation light yield of bismuth germanate

TL;DR

This study measures the nonproportionality of bismuth germanate (BGO) scintillation light yield at low gamma-ray energies using APDs at cryogenic temperatures, providing data relevant for neutron decay experiments.

Contribution

It provides new measurements of BGO nonproportionality at low energies and under various conditions, aiding detector calibration for neutron decay research.

Findings

Nonproportionality varies with gamma-ray energy and experimental conditions.

Data are consistent across different setups, confirming BGO's behavior at low energies.

Results support improved detector modeling for low-energy gamma-ray detection.

Abstract

We present measurements of nonproportionality in the scintillation light yield of bismuth germanate (BGO) for gamma-rays with energies between 6 keV and 662 keV. The scintillation light was read out by avalanche photodiodes (APDs) with both the BGO crystals and APDs operated at a temperature of approximately 90 K. Data were obtained using radioisotope sources to illuminate both a single BGO crystal in a small test cryostat and a 12-element detector in a neutron radiative beta-decay experiment. In addition one datum was obtained in a 4.6 T magnetic field based on the bismuth K x-ray escape peak produced by a continuum of background gamma rays in this apparatus. These measurements and comparison to prior results were motivated by an experiment to study the radiative decay mode of the free neutron. The combination of data taken under different conditions yields a reasonably consistent picture for BGO nonproportionality that should be useful for researchers employing BGO detectors at low gamma ray energies.