scCVD Diamond Detector Response to Fast Neutrons and γ-Rays at Cryogenic Temperatures

The response of a single crystal chemical vapor deposition (scCVD) diamond detector was studied with 14.1 MeV neutron and 440 keV $\gamma $ -rays from room temperature down to 46 K. Induced charge in the detector was acquired using both a charge and current sensitive preamplifier to analyze the charge collection efficiency (CCE) and transient current technique (TCT) profiles. A similar decreasing trend of the detector CCE was observed for all types of radiation, however, with different critical temperatures and magnitudes. The detector CCE for 440 keV $\gamma $ -rays decreased to 86.2% ± 0.5% while at 70 K, the CCE for neutrons was at 50%. The final magnitude of the detector CCE decrease for neutron radiation could not be calculated since the signal was indistinguishable from the background below 70 K. The pulse shapes of the TCT were also investigated for both neutron and $\gamma $ -rays. Pulse shapes along with discrimination techniques were benchmarked with datasets acquired at 120 and 55 K. Discrimination between neutron and $\gamma $ -ray TCT pulse shapes was achieved at 120 K, however, due to the low signal-to-noise ratio (SNR) of pulses at 55 K, discrimination was not possible. The drop in the CCE at low temperatures decreases the SNR which increases the impact of noise on the shape of the signal, and consequently, sets a lower limit to the detectable neutron energy.