Pulsed neutron generator — gamma ray spectrometer measurements of venus elemental composition

Bulk elemental composition measurements are difficult to make on the surface of Venus since all of a lander's instruments have to be housed inside a pressure vessel with sufficient thermal control systems to protect the equipment from the harsh surface conditions (462°C, 93 bars pressure) for at least one hour. The Bulk Elemental Composition Analyzer (BECA) instrument combines a Pulsed Neutron Generator (PNG) with a Gamma-Ray Spectrometer (GRS) placed inside a Venus lander pressure vessel. BECA allows the measurement of the bulk elemental composition over a large volume beneath a landed probe (∼30 cm deep, ∼50 cm radius). The combination of a high intensity PNG (emitting 5×10
⁸
isotropic neutrons per second) and a scintillator GRS with a fast light-decay time (19 ns for CeBr
3
) allows for gamma-ray count rates in excess of 2 MHz. This extremely high gamma-ray throughput is necessary to provide the counting statistics needed for the ∼1 hour measurement times currently available for Venus landers. Preliminary results from experimental measurements of a BECA prototype in a surface configuration are presented to show the precision and accuracy possible with BECA.