Results 2016
TASK 1: PERSPECTIVE DETECTORS
The capabilities for neutron activation analysis of planetary substance composition of vacuum-tube and gas-tube based neutron generators have been compared in laboratory environment using the newly created Synchronization and Control Module (SCM) test equipment and the constructed TF-NP-04 test facility. The mass content of the rockforming elements С, O, Fe, Al, Si, N has been shown to be more efficiently estimated from the fast neutron inelastic scattering reactions using an active gamma-ray spectrometer and a gas-tube neutron generator. On the other hand, vacuum-tube neutron generators are more efficient at estimating the elements’ mass content from the gamma-ray lines of neutron activation and radiative neutron capture for elements like H, O, Na, Mg, Al, Si, Са, Cl, Fe, Mn. Based on these findings different kinds of neutron generator have been suggested for the studies of Venus (a gas-tube one) and Mars (a vacuum-tube one).
An additional series of experiments on the TF-NP-04 facility using an industrial gas-tube generator ING-27 with a built-in alpha-particle detector has been planned, which will use the tagged neutrons technology to reduce the intensities of background lines during the rockforming elements’ nuclear gamma-ray line measurements. This series will be included in the project extension application for 2017–2018.
The capabilities for planetary studies of a CeBr3-crystal-based scintillation detector and a high-purity germanium (HPGe) detector have been compared on analog samples of planetary substance under thermal and fast neutron irradiation. In spite of significantly lower energy resolution, the scintillation detector has been shown to be capable of identifying and measuring the basic gamma-ray lines of the primary rockforming elements (H, O, Na, Mg, Al, Si, Са, Cl, Fe) with high statistical significance, which is enough to identify up to 90% by mass of the planetary substance. A low-background gamma-ray spectrometer utilizing the technology of tagged charged particle of galactic cosmic rays for studies of celestial bodies has been proposed for laboratory modeling and testing. This proposal will also be included in the project extension application for 2017–2018.
The performance properties have been tested of rigidized PMTs and proportional neutron counters used in space experiments. The main focus was on noise appearing in the measurement signal under exposure to weak vibrations on board of the spacecraft (microphonic effect). One of the PMTs under test, Hammamatsu R1840, has been found to be prone to the effect under vibrations exceeding 0.07 g amplitude. Following this, special vibration dampers have been designed and tested that may be installed on the instrument mounting points to eliminate the negative impact of vibration on the measuring circuits.
TASK 2: LABORATORY EXPERIMENTS AND MODELING
The “thick target” data have been processed on analog samples of planetary substance under fast neutron irradiation with vacuum-tube and gas-tube neutron generators on TF-NP-04. The measured integral gamma-ray spectra for the analog samples of planetary substance and the gamma-ray line profiles for the primary rockforming elements (H, O, Na, Mg, Al, Si, Са, Cl, Fe) from both CeBr3 and HPGe detectors have been put into the RSF project database along with the program and technique descriptions of the studies performed. Summary tables containing the statistical significance values for the detected gamma-ray lines have also been placed in the database.
The “gamma-station” data on analog samples of planetary substance under thermal neutron irradiation on TF-NP-03 have also been processed. The measured integral gamma-ray spectra for the analog samples of planetary substance from both CeBr3 and HPGe detectors, the list of identified gamma-ray lines with intensity estimates and comparisons to numerical simulations have been put into the RSF project database along with the program and technique descriptions of the studies performed.
TASK 3:PLANETARY SOIL COMPOSITION ANALYSIS
A number of different experiments using the TF-NP-04 facility have been numerically simulated to verify the PSCA-Surface software package, which evaluates the sensitivity of the planetary substance neutron probing for different kinds of neutron generators and stationary high-energy neutron sources for measuring the mass content of the primary rock-forming elements and the inhomogenuity of their distribution in the depth of the surface. Over ten comprehensive simulations have been performed enabling the comparison between numerical simulations and CeBr3 gamma-ray spectrometer measurements for the neutron activated gamma-ray line intensities for the primary rockforming elements (O, Na, Al, Mg, Si, Fe) resulting from the planetary substance irradiation with neutron generator pulses. The neutron probing sensitivity to inhomogenuity in the vertical structure of the surface, primarily with regards to H/H2O, has also been measured. These results will be used in the work on on future gamma-ray spectrometers for Moon and Venus.
The PSCA-Orbit software package has also passed first-time verification based on the TF-NP-03 measurements and the PSCA-Surface-GCR software adaptation. Over 30 comprehensive simulations have been performed enabling the comparison between numerical simulations and and CeBr3/HPGe gamma-ray spectrometer measurements for the neutron radiative capture gamma-ray line intensities for several rockforming elements (Cr, Ti, Si) resulting from the planetary substance analog sample and single-element sample irradiation by thermal neutrons.
Consequently, development and verification of software packages was completed in 2016 that enable the space experiment data processing for gamma-ray and secondary neutron detectors on landers under GCR bombardment (PSCA-Surface-GCR) and high energy neutron irradiation with pulse neutron generators (PSCA-Surface-PNG) using end-to-end numerical simulations of the planetary substance composition. Yet another software package, PSCA-Orbit, has been created to simulate neutron and gamma-ray spectrometers on space orbiters.
PSCA-Surface-DAN, a special adaptation of the PSCA-Surface-PNG software package, has been developed and verified for end-to-end numerical simulations of the DAN experiment on board of the Curiosity rover on Mars. The PSCA-Surface-DAN software allows to estimate the mass content of water and chlorine in martian soils of different types with different structure, density and elemental composition from the experimental data and numerical simulations. This software package is used for water and chlorine content estimation along the whole Curiosity path in the Gale crater. Several unusual areas with individual soil properties, such as active sand dunes, have been also studied in more detail separately.
Numerical simulations of both laboratory tests at TF-NP-04 test facility have been cross-verified with two most used nuclear simulation software packages: Geant4 and MCNPX. While the simulation results closely matched each other, the open-source Geant4 code was found to enable more flexible approaches to nuclear process simulation and higher physical properties variability. Migration of the software packages mentioned above to Geant4 is considered reasonable.