We used a pulsed 14 MeV neutron generator (NG) to acquire two concurrent gamma-ray spectra induced by inelastic neutron scattering (INS) and thermal neutron capture (TNC) in Si, O, and C, which are key elements in soil analyses. These separate spectra were acquired by gating the data acquisition system during the neutron pulse, to obtain an INS spectrum, and in between the neutron pulses, to obtain a TNC spectrum. Despite this separation, TNC gamma rays are still counted in the INS window due to the steady state achieved in the former reaction. With the NG operating at 10 kHz and a 25% duty cycle, the magnitude of the single-escape gamma rays from the Si 4.93 MeV gamma-ray peak in the TNC spectrum to the 4.43 MeV carbon region in the INS spectrum is 10.1% of the 4.93 MeV peak intensity. This percentage depends on the neutron repetition rate and duty cycle. It can be reduced to 4.9% by using a narrower gate-pulse that closely fits the neutron burst. We also show that under these conditions the net count rate in the individual peaks of soil elements, Si and O (6.13 MeV) of the TNC spectrum reaches a steady state between the neutron pulses, but the total count rate from the entire spectrum does not.
Life on Earth is characterized by a select group of low Z elements: C, H, N, O, P, K, S, Na, Cl. The presence of these elements and their ratios can provide indications of possible biogenicity and thus they may constitute valuable biomarkers that may help determine the best locations to seek more definitive evidence of life. We discuss the possible applications and significance of the inelastic neutron scattering induced gamma spectroscopy (INSGS) for future Astrobiology Missions to Mars or other solar System bodies. The general
requirements and capabilities of the proposed approach are presented.
Gamma-Ray Resonant Absorption (GRA) is an automatic-decision radiographic screening technique that combines high radiation penetration with very good sensitivity and specificity to nitrogenous explosives. The method is particularly well-suited to inspection of large, massive objects (since the resonant γ-ray probe is at 9.17 MeV) such as aviation and marine containers, heavy vehicles and railroad cars. Two kinds of γ-ray detectors have been employed to date in GRA systems: 1) Resonant-response nitrogen-rich liquid scintillators and 2) BGO detectors. This paper analyses and compares
the response of these detector-types to the resonant radiation, in terms of single-pixel figures of merit. The latter are sensitive not only to detector response, but also to accelerator-beam quality, via the properties of the nuclear reaction that produces the resonant-γ-rays. Generally, resonant detectors give rise to much higher nitrogen-contrast sensitivity in the radiographic image than their non-resonant detector counterparts and furthermore, do not require proton beams of high energy-resolution. By comparison, the non-resonant detectors have higher γ-detection efficiency, but their contrast sensitivity is very sensitive to the quality of the accelerator beam. Implications of these detector/accelerator
characteristics for eventual GRA field systems are discussed.
The study of root growth and development in soil has been intellectually and technically challenging. In response to concern about increasing levels of atmospheric carbon dioxide (CO2), resulting from increase in global energy use, the cycling of carbon has become the object of many intensive investigations.. Terrestrial ecosystems are a huge, natural biological scrubber for CO2 currently sequestering, directly from the atmosphere, about 22% of annual anthropogenic carbon emissions. It is assumed that a significant fraction of this carbon uptake goes into roots. Presently, there are no means by which root morphology, distribution, and mass can be measured without serious sampling artifacts that alter these properties. This is because the current methods are destructive and labor intensive. A non-invasive, imaging procedure for examining roots in situ would be a powerful tool quantifying subsurface storage, as well as for documenting changes in root structure. Preliminary results using a high frequency, 1.5 Ghz, impulse Ground Penetrating Radar (GPR) for nondestructive imaging of tree root systems in situ are presented. Two 3D reconstructed images taking advantage ofthe polarization effect are used to assess root morphology and dimensions. The constraints, limitations, and potential solutions for using GPR for tree root systems imaging and analysis are discussed.
Predictions of global energy use in this century suggest a continued increase in carbon emissions and rising concentrations of carbon dioxide (CO<SUB>2</SUB>) in the atmosphere. This represents a serious environmental problem and contributes significantly to greenhouse gases that affect global warming. Terrestrial ecosystems are a huge natural biological scrubber for CO<SUB>2</SUB> currently sequestering, directly from the atmosphere, about 25% (approximately 2 GtC) of the 7.4 Gt of anthropogenic carbon emitted annually into the atmosphere. The major carbon pathways into soil are through plant litter and roots. Presently, there are no means by which root morphology, distribution, and mass can be measured without serious sampling artifacts that alter these properties. The current methods are destructive and labor intensive. Preliminary results using a high frequency, 1.5 Ghz, impulse Ground Penetrating Radar (GPR) for nondestructive imaging of tree root systems in situ are presented. The 3D reconstructed image is used to assess root morphology and dimensions. The constraints, limitations, and potential solutions for using GPR for tree root systems imaging and analysis are discussed.