Development of X-ray Generator for Active X-ray Fluorescence Spectroscopy of Future Lunar Landing Mission and Its Contribution to Lunar Science

Abstract

Active X-ray fluorescence Spectrometer (AXS) is designed and developed as an elemental analyzer to induce fluorescence X-rays from rock samples without radioactive sources for future lunar and planetary landing missions in Japan. Pyroelectric crystal is applied for X-ray generator because of its compact package, lightweight, low-power consumption, and radioactive source-free. As the X-ray emission intensity from Pyroelectric X-ray Generator (PXG) is not strong enough to be applied for space missions, we have been developing the PXG with an increased intensity to be used in future lunar and planetary landing missions. In future landing mission to the Moon, several putative landing sites are expected in the Procellarum KREEP Terrane and South Pole-Aitken Terrane, which are interesting for investigating lunar igneous activity and mantle composition, respectively. In this paper, the current status of development and science targets of AXS is reported and discussed.

Electric discharge relevant to pyroelectric spontaneous polarization inducing irreproducibility of pyroelectric x-ray generation

“…Large X-ray counts were measured during the cooling phase, i.e., X-ray emission from the Cu target. This tendency was common in the previous studies 8, [10][11][12] . Some irregular increases and stops of X-ray counts appear in the 1 cm × 5 cm (Fig.…”

“…This effect is large when the crystal is large. Our previous works obtained large X-ray counts with a cylindrical support may be due to these effects 11 .…”

“…The crystals of 4.3 mm × 4 mm and 7.1 mm × 4 mm with the relative permittivity, 46, of LiTaO3 (LT) 13 , were fixed as their bottom center locate at the coordinate origin. The crystal sizes correspond to those which were used in our previous study 10,11 . Targets were assumed as simple conductive plates of 10, 3, and 1 cm plates and 3 cm plate with a 1 mm × 4 mm needle at the distance of 6 mm from the crystal top.…”

Improvements of portable energy dispersive X‐ray fluorescence instrument: Resolution with Silicon Drift Detector, measurements stability using pyroelectric sources, and adaptation for space use

“…Besides, PXG should allow shorter measurement time than radioisotopes: one Amptek COOL‐X is equivalent to 2 mCi source (data from manufacturer) and the geometry of our instrument allows to use 6 PXG. If we use the same geometry but with latest PXG, which is 70 times more intense than COOL‐X, 11 we would have a source equivalent to ~840 mCi, 21 times the activities of the radioisotopes sources onboard APXS 14 instrument on Mars.…”

“…This type of source has already been used in energy dispersive X‐ray fluorescence instruments 9,10 . The use of PXG for planetary XRF instrument has been studied previously with focus on source development 11,12 . The present work uses a commercial source and is focused on the improvement of detector resolution, measurement reproducibility, and peak selection algorithm implementation.…”