Search

Orbital data indicate that the youngest volcanic units on the Moon are basalt lavas in Oceanus Procellarum, a region with high levels of the heat-producing elements potassium, thorium, and uranium. The Chang’e-5 mission collected samples of these young lunar basalts and returned them to Earth for laboratory analysis. We measure an age of 1963 ± 57 Ma for these lavas and determine their chemical and mineralogical compositions. This age constrains the lunar impact chronology of the inner Solar System and the thermal evolution of the Moon. There is no evidence for high concentrations of heat-producing elements in the deep mantle of the Moon that generated these lavas, so alternate explanations are required for the longevity of lunar magmatism.

Curve fitting is the most utilized technique to measure peak areas in time of flight secondary ion mass spectrometry (TOF-SIMS) spectra. Reliable estimations of peak parameters should be provided. However, there is not currently a reliable method to estimate the half-width of spectral peaks. In this study, we present a method for peak detection in TOF-SIMS spectra, incorporating continuous wavelet transform and curve fitting. The half-width was estimated by derivative spectrometry based on continuous wavelet transform. Accurate parameters of each peak were obtained by subsequent curve fitting. The method was evaluated with simulated and real TOF-SIMS spectra of silicon isotopes. The results showed this proposed method obtained more accurate half-width estimations of spectral peaks. The fitted results also showed that the method has better performance on overlapping peaks and better resistance to noise.

A high spatial resolution and high brightness ion beam from a cold cathode duoplasmatron source and primary ion optics are presented and applied to in-situ analysis of micro-scale geological material with complex structural and chemical features. The magnetic field in the source as well as the influence of relative permeability of magnetic materials on source performance was simulated using COMSOL to confirm the magnetic field strength of the source. Based on SIMION simulation, a high brightness and high spatial resolution negative ion optical system has been developed to achieve Critical (Gaussian) illumination mode. The ion source and primary column are installed on a new Time-of-Flight secondary ion mass spectrometer for analysis of geological samples. The diameter of the ion beam was measured by the knife-edge method and a scanning electron microscope (SEM). Results show that an O 2 - beam of ca. 5 µm diameter with a beam intensity of ∼5 nA and an O - beam of ca. 5 µm diameter with a beam intensity of ∼50 nA were obtained, respectively. This design will open new possibilities for in-situ elemental and isotopic analysis in geological studies.

Sensitive high resolution ion microprobe (SHRIMP) IIe MC has been widely used in the oxygen isotopes analysis of zircon, apatite, calcium carbonate, etc. This study described the procedures for SHRIMP IIe MC high precision O-isotope analysis. We simulated the SHRIMP II secondary extraction system using SIMION and discussed the cause and influence factors of edge effect and X-Y effect in the oxygen isotopes analysis. Higher δ18O precision can be achieved by limiting O-isotope analysis positions to the central region about 10 mm in diameter of the sample mount and ensuring that the target surface roughness is less than 1 µm. The internal precision of single spot of zircon δ18O is better than 0.15‰ (1σ), with external precision better than 0.5% (95% confidence); the internal precision of the single analysis of Carbonate δ18O is better than 0.20‰ (1σ), with external precision better than 0.6‰ (95% confidence).