Calibration of Mars Energetic Particle Analyzer (MEPA)

The first Mars exploration mission of China(Tianwen-1)is scheduled to be launched in 2020;a charged particle telescope,the Mars Energetic Particle Analyzer(MEPA),is carried as one of the payloads on the orbiter.The MEPA is designed to measure solar energetic particles(SEPs)and galactic cosmic rays(GCRs)in the near-Mars space and in the transfer orbit from Earth to Mars.Before the launch,the MEPA was calibrated in ground experiments with radioactive sources,electronic pulses,and accelerator beams.The calibration parameters,such as energy conversion constants,threshold values for the triggers,and particle identification criteria,were determined and have been stored for onboard use.The validity of the calibration parameters has been verified with radioactive sources and beams.The calibration results indicate that the MEPA can measure charged particles reliably,as designed,and that it can satisfy the requirements of the Tianwen-1 mission.

Synthesis of 5-methyl-2-(2,4,4,7-tetramethylchroman-2-yl) Phenol as an Impurity in Thymol

[Objectives] To optimize the preparation process of 5-methyl-2-(2,4,4,7-tetramethylchromanyl) phenol(impurity C) and the liquid phase determination method of the impurity, and to provide an important basis for the establishment of material methods and quality control of thymol. [Methods] The 4,7-dimethylcoumarin as the starting material was hydrolyzed by potassium hydroxide to obtain the substance II 5-methyl-2-(1-propylene-2-yl) phenol, and then purified and treated with hydrochloric acid to obtain a pale yellow solid. High-purity main peak was obtained by high-performance liquid phase method, and it was identified as impurity C by ~1H-NMR measurement and spectrum analysis. [Results] After the method was optimized, the synthesis route to the impurity C was simple, and the purity of impurity C was high. The obtained impurity C was confirmed by ~1H-NMR to be a compound 5-methyl-2-(2,4,4,7-tetramethylchromanyl) phenol. The liquid phase detection method was successfully established to identify the compound. [Conclusions] The optimized method is easy to control and the impurity C has high purity and it is expected to provide quality assurance for the study of related substances in the quality control of thymol.