Y. Kamata, T. Takeshima, T. Okada, K. Terada
We present the results of an analysis by ASCA (Japanese X-ray astronomysatellite) observation of the lunar surface on July 10th - 11th, 19 93. Inspite of the fact that the X-ray surface brightness is estimated to be atnearly CXB (Cosmic X-ray Background) level, the X-ray spectrum showss ignificant deviations in relation to Al-K¿ and Si-K¿fluorescence X-rays. According to the intensity ratios of Al/Si (1-2) andMg/Si (<0.4), t he properties of the X-ray spectrum is consistent with anintermediate abunda nce ratio between highlands and mares (or relativelysimilar to highland valu es). However, the X-ray illuminated region on thelunar surface are mainly co vered with mare regions and the emission of Al-Kand Si-K fluorescence arises from both day side and night side region of themoon. These facts indicate t he existence of X-ray production due tobremsstrahlung, with high energy part icles impacting even on the night side.