Beam calibration of heavy ion telescope on board MIDORI satellite

Abstract

The satellite MIDORI was launched by NASDA for the Earth observation. A Heavy Ion Telescope (HIT) was on board this satellite to observe the galactic cosmic rays and the geomagnetically trapped particles. Geometric factor of HIT is approximately 25 sq cm sr and the observable energy range is e.g. 18 - 53 MeV/nucleon for oxygen. The 40 Ar beam with energy of 95 MeV/nucleon was irradiated to examine the particle identification ability of the HIT. The HIT consists of two Position Sensitive Detectors (PSD) and four pin type detectors. The PSD has 62 mm x 62 mm effective area with 0.4 mm thickness and the pin type detector has circular effective area with diameter of 85 mm and 0.5 mm thickness. A collimator was placed in front of the telescope. The collimator has 5 mm thickness of brass with 13 x 13 grid of narrow holes at 5 mm interval. The histogram of atomic number resolution obtained by a Delta E-E method is shown. The mean charge is 17.9 and the resolution is 0.66. This results demonstrate the satisfactory performance of the HIT. The distortion of PSD with this collimator was examined. From two PSD position information, the particle incidence angle is determined. Mean angle of each corrected case is 20.1 deg and 34.5 deg and the FWHM (Full Width at Half Maximum) is 0.9 deg and 1.3 deg respectively.

みどり衛星はNASDAにより地球観測用として打ち上げらた。重イオン望遠鏡(HIT)をこの衛星に搭載し、銀河宇宙線および地磁気捕獲粒子を観測する。HITの形態係数は約25平方センチメートルsrで、観測可能エネルギー範囲はたとえば酸素に対して18?53MeV/核子である。95MeV/核子のAr-40ビームを照射し、HITの粒子弁別能力を調べた。HITは2つの位置有感検出器(PSD)と4つのピン型検出器からなる。PSDは0.4mm厚さの62mm×62mmの有効面積で、pin型検出器は0.5mmの厚さの直径85mmの円形有効面積である。コリメータは望遠鏡の前面に置かれ、5mm間隔で狭い穴の13×13グリッドの5mm厚さの黄銅である。ΔE-E法による原子数分解能ヒストグラムを示し、平均電荷17.9、分解能0.66を得た。この結果はHITの満足な性能を示す。コリメータによりPSDの歪みを調べた。2つのPSD位置情報から粒子入射角を決定した。補正した平均角は20.1度と34.5度で、FWHM(半値全幅)はそれぞれ0.9度と1.3度である。