超小型電離箱の飽和特性と極性効果 Saturation Characteristic and Polarity Effect for Very Small Ionization Chambers

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著者

    • 平岡 武 HIRAOKA Takeshi
    • 放射線医学総合研究所 放射線科学研究部 Division of Radiation Research, National Institute of Radiological Sciences
    • 福村 明史 FUKUMURA Akifumi
    • 放射線医学総合研究所 放射線科学研究部 Division of Radiation Research, National Institute of Radiological Sciences
    • 小俣 要 OMATA Kaname
    • 放射線医学総合研究所 放射線科学研究部 Division of Radiation Research, National Institute of Radiological Sciences

抄録

With increasing use of linear accelerators for photon beam radiosurgery, many kinds of very small ionization chambers have been commercially developed. Ion recombination loss and polarity effect are the most important factors to express chamber characteristics. To investigate the characteristics, one parallel plate chamber, six cylindrical and two hemispherical ionization chambers, which had nominal volumes between 0.1m1 and 3μl, were used.<BR>Measurements were made using 10MV X-rays and 70MeV proton beams for saturation characteristics and the polarity effect. The polarity effect as a function of applied voltage was evaluated as the charge ratio for vertical irradiation of the 10MV X-ray beam. All the chambers showed that the effect was less than 5%, except for one chamber which was larger than 50%.<BR>The experimental points of ion collection efficiency measured for all ionization chambers were plotted as a function of d<SUP>2</SUP>/V, where is the gap length and V, the applied voltage. If the ionization density generated in each chamber gas is identical, the experimental values are ideally expressed as one line. The actual values differed for the chambers because their shapes deviated from ideal cylindrical or spherical shapes. It was concluded that the ion recombination correction factor for very small ionization chambers must be determined experimentally for the actual beam to be used.

収録刊行物

  • 放射線医学物理

    放射線医学物理 18(2), 224-229, 1998-06-30

    Japan Society of Medical Physics

参考文献:  3件中 1-3件 を表示

被引用文献:  2件中 1-2件 を表示

各種コード

  • NII論文ID(NAID)
    10003724831
  • NII書誌ID(NCID)
    AA11137895
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    09188010
  • データ提供元
    CJP書誌  CJP引用  J-STAGE 
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