1995 Fiscal Year Final Research Report Summary
Liquid Ar Ionization Chamber for Isotope Identification of heavy ions with the energy of 100 MeV/n
Grant-in-Aid for Developmental Scientific Research (B)
|Allocation Type||Single-year Grants |
|Research Institution||Waseda University |
DOKE Tadayoshi Waseda University, Advanced Research Institute for Science and Engineering, Professor -> 早稲田大学, 理工学総合センター, 顧問研究員 (60063369)
MASUDA Kimiaki Nagoya University, STE-Institute, Assistant Professor, 助教授 (40173744)
SHIBAMURA Eidou Saitama College of Health, Professor, 教授 (30100605)
TANIHATA Isao Riken Institute, Linear Accelerator Laboratory, Chief Staff of the Laboratory, リニアック研究室, 主任研究員 (10089873)
|Project Period (FY)
1994 – 1995
|Keywords||allene / liquid Ar / Ionization chamber / identification of isotopes / energy resolution / recombination of electron-ion pairs / Bragg Curve spectrometery|
Until recently, it has been considered that liquid Ar is not suitable as detector medium of ionization chamber for heavy ions because high density of electron-ion pairs were produced along a heavy ion track and a considerable fraction of the electron-ion pairs recombines even if some electric field is applied. In the recombination, however, many vacuum ultra violet (VUV) photons are produced. therefore, if liquid Ar includes a small amount of organic molecules which have high photo-ionization cross section, the emitted VUV photons are absorbed by the molecules and new electron-ion pairs are produced by photo-ionization effect of the excited molecules. As a result, the electron collection yield in liquid Ar ionization chamber increases even for heavy ions. From this view-point, the response of a small allene doped liquid Ar ionization chamber were measured for O,Al and Xe of the energy of 23-34 MeV/n. The result shows that the energy resolutions for O and Al ions are better than 1% but
that for Xe ions is 1.7%. The latter value is considered to be caused by the energy loss fluctuation in passing of Xe ions through the window material. On the basis of this experiment, we have been constructed an allene doped liquid Ar gridded ionization chamber with a sensitive volume of 4.8cm * 4.8cm * 4.0cm and its performances were investigated for O,Ne, Ar and Ca ions with the energy of -100 MeV/n. The results are described by classifying into three following parts.
i) Ar and Ca ions :
As expected, the energy resolution of 0.5% (FWHM) was obtained for Ar and Ca ions. The energy resolution deteriorates with increase in counting rate but it is small compared with that for O and Ne ions which will be described later. For Ar and Ca ions, the 0.5% resolution is kept until about 100 counts per second.
ii) O and Ne ions :
The best energy resolution for these ions was 1% (FWHM) and its counting rate dependency was much larger than that for O and Ne ions. To realize the energy resolution of 1%, the counting rate should be less than 10 counts per second. This counting rate dependence can be explained by reduction of the effective electric field due to space charge effect of positive ions remained in the sensitive region.
iii) Bragg Curve Spectrometry for O and Ne ions :
The wave shape of an anode signal obtained by the amplification system with a small differntial time constant should give a Bragg Curve for an incident ion. In fact, we could obtain such wave shapes for O and Ne ions when the counting rate is less than 10 counts per sec. It was experimentally shown that the identification of element or isotope of ions is possible for O and Ne ions. Less
Research Products (12 results)