1988 Fiscal Year Final Research Report Summary
Development of a small mass spectrometer for K-Ar dating with a low-cost
| Project/Area Number |
62840026
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| Research Category |
Grant-in-Aid for Developmental Scientific Research
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Earthquake Research Institute, University of Tokyo |
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Principal Investigator |
KANEOKA Ichiro Associate Professor,Earthquake Research Institute, University of Tokyo, 地震研究所, 助教授 (30011745)
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| Project Period (FY) |
1987 – 1988
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| Keywords | K-Ar dating / Small mass spectrometer / Ar isotope analyses / Movable mechanisms for the ion-source part and the collecotor part / イオン・コレクター / 移動機構 / 二次電子増倍管 |
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| Research Abstract |
Through this project, i have developed a small mass spectrometer which is mainly used for K-Ar dating and produced with a relatively low-cost in comparison with a commercial one. The machine should have a sufficient precision in Ar isotope analyses for precise K-Ar dating, but it does not require high cost and should be compact as much as possible.
To fulfil such conditions, a Dempster-type mass spectrometer(6cm radius, 180゜) wa planned, which is used in static mode. It is also equipped with movable mechanisms for the ion-source part and the ion-collector part from the outside, respectively.
The produceed mass spectrometer shows a good peak shap with a complete flat-top and a resolving power of about 70 at 1% valley of the peak. The movable mechanisms for the ion-source part and the ion-collector part seem to work effectively. A rhenium ribbon is used for the filament to ionize an atom. 70V is applied as the potential to ionize an atom. In a normal mode, a Farady-cage is used to detect ions. With the emission current of 3.2mA, the obtained sensivity for the ion-source is_<40> estimated to be about 2x10^<-4>A/Torr. To measure very small amount of radiogenic Ar as is observed in basic volcanic rocks with an age of less than 1Ma, the sensitivity is not sufficient enough to get precise values. To overcome this defficiency, an ion collector with both a Farady-cage and a secondary electron multiplier has been developed. Such an ion-collector would be useful for measuring Ar isotopes with a wide range of ar quantity.
With the addition of a micro-computer system, more precise analyses will be made thorugh the controlling of the mass spectrometer and the data acqusition and reduction systems, though some addidional budget is required to purdhase it.
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