The Study on a Secondary Electron Multiplier Tube(III)

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A 12-stage Cu-Be electron multiplier tube was constructed and mounted in the high vacuum mass spectrometer at Osaka University. The following improvements for the construction, comparing with the similar tube previously reported, were made: 1)plane electrodes for deflecting the ion beam injecting the conversion dynode of multiplier were located behind the defining slit, 2)The several dynodes near the top of the tube were covered by a permalloy cylinder for shielding stray magnetic field of the magnet. The output current of multiplier was measured by a vibrating reed electrometer. As the results of the preliminary investigation of multiplier characteristics, the shape and height of mass peaks were found to be considerably affected by the voltage supplying on the deflecting electrodes and the proper voltage depended on the ion energy. The stability of multiplier gain(∼6×103)was fairly sufficient for measuring isotope ratio. For example, the measured 20Ne/22Ne ratio was 10. 563±0.006(not corrected for mass discrimination). At the ultimate pressure in the mass spectrometer, the background mass spectra up to m/e∼150 were recorded and some hydrocarbon fragment peaks corresponding to 10-16-10-18 amps. were found in C2-C7 region. And mass peaks below 10-16 amps. show very fluctuated top, but such statistical fluctuation could be smoothed out by using the amplifying system with sufficiently time constant and low speed scanning. Under such condition, the ion current down to 1-2×10-19 amps. could be detected the noise level of amplifying system.kn-abstract=
日本質量分析学会の論文

The Study on a Secondary Electron Multiplier Tube(III)

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