Yuji Tazawa

Photon Stimulated Desorption of Positive Ions from LiF

Photon stimulated desorption (PSD) of positive ions from LiF is observed in the photon energy region between 30 and 70 eV. The creation of the Li+(1s→2s) core exciton leads to the rapid rise of both Li+ and F+ desorption yields. It is found that PSD of positive ions from LiF is due to the interatomic Auger transition. The yield spectrum of F+ ions is different from that of Li+ ions above 60 eV. The F+ yield spectrum has a deep valley at around 63 eV, while the Li+ spectrum shows a plateau in the same region. However the difference in the yield spectra of Li+ and F+ ions can not be explained at present.

Photoionization efficiency curves in the threshold region for Bin (n ⩽ 4) molecules

Photoionization efficiency curves for Bin (n ≤ 4) in their threshold region (7.05 to 8.40 eV) have been measured by using synchrotron radiation, which crosses a molecular beam coupled with a time-of-flight mass spectrometer. Resonance lines due to autoionization are observed only for the monomer. The photoionization spectrum of Bi2 shows a depletion of intensity, which indicates a predissociation of Bi2 to Bi+ + Bi. Bi3 and Bi4 show only slowly varying profiles.

Isotopic Fractionation of Magnesium Sputtered by 2 keV He^+ Ions

Mass spectrometric measurement is made to see isotopic fractionation of magnesium caused by bombardment with 2 keV He-ions. A thin layer of magnesium of thickness 100~1000 A is prepared and irradiated with a dose of 1017~1018 ions/cm2. Comparison of mass spectrometric data on bombarded and non-bombarded samples shows an increase of 2% for the isotopic ratio 26Mg/24Mg and 1% for 25Mg/24Mg. The mechanism of enrichment is looked for in the sputtering, and the model of cascade atomic collisions for sputtering is found to give a reasonable explanation.

Status of the Kyoto University AMS system

The status of the Kyoto University accelerator mass spectrometry (AMS) system is described. A sequential injection system with slow cycling has been developed for 14C measurements. The reproducibility in the measurements and the performance of the system have been examined.

Accelerator mass spectrometry at the Kyoto University tandem accelerator

Abstract An accelerator mass spectrometry system based on an 8UDH Pelletron at Kyoto University is described. The terminal voltage was controlled using 13C4+ ions which were dissociated at the terminal from molecular ions of 13CH−. Measured 14 C 12 C ratios show good reproducibility for the AMS system.

Threshold behavior of synchrotron radiation photoionization for Bin (n≤4)

Ionization profiles in the threshold region (7.05 to 8.40 eV) have been measured for Bi n ( n ≤4) by using synchrotron radiation, which crosses a molecular beam coupled with a time-of-flight mass spectrometer. Resonance lines due to autoionization are observed only for monomer. The photoionization spectrum of Bi 2 shows a depletion of intensity, which indicates a predissociation of Bi 2 to Bi + + Bi. Bi 3 and Bi 4 show only slowly varying profiles.

Isotopic compositions of potassium and calcium in magnetic spherules from marine sediments

Abstract Isotopic compositions of potassium and calcium in individual magnetic spherules were determined. No significant anomaly was observed for potassium within twice the statistical error (2σ), although for calcium isotopes enrichments of 46 Ca, 44 Ca and 42 Ca were observed in one spherule. The relative excess of 46 Ca, 44 Ca and 42 Ca in the spherule agrees with the relative yield of spallogenic calcium isotopes observed in iron meteorites. This fact indicates that the enrichment in the calcium isotopes was caused by cosmic ray irradiation of the spherule in outer space.

Radiation damage of the x-ray CCD

We studied the proton damage effects of the x-ray CCD. We have measured x-ray CCD performances after the irradiation of energies at 2 and 9.5 MeV, and confirmed clear degradation of charge transfer efficiency (CTE) and the energy resolution. To recover degraded CTE and the energy resolution, we tried the charge injection technique, and found the improvement of CTI and the energy resolution to be one-quarter and one-third, respectively. We also estimated the energy level of the deep trap, which causes the quantization of the dark current from the radiation-damaged pixels. The trap energy level is about 0.57 eV, or near the center of forbidden band.