The authors have developed a method to produce a microbeam of slow highly charged ions based on a self-organized charge-up inside a tapered glass capillary. A transmission of 8 keV Ar 8+ beam through the capillary 5 cm long with 800/ 24 m inlet/outlet inner diameters was observed stably for more than 1200 s. The transmitted beam had the same size as the outlet with a beam density enhancement of approximately 10 and a divergence of ±5 mrad. The initial beam was guided through a capillary tilted by as large as ±100 mrad, and it still kept the incident charge.

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Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.

Using a photon-ion merged-beam technique, we measured the relative yield spectra of Xe 2+ and Xe 3+ ions created by photoionization of Xe + ions as a function of the photon energy in the 4d ionization region. The Xe 3+ ion production, i.e. the double-electron ionization process is found to be dominant throughout the energy range investigated. A broad structure of 4d excitation ionization around 100 eV photon energy was observed in the Xe 3+ yield spectrum. A spectral shoulder was observed for Xe 3+ at around 85 eV, which was absent in the photoionization of neutral Xe. Some discrete lines were observed for both the Xe 2+ -and Xe 3+yield spectra below 75 eV. The experimental spectra were analysed by a multiconfiguration Dirac-Fock calculation. The largest structure at around 100 eV is attributable to 4d 10 5s 2 5p 5 → 4d 9 4f5s 2 5p 4 np (n = 6, 7) two-electron transitions. The discrete lines were found to be due to 4d → np, nf transitions. A serious 4f-orbital collapse is suspected in the 4fnp two-electron excited states, whereas the collapse is moderate in the singly excited 4f-orbitals.

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We made a new type of collagen gel by gamma-ray irradiation of an acidic solution of type-I collagen, and performed comparative studies on a conventional gel and the new type of gel. The neutral gel, a conventional 0.3% (w/v) collagen gel, was formed at neutral pH and then irradiated by gamma-rays. The acidic gel, a 0.3% (w/v) collagen gel, was formed directly from the acidic solution of collagen by y-ray irradiation. Both types of gel were prepared, swollen in water and then dried for the measurement of specific water content. The neutral gel showed a relatively high specific water content and shrunk moderately, depending on the dose, while the acidic gel showed lower specific water content and shrunk clearly by y-ray irradiation. A three-dimensional tangled network of microfibrils was clearly observed in the neutral gels by scanning electron microscopy, but not in the acidic gels. From these results, we concluded that the acidic gel was quite different from a conventional collagen gel. Sodium dodecylsulfate-polyacrylamide gel electrophoresis showed that the alpha1 subunit and alpha2 subunit of the collagen molecule were cross-linked. The triple-helical structure of collagen was only partially perturbed, but not denatured completely, because the circular dichroism spectrum of the collagen solution irradiated at 1.3 kGy was similar to that of native collagen solution. Amino-acid analysis revealed that tyrosine, phenylalanine and histidine decreased by irradiation in the neutral gel. In the case of the acidic gel, these three amino acids and methionine decreased. We considered that these amino acids were cross-linking points between the collagen subunits during the gamma-ray irradiation.

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A new positron accumulation scheme compatible with ultrahigh vacuum conditions has been developed, which is realized by preparing a high density electron plasma as high as approximately 10(11) cm(-3) and an ion cloud as energy absorbers. The present accumulation rate normalized by the intensity of 22Na positron source is (3.6+/-0.3)x10(2)e(+)/s/mCi, which is more than one and a half orders of magnitude higher than other ultrahigh vacuum compatible schemes so far reported.