Minoru Yanokura

Development of heavy ion beam sputtering method for long-lived carbon stripper foils

Abstract A heavy noble gas ion beam sputtering (HIBS) technique was developed to prepare carbon stripper foils with a characteristic of long lifetime. The dependence of lifetimes on the mass of noble gas was also investigated. Compared with foils made by lighter ions such as Ne and Ar, the foils made by Kr and Xe noble gases were not so much stronger mechanically, but were long-lived under bombardment with a 3.2 MeV Ne+ ion beam 3 μA in intensity and 3.5 mm in diameter. The mean lifetime in the case of Kr sputtering gas was around 51 mC, 20 times longer than that of commercially available foils. The key point in producing long-lived foils with Kr or Xe noble gas ions was found to be to decrease the amount of oxygen contaminants as much as possible.

High sensitivity analysis of deuterium in solids by 15N-induced nuclear reactions

Abstract We have found a new method of determining deuterium in solids by the use of the following15 N-induced nuclear reactions: 2 H ( 15 N, p γ) 16 N 7.13 → s16 O and 2 H ( 15 N, n γ) 16 O . The energetic gamma-rays from the excited states of the 16 O (E γ = 6013, 7.12 MEV ) are measured. This method gives the high sensitivity of 1018 at. cm−3 and is practically free from any interference even in the presence of hydrogen. These are not resonance reactions and thus cannot be applied to depth profiling. Results are reported for this method applied to the tracer study of hydrogen in various solids.

Studies of a‐Si:H growth mechanism by Rutherford recoil measurement of H and D in films prepared from SiH4‐D2 and SiD4‐H2

a‐Si:H films were prepared by rf glow discharge in SiH4‐D2 or SiD4‐H2 mixtures and analyzed for H and D by Rutherford forward recoil measurement in order to study its growth mechanism. In a low power rf discharge, more H atoms than D atoms were incorporated in the a‐Si:H film even in the SiH4(1 vol)‐D2(4 vol) mixture. With increase in the rf power, the H to D ratio in the film approaches the ratio in the gas for rf power ranges relatively high in our experiment, but is usual in practical production of a‐Si:H. The two ratios were found to be almost equal, independent of the gas composition.

The (p, n) Reaction on 209Bi and Pre-Compound Process

Cross sections and mean projected ranges of the recoil ions for 209 Bi( p , n ) reaction with E p from 18 MeV to 64 MeV were obtained. The cross sections were analysed both by the hybrid model and by the geometry dependent hybrid model. The geometry dependent hybrid model was found to reproduce the experimental ( p , n ) cross sections upto E p of 64 MeV, while the calculated cross sections by the hybrid model deviate from the experimental ones at the proton energies higher than 40 MeV. Dependence of decay rates of the exciton states on the nuclear density was discussed and it was concluded that the pre-compound model is essentially concerned with averaging of the doorway states. Recoil ranges of the reaction residuals were analysed, introducing a 90° asymmetry term P 1 (cos θ) for the angular distributions of the residuals in CM system.

Origin of hydrogen in amorphous silicon produced by glow discharge in Si2H6+D2 and Si2D6+H2

Hydrogenated amorphous silicon was grown from disilane by rf glow discharge. Deuterium (D) was used as a tracer gas in this investigation, in which two gas mixtures (Si2H6+D2 and Si2D6+H2) were employed. Amorphous silicon so produced was analyzed for 1H and D by Rutherford recoil measurement to determine whether these elements came from disilane or dilution gas. When the rf power is low, a much larger proportion of hydrogen atoms in disilane (1H in case of Si2H6, D in case of Si2D6) than in the dilution gas is found in the amorphous silicon. The exact reverse is true as the rf power becomes large.

Production of 119mSn by alpha particle bombardment of 116Cd and its carrier-free separation

Abstract The production method of high specific 119 m Sn was studied by using the reaction of alpha particles with enriched cadmium. The excitation function for the 116 Cd( α , n ) 119 m Sn reaction and its thick-target yields were investigated with the stacked foil technique at the incident alpha particle energy of 25 MeV. When the incident alpha particle energy of 20 MeV was chosen, 0.1 μCi/μA·h of 119 m Sn could be produced at the end of bombardment. The procedure for the carrier-free separation of tin activity from the cadmium target and the copper backing by coprecipitation, organic solvent extraction and anion exchange is described.

Isotopic Dependence of the Strongly Damped Events in the 115 MeV Nitrogen Induced Reactions on Nickel

The heavy-ion reactions induced by 115 MeV 14 N ions on 58 Ni and 64 Ni were investigated by a Δ E - E gas counter telescope. The yields of the strongly damped events ( Z ≧10) were found to be twice to three times larger for the 14 Nl+ 58 Ni system than for the 14 N+ 64 Ni system. This isotopic effect was observed not only for the products that exhibit the 1/sin θ distributions but also for those with forward-peaked angular distributions.

Depth and State Analyses of Deuterium and Helium in D2-Annealed He+-Implanted Yttrium Iron Garnet

Simultaneous depth analysis of deuterium and helium in the surface layer of deuterium-annealed He+-implanted yttrium iron garnet (YIG) was achieved by means of elastic recoil depth analysis (ERDA) and the results were compared with those of state analysis of deuterium and helium extracted by thermal desorption mass spectrometry (TDS). As a result, it was shown that both deuterium and helium moved to the strained lattice sites due to implantation via thermal annealing of the samples. By annealing the critically helium-saturated sample, helium atoms remained at the stable sites in the lattice, while deuterium occupied the less stable sites. Stabilization of helium sites at annealing temperature of around 350° C was observed for unsaturated and critically saturated samples. In the case of an oversaturated sample, three kinds of sites for helium were found, and it was observed that helium formed bubbles and that deuterium concentrated at sites corresponding to those of helium via annealing.

A new technique for the preparation of very high purity enriched 100Mo disk targets

Abstract For a source of double beta-decay neutrino experiments, very high purity enrichied 100 Mo disk targets 50–80 mg/cm 2 in thickness and 30 mm in diameter were developed by using a new technique with sintering. The disk targets prepared by this method were strong enough to withstand mechanical shocks and also satisfactorily uniform in thickness.

Thermal-neutron induced fission of 226Ra

226Ra was irradiated by thermal neutrons, and fission events in coincidence were searched for by using two surface-barrier detectors placed face-to-face to each other. No meaningful number of events could be observed, and the upper limit for the fission cross section was set to be of the order of a few microbarns. The reason for the disagreement with the previously reported value (0·46 m.b.) determined by the fission track method is not clarified yet.