H. Yonezawa

Production of the radioisotope88Y

Carrier-free88Y radioisotope, which has the longest half life /T=106.6 d/ of yttrium radioisotopes and is a γ-ray emitter, was obtained by proton irradiation of strontium, followed by cooling for one month. Then,88Y was purified by precipitating strontium as strontium nitrate and extracting yttrium with tri-n-butyl phosphate /TBP/. The decontamination factor of strontium to yttrium was more than 4×103 and chemically pure yttrium radioisotope was obtained.

Charged particle activation analysis of light elements at sub-ppb level

We have developed charged particle activation analysis to determine light elements at a sub-ppb level. This analytical method is characterized by sample bombardment with charged particles at a few tens of mA and substoichiometric separation for13N,11C and18F within two half-life times and with decontamination factors of more than 108. Nuclear reactor interference is also estimated with this method. This analytical method is confirmed to be useful for characterizing highly purified materials from analytical results for boron, carbon, nitrogen and oxygen in Nb refined by the floating zone melting method.

Substoichiometric precipitation of nitrogen as ammonium tetraphenylborate for deutron activation analysis

The radiochemical separation of nitrogen was studied for the determination of ultra trace carbon in gallium arsenide by deutron activation analysis using the12C/d, n/13N reaction. It is based on steam distillation as ammonia and successive substoichiometric precipitation as ammonium tetraphenylborate. It was found that the decontamination factors of coexistent elements such as72Ga,76As and11Co to13N are enough large to determine carbon as low as 1 ppb in gallium arsenide.

Deuteron activation analysis of carbon in gallium arsenide using substoichiometric precipitation

Ultra trace carbon in gallium arsenide has been determined by deuteron activation analysis. It consists of steam distillation of nitrogen as ammonia and successive substoichiometric precipitation as ammonium tetraphenylborate. It is confirmed that nitrogen is precipitated substoichiometrically as ammonium tetraphenylborate in spite of the various chemical species of13N. The procedure developed was applied to the deuteron activation analysis of carbon in carbon-doped and undoped gallium arsenides. It took 30 minutes from the end of irradiation to the start of the radioactivity measurement. The detection limit of carbon in gallium arsenide was as low as 1 ppb.

Study on the comparator method using substoichiometry

The comparator method using substoichiometry is developed. In the method, the contents of the elements can be determined simultaneously by the measurement of radioactivities of the comparator elements and of simultaneously separated parts of the elements in question. The method is applied to the simultaneous determination of rare earth elements, such as lanthanum, europium and terbium in NBS botanical standard reference materials. It is confirmed that the method is reliable for simultaneous multielement determination.

Deuteron activation analysis of ultra-trace carbon in boron-doped Si single crystals

The charged particle activation analysis of ultra-trace carbon in boron-doped silicon with the12C(d,n)13N reaction has been developed. In order to apply13N substoichiometric separation to determine carbon in silicon, we studied the rapid dissolution of silicon using nitric acid as the13N carrier. Its amounts were as small and definite as possible and the nitrogen oxide gas produced during the dissolution was collected. Silicon was dissolved for 6 min in a mixture of hydrofluoric acid, acetic acid and phosphoric acid, which contained potassium nitrate as the13N carrier and nitrogen oxide was collected in the sodium hydroxide solution. In order to combine the dissolution method with13N substoichiometric separation, the conditions for steam distillation as pre-separation were also refined in relation to increases in the amount of carrier. Nitrogen-13 was separated substoichiometrically after silicon dissolution and steam distillation. This analytical procedure was used to determine carbon in boron-doped CZ−Si. Carbon at 0.7–12.7·1015 atoms/cm3 was determined with good reproducibility. It took less than 30 min to start the radioactivity measurement after the end of iradiation. The detection limit was 2·1013 atoms/cm3 (0.2 ppb).

Substoichiometric determination of yttrium in superconducting oxide ceramics by means of carrier-free radioisotope addition

A substoichiometric analytical method, using a carrier-free radioisotope, is developed for the accurate and precise determination of yttrium. The method is applied to yttrium determination in high-Tc superconducting oxide ceramics. The error of the analytical results is estimated to be within 1%.

Determination of constituent elements in superconducting oxide, BaPb1−x Bix O3

The composition of superconducting oxide, BaPb1−xBixO3 (BPB), was analyzed in order to decide the accurate x value. Oxygen and barium were determined non-destructively by3He and neutron activation analysis. Lead and bismuth were determined by substoichiometric isotope dilution analysis. Precision was within 3%. The x value determined xd, was larger than the initial composition, x.

Neutron activation analysis of iron and copper at 1013–104 atoms·m−2 on silicon wafer surface

The surface concentrations of copper and iron in currently used silicon wafers are lower than 1014 atoms·m−2. To determine such ultra-trace elements accurately by neutron activation analysis, we measured the efficiencies of a well-type Ge detector for59Fe γ-rays and64Cu annihilation γ-rays. We also developed methods for preparing samples for copper and iron analysis including a low-temperature silicon direct-bonding technique. We have applied these techniques to determine copper and iron on the surface of clean silicon wafers, and obtained concentrations of 1013–1014 atoms·m−2.

Alpha-activation analysis of boron on Si surface and in Si and SiO2 films

The effectiveness of charged particle (alpha) activation analysis in determining the content of ion-implanted boron on the surface of Si wafers and the doped boron in epitaxially grown Si film and SiO2 film was evaluated. The method was found to be accurate and precise if interference from surface contamination and the matrix were accounted for and an appropriate standardization method was used.