K. Fukumura

Helium-filled proportional counter operated at low temperatures higher than 13 K

Abstract The operation of a proportional counter filled with pure helium gas was examined at low temperatures higher than 13 K. The counter was cooled in a cryostat by using adiabatic expansion of high-pressure helium gas. It was ensured that the counter works stably at temperatures lower than 15 K but it fails to operate at higher temperatures. This counter was applied to the observation of conversion electron Mossbauer spectra.

Hydrogen-filled proportional counter operated at low temperatures and its application to CEMS

Abstract The operation of a proportional counter filled with hydrogen gas was investigated at temperatures between 15 K and room temperature. It was found to work stably at any temperature in this range. This counter was then applied to conversion electron Mossbauer spectroscopy (CEMS).

Operation of a gas-filled proportional counter for CEMS at temperatures between 15–77 K

Abstract A proportional counter was operated by filling purified helium, purified neon and two gas mixtures, He + 5%N2 and He + 10%CO. It was confirmed that these gases and gas mixtures make it possible to operate a proportional counter for the observation of CEMS spectra at any temperature between 1.75–300 K.

Gamma-x ray coincidence Mössbauer measurements

Abstract A new method for Mossbauer measurements is proposed in order to investigate the after effect accompanying the EC decay of 57 Co.

Proportional counter operated at 13–300 K and its application to CEMS

The operation of a proportional counter was investigated at temperatures between 13–300K. It was found that the suitable gases filled in the counter are purified belium at temperatures below 22K, purified neon at temperatures between 22–53K and He+5%N2 or He+10%CO at temperatures above 46 or 47K, respectively. This experimental technique was applied to CEMS with natural iron and with a thin foil of iron oxide.

Cems study of corrosion on iron foil at low temperatures

Conversion electron Mössbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the corrosion of the surface of iron foils, which consists of small particles of γ-Fe2O3. When the average particle sizes of the corroded layer are approximately 4 and 5 nm, magnetic hyperfine splitting was observed in the spectra at 6.3 and 78 K. However, for a corroded layer composed of smaller particles, the splitting was noticed only at 6.3 K. The anisotropy constantK of the small particles was estimated using the magnetic hyperfine fields obtained from the spectra at 6.3 and 78 K.

Magnetic properties of corrosion products investigated by CEMS at low temperatures near 4.2 K

Conversion electron Mössbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the magnetic properties of the corrosion products formed on the surface of iron foils, which consist of small particles of γ-Fe2O3. The growing period of the corroded layer formed in a solution of low oxygen concentration has insignificant influence on the size of particles composing the layer, however, when the corroded layer is grown in a solution of comparatively high oxygen concentration, the particle size becomes large with growing period of the layer.

Cryogenic resonance-electron Mössbauer spectroscopy with a helium-filled proportional counter

Abstract As studied in our previous works, a proportional counter filled with pure helium gas works well at low temperatures near 4.2 K. The helium-filled proportional counter (HFPC) provides us with a new method to detect nuclear radiations at low temperatures. A typical application of this counter is resonance-electron Mossbauer spectroscopy (REMS) at low temperatures (

CEMS measurements at low temperatures with Fe-Implanted sapphire

A single crystal of sapphire was implanted with 100-keV57Fe to a dose of 3.4×1015 ions/cm2. The charge states of iron ions were investigated with the CEMS technique at low temperatures. The formation of the observed charge states Fe2+(1) and Fe2+(2) were elucidated in terms of crystal structure.

Gamma-x ray coincidence Mössbauer spectroscopic study of the aftereffects in sulfate hydrates

The anomalous charge states formed after the electron capture decay, of57Co in FeSO4·H2O and FeSO4·7H2O are investigated using the conventional Mössbauer emission spectroscopy and a gamma-X ray coincidence method. This method is based on the idea that a Mössbauer spectrum observed with the coincidence technique only when K-X rays are emitted is reflected by isolated events with a reduced influence of the Auger-electron self-irradiation. The formation of the anomalous electronic and structural configuration is attributed to the self-radiolysis of the H2O and SO42− ligands in the nearest and the second nearest coordination shells around the decaying atom.