Daisuke Ohsawa

Further developments of series-connected superconducting tunnel junction to radiation detection

One of the promising radiation detection devices for various practical applications is the series-connected superconducting tunnel junction (STJ) detector. In this article, interesting topics of the detectors are described since our previous work: e.g., more than two order higher detection efficiency compared with single STJ detectors, high count rate detection, and position resolution. Detectors were cooled to 0.35–0.4 K by means of a convenient 3He cryostat. The 5.9 and 6.5 keV x rays from 55Fe are separated by a detector specially designed for x-ray detection. The possible count rate of the series-junction detector estimated from the shaping-time constant applied in the measurements is high, e.g., over 104 counts per second. A series-junction detector equipped with a position sensing mechanism has shown a position resolution of about 35 μm in a sensing area with a radius of 1.1 mm. The position resolution of series junctions improves the energy resolution. A new type series-connected STJ detector is al...

Resolution of a position-sensitive proportional-counter with a resistive anode wire of carbon fiber

Theoretical and experimental analyses have been performed to examine the position resolution of a proportional counter with a 7-microm diameter carbon fiber as a resistive anode, which is used to encode one-dimensional positions of incident photons according to the charge-division method. These analyses have clearly shown that the carbon fiber is applicable to the position sensing of the order of 100-200 microm as long as the filled gas is pressurized at near 10 atm.

Secondary Electrons from Water Vapor with the Impact of 6.0 MeV/u He2+ Ions: Atomic Data and their Application to Biomedical Investigations

We measured the energy and angular distributions (7 eV–10 keV and 20°–160°) of secondary electrons produced in collisions of 6.0 MeV/u He2+ ions with water vapor. Binary‐encounter collision peaks were clearly observed at the calculated energies at angles of 3keV. To assess the new cross sections, these values were incorporated in the kurbuc Mont...

A simple crystal spectrometer for low-energy photons emitted from radioactive sources, Part II

Abstract Further developing our previous crystal spectrometer, a new spectrometer has been fabricated for observing lowenergy photons (2–5 keV) emitted from radioactive sources. The absorption of such low-energy photons in air has been diminished by flowing hydrogen gas in a chamber, inside which the spectrometer is mounted. Large background counts caused by electrons from the source have been greatly decreased by a small magnet placed in front of the source. With the present spectrometer, we have succeeded in high-resolution observation of photons of very weak intensity in radiations emitted from the β-active nuclide 35S, i.e., the 2.62 keV Cl K X rays which are emitted as a result of filling up K-holes produced by the K-shell internal ionization and excitation during the β decay of 35S.