Nobuyuki Hasebe

New two-dimensional position sensitive silicon detector with good position linearity and resolution

Abstract A two-dimensional position sensitive silicon detector (PSSD) with a good linear response, consisting of a square ion-implanted resistive anode with a boundary of an additional resistive-strip electrode, was newly developed. Linearity and resolution for the PSSD were investigated using 40 MeV helium and 95 MeV nitrogen ion beams. The PSSD has an effective area of 45 mm×45 mm, a thickness of 400 μm, a junction capacitance of 500 pF, a surface resistance of the ion-implanted resistive anode of 18 kω□ and a resistance of the strip line of 1.4 kω. The nonlinearities and resolutions (FWHM) of the position were 0.75% and 1.97 mm for 40 MeV helium ions obtained by 6 μs pulse shaping, and 0.47% and 0.71 mm for 95 MeV nitrogen ions obtained by 12 μs pulse shaping, respectively.

Real time measurement of LET distribution in the IML-2 Space-Lab (STS-65)

Abstract The real time monitoring of environmental radiation in the Space-Lab of STS-65 (IML-2: inclination 28.5°, mitude 300 km) has been achieved successfully through the flight by a new silicon detector telescope called “Real time Radiation Monitoring Device” (RRMD). It consists of two 2-dimensional position sensitive silicon detectors and six diode type silicon detectors. In this monitoring, the temporal variation of rates of particle flux, together with the dose equivalent and the LET distribution at three locations in the Space-Lab, were reasonably given in real time. The LET distribution obtained by the RRMD and CR-39 track detectors measured at the same location is in good agreement except at the highest LET region >200 keV/μm and the lowest LET region

CHARGE WAVEFORM OF A NEW TWO-DIMENSIONAL POSITION-SENSITIVE SILICON DETECTOR.

The operation principles of the two-dimensional position-sensitive silicon detector newly developed by Doke et al. were studied using a simple model. This model treats the detector as an area of continuously distributed capacitance C and resistance Rs of position surface layer. A linear relationship can then be obtained between the position of the incident particle and change collected at the contacts of the detector. The kinetics of charge collected at corner contacts, ballistic deficit and noise were calculated. Rise time of the charge pulse (10–90%) was found to vary with the position of incidence up to about RsC/8. It was found that a shaping time constant longer than RsC/3 is required for pulse shaping with single CR-differentiation and single CR-integration in order to obtain a ballistic deficit of less than 1%.

A New Silicon Detector Telescope for Measuring the Linear Energy Transfer Distribution over the Range from 0.2 to 400 keV/µm in Space

A new telescope consisting of three two-dimensional position-sensitive silicon detectors which can measure the linear energy transfer (LET) distribution over the range from 0.2 to 400 keV/µ m has been developed as a real-time radiation monitor in manned spacecraft. First, the principle of LET measurement and its design method are described. Second, suitable electronic parameters for the LET measurement are experimentally determined. Finally, the telescope performance is investigated by using relativistic heavy ions. The first in-flight test of this type of telescope on the US Space Shuttle (STS-84) is scheduled for May, 1997.

Radiation Dosimetry Measurements with Real Time Radiation Monitoring Device (RRMD)-II in Space Shuttle STS-79

The real-time measurement of radiation environment was made with an improved real-time radiation monitoring device (RRMD)-II onboard Space Shuttle STS-79 (S/MM#4: 4th Shuttle MIR Mission, at an inclination angle of 51.6 degrees and an altitude of 250-400km) for 199 h during 17-25 September, 1996. The observation of the detector covered the linear energy transfer (LET) range of 3.5-6000 keV/micrometer. The Shuttle orbital profile in this mission was equivalent to that of the currently planned Space Station, and provided an opportunity to investigate variations in count rate and dose equivalent rate depending on altitude, longitude, and latitude in detail. Particle count rate and dose equivalent rate were mapped geographically during the mission. Based on the map of count rate, an analysis was made by dividing whole region into three regions: South Atlantic Anomaly (SAA) region, high latitude region and other regions. The averaged absorbed dose rate during the mission was 39.3 microGy/day for a LET range of 3.5-6000 keV/micrometer. The corresponding average dose equivalent rates during the mission are estimated to be 293 microSv/day with quality factors from International Commission on Radiological Protection (ICRP)-Pub. 60 and 270 microSv/day with quality factors from ICRP-Pub. 26. The effective quality factors for ICRP-Pub. 60 and 26 are 7.45 and 6.88, respectively. From the present data for particles of LET > 3.5keV/micrometer, we conclude that the average dose equivalent rate is dominated by the contribution of galactic cosmic ray (GCR) particles. The dose-detector depth dependence was also investigated.

Mass and Energy Limit of Isotope Identification of Heavy Ions Using ΔE–E Silicon-Detector Telescope

The technical limit of isotope identification of ions heavier than iron using a ΔE–E silicon detector telescope is presented. The identification of iron or heavier ions with energies less than 30 MeV/n is limited by the nonuniformity of the thickness in a thin silicon detector, and a decrease in the effective charge of low-velocity ions passing through a silicon medium. In an energy region higher than 300 MeV/n, the slope of the stopping power for heavy ions becomes smaller, which limits the capability of isotope identification. In the intermediate energy range, some ions heavier than iron can be identified with a resolution of σm=0.22 amu; the maximum mass identifiable in this ΔE–E algorithm is about 100 amu because of the restriction of the nonuniformity of detector thickness and the straggling of the energy loss of ions passing through a silicon detector.

Position Linearity and Resolution of Large Position-Sensitive Silicon Detector with a Highly Uniform Thickness

Large two-dimensional position-sensitive silicon detectors (PSDs) with good position linearity, resolution and thickness uniformity have been developed. The PSDs have an effective area of 62 mm×62 mm and a thickness of 500 µm. The non-linearity and position resolution for the whole sensitive area are found to be less than 0.26 mm in rms and 0.44 mm in fwhm, respectively, when an energy of 157 MeV is deposited in the detector and a shaping time constant of 12 µs is used in the pulse processing. The non-uniformity of detector thickness is ≤0.1% in rms. The PSDs recently developed are good enough to separate iron isotopes in a telescope aboard the GEOTAIL spacecraft scheduled to be launched at July in 1992.

Determination of charge and energy for particles penetrating a silicon ΔE × E telescope in space radiation

A method of determination of charge and energy for energetic particles penetrating (not stopping) a multilayer silicon Δ E×E telescope with a finite thickness (12 mm) is examined in the energy region up to several hundreds of MeV/nucleon. From the results of the accelerator experiment, an energy resolution σE of 1.2% in rms and a charge resolution σZ of 0.11 charge unit in rms for Fe-group nuclei with energies between 190 and 230 MeV/nucleon are obtained. For lighter elements such as hydrogens and helium ions, an energy resolution σE of 2.9% is obtained in the energy region between 33 and 42 MeV/nucleon and even their individual isotopes are separated. Also, the energy dependences of these resolutions suggest that this method can be utilized for particles with energies about two times larger than that corresponding to the range of telescope thickness for the evaluation of the space radiation effects even under the limitations of weight, size, and electric power supply.

Measurements of relativistic electron energy loss distributions in thin gas layers

Abstract Experimental data on deposited energy loss in the Fermi plateau region for relativistic electrons in a proportional counter filled with Ar + 10% CH4 and Xe + 10% N2 are presented and compared with the theoretical distributions of Ermilova et al.

Energy loss straggling of heavy charged particles in thick silicon absorbers

The energy loss straggling of heavy charged particles with relatively high energies passing through thick uniform Si detectors (1.0 mm–9.2 mm) has been studied in a wide range of the ratio Δ E / E 0 where Δ E is the energy loss and E 0 is the initial energy of the incident particles. The experimental results are compared with those predicted by straggling theories. It suggests that the measured distributions are in good agreement with those predicted from the Bohrs or Livingston-Bethes theories when Δ E / E 0 0.3.