Teruo Suehiro

Fabrication of a nuclear radiation detector using the PbI/sub 2/ crystal and its response characteristics for gamma-rays

We have been studying a /spl gamma/-ray detector which uses a lead iodide PbI/sub 2/ crystal. The detector was fabricated from a PbI/sub 2/ crystal grown by the 10-pass zone travelling molten zone (TMZ) method. The /spl mu//spl tau/ product of this crystal is estimated to be about 1/spl times/10/sup -6/ cm/sup 2//V for electrons and about 6/spl times/10/sup -7/ cm/sup 2//V for holes. The resistivity of the PbI/sub 2/ crystal is estimated to be about 10/sup 12/ /spl Omega/cm. The FWHM energy resolution of the detector for a photoelectric peak for the 59.5 keV /spl gamma/-rays is found to be about 5 keV.

Fabrication of radiation detector using PbI/sub 2/ crystal

Radiation detectors have been fabricated from lead iodide (PbI/sub 2/) crystals grown by two methods: zone melting and Bridgman methods. In response characteristics of the detector fabricated from crystals grown by the zone melting method, a photopeak for /spl gamma/-rays from an /sup 241/Am source (59.5 keV) has been clearly observed with applied detector bias of 500 V at room temperature. The hole drift mobility is estimated to be about 5.5 cm/sup 2//Vs from measurement of pulse rise time for 5.48 MeV /spl alpha/-rays from /sup 241/Am. By comparing the detector bias versus saturated peak position of the PbI/sub 2/ detector with that of the CdTe detector, the average energy for producing electron-hole pairs is estimated to be about 8.4 eV for the PbI/sub 2/ crystal. A radiation detector fabricated from PbI/sub 2/ crystals grown by the Bridgman method, however, exhibited no response for /spl gamma/-rays. >

(p, d) Reactions at 52 MeV. I. 58Ni(P, d) 57Ni(Experimental)

The 58 Ni(p, d) 57 Ni reaction was studied at E p =51.93 MeV with a magnetic spectrometer. Experimental results and spectroscopic information obtained are presented.

The (p. t) Reaction on Even-Even Deformed Nuclei

The (p, t) reactions on 158 Gd, 164 Dy, 172 Yb, 176 Hf and 184 W have been studied with 51.7 MeV protons. Triton spectra have been measured with a broad-range magnetic spectrometer with a 200 proportional-counter array. The cross sections for the states of the ground state rotational band which have been found to depend on mass number, have been analyzed by the distorted-wave Born-approximation. Especially Y 4 -diformation parameter β 4 for each nucleus has been obtained from the cross section for the 4 + state of the ground state rotational band. The cross sections for the first excited 0 + states have been found to have a mass number dependence and this dependence was compared with the prediction based on the pairing vibrational mode.

(p, d) Reactions at 52 MeV. II. 58Ni(p, d)57Ni(Analysis)

Angular distributions for the 58 Ni(p, d) 57 Ni reaction at E p =51.93 MeV are analyzed using the distorted wave Born approximation theory and the adiabatic theory for the deuteron breakup. dependence of the calculated results is investigated in detail. Modification of low-partial wave contributions is required to obtain reasonable fit with DWBA. well-radius description in the form factor calculation is found to show general superiority to conventional well-depth description.

Characterization of PbI/sub 2/ radiation detectors using the response of /spl alpha/-rays

An improved method is proposed for the production of single crystals of lead iodide (PbI/sub 2/). For the work reported here a modified Bridgman method is used. Bulk-type nuclear radiation detectors have been fabricated by use of crystals grown by this method. The characteristics of the detectors, particularly the response for 5.48 MeV /spl alpha/-particles from /sup 241/Am source, have been measured and compared with characteristics of other detectors fabricated with crystals grown by the ordinary Bridgman method. An /spl alpha/-peak has been clearly observed in the pulse-height spectrum. On the other hand, no peak has been observed in the detectors made from crystals grown by the ordinary Bridgman method. From the relations of peak position versus applied bias voltage, the average energy to produce electron-hole pairs and the /spl mu//spl tau/ product of holes are estimated to be about 30 eV and 10/sup -7/ cm/sup 2//V, respectively. >

Radiation damage effects by 25 MeV protons and thermal annealing effects on thallium bromide nuclear radiation detectors

In this study, TlBr detectors were irradiated with 25 MeV protons accelerated by an AVF cyclotron. Isothermal annealing was performed to restore the performance of the detectors. In order to characterize the radiation damage and thermal annealing effects on the TlBr detectors, we measured current-voltage (I-V) characteristics, mobility-lifetime (/spl mu//spl tau/) products and spectrometric responses. The I-V and /spl mu//spl tau/ measurements suggest that electron traps have been induced by 25 MeV protons in the TlBr crystals. X- and /spl gamma/-ray energy spectra were measured for two different electronic conditions: the electric signals induced mainly by electron carriers traversing the crystal were used for one case and the signal induced by hole carriers were used in the other case. After irradiation of 25 MeV protons, the /sup 241/Am X- and /spl gamma/-ray spectra obtained in the former showed significantly degraded energy resolution. No degradation of energy resolution, however, was observed in the latter case. Noticeable improvements of the degraded detector performance have been observed after the thermal annealing.

Properties of CdTe(Cl) crystal used for radiation detector

A new method is described for growing CdTe crystals doped with chloride by using a radiofrequency traveling heater method (THM) which can provide excellent uniformity for the Cl atoms in the crystal. The relationship between response characteristics by gamma -ray detection and crystal properties studied by photoluminescence (PL) measurements is discussed. In the RF-THM crystal sample, the emission intensity ratios between the 1.5932 eV and 1.5905 eV lines due to bound excitons from chlorine are nearly constant for all parts of one ingot. From this result, it is suggested that the Cl atoms are uniformly distributed through the whole of the crystal. Using crystals grown by this method, a large number of high-quality radiation detectors which exhibit the same characteristics can be produced from one CdTe ingot. >

Characterization of the PbI/sub 2/ crystal as a material for radiation detectors

We have been studying a radiation detector which uses lead iodide crystal. The growth of PbI/sub 2/ crystal used two kinds of method. One is the zone melting method and the other is the vapor phase epitaxy method. The performance of the detector fabricated from a crystal grown by the former method showed better characteristics than the detector fabricated from the crystal grown by the latter. Results of XPS and photoluminesence measurement, suggest that the behavior of the iodine atoms in the crystal influenced and controlled the performance of the detector.

(p, d) Reactions at 52 Mev. III. 28Si(p, d) and 18O(p, d)

The 28 Si(p, d) and 18 O(p, d) reactions have been studied at E p =51.9 MeV with a magnetic spectrometer. Experimental angular distributions are compared with the distorted-wave Born approximation theory and the adiabatic theory for deuteron breakup. Results of the analysis corroborate the conclusions obtained in a previous study of the 58 Ni(p, d) reaction, indicating the deficiency of the conventional DWBA theory in describing (p, d) angular distributions at relatively high incident energies.