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Journal Articles

Theoretical study of photoproduction of an $$eta ^{prime} N$$ bound state on a deuteron target with forward proton emission

Sekihara, Takayasu; Sakai, Shuntaro*; Jido, Daisuke*

Physical Review C, 94(2), p.025203_1 - 025203_11, 2016/08

AA2016-0236.pdf:0.92MB

 Times Cited Count:4 Percentile:33.65(Physics, Nuclear)

Oral presentation

Positron annihilation lifetime measurement by use of LSO scintillators

Hirade, Tetsuya; Minei, Shuntaro; Sakai, Hiroaki

no journal, , 

LSO scintillators have high density, short lifetime of light emission and high light strength, and that are applied for PET. The commonly used positron annihilation lifetime measurement system has BaF$$_{2}$$ scintillators, because BaF$$_{2}$$ scintillator has very fast light emission which is a great advantage for a good time resolution. On the other hand, LSO has a advantage on the high counting rate. We have tried to use LSO scintillators for the positron annihilation lifetime measurements. The system with LSO scintillators gave 5 times higher counting rate than with BaF$$_{2}$$ scintillators, and 315ps time resolution (FWHM) which is just 50 ps worth than BaF$$_{2}$$. The irradiation effects on the sample for long measurement time is not negligible and then LSO scintillators provide a better system for these measurements.

Oral presentation

Simple method for measurement of radioactivity of cesium-134

Hirade, Tetsuya; Sakai, Hiroaki; Minei, Shuntaro

no journal, , 

After the TEPCO Fukushima Nuclear power plant accident, there are several radio isotopes released from the plant. To detect these radioisotopes, photo-peaks on the energy spectra obtained by HPGe semiconductor detectors or scintillation detectors are used. The detection efficiency is in invers proportion to square of the distance between the detector and the radioisotopes. Therefore the detector and the sample must be inside of the heavy and expensive shield box made of lead. Cs-134 is the only radioisotope emitting several $$gamma$$-rays in our environment, now. In the case of the simultaneous measurement of the $$gamma$$-rays from Cs-134, the detection efficiency can be in invers proportion to the fourth power of the distance, and hence the shield is not needed. Therefore, this method can be applied not just in laboratory.

Oral presentation

Ago-momentum correlation (AMOC) measurements by use of LSO scintillators

Hirade, Tetsuya; Minei, Shuntaro; Sakai, Hiroaki

no journal, , 

LSO(Lu$$_{2}$$SiO$$_{5}$$:Ce) scintillator is often used for PET (Positron Emission Tomography) because of the high efficiency of $$gamma$$-ray detection. By use of this scintillator, we succeeded to obtain high efficiency on the measurements of positron annihilation methods, such as positron annihilation lifetime measurement and age-momentum correlation measurement (AMOC). It can supply the smaller change of the sample during measurements caused by the positron irradiation effect.

Oral presentation

Electric field effects on positron annihilation lifetime in kapton

Sakai, Hiroaki; Minei, Shuntaro; Hirade, Tetsuya; Oshima, Nagayasu*; Kobayashi, Yoshinori*; Kinomura, Atsushi*; Suzuki, Ryoichi*

no journal, , 

It was reported that positronium (Ps) formation probability was enhanced very much with very high electric fields. The spur reaction model can not explain this Ps formation. We tried to investigate this Ps formation with high electric fields in polyimide (kapton) that has no Ps formation with no electric field. Then we found out that Ps formation was not possible even at high electric fields. However, the annihilation lifetime of free positrons was elongated and it was probably caused by the positron drift movement.

Oral presentation

Electric field effect on positron annihilation lifetime in Kapton

Sakai, Hiroaki; Minei, Shuntaro; Hirade, Tetsuya; Oshima, Nagayasu*; Kobayashi, Yoshinori*; Kinomura, Atsushi*; Suzuki, Ryoichi*

no journal, , 

It was reported that the positronium (Ps) formation in polymers was enhanced near breakdown voltage. It cannot be explained by the Spur Reaction Model. We investigated the electric field effect on positron annihilation lifetime for Kapton that has no Ps formation. We observed elongation of the free positron annihilation lifetime instead of the enhancement of Ps formation. It is possible to explain that drift of positrons causes smaller annihilation probability, i.e. longer lifetime. Now it is possible to explain the Ps formation enhancement reported previously could be caused by the elongation of the lifetime of the free positrons.

Oral presentation

Electric field effect on positron annihilation lifetime in Kapton

Sakai, Hiroaki; Minei, Shuntaro; Hirade, Tetsuya; Oshima, Nagayasu*; Kobayashi, Yoshinori*; Kinomura, Atsushi*; Suzuki, Ryoichi*

no journal, , 

It was reported that psoitronium (Ps) formation probability in polymers under high electric fields were enhanced. The spur reaction model explaining Ps formation in insulating materials cannot be applied for the enhancement under high electric fields. Then we studied the Ps formation mechanism under high electric fields by observing positron annihilation lifetime in Kapton (polyimide) that does not have any Ps formation. Then Ps was not formed even under high electric fields and the elongation of the lifetime of the positrons free from Ps formation. The elongation of the lifetime of the positron and Ps formation enhancement could not be judged by the methods applied in the previously reports.

Oral presentation

Effect of focused ion beam processing on stainless steel studied by positron annihilation lifetime measurements

Minei, Shuntaro; Oshima, Nagayasu*; Sakai, Hiroaki; Okubo, Nariaki; Kondo, Keietsu; Suzuki, Ryoichi*; Hirade, Tetsuya

no journal, , 

In nuclear reactor materials, subnanometer-size vacancy type defects are induced by neutron irradiation. Although positron annihilation methods are effective techniques for evaluation of the vacancy type defects, it may be difficult to apply the methods for neutron irradiated samples, because of $$gamma$$-rays from highly neutron irradiated, i.e. radioactivated, samples. Recently, positron micro beam has been developed at AIST. Therefore, we are suggesting that smaller radioactivated samples emit fewer $$gamma$$-rays. Focused Ion beam (FIB) is one of the tools to prepare micrometer scale samples by ion sputtering, for example, for the transmission electron microscope. There is some possibility to have vacancy type defects in the samples induced by the FIB processing and it can make estimation of the pre-existing defects in the samples difficult. The results investigated by positron annihilation lifetime measurements for SUS316L showed that FIB can be applied.

Oral presentation

Theoretical study of photoproduction of $$eta ^{prime} N$$ bound state on deuteron target with forward proton emission

Sekihara, Takayasu; Sakai, Shuntaro*; Jido, Daisuke*

no journal, , 

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