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Hirade, Tetsuya
JJAP Conference Proceedings, Vol.2 (Internet), p.011003_1 - 011003_6, 2014/11
Ps has negative work function in insulating materials and the repulsion between Ps and surrounding molecules can form a bubble in liquids. However, it is needed to lose energy to be in a stable bubble state. Therefore the oscillation of the bubble size is expected. The ortho-Ps pick off annihilation probability depends on the size of the Ps bubble and hence the oscillation on the lifetime spectra is expected. In the case of usual liquids, bubble formation time is not so slow and then the oscillation can not be observed by the positron annihilation lifetime measurements with the time resolution of about 200 ps. Now the bubble formation in IL is slow and then the expected oscillation on the lifetime spectra was successfully observed.
Maekawa, Masaki; Zhang, H.; Li, H.; Fukaya, Yuki; Kawasuso, Atsuo
JJAP Conference Proceedings, Vol.2 (Internet), p.011305_1 - 011305_7, 2014/11
Zhang, H.; Yamamoto, Shunya; Li, H.; Fukaya, Yuki; Maekawa, Masaki; Kawasuso, Atsuo; Seki, Takeshi*; Saito, Eiji*; Takanashi, Koki*
no journal, ,
Li, H.; Zhang, H.; Maekawa, Masaki; Fukaya, Yuki; Kawasuso, Atsuo
no journal, ,
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.
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 
-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 -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.
