共查询到20条相似文献,搜索用时 15 毫秒
1.
This work demonstrates that a significant improvement of the timing resolution, simultaneously keeping coincidence count rate high enough, can be achieved by use of the state-of-the-art ultra fast 8-bit digitizers which replace the traditional analog timing modules. Performance of the digital spectrometer in conditions of a routine measurement is compared with that of the same detectors connected to the analog setup. It was found that employment of the digital setup leads to an improvement of timing resolution from 169 ps for the traditional analog setup down to 146 ps for the digital setup. 相似文献
2.
Hydrogen in nano-voids in neutron-irradiated nickel has been detected using positron annihilation lifetime spectroscopy (PALS). As positron lifetime is greatly affected by nano-voids bound with hydrogen, special attention was paid to the analysis. The positron lifetime of neutron-irradiated nickel at higher irradiation doses increased with the dose, which is an indicator for vacancy cluster (nano-void) formation in the lattice. The introduction of hydrogen in well-annealed nickel by electrical charging also resulted in an increase in positron lifetime due to vacancy formation. In neutron-irradiated nickel specimens, hydrogen charging shortened the positron lifetime from 456 to 334 ps (irradiation dose: 3 × 10?3 dpa). Isochronal annealing behaviour of hydrogen-charged nickel and neutron-irradiated nickel was also studied. Positron trapping rate was calculated using a simple trapping model. Thermal desorption spectroscopy was used for the investigation of hydrogen behaviour in non-irradiated hydrogen-charged nickel. 相似文献
3.
4.
5.
Study of the ionic transport in polymer electrolyte using positron lifetime distribution method 总被引:1,自引:0,他引:1
Z. L. Peng Y. Itoh S. Q. Li S. J. Wang 《Applied Physics A: Materials Science & Processing》1996,63(3):267-270
Positron annihilation spectroscopy has been applied to measure the free-volume hole distribution in poly(ether urethane) as a function of temperature. The hole radius distribution determined from orthopositronium lifetime distribution is found to shift to a larger values with increasing temperature. This result, combined with the variation of ionic conductivity, suggests that carrier ions do not migrate naked but are bound to polymer segments through ion-dipole interaction forces, and the ion migration is controlled primarily by segmental motion of the polymer. 相似文献
6.
7.
A method using ion-implantation of Na22 to produce source-sample systems applicable to positron annihilation lifetime experiments at elevated temperatures in metals is presented. 相似文献
8.
The damaged produced by proton beam slowed down in CR-39 polymer results in highest degree of disorder with change of free volume proprieties. Positron annihilation lifetime spectroscopy (PALS) is nowadays well recognized as powerful tool of microstructure investigations. PALS is used in order to get more information at an atomic scale of modifications induced by irradiation of polymers particularly the variation of free volume in the irradiated region. In this paper, the mean free volume hole radii and average free volume of the micro-voids in CR-39 polymer irradiated with 200 MeV therapy proton beam at different positions in spread out Bragg Peak region (SOBP) at Ithemba proton therapy facility have been determined using PALS. © 2006 Elsevier Ltd. All rights reserved. 相似文献
9.
Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate ~8 cps/μCi were achieved. A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures. 相似文献
10.
LI Dao-Wu LIU Jun-Hui ZHANG Zhi-Ming WANG Bao-Yi ZHANG Tian-Bao WEI Long 《中国物理C(英文版)》2011,35(1):100-103
Using LYSO scintillator coupled on HAMAMATSU R9800(a fast photomultiplier)to form the small size γ-ray detectors,a compact lifetime spectrometer has been built for the positron annihilation experiments.The system time resolution FWHM=193 ps and the coincidence counting rate -8 cps/μCi were achieved.A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested,which is in agreement with the typical values published in the previous lectures. 相似文献
11.
As the digital equipment to measure positron lifetimes gets cheaper and more widely used, it is decided that EPOS, the ELBE positron source will sample the signals from the photomultipliers directly and evaluate it online or offline by digital means.Still using isotope sources, the EPOS lifetime spectrometer results in a timing resolution of around 170 ps (with 60Co), which compares good to analog equipment. A distinct improvement is expected when a coincidence setup will be used at ELBE. However, also the software needs further improvement: while one of the goals is of course to achieve the best time resolution, there is also the aspect of runtime and expandability. Results of evaluations will be presented and compared with results from other groups. 相似文献
12.
13.
In
- in Zn-doped p-InP. The line-shape parameter measured by an improved Doppler-broadening spectrometer shows a significant difference
between n-type and Fe-doped SI-InP materials: the S-parameter varies from 0.5203 in n-InP to 0.5184 in Fe-doped SI-InP by
four times the standard deviation. A possible reason for this difference is discussed.
Received: 7 January 1997/Accepted: 8 September 1997 相似文献
14.
15.
在局域密度近似理论(LDA)和广义梯度近似理论(GGA)的基础上,用中性原子叠加的方法(ATSUP),理论上对亚铜的卤化物(CuF除外,因为它不是闪锌矿结构)及某些硼化物进行计算,计算结果与实验符合得很好;其次,计算了其他具有闪锌矿结构的众多晶体的正电子体寿命,得到的结果与其他文献计算的结果符合得较好,文中以CuCl晶体为例,给出了正电子在其中的势能分布,概率密度分布与湮没率分布;最后,这些系统性的正电子体寿命结果被拟合成晶格常数的函数,拟合结果与其他一些文献的结果做了比较.
关键词:
正电子体寿命
闪锌矿结构 相似文献
16.
Streak camera has high temporal resolution and high sensitivity, and is a powerful tool in biomedical study to measure fluorescence lifetime and perform fluorescence lifetime imaging. However, nonuniformity of the gain in the streak tube and nonlinearity of the sweeping speed limit the precision of fluorescence lifetime measurement, particularly when fluorescence lifetimes are short. We have constructed a two-photon excitation fluorescence lifetime measurement system that is based on a synchroscan streak camera and have developed accordingly a method to correct the effect of gain nonuniformity and nonlinearity of sweeping speed on the measurement precision. A continuous-wave laser of high stability is used to calibrate the gain of the streak camera, and a Fabry-Perot etalon is used to calibrate the nonlinearity of the sweeping speed. Fitting algorithms are used to correct the gain of the streak camera and nonlinearity of the sweeping speed respectively, which significantly improves the measurement precision of the system, as characterized through the fluorescence lifetime of the short-lived fluorescence dye, Rose Bengal. Experimental results show that the measurement fluctuation of the lifetime has been improved from more than 10% to 2% after correcting the effects of gain nonuniformity and sweeping speed nonlinearity. 相似文献
17.
Positron lifetime has been measured as a function of temperature in Sidoped GaAs single crystals subjected to various heat
treatments. Defects produced by these heat treatments trap positrons. In all the GaAs samples containing defects positron
lifetime was found to decrease with temperature in the range from 375 K to 16 K. The decrease is explained as due to the decrease
in the trapping rate. The trapping rate is mainly controlled by the diffusion of the positron to the trap. The diffusion constant
is determined mainly by the scattering from charged Si impurities. 相似文献
18.
19.