共查询到20条相似文献,搜索用时 37 毫秒
1.
K. Wada F. Saito N. Shinohara T. Hyodo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(4):108
Positronium quenching through its collisions with gaseous atoms and molecules is discussed. It is found that the values of
the normalized pick-off quenching parameter, 1Zeff, at room temperature are roughly proportional to the geometric collisional cross-sections estimated from the radius of the
positronium and those of the atoms and molecules derived from the viscosity. This suggests that the probabilities of the pick-off
quenching of the thermalized positronium per collision with various atoms and molecules are almost constant. 相似文献
2.
The progress of research into the behavior of the positronium in molecular substances in the last several years is reviewed. The Ps atom can be treated as a solute in a liquid. The repulsive exchange force is the dominant force which reacts against the van der Waals attractive force. One of the most useful general relationships found is the one between the pick-off quenching rate and the surface tension of the liquid. The pick-off quenching rate is found, in general, to be an additive property of the functional groups of a molecule. The quenching of theo-Ps atom by an active quenching agent in an inert solvent has been found to be primarily diffusion controlled. Some deviations from the simple Arrhenius equation have been found. For gases, more theoretical work on the collision problems of Ps with atoms or molecules is needed. For amorphous molecular solids, it is likely that the property of pick-off quenching ofo-Ps is similar to that in liquids. However, in crystalline molecular solids, the situation is quite different. A few definite cases have been found where a Ps atom does not form or exist. Further work in this area should be very interesting. The foregoing leads us to believe that positronium or positron annihilation can be useful in the study of fundamental properties of molecular liquids and solids. 相似文献
3.
Position mobility and electric field dependence on positronium formation in some liquid hydrocarbons
The change in the fraction of positrons forming positronium in an oscillating electric field is measured in n-pentane, n-hexane and n-decane. Positron mobilities, at room temperature, of 6, 8.5 and 11.5cm2/V are found for the three liquids. The results are discussed in the light of the Ore model and the spur model of positronium production. 相似文献
4.
I. Pepe D. A. L. Paul F. Gimeno-Nogues J. Deutsch R. Prieels 《Hyperfine Interactions》1994,89(1):425-434
We have made new measurements of the lifetimes at 4.19 and 2.92 K in HeI, and at 2.14 and 1.67 K in HeII, without and with electric field. The ortho-positronium lifetime is independent of field up to 20 kV/cm. At 4.19 K, there is no increase observed in the positronium fraction from zero field to 20 kV/cm, in strong disagreement with Manuzio and Rizzuto. Some additional positronium is, however, formed above 20 kV/cm, with a corresponding decrease in lifetime of the free component. At 4.19 K the free positron mean life rises sharply with increasing electric field to a constant value of about 2.14 ns above 5 kV/cm. The increase in the free positron lifetime with field is less marked at 2.92 K. In liquid argon measurements were made at the normal boiling point only, at fields up to 20 kV/cm, above which we experienced electrical breakdown. The ortho-positronium intensity is 7% at zero field and begins to increase at 2.5 kV/cm, reaching 13% at 20 kV/cm at which field value it was still increasing. The ortho-positronium lifetime displayed an 8% increase over this field range. For liquid nitrogen we repeated some of our earlier measurements at 77.3 K and made some measurements at 64.5 K so as to test models for positronium formation in the spur. A good fit to a simple exponential formula is obtained at both temperatures, yielding a single drop-off rate of 0.21 cm/kV.On leave from the Physics Department, University of Toronto, Canada. 相似文献
5.
O.E. Mogensen 《Physics letters. A》1983,96(5):250-254
The enhancement of the positronium (Ps) formation in polyethylene on the application of an electric field above 0.35 MV cm-1, measured by Bisi et al., is discussed in terms of the spur model of Ps formation. Apparently, two effects can explain the results, namely (1) Ps formation by positron reaction with electrons injected in the charging processes at a high field, and (2) field dependent thermionic emission of excess electrons and positron trapped in the positron spur. The Ps enhancement in high fields does not disprove the spur model, even if the heating up of the positrons in high fields is assumed to take place. 相似文献
6.
O. E. Mogensen 《Applied Physics A: Materials Science & Processing》1975,6(3):315-322
The decrease of positronium (Ps) formation in condensed matter caused by the presence of an external electric field is discussed in terms of the spur reaction model of Ps formation. The rather few experimental results available are shown to be in good agreement with the predictions of the model. Many new results are predicted by use of the available radiation-chemistry results. The work is also a reply to Brandt, who estimated that the spur process of Ps formation is insignificant in hydrocarbons. It is shown that Brandt's estimate disagrees with well established results of radiation chemistry. 相似文献
7.
M. Bertolaccini A. Bisi G. Gambarini G. Padovini L. Zappa 《Applied Physics A: Materials Science & Processing》1977,12(1):93-96
The transient and steady effects of positronium yield in polyethylene, due to the application and removal of an external electric
field, have been studied. The time-dependent electric field effective in the Ps formation region was deduced from yield measurements. 相似文献
8.
M. Hasegawa Y. Saitoh S. Yamaguchi H. Takahashi S. Ohnuki 《Hyperfine Interactions》1994,84(1):389-396
Angular correlation of two-photon annihilation radiation (ACAR) measurements have been performed to study the effect of interstitial impurities (O, C and D) on positronium (Ps) formation in irradiation-induced voids of vanadium. It has been observed that Ps formation is sensitively affected by doping with the interstitial impurities, irradiation dose, irradiation temperature, and also by post-irradiation annealing. The Ps component intensity is found to be related to segregation of the interstitial impurities and provides a new experimental method to study void surfaces. 相似文献
9.
The positronium-determined characteristics of electron-positron annihilation in semiconductors in the presence of an external magnetic field are calculated. It is assumed that the positronium atoms can be in one of two states, delocalized or localized (at defects), and undergo not only pick-off annihilation but also orthoparaconversion (3S1 1S0) on free carriers. Numerical calculations were made for a field H=15 kG. The field has very different effects on localized and delocalized positronium, and in the first case the effect depends strongly on the nature of the defect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.11, pp. 75–78, November, 1980. 相似文献
10.
The positron annihilation lifetime method (PAL) has been applied to study the characteristics of polyethylenes (PEs) at low temperatures between 273 and 100 K. It has been found that the intensity (I
3) of the long-lived component of positronium (Ps) showed an increase in non-annealed PE and annealed PE in vacuo. However, PAL in PEs annealed in an atmosphere containing oxygen did not show such an increase. It has been indicated that the latter effect is due to formation of carbonyl groups through oxidation during the annealing. 相似文献
11.
We theoretically studied photorefractive surface waves supported by polymers with orientationally enhanced photorefractive effect. We find that the orientational enhancement and the dependency of the quantum efficiency of generating mobile holes on the electric field make the diffusion nonlinearity in photorefractive polymers dependent not on only the variation of light intensity but also on external electric field, which is very different from the external electric field independent diffusion nonlinearity in inorganic photorefractive crystals. Consequently the profile, frequency and especially the penetration depth of polymeric photorefractive surface waves strongly depend on external electric field, which makes it more controllable than that in photorefractive inorganic crystals. The stability of polymeric photorefractive surface waves, the effects of birefringence component and electro-optic component of orientationally enhanced photorefractive nonlinearity on the formation of x or y-polarized polymeric photorefractive surface waves are also discussed. 相似文献
12.
Effect of electric field,stress and environment on delayed fracture of a PZT-5 ferroelectric ceramic
WANG Yi SU Yanjing CHU Wuyang & QIAO Lijie Department of Material Physics University of Science Technology Beijing Beijing China School of Mechanic Electric Control Engineering Beijing Jiaotong University Beijing China 《中国科学G辑(英文版)》2005,48(1):89-100
The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen. The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil, i.e. stress corrosion cracking, decrease linearly with the increasing applied electric field, either positive or negative. For the PZT-5 ferroelectric ceramics, delayed fracture in silicone oil under sustained positive or negative field can occur, and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor. The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes field-enhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field. 相似文献
13.
A. P. Mills Jr. 《Hyperfine Interactions》1989,44(1-4):105-123
We review the physics of the negative affinity and hot-positron moderators that allow us to produce intense beams of slow
positrons. By repeated staes of remoderation a positron beam can be focused to a microscopic spot on a solid target with little
loss of intensity. The positronium (Ps) and positronium negative ions (Ps−) produced by such a spot will be bright enough to permit the formation of well-collimated Ps beams suitable for gravitational
free fall and other experiments. 相似文献
14.
A high-performance positron age-momentum correlation (AMOC) spectrometer was newly developed. The counting rate is increased up to 200 cps much larger than the value 20~cps reported by other international groups. And at the same time, the time resolution still keeps at the international level of 220 ps. Furthermore, positronium (Ps) annihilation in silica aerogel was investigated by AMOC, which indicates: (1) Ps annihilation between the grains dominantly undergoes pick-off process and spin conversion from o-Ps to p-Ps; (2) Annealing below 400 ℃ changes the grain surface conditions, i. e. the desorption of hydrogen and the decrease of the defect centers concentration. 相似文献
15.
Magnetized Rydberg positronium forms when an energetic positron ( e(+)) slows within a tungsten crystal and picks up an electron ( e(-)) as it emerges in a strong magnetic field. The signature is equal numbers of e(+) and e(-) when a weak electric field is applied, either of which can be accumulated and counted. The new e(+) accumulation technique is simple, robust, and much more efficient than any other demonstrated to be compatible with a cryogenic vacuum. Possible applications include the study of cold single component plasmas of e(+) and the formation of cold antihydrogen. 相似文献
16.
17.
H. Gobrecht H. -E. Gumlich H. Nelkowski K. Lacmann 《Zeitschrift für Physik A Hadrons and Nuclei》1962,168(3):273-282
The x-ray excited luminescence of a zinc-cadmium sulfide phosphor activated by manganese and cobalt can be enhanced by infrared or red light, by alternating electric fields, and by both together. The infrared light as well as the electric field enhance the same emission band caused by manganese. The dependence of the enhancement on the strength and on the frequency of the electric field, and on the intensity and on the wavelength of the stimulating radiation has been investigated. Maximum enhancements are observed at frequencies of about 20 cps and at wavelengths of 0.77 and 1.35 μ of the stimulating light. When both the electric field and the stimulating light are applied together, the enhancement is lower than the sum of both effects. While at small intensities of the infrared the emission is increased by an additional electric field, it is diminished at high intensities. If the non-excited phosphor is exposed to the infrared a memory effect is found quite similar to that produced by electric fields reported byDestriau. The results are discussed using a model published earlier. 相似文献
18.
V. S. Borisov Yu. V. Agrafonov L. A. Shcherbachenko Ya. V. Ezhova S. S. Baryshnikov O. B. Rubtsova 《Physics of the Solid State》2011,53(1):53-58
A theoretical model has been proposed which makes it possible to introduce the correction into the complex permittivity of
electrically active condensed systems that contain a polar liquid matrix and low-dimensional solid particles with a developed
electrically active surface. It has been established that there is an interfacial electrical interaction between surface charges
of the solid component and polar molecules of the liquid matrix. The processes occurring during this interaction lead to the
appearance of an intrinsic internal electric field in the system under investigation. The contribution from surface effects
to the formation of the polarized state of the polar liquid medium has been investigated in terms of the proposed model. The
possibility of controlling the processes of local change in the structure of the polar liquid component under the effect of
the internal electric field by varying the electrically active specific surface area of the solid phase and the intrinsic
dipole moment of molecules of the liquid matrix has been analyzed in the studied systems. The conditions providing for the
appearance of a controlled potential gradient of the internal electric field have been determined for the dispersed systems
under consideration. The parameter that makes it possible to evaluate the contribution from the interfacial electrical contact
interaction to the dielectric response of the liquid component and the entire system has been introduced for the first time. 相似文献
19.
WANG Dan-Ni ZHANG Lan-Zhi WANG Bao-Yi YU Run-Sheng ZHANG Zhi-Ming LI Dao-Wu WEI Long 《中国物理C(英文版)》2009,33(1):81-84
A high-performance positron age-momentum correlation (AMOC) spectrometer was newly developed.The counting rate is increased up to 200 cps much larger than the value 20 cps reported by other international groups.And at the same time,the time resolution still keeps at the international level of 220 ps.Furthermore,positronium (Ps) annihilation in silica aerogel was investigated by AMOC,which indicates:(1) Ps annihilation between the grains dominantly undergoes pick-off process and spin conversion from o-Ps to p-Ps;(2) Annealing below 400 ℃ changes the grain surface conditions,i.e.the desorption of hydrogen and the decrease of the defect centers concentration. 相似文献
20.
S. J. Tao 《Applied physics. B, Lasers and optics》1976,10(1):67-79
The theories regarding the formation of positronium in molecular substances are discussed. A modified theory based upon the
“spur” theory is described. Theoretical derivation and experimental results suggest that the fraction of the long lifetime
component due too-positronium annihilation has a complex origin. Initially, the electron of the positron-electron pair is likely to be separated
from the positron by medium molecules even when the total kinetic energy of the pair is less than the potential energy between
them. The formation of positronium depends on the mobilities of the positron and electron, the slowing down process and the
potential energy between them. Positronium is formed in less than 10 ps. Then the positronium produced may react with the
radicals created in the “spur” due to the positron. Only the fraction ofo-positronium able to escape the “spur” will have a long lifetime. Therefore, positronium formation is highly related to the
fast reactions in the “spur” during the first 100 ps. 相似文献