“…Results for e + + H 22 and e + + He 20 yield lognormal fits with R 2 > 0.95. Determinations for the alkali metals 23 – 26 are also consistent with lognormals ( R 2 > 0.92). It should be noted that Ps formation for these atoms is exothermic (i.e.…”
Section: Resultssupporting
confidence: 68%
“… Figure 2 Ionization and electron capture by positron impact: comparison of measurements with lognormal fits (R 2 values in the legends). ( a ) Single ionization for the inert atoms 20 , 21 ; ( b ) Positronium formation cross sections for H 22 , He 20 and the alkali metals 23 – 26 . The cross section for He has been multiplied by a factor of 2 to aid visual inspection.…”
Quantum physics is undoubtedly the most successful theory of the microscopic world, yet the complexities which arise in applying it even to simple atomic and molecular systems render the description of basic collision probabilities a formidable task. For this reason, approximations are often employed, the validity of which may be restricted to given energy regimes and/or targets and/or projectiles. Now we have found that the lognormal function, widely used for the probability distribution of macroscopic stochastic events (as diverse as periods of incubation of and recovery from diseases, size of grains, abundance of species, fluctuations in economic quantities, etc.) may also be employed to describe the energy dependence of inelastic collisions at the quantum level (including ionization, electron capture and excitation by electrons, positrons, protons, antiprotons, etc.), by allowing for the relevant threshold energy. A physical interpretation is discussed in this article by analogy with the heat capacity of few-level systems in solid state physics. We find the generality of the analysis to extend also to nuclear reactions. As well as aiding the description of collision probabilities for quantum systems, this finding is expected to impact also on the fundamental understanding of the interface between the classical and quantum domains.
“…Results for e + + H 22 and e + + He 20 yield lognormal fits with R 2 > 0.95. Determinations for the alkali metals 23 – 26 are also consistent with lognormals ( R 2 > 0.92). It should be noted that Ps formation for these atoms is exothermic (i.e.…”
Section: Resultssupporting
confidence: 68%
“… Figure 2 Ionization and electron capture by positron impact: comparison of measurements with lognormal fits (R 2 values in the legends). ( a ) Single ionization for the inert atoms 20 , 21 ; ( b ) Positronium formation cross sections for H 22 , He 20 and the alkali metals 23 – 26 . The cross section for He has been multiplied by a factor of 2 to aid visual inspection.…”
Quantum physics is undoubtedly the most successful theory of the microscopic world, yet the complexities which arise in applying it even to simple atomic and molecular systems render the description of basic collision probabilities a formidable task. For this reason, approximations are often employed, the validity of which may be restricted to given energy regimes and/or targets and/or projectiles. Now we have found that the lognormal function, widely used for the probability distribution of macroscopic stochastic events (as diverse as periods of incubation of and recovery from diseases, size of grains, abundance of species, fluctuations in economic quantities, etc.) may also be employed to describe the energy dependence of inelastic collisions at the quantum level (including ionization, electron capture and excitation by electrons, positrons, protons, antiprotons, etc.), by allowing for the relevant threshold energy. A physical interpretation is discussed in this article by analogy with the heat capacity of few-level systems in solid state physics. We find the generality of the analysis to extend also to nuclear reactions. As well as aiding the description of collision probabilities for quantum systems, this finding is expected to impact also on the fundamental understanding of the interface between the classical and quantum domains.
“…Available in the literature is a multitude of theoretically [35,[46][47][48][49]36,[50][51][52] and experimentally determined [37,[53][54][55]] electron collision excitation cross sections for caesium. CsðiÞþe À -Cs þ þ 2e À [38] Recombination of Cs þ Cs þ þ 2e À -CsðjÞþe À [38], Saha equation…”
Section: Electron Collision Excitation and De-excitationmentioning
a b s t r a c tA collisional radiative (CR) model for caesium in low-temperature, low-pressure hydrogen-caesium plasmas is introduced. This model includes the caesium ground state, 14 excited states, the singly charged caesium ion and the negative hydrogen ion. The reaction probabilities needed as an input are based on literature data, using some scaling and extrapolations. Additionally, new cross sections for electron collision ionization and threebody recombination have been calculated.The relevance of mutual neutralization of positive caesium ions and negative hydrogen ions is highlighted: depending on the densities of the involved particle species, this excitation channel can have a significant influence on the population densities of excited states in the caesium atom. This strong influence is successfully verified by optical emission spectroscopy measurements performed at the IPP prototype source for negative hydrogen ions.As a consequence, population models for caesium in electronegative low-temperature, low-pressure hydrogen-caesium plasmas need to take into account the mutual neutralization process. The present CR model is an example for such models and represents an important prerequisite for deducing the total caesium density in such plasmas.
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