Autoionization spectra of positrons in heavy-ion collisions

Peitz, Heinrich; Müller, Berndt; Rafelski, Johann; Greiner, Walter

doi:10.1007/bf02727627

Cited by 41 publications

(13 citation statements)

References 8 publications

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“…Independently, and stimulated by the nuclear molecular phenomena 4a and by the nuclear two center shell model 4b , the idea of intermediate electronic molecular states formed in the collision of heavy ions was put forward in connection with possible tests of fundamental problems like quantum electrodynamics of strong fields [5][6][7][8] and possible direct measurements of vacuum polarization in superheavy systems 5~7 . For the Russian work in the field cf.…”

Section: Introductionmentioning

confidence: 99%

“…U -U, where at distances smaller than 35 fm the two nuclei act combined as source of an overcritical electric field. The expected cross sections for positrons have been calculated by Peitz et al 8 and with inclusion of the non-adiabatic effects in a heavy ion collision by Smith et al 19 . Cross sections of up to 1/100 barns can be expected.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Two Centre Dirac Equation

Müller

Greiner

1976

Zeitschrift Für Naturforschung A

101

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During collisions of heavy ions with heavy targets below the Coulomb barrier, adiabatic molecular orbitals are formed for the inner electrons. Deviations from adiabaticity lead to coupling between various states and can be treated by time-dependent perturbation theory. For high charges (Z1+Z2 60) the molecular electrons are highly relativistic. Therefore, the Dirac equation has to be used to obtain the energies and wave functions. The Dirac Hamiltonian is transformed into the intrinsic rotating coordinate system where prolate spheroidal coordinates are introduced. A set of basis functions is proposed which allows the evaluation of all matrix elements of the Dirac Hamiltonian analytically. The resulting matrix is diagonalized numerically. The finite nuclear charge distribution is also taken into account. Results are presented and discussed for various characteristic systems, e. g. Br-Br, Ni-Ni, I-I, Br-Zr, I-Au, U -U, etc.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Two Centre Dirac Equation

Müller

Greiner

1976

Zeitschrift Für Naturforschung A

101

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“…It is larger by nearly 2 orders of magnitude than the corresponding one for purely spontaneous positron autoionization. 6 This feature is due to the induced transitions (nonadiabatic effects). In systems with higher total charge Z 1 +Z 2 , the transitions to higher levels (2/> 1/2 , 2s 1/2 ) which come close to diving or are just diving (2p 1/2 ) must be taken into account and will further increase the cross sections.…”

Section: W D (E P Ej6) = \C D \ 2 De Pmentioning

confidence: 99%

“…4 Up to now calculations were done for the spontaneous positron creation. 6 The cross sections will be increased, however, by two effects because of the nonadiabacticity of the heavy-ion collision: First, during the "diving" process e*e" pairs are created, in addition to the spontaneous ones, by induced autoionization. Second, before and after the diving a large number of positrons will be created by induced transitions from the negative-energy continuum to the ls 1/2 level.…”

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confidence: 99%

Induced Decay of the Neutral Vaccum in Overcritical Fields Occurring in Heavy-Ion Collisions

et al. 1974

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In critical o r nearlg-critical heavy-ion collisions, induced as well as spontaiieous eriergyless e -e + pair creation result in the decay of the neutral vacuum. Induced transitions from the negative-energy continuum into a vacant molecular 1s level can occur even in the absence of diving and produce a substantial enhancement and broadening of the previously considered spontaneous positron spectrum. Total c r o s s sections of 5 b have been calculated for C-I! collisions.Intermediate quasimolecules, which will be formed in the collision of very heavy nuclei, show with respect to their electronic structure all properties of superheavy at0ms.l-' In the c a s e that the charge number 2, + Z , of the colliding nuclei is larger than the critical charge number Z u 169-172, the ls, , level enters the negative-energy continuum. If the K shell i s ionized, e'e -creation results. This has to be interpreted a s the decay of the neutral vacuum, which i s unstable in overcritical fields. ' Up to now calculations were done for the spontaneous positron ~r e a t i o n .~ The c r o s s sections will be increased, however, by two effects because of the nonadiabacticity of the heavy-ion collision: First, during the "diving" process e t e -pairs a r e created, in addition to the spontaneous ones, by induced autoionization. Second, before and after the diving a large number of positrons will be created by induced transitions from the negative-energy continuum to the ls", level. The latter transitions will occur even if there i s no level-diving during the collision.To calculate the total transition amplitude, all the transitions, from the negative-energy continuum to the ls", level, along the classical ion path must be added coherently . 7 These transitions niay be approximately grouped into first, pre-and after-diving amplitudes C","and second, the duringdiving amplitude C,. Then we have j -t~i d t ,and r ( t v )represents the decay ls", level due to the interaction with the continuum (to be determined later) and t u denotes the "critical" time a t uThich diving occurs. 1 4 2 and I cp a r e the wave functions for the positron (negative-energy continuum) and the l s U l vacancy, respectively. The time integration can be replaced by an integration over clR/z, along the ion hyperbola, where ri' i s the distance of the two ions and z , the radial velocity. The matrix element .iI,(tl) can be computed by expanding the bound state I ~l ( t ' ) )

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“…The transition amplitude a if can be calculated within the adiabatic basis of eigenstates in the two-center potential of the colliding nuclei [26] . Since in a close collision inner shell electrons cannot adjust quickly enough to the rapidly changing Coulomb potential, the first order adiabatic perturbation approximation is, in principle, not sufficient and calculations have to be performed in the coupled-channels approach.…”

Section: Basic Theoretical Backgroundmentioning

confidence: 99%

Investigation of the dynamics of dissipative U+Au collisions with δ-electron spectroscopy

Stroth

Backe

Begemann-Blaich

et al. 1997

Z Phys A - Particles and Fields

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δ-electron emission in elastic and dissipative collisions of U+Au at E/A = 8.65 MeV has been investigated. The velocity vectors of the reaction products were measured in coincidence with electrons of energies up to 3.2 MeV. The δ-electron yield measured for elastic collisions is in good agreement with coupled-channels calculations. The δ-electron spectra of dissipative reactions show a clear dependence on the violence of the collision, i.e. the total kinetic energy loss (TKEL). The shape of the spectra are analysed with an atomic model by a fitting procedure using phenomenological trajectories. The results indicate an increasing contact time of the united system with increasing total kinetic energy loss reaching 1.16(4) × 10 −21 s at < T KEL > = 375 MeV.

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Autoionization spectra of positrons in heavy-ion collisions

Cited by 41 publications

References 8 publications

The Two Centre Dirac Equation

The Two Centre Dirac Equation

Induced Decay of the Neutral Vaccum in Overcritical Fields Occurring in Heavy-Ion Collisions

Investigation of the dynamics of dissipative U+Au collisions with δ-electron spectroscopy

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