Reaction dynamics studied via positron and electron spectroscopy

Krieg, R.; Boek, Edo S.; Gollerthan, U.; Kankeleit, E.; Klotz-Engmann, G.; Kramer, M. A.; Meyer, U.; Oeschler, H.; Senger, P.

doi:10.1103/physrevc.34.562

Cited by 29 publications

(19 citation statements)

References 18 publications

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“…Therefore we have used the Nucleon Exchange Transport model, [25] which has no adjustable parameters and has successfully reproduced such diverse phenomena as energy dissipation in damped reactions, [26] entrance-channel mass asymmetry dependence of the probability for fusion, [27] and the time delay observed in collisions of very heavy nuclei as probed by electron-positron production. [28] With regard to dissipative reactions, the model successfully accounts for the energy loss dependencies of the variances of the Nand Z distributions, [29] the magnitude and alignment of the transferred angular momentum, [30] and the partition of the excitation energy between projectile-like and target-like fragments. [31] Second, we wish to determine to what extent one ca~ understand the qualitative features of such pre-equilibrium emission, especially the apparent source velocity and the spectral shape, in terms of energy dissipation prior to the particular nucleon transfer that led to pre-equilibrium emission.…”

Section: Introductionmentioning

confidence: 99%

Pre-equilibrium neutron emission in the nucleon exchange transport model

Randrup

Vandenbosch

1987

Nuclear Physics A

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LBL-23359We extend the Nucleon Exchange Transport model to include the emission of pre-equilibrium neutrons as a result of nucleon transfer to unbound states. The treatment takes account of the heating of the two nuclei caused by the energy dissipation and the cooling due to the pre-equilibrium emission. Furthermore, the transferred nucleons may induce cascading in the receptor nucleus by means of direct two-body scattering with the resident nucleons, based on a reduced, Pauli-blocked, energy-dependent free N N cross section. Qualitative agreement with experimental data is achieved, but the absolute multiplicities are systematically underestimated by about a factor of two. The dependence of multiplicity on bombarding energy is reproduced. The energy spectra and their variation with angle are generally reproduced, although the yield of the highest energy particles is sometimes underestimated.

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Section: Introductionmentioning

confidence: 99%

Pre-equilibrium neutron emission in the nucleon exchange transport model

Randrup

Vandenbosch

1987

Nuclear Physics A

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“…An interesting feature of the electron spectrum at large Q-values is the occurrence of two different slopes which may be interpreted as a remnant of an oscillation pattern showing up in a semi-classical calculation for a well-defined nuclear sticking time 240 . Friction effects in S-electron spectra have also been observed for I + Au collisions 14 and U + U collisions 236 .…”

Section: E^(mev)mentioning

confidence: 66%

Theoretical Models for Atomic Charge Transfer in Ion-Atom Collisions

Jakubaßa-Amundsen

1989

Int. J. Mod. Phys. A

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The current theoretical models for the description of electron transfer in adiabatic, intermediate and high-energy collisions are reviewed. Particular emphasis is laid on the recent development of atomic theories suited for fast or asymmetric ion-atom encounters. The comparison with other theories and with experimental data on total as well as differential capture cross sections is used to determine the applicability of a specific model. The selected examples concern capture to bound states, to continuum states, radiative transfer as well as capture in the presence of an isolated nuclear resonance.

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“…Since a direct determination of the y-ray multipolarity is precluded by these experiments, one has to rely on the previous experimental findings [3,32] that the multipolarity (mainly El) does not change significantly in a series of light collision systems and that there is so far no evidence for an opposite behaviour by the heavy systems, as long as quasi-elastic (binary) reactions at the Coulomb barrier are concerned (see e.g. [34]). As already mentioned, the investigation of the light collision system U § Pd confirms these features.…”

Section: Evahtation Of the Nuclear Positron Backgroundmentioning

confidence: 98%

“…It should be mentioned here that E2 transitions are expected to dominate in the y-ray spectra for transition energies below than about 1.3 MeV (see e.g. [34]), and, hence, its small contribution (~ 10%) in the (El~E2) fixed ratio has practically no influence on the calculated nuclear background, at least for positron energies larger than 300-400 keV. This rather complex method, which is widely used by the three groups at GS!…”

Section: Evahtation Of the Nuclear Positron Backgroundmentioning

confidence: 98%

“…At present, no convincing explanation can incorporate these findings, despite considerable investigations in heavy-ion collisions [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and in related Bhabha-scattering experiments [26][27][28][29] as well as theoretical [30,31] efforts in the last years. The TORI group could not confirm unambiguously this phenomenon [36], addressing itself mainly to studies at higher beam energies for which no structures are reported [33][34][35].…”

Section: Introductionmentioning

confidence: 98%

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Systematic studies of positron production in heavy-ion collisions near the Coulomb barrier

Tsertos¹,

Berdermann²,

Bosch³

et al. 1992

Z. Physik A - Hadrons and Nuclei

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We present the results obtained from systematic studies of positron creation for a series of heavy-collision systems, with united charge Z,=Z I+Z 2 ranging from Z,= 164 (Pb+Pb) to Z,,= 184 (U+U) at bombarding energies close to the Coulomb barrier, using the Orangefl-spectrometer at GSI. For each collision system studied, the dominating continuous distributions due to quasiatomic and nuclear positron emission are determined accurately. This is essential in obtaining the characteristics of the still unexplained monoenergetic positron lines which appear in the energy range between 200 keV and 400 keV. Our results are compared with coupled-channels calculations for quasi-atomic positron creation. The latter describe quite well the global features of the measured spectra, but overestimate systematically their absolute values. From the comparison, a common normalization factor of about 0.75 can be established for the calculated spectra. In particular, the dependence on Z,, of the measured emission probabilities was found to follow a power law (ocZ,~95-+~), in fair agreement with the theoretical prediction.

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Reaction dynamics studied via positron and electron spectroscopy

Cited by 29 publications

References 18 publications

Pre-equilibrium neutron emission in the nucleon exchange transport model

Pre-equilibrium neutron emission in the nucleon exchange transport model

Theoretical Models for Atomic Charge Transfer in Ion-Atom Collisions

Systematic studies of positron production in heavy-ion collisions near the Coulomb barrier

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