High energy gamma-ray production in heavy-ion reactions

doi:10.1016/0370-2693(86)90700-8

Physics Letters B

Volume 175, Issue 2, 31 July 1986, Pages 125-128

https://doi.org/10.1016/0370-2693(86)90700-8 Get rights and content

Abstract

The doubly-differential cross section for the production of gamma-rays with energies larger than 20 MeV has been measured in the reaction ⁴⁰Ar+¹⁹⁷ Au at 30 MeV/u incident energy. It is found that the spectra are thermal-like, the emitting source having half the beam velocity and an apparent temperature around 7.3 MeV. The non-observation of a collective component is discussed.

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The investigation of hot and compressed nuclear matter by means of heavy-ion collisions requires the development of probes that are sensitive to the time evolution of the nuclear phase-space density. Hard particles, such as energetic photons or mesons, which are produced during the reaction, may provide such probes. In the first part of this article we describe the time evolution of the nuclear many-body system within a nonperturbative transport approach as well as the methods employed for the evaluation of the elementary nucleon-nucleon-particle cross sections. The second part contains a description of the experimental set-ups used for the detection of hard photons in heavy-ion experiments and a discussion of the empirical systematics of data gained so far. In the third part of this article we compare the theoretical predictions for differential particle yields with the available data. Detailed comparisons are presented for hard photons at bombarding energies from 15 MeV/u to 125 MeV/u, for dileptons at 1 GeV/u and for mesons (π's, η's, K⁺'s) from 30MeV/u to 2 GeV/u. We finally discuss selection criteria for optimal probes with respect to the experimental determination of the nuclear equation of state at high densities.
Photon production in relativistic heavy-ion collisions
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Hard-photon production in heavy-ion collisions and the nuclear structure function
1990, Nuclear Physics, Section A
The production of hard photons in heavy-ion collisions at intermediate energies is studied. The particles result from first-chance single proton-neutron collisions. The cross sections are expressed in terms of the product of the structure functions of the nuclei. At large momentum transfers the structure function is related to the momentum distribution of the nucléons. The parametrization obtained from high-energy proton scattering gives a good description of the photon production data. The mass dependence of the reaction phase space and its implications are examined. An energy conservation condition that describes correctly the mass of the system is used. The Pauli principle is discussed. The experimental data are in agreement with the assumption that photons are produced before the colliding nuclei overlap.
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Energy spectra and angular distributions of hard photons produced by proton-neutron collisions following nucleon between heavy-ion collision partners have been calculated. The model is a direct extension of our recent model for pre-equilibrium nucleon emission, where the importance of nucleon scattering in the receptor nucleus was demonstrated. The model has no adjustable parameters and provides a near-quantitative account of a large body of both inclusive and exclusive photon yields and angular distributions.

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^☆: This experiment was made possible owing to the efficiency of the SARA operating team. We thank Mrs. C. Petit for typing this manuscript. We are especially grateful to A. Veyssières, P. Bourgeois and P.J. Carlos who made the calibration measurements possible at the Saclay LINAC, and were very helpful by giving us advantage of their experimental facility and data acquisition system. Last but not least we thank S. Bjornholm for careful proofreading of the manuscript and many inspiring discussions and comments.

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High energy gamma-ray production in heavy-ion reactions☆

Abstract

Nucl. Phys.

Nucl. Phys.

Phys. Rev. C

J. Phys. G