The production of nuclear bremsstrahlung photons (E\(_{\gamma}>\) 30 MeV) has been studied in inclusive and exclusive measurements in four heavy-ion reactions at 60{\it A} MeV. The measured photon ...spectra, angular distributions and multiplicities indicate that a significant part of the hard-photons are emitted in secondary nucleon-nucleon collisions from a thermally equilibrated system. The observation of the thermal component in multi-fragment \(^{36}\)Ar+\(^{197}\)Au reactions suggests that the breakup of the thermalized source produced in this system occurs on a rather long time-scale.
Inclusive and exclusive hard-photon (E\(_\gamma >\) 30 MeV) production in five different heavy-ion reactions (\(^{36}\)Ar+\(^{197}\)Au, \(^{107}\)Ag, \(^{58}\)Ni, \(^{12}\)C at 60{\it A} MeV and ...\(^{129}\)Xe+\(^{120}\)Sn at 50{\it A} MeV) has been studied coupling the TAPS photon spectrometer with several charged-particle multidetectors covering more than 80% of 4\(\pi\). The measured spectra, slope parameters and source velocities as well as their target-dependence, confirm the existence of thermal bremsstrahlung emission from secondary nucleon-nucleon collisions that accounts for roughly 20% of the total hard-photon yield. The thermal slopes are a direct measure of the temperature of the excited nuclear systems produced during the reaction.
We report on a measurement of hard photons (Eg>30 MeV) in the reaction Ar+Ca at 180A MeV at an energy in which photons from the decay of pi0 mesons are dominating. Simultaneous measurement with the ...TAPS spectrometer of the photon spectrum and photon-photon coincidences used for the identification of pi0 enabled the subtraction of pi0 contribution. The resulting photon spectrum exhibits an exponential shape with an inverse slope of E0=(53+-0.03(stat)-5+8(syst)) MeV. The photon multiplicity, equal to (1.21+-0.03(stat)+0.3-0.2(syst))10E0-2, is roughly one order of magnitude larger than the value extrapolated from existing systematics. This enhancement of the hard photon production is attributed to a strong increase in the contribution of secondary np collisions to the total photon yield. We conclude that, on average, the number of np collisions which contribute to the hard photon production is 7 times larger than the number of first chance np collisions in the reaction Ar+Ca at 180A MeV.
