Abstract
The interaction between medium-weight nuclei and a strong zeptosecond laser pulse of MeV photons is investigated theoretically. Multiple absorption of photons competes with nuclear equilibration. We investigate the sudden regime. Here the rate of photon absorption is so strong that there is no time for the nucleus to fully equilibrate after each photon absorption process. We follow the temporal evolution of the system in terms of a set of rate equations. These account for dipole absorption and induced dipole emission, equilibration (modeled in terms of particle-hole states coupled by the residual nuclear interaction), and neutron decay (populating a chain of proton-rich nuclei). Our results are compared with earlier work addressing the adiabatic regime where equilibration is instantaneous. We predict the degree of excitation and the range of nuclei reached by neutron evaporation. These findings are relevant for planning future experiments.
Highlights
Exciting experimental developments at petawatt laser facilities [1] combined with experimental, computational, and theoretical advances in the production of high-energy laser pulses [2,3,4,5,6,7,8,9] give rise to the hope that intense pulses with photon energy hω0 in the few MeV range and with a typical energy spread σ in the 10-keV range will become available in the near future
We investigate the temporal evolution of the nucleus over the laser pulse duration, and we follow the chain of neutron evaporation processes towards proton-rich nuclei
We use the Chebyshev rational approximation method (CRAM) which is known for its success in solving burnup equations [35,36]
Summary
Exciting experimental developments at petawatt laser facilities [1] combined with experimental, computational, and theoretical advances in the production of high-energy laser pulses [2,3,4,5,6,7,8,9] give rise to the hope that intense pulses with photon energy hω0 in the few MeV range and with a typical energy spread σ in the 10-keV range will become available in the near future. Theoretical and numerical studies [25,26] in that regime are based on a statistical approach and make use of rate equations These have shown that multiple photon absorption produces compound nuclei in the so-far unexplored regime of several hundred MeV excitation energy and low angular momentum. These describe the time evolution of the average occupation probabilities of classes of mp-mh states under the influence of the external field of the laser They account for the following competing processes: photoabsorption and its inverse process stimulated photon emission, equilibration, and neutron evaporation. The combination of repeated neutron emission and continued dipole absorption by the daughter nuclei produces proton-rich nuclei far from the valley of stability This picture is qualitatively similar to but quantitatively somewhat different from the results for the quasiadiabatic regime.
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