Jun 11 – 15, 2018
Villa Monastero
Europe/Zurich timezone

The role of nucleon knockout in pre-equilibrium reactions

Jun 15, 2018, 12:20 PM
20m
Villa Monastero

Villa Monastero

Varenna (Italy)
Nuclear reactions Nuclear reactions

Speaker

Brett Carlson (Instituto Tecnológico de Aeronáutica)

Description

Nucleon-induced pre-equilibrium reactions are predominantly direct reactions. At low incident energies, excitation of all but the lowest energy collective states can be well described in terms of one-step reactions that produce particle-hole pairs. As the incident energy is increased, more complex excitations involving two or more particle-hole pairs become accessible through multi-step reactions. Quantum mechanical models of such multi-step direct reactions were developed many
years ago [1,2,3] and have been studied and improved many times over since then [4,5,6,7]. In these models, a leading continuum particle initiates the reaction and remains in the continuum as it scatters repeatedly from the nucleus to produce successive particle-hole pairs. However, as the incident energy increases, the probability of exciting a nucleon to the continuum rather than to a bound particle state also increases. [8] These knockout nucleons can escape the nucleus or induce
secondary collisions that create still other continuum or bound particle-hole pairs. Calculations using Blann and Chadwick’s DDHMS pre-equilibrium simulation model [9,10] reveal that a 20 MeV neutron incident on 56Fe produces an additional continuum particle in 10% of its scatterings with nucleons in the nucleus and yields a knockout cross section of approximately 4% of the reaction cross section. At 200 Mev, knockout of at least one nucleon, that is, emission of two or more pre-equilibrium nucleons, corresponds to almost 80% of the pre-equilibrium reaction cross section. Here we discuss these calculations in more detail. We also analyze and compare the typical energy and angular distributions obtained from one-step quantum mechanical calculations of inelastic excitation and knockout reactions.

References
[1] H. Feshbach, A. Kerman, S. Koonin, Ann. Phys (N.Y.). 125 (1980) 429.
[2] T. Tamura, T. Udagawa, H. Lenske, Phys. Rev. C 26 (1982) 379.
[3] H. Nishioka, H. A. Weidenmüller, S. Yoshida, Ann. Phys. (N.Y.) 183 (1988) 166.
[4] A. Koning, M. Chadwick, Phys. Rev. C 56 (1997) 970.
[5] T. Kawano, S. Yoshida, Phys. Rev. C 64 (2001) 024603.
[6] M. Dupuis, T. Kawano, J. P Delaroche, E. Bauge, Phys. Rev. C 83 (2011) 014602.
[7] M. Dupuis, E. Bauge, S. Hilaire, S. F. Lechaftois, S. Péru, N. Pillet, C. Robin, Eur. Phys. J. A 51 (2015) 168.
[8] B. V. Carlson, J. E. Escher, M. S. Hussein, 41 (2014) 094003.
[9] M. Blann, Phys. Rev. C 54 (1996) 1341.
[10] M. Blann, M. Chadwick, Phys. Rev. C 57 (1998) 233.

Primary authors

Brett Carlson (Instituto Tecnológico de Aeronáutica) Mr Emanuel V. Chimanski (Instituto Tecnológico de Aeronáutica, NAPC-Nuclear Data Section, International Atomic Energy Agency) Dr Roberto Capote (NAPC-Nuclear Data Section, International Atomic Energy Agency) Dr Arjan J. Koning (NAPC-Nuclear Data Section, International Atomic Energy Agency)

Presentation materials