Light element ( $$Z=1,2$$ Z = 1 , 2 ) production from spontaneous ternary fission of $$^{252}$$ 252 Cf
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Regular Article - Theoretical Physics
Light element (Z = 1, 2) production from spontaneous ternary fission of 252 Cf G. Röpke1,a , J. B. Natowitz2,b , H. Pais3,c 1
Institut für Physik,Universität Rostock, 18051 Rostock, Germany Cyclotron Institute, Texas A&M University, College Station, TX 77843, USA 3 CFisUC, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal
2
Received: 13 August 2020 / Accepted: 7 September 2020 © The Author(s) 2020 Communicated by Cedric Simenel
Abstract The yields of light elements (Z = 1, 2) obtained from spontaneous ternary fission of 252 Cf are treated within a nonequilibrium approach, and the contribution of unstable nuclei and excited bound states is taken into account. These light cluster yields may be used to probe dense matter, and to infer in-medium corrections such as Pauli blocking which is determined by the nucleon density. Continuum correlations are calculated from scattering phase shifts using the BethUhlenbeck formula, and the effect of medium modification is estimated. The relevant distribution is reconstructed from the measured yields of isotopes. This describes the state of the nucleon system at scission and cluster formation, using only three Lagrange parameters which are the nonequilibrium counterparts of the temperature and chemical potentials, as defined in thermodynamic equilibrium. We concluded that a simple nuclear statistical equilibrium model neglecting continuum correlations and medium effects is not able to describe the measured distribution of H and He isotopes. Moreover, the freeze-out concept may serve as an important ingredient to the nonequilibrium approach using the relevant statistical operator concept.
1 Introduction Thermal neutron induced and spontaneous ternary fission is a process in which the emission of two medium-mass fragments is accompanied by equatorially emitted light particles and clusters formed in the neck region at the time of scission, see [1–3] and references therein. Data for cluster yields obtained from ternary fission experiments with thera e-mail:
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mal neutrons are shown, e.g., in [4–6]. In particular, data for the ternary fission yields of 241 Pu(n th ,f) are presented. An interpretation of the Koester et al. data [4] was given in Ref. [7], where a suppression of the yields of the larger clusters is found, due to cluster formation kinetics. Also, ternary fission has been observed from other actinides such as 239 Pu, 233 U, 235 U, and 245 Cm. For more recent work on ternary fission see Refs. [8–13]. Different approaches have been employed to interpret these data, see [5], and often a Boltzmann distribution has been used. An interpolation formula has been presented in [14] which describes the general behavior of the measured yields but cannot explain the details of the observed distributions. More fundamentally, the use of a Boltzmann distribution as known from thermodynamic equi
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