Prompt Neutron Emission in the Neutron-Induced Fission of 239Pu and 235U

Batenkov, O; Boykov, G. A.; Hambsch, F.‐J.; Hamilton, J. H.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A.; Sokolov, V. E.; Vorobyev, A. S.

doi:10.1063/1.1945175

Cited by 18 publications

(5 citation statements)

References 1 publication

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“…In the case of 235 U(n th , f) reaction, the calculation of the average prompt fission neutron multiplicity as a function of mass number is reported in fig. 8 and compared with experimental results from [41,45,46] and [47]. The calculation exhibits a minimum around mass 132 as expected by the model discussed above.…”

Section: Multiplicitysupporting

confidence: 53%

Fission modelling with FIFRELIN

2015

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The nuclear fission process gives rise to the formation of fission fragments and emission of particles (n, γ, e −). The particle emission from fragments can be prompt and delayed. We present here the methods used in the FIFRELIN code, which simulates the prompt component of the de-excitation process. The methods are based on phenomenological models associated with macroscopic and/or microscopic ingredients. Input data can be provided by experiment as well as by theory. The fission fragment deexcitation can be performed within Weisskopf (uncoupled neutron and gamma emission) or a Hauser-Feshbach (coupled neutron/gamma emission) statistical theory. We usually consider five free parameters that cannot be provided by theory or experiments in order to describe the initial distributions required by the code. In a first step this set of parameters is chosen to reproduce a very limited set of target observables. In a second step we can increase the statistics to predict all other fission observables such as prompt neutron, gamma and conversion electron spectra but also their distributions as a function of any kind of parameters such as, for instance, the neutron, gamma and electron number distributions, the average prompt neutron multiplicity as a function of fission fragment mass, charge or kinetic energy, and so on. Several results related to different fissioning systems are presented in this work. The goal in the next decade will be i) to replace some macroscopic ingredients or phenomenological models by microscopic calculations when available and reliable, ii) to be a support for experimentalists in the design of detection systems or in the prediction of necessary beam time or count rates with associated statistics when measuring fragments and emitted particle in coincidence iii) extend the model to be able to run a calculation when no experimental input data are available, iv) account for multiple chance fission and gamma emission before fission, v) account for the scission neutrons. Several efforts have already been made to replace macroscopic ingredients and phenomenology by microscopic ingredients provided in various nuclear parameter libraries such as electric dipole photon strength functions or HFB level densities. First results relative to theses aspects are presented in this work.

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Section: Multiplicitysupporting

confidence: 53%

Fission modelling with FIFRELIN

2015

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“…However, because prompt neutron emission, it is not possible to measure the primary fragment mass; and the experimental values associated with ν as a function of fragment mass depend on the used measurement technique. This has been shown for reactions 233 U(nth, f), 235 U(nth, f), 252 Cf(sf) [2][3][4][5][6][7][8][9][10], 239 Pu(nth, f) [11][12][13][14][15], and spontaneous fission of 252 Cf [16], respectively.…”

Section: Introductionmentioning

confidence: 78%

Monte Carlo simulation of the measurement by the 2E technique of the average prompt neutron multiplicity as a function of the mass of fragments from thermal neutron-induced fission of 239Pu

Montoya¹,

Páucar

Obregon³

et al. 2021

Rev. Mex. Fís.

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Using a Monte Carlo method, we simulate the measurement, by the 2E technique, of the average prompt neutron multiplicity as a function of the mass of fragments from the thermal neutron-induced fission of 239Pu. The input data for the simulation, associated with the primary fragment mass (A), consist of the yield (Y), the distribution of the total kinetic energy characterized by its average ((TKE) ̅) and its standard deviation (σ_TKE), the average prompt neutron multiplicity (ν ̅_s, a sawtooth approach of experimental data), and the slope of neutron multiplicity against total kinetic energy (dν_s/d<TKE>). The output data, associated with the simulated as the fragment mass measured by the 2E technique (µ), consist of the yield (y), the distribution of the total kinetic energy characterized by its average ((tke) ̅) and its standard deviation (σ_tke), and the average prompt neutron multiplicity (ν ̅_µ). In the mass regions A≈115 and A>150, ν ̅_µ is higher than ν ̅_s. This result suggests that, in those mass regions, the 2E experimental values associated with the average neutron multiplicity are overestimated, referred to the corresponding to the primary fragments.

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“…The mean neutron multiplicity, v, as a function of the mass number of the primary fission fragment, A, for 235 U(n th ,f). The calculated results (blue diamonds) are shown together with available experimental data: Nishio et al [8] (black squares), Apalin et al [9] (yellow circles), Vorobyev et al [10] (green triangles), Batenkov et al [11] (orange diamonds), Boldeman et al [12] (purple stars), Maslin et al [13] (brown triangles), Göök et al [14] (red circles). The red/blue arrows point to the mass divisions examined in Fig.…”

Section: Scissionmentioning

confidence: 97%

Energy sharing based on microscopic level densities

et al. 2021

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The transformation of a moderately excited heavy nucleus into two excited fission fragments is modeled as a strongly damped evolution of the nuclear shape. The resulting Brownian motion in the multi-dimensional deformation space is guided by the shape-dependent level density which has been calculated microscopically for each of nearly ten million shapes (given in the three-quadratic-surfaces parametrization) by using a previously developed combinatorial method that employs the same single-particle levels as those used for the calculation of the pairing and shell contributions to the five-dimensional macroscopic-microscopic potential-energy surface. The stochastic shape evolution is followed until a small critical neck radius is reached, at which point the mass, charge, and shape of the two proto-fragments are extracted. The available excitation energy is divided statistically on the basis of the microscopic level densities associated with the two distorted fragments. Specific fragment structure features may cause the distribution of the energy disvision to deviate significantly from expectations based on a Fermi-gas level density. After their formation at scission, the initially distorted fragments are being accelerated by their mutual Coulomb repulsion as their shapes relax to their equilibrium forms. The associated distortion energy is converted to additional excitation energy in the fully accelerated fragments. These subsequently undergo sequential neutron evaporation which is calculated using again the appropriate microscopic level densities. The resulting dependence of the mean neutron multiplicity on the fragment mass, as well as the dependence of on the initial excitation energy of the fissioning compound nucleus, exhibit features that are similar to the experimentally observed behavior, suggesting that the microscopic energy sharing mechanism plays an important role in low-energy fission.

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Prompt Neutron Emission in the Neutron-Induced Fission of 239Pu and 235U

Cited by 18 publications

References 1 publication

Fission modelling with FIFRELIN

Fission modelling with FIFRELIN

Monte Carlo simulation of the measurement by the 2E technique of the average prompt neutron multiplicity as a function of the mass of fragments from thermal neutron-induced fission of 239Pu

Energy sharing based on microscopic level densities

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