Parameterisation of the residual temperature distribution based on the modelling of successive emission of prompt neutrons

A new deterministic modelling taking into account the successive emission of prompt neutrons from initial fragments of a fragmentation range {A, Z, TKE} constructed as in the Point-by-Point (PbP) treatment is described. The good agreement of different prompt emission quantities obtained from this modelling (e.g. v(A), v(TKE), E-γ(A), E-γ(TKE), etc.) with the experimental data and the results of the PbP model and other Monte-Carlo models validates the present modelling of sequential emission. The distributions of different residual quantities, including the residual temperature distributions P(T) of light and heavy fragments allow to obtain a new parameterisation of P(T) which can be used in the PbP model and the Los Alamos model

Detailed validation of two deterministic models of prompt emission. Systematic behaviours of residual quantities from the sequential emission

The results of the PbP and sequential emission modellings describe very well the recent experimental data of 235U(n,f). The application of the sequential emission treatment to 49 fission cases has emphasized systematic behaviours of different quantities characterizing the fragments and the prompt emission. These allowed the determination of a general form of the residual temperature distribution for each emission sequence and the inclusion of sequential emission into the Los Alamos model

Correlation between the excitation energy of pre-neutron fragments and the kinetic energy of post-neutron fragments; application for

The present paper continues a recently published study (devoted to the influence of energy partition in fission and pre-neutron fragment distributions on post-neutron fragment yields) by the investigation of possible correlations between quantities characterizing the pre- and post-neutron fragments. An interesting correlation between the excitation energy of fully accelerated pre-neutron fragments and the kinetic energies of post-neutron fragments is found. The influence of both the energy partition in fission and the pre-neutron fragment distributions on the behaviour of the excitation energy of pre-neutron fragments as a function of the kinetic energy of post-neutron fragments is investigated, too

Validation of two deterministic modelings of prompt emission in fission on the basis of recent experimental data

New experimental prompt fission neutron and fragment data for 235U(n, f ) measured at JRC-Geel offer the possibility of a detailed validation of the PbP and sequential emission modelings. The very good agreement of the prompt neutron multiplicity matrices $$\nu (A,\mathrm{TKE})$$ with these data constitutes a primary and valuable validation of the models themselves. Other data from this experiment are also well described by both model results obtained by averaging the corresponding multi-parametric matrices over an $Y(A,\mathrm{TKE})$ distribution measured at JRC-Geel. This is considered as a secondary validation (i.e., of the models together with the $Y(A,\mathrm{TKE})$ distribution)

Prompt

The paper includes prompt \upgamma -ray results provided by two deterministic modelings of prompt emission developed at the University of Bucharest. The very good description of experimental prompt \upgamma -ray data as a function of A and TKE by the multi-parametric matrices as primary results of both modelings assures a supplementary validation of the models themselves. The very good agreement of the single distributions of different prompt \upgamma -ray quantities (as a function of A and as a function of TKE) with the experimental data constitutes a supplementary validation of the models together with the fragment distributions used. Linear correlations between different prompt \upgamma -ray quantities and the prompt neutron multiplicity are emphasized, too. A new method to calculate the prompt \upgamma -ray spectrum consisting of a global treatment based on the distribution of prompt \upgamma -ray energy per quanta is proposed

Systematics of input parameters for the Los Alamos model with sequential emission

The application of the Point-by-Point treatment to numerous fission cases (i.e. 74 cases including many actinides fissioning spontaneously or induced by thermal neutrons and fast neutrons with energies up to the threshold of the second chance fission) has emphasized interesting systematic behaviors of different quantities characterizing the fission fragments. Such systematics can provide values of the input parameters for a new version of the Los Alamos (LA) model including the sequential emission of prompt neutrons, which was recently developed and validated. The prompt neutron spectrum results based on the systematics of input parameters are obtained in good agreement with the experimental data of many actinides. The LA model with sequential emission together with the proposed systematics of its input parameters can predict prompt neutron spectra of fissioning nuclei without any experimental information, thus it becomes an useful tool for prompt neutron spectrum evaluations

Influence of energy partition in fission and pre-neutron fragment distributions on post-neutron fragment yields, application for

The key role in the calculation of post neutron fragment yields (independent fission product yields FPY) is played by (a) the pre-neutron fragment distributions Y(A,Z,TKE) and (b) the prompt neutron multiplicity (calculated in the frame of a prompt emission model). The knowledge of excitation energies of fully accelerated fragments is crucial in any modeling of prompt emission. Consequently in this paper the influence on independent FPY and kinetic energy distributions of post neutron fragments of both the pre-neutron fragment distribution and the partition of total excitation energy (TXE) is investigated. To do that, two reliable experimental Y(A,TKE) distributions of the standard fissioning nucleus 235U(nth,f) and two methods of TXE partition are considered. Nowadays two types of TXE partitions are employed in different prompt emission models, i.e. energy partitions based on different modelings at scission and different parameterizations which allow the TXE sharing by avoiding what is happening at scission. For this reason the methods of TXE partition chosen in this work belong to both types, i.e. (i) the TXE partition based on modeling at scission used in the deterministic prompt emission models PbP and DSE and (ii) the TXE partition according to the temperature ratio RT = TL/TH of complementary fully accelerated fragments (employed in the deterministic HF3D model and the probabilistic Monte-Carlo code CGMF). The independent FPY results (Y(Z,Ap) and Y(Ap)) obtained with both TXE partition methods and both Y(A,TKE) data describe reasonably well the experimental data. The use of different TXE partitions and Y(A,TKE) data does not change the position of the most pronounced peaks and dips in the Y(Ap) structure (e.g. at Ap = 134, 138, 94 and Ap = 136, 141, 97, respectively) and Y(Np) structure (e.g. at Np = 82, 84, 56 and Np = 83, respectively) only their magnitude is influenced by Y(A,TKE) distribution, while the TXE partition influences the position of less pronounced peaks and dips in the structures of Y(Ap) and Y(Np). The TXE partition has an insignificant influence on different kinetic energy distributions of post-neutron fragments, while the differences existing between the kinetic energy distributions of pre-neutron fragments are reflected in the kinetic energy distributions of post-neutron fragments

Systematic behaviours of different quantities related to sequential prompt emission in fission

The deterministic modelling of sequential prompt emission in fission based on recursive equations of residual temperature was applied to numerous fission cases. This fact emphasized systematics and correlations between different quantities characterizing the residual fragments and the sequential emission. General forms of residual temperature distributions for each emission sequence are determined on the basis of these systematics, having as application the inclusion of sequential emission into the Los Alamos model. Also the systematics can serve to obtain indicative values of different average quantities in the absence of any prompt emission model

Inclusion of sequential emission into the most probable fragmentation approach (Los Alamos model) and its validation

A new version of the Los Alamos (LA) model, based on more physical considerations than the previous versions by taking into account the sequential emission of prompt neutrons, is proposed. A residual temperature distribution for each emission sequence P$$_{\mathrm {k}}$$(T) is considered, so that this new version can provide the prompt neutron spectrum in the center-of-mass and laboratory frames of each neutron successively emitted from the light and heavy fragment. The LA model with sequential emission is applied on 15 fission cases which were not included in the 49 cases used in the elaboration of the systematics of different quantities of residual nuclei, on which the general form of $$\hbox {P}_{\mathrm {k}}$$(T) is based. The good description of experimental prompt neutron spectrum data of these fission cases by the model results constitutes a relevant validation of the LA model with sequential emission. Systematic behaviours of the average energies (in the center-of-mass and laboratory frames) provided by this model for each neutron sequentially emitted, are also emphasized

Influence of energy partition in fission and pre-neutron fragment distributions on post-neutron fragment yields, application for

The key role in the calculation of post-neutron fragment yields (independent FPY) is played by the pre-neutron fragment distributions Y(A,TKE) and the prompt neutron multiplicity (calculated in the frame of a prompt emission model). The knowledge of excitation energies of fully accelerated fragments is crucial in any prompt emission model. So that the influence on independent FPY of two methods of total excitation energy (TXE) partition, one based on modeling at scission and another on a parameterization at the full acceleration of fragments, and of two reliable Y(A,TKE) data of 235U(nth,f) is investigated by using the deterministic prompt emission model with a detailed treatment of sequential emission DSE. The independent FPY results Y(Ap) and Y(Z,Ap) obtained with both methods of TXE partition and both Y(A,TKE) distributions describe reasonably well the experimental data. The use of different TXE partitions and Y(A,TKE) data does not change the positions of the most pronounced peaks and dips in the Y(Ap) structure, only their magnitude is influenced by Y(A,TKE), while the TXE partition influences the position of less pronounced peaks and dips in the structures of Y(Ap) and Y(Np) (Np=Ap-Z). The influence of both the TXE partition and the Y(A,TKE) data on different kinetic energy distributions of post-neutron fragments is less pronounced than that on Y(Ap) and Y(Np