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In the last decade, there has been a renaissance of fission research resulting in new high-precision experiments and advanced fission modeling. For instance, the Chi-Nu and CEA teams supplied, for the first time, the 239Pu prompt fission neutron spectrum (PFNS) for broad ranges of incident and outgoing neutron energies. The CEA team also measured 239Pu average prompt neutron multiplicities, ν̄p, with lower statistical uncertainties and a technique significantly different than the one used in the past. The NIFFTE collaboration provided 239Pu(n,f)/235U(n,f) cross section shape ratios with uncertainties below 1% utilizing a novel detector type. Advanced fission event generators were developed, among them CGMF, FIFRELIN, FREYA, and GEF, which calculate post-scission fission observables in a correlated manner. These new experimental data and more consistent fission models change the evaluated PFNS, ν̄p, and (n,f) cross sections, some only modestly, compared to ENDF/B-VIII.0. In turn, the individual new nuclear data distinctly change simulated effective neutron multiplication factors of fast critical assemblies, but their combined impact is small, while affecting the prediction of LLNL pulsed sphere neutron leakage spectra and reaction rates only within experimental uncertainties. Also, the parameters obtained from fitting to ν̄p reproduce various post-scission fission observables within the uncertainties of experimental data. This indicates that new differential experiments and consistent fission modeling reduce compensating errors present in ENDF/B-VIII.0.

The experimental data concerning 239Pu prompt fission neutron spectrum above 10 MeV are sparse, and no spectrum averaged cross section has been measured in this neutron field yet. The first measurement was performed at the IBR-2 reactor, which uses plutonium dioxide fuel. The present work aimed at the measurement of spectral averaged cross sections for high threshold reactions such as 46Ti(n,p)46Sc, 54Fe(n,p)54Mn, 58Ni(n,X)57Co, 89Y(n,2n)88Y, and 209Bi(n,3n)207Bi to explore the high energy region of the 239Pu prompt fission neutron spectrum. Measurement of spectrum averaged cross section for the 89Y(n,2n)88Y reaction is included in NEA high priority request list. The 58Ni(n,p)58Co reaction was employed as a monitor reaction. The experimental spectral averaged cross sections were derived from reaction rates measured by means of high purity Germanium spectrometry. The experimental values were compared with spectrum averaged cross sections compiled from either ENDF/B-VIII.0, GMA or JEFF-3.3 239Pu prompt fission neutron spectrum and IRDFF-II cross sections. The best agreement, i.e. within uncertainties, was achieved using GMA 239Pu prompt fission neutron spectrum for all reactions under study. Calculation results using JEFF-3.3 and ENDF/B-VIII.0 evaluations of the 239Pu prompt fission neutron spectrum agree well with the experimental data except for the high energy region reflected in the disagreement with the 209Bi(n,3n)207Bi reaction. • Measurement of 239Pu SACS using IBR-2 reactor. • 46Ti(n,p)46Sc, 54Fe(n,p)54Mn, 58Ni(n,X)57Co, 89Y(n,2n)88Y, and 209Bi(n,3n)207Bi reactions investigation. • Comparison of SACS with the evaluated values of JEFF-3.3, ENDF/B-VIII.0 and IAEA GMA 239Pu PFNS evaluations. [ABSTRACT FROM AUTHOR]

The spectra of neutrons emitted in fission of 238 U induced by 2.8 MeV neutrons were measured by N-4 nuclear emulsion. Details like the experimental layout and conditions, and the track data reading, processing and correction were described. Also the energy-range relation of recoil protons among the N-4 nuclear emulsion was derived by Monte Carlo simulation and fitting method for the first time. The experimental results were presented as relative yields and were compared to the calculations using Maxwell and Watt models. The results were approximately the same as the theoretical PFNS, especially for those 3–6 MeV and 11–14 MeV outgoing neutrons, and the availability of nuclear emulsion measurement in the high-energy part of PFNS was proved. [ABSTRACT FROM AUTHOR]

Compared to the extensively studied proton even-odd effects in fission fragment distributions, the even-odd effects in prompt emission received less attention. In this context the present paper is focusing on the even-odd effects (in both Z and N) appearing in prompt neutron and gamma ray emission. The study of even-odd effects in the prompt emission of four fissioning nuclei with even Z and even N, 233,235U(nth,f), 239Pu(nth,f) and 252Cf(SF), shows that these effects are mainly due to the Z even-odd effects in fragment distributions and charge deviations and the N even-odd effect in average neutron separation energies. The most pronounced even-odd effect in prompt emission is for the prompt neutron multiplicity. The average multiplicity as a function of Z, ν(Z), has a sawtooth shape and exhibits a visible staggering for asymmetric fragmentations. The size of the global even-odd effect in prompt neutron multiplicity shows a decrease with increasing fissility. The N even-odd effect in average neutron separation energy influences the global even-odd effect in prompt neutron multiplicity often in an opposite way compared to the Z even-odd effect. The average prompt neutron multiplicity as a function of TKE shows an increase of the Z even-odd effect with increasing TKE and this effect is decreasing for heavier fissioning systems. The Z even-odd effects in the average prompt-ray energy and the average prompt neutron energy have comparable sizes and are lower than the even-odd effects in prompt neutron multiplicity. Different average prompt emission quantities (as a function of A, of Z, of TKE and total average ones)-being dependent on fragment distributions-are affected by the even-odd effects in. The N even-odd effect in neutron separation energy and the Z even-odd effect in the charge deviation enter the primary multi-parametric matrices of prompt emission quantities (e.g.) which are not depending on fragment distributions. [ABSTRACT FROM AUTHOR]

Abstract: Prompt emission quantities of 234U( ) (average quantities as a function of fragment mass, average quantities as a function of total kinetic energy (TKE) and total average quantities) have been calculated within the Point-by-Point model. The recently measured fission fragment distributions at incident energies (En) ranging from 0.2 MeV to 5 MeV have been used. The insensibility of the fragment pair multiplicity to the partition of total excitation energy (TXE) between complementary fully accelerated fission fragments has been confirmed. This gives confidence in the predicted total average prompt emission data as a function of En and of average quantities as a function of TKE at different incident energies of 234U( ). The systematic behavior of experimental ratios as a function of heavy fragment mass number together with the TXE partition based on modeling at scission allow the parameterization of the excitation energy ratio . This opens up the possibility to provide of 234U in the absence of any experimental data. For the first time the calculation of at many En revealed two interesting aspects: the slope does not vary with En and the flattening of at low TKE values is more pronounced at low incident energies. The correlation between the sub-barrier resonant behavior of the fission cross section of fertile actinides (characterizing the pre-scission stage) and the visible fluctuations of their fission fragment and prompt neutron emission data (characterizing the post-scission stage), already discussed in the case of 238U( ) is outlined and quantitatively supported by 234U( ), too. The pronounced vibrational resonances in the experimental fission cross section of 234U placed below 1 MeV can be described by the statistical model for reaction cross section calculation including the optical model for fission. [Copyright &y& Elsevier]

Abstract: Model calculations of prompt neutron and gamma-ray emission of 232Th(n,f) up to the incident energy of 20 MeV are reported. For the first time the experimental average prompt gamma-ray energy data of this fissioning nucleus are very well described by a model result. The calculated total average prompt neutron multiplicity gives an excellent description of experimental data over the entire fast neutron energy range, including the variations around the energies of fission cross-section resonances and the sudden increase at the incident energy where the second fission chance is opening. The behavior consisting in the multiplicity increase with the incident energy for heavy fragments only, experimentally observed for 235U(n,f) and 237Np(n,f) and confirmed by model calculations, is supported by the Point-by-Point model results in the case of 232Th(n,f), too. The correlation between the sub-barrier resonances in the fission cross-section and the non-statistical variations of fragment and prompt emission data around the resonance energies, already discussed for the fertile actinides 238U and 234U, is confirmed by the present results of 232Th(n,f). The average prompt gamma multiplicity result, almost constant with the incident neutron energy, is in agreement with the experimental observation of Fréhaut. The calculated prompt fission neutron spectra describe well the existing experimental data. The lump around 8 MeV, exhibited by the experimental spectrum data measured at 14.6 MeV, is well described by the present calculations by including the contribution of the (n,xn) spectra of neutrons emitted prior to the scission provided by nuclear reaction calculations. [Copyright &y& Elsevier]

Abstract: The neutron emission energy spectra in the CMS (center-of-mass) frame from two compound nuclei produced by fission are studied. The neutron spectra calculated with the Hauser–Feshbach statistical model are compared with the evaporation theory, and the definition of the temperature is revisited. Using the Monte Carlo technique we average the CMS neutron spectra from many fission fragments to construct the representative CMS spectrum from both the light and heavy fragments. The CMS spectra for each fission fragment pair are also converted into the laboratory frame to calculate the total prompt fission neutron spectrum that can be observed experimentally. This is compared to measured laboratory data for thermal neutron induced fission on 235U. We show that the Hauser–Feshbach calculation gives a different spectrum shape than the Madland–Nix model calculation. [Copyright &y& Elsevier]

Abstract: As output of the Point by Point model (taking into account the entire fission fragment range) and of the most probable fragmentation approach (working with one fragmentation and average values of model parameters) not only prompt neutron quantities are provided but also the prompt γ-ray energy as a function of fragment Eγ(A) and the total average prompt γ-ray energy . The almost linear behaviour of the total average with the prompt neutron multiplicity was observed experimentally in the incident neutron energy range where only the first fission chance is involved. This was parameterised as a function of Z and A of the fissioning nucleus. This parameterisation was validated by calculations in the frame of the most probable fragmentation approach. The results describe well the experimental data measured by J.FrŽhaut from thermal up to about 15 MeV incident energy for three fissioning systems 235U(n,f),237Np(n,f) and 232Th(n,f).The Point by Point model provides average prompt γ-ray energy as a function of the fragment pair in very good agreement with the existing experimental data of 252Cf(SF) and 233U(nth,f). The unique experimental data of prompt γ-ray energy as a function of fragment measured for 235U(nth,f) is very well described by the Point by Point model results obtained by using two methods of total excitation energy partition between complementary fission fragments. [Copyright &y& Elsevier]

Abstract: A method of total excitation energy (TXE) partition between fully-accelerated fission fragments based exclusively on the systematic behaviour of experimental ( as a function of being parameterized) is proposed. This TXE partition method has the advantage to be not dependent on models and assumptions made at scission and in this sense it can be taken as a possible reference method. From this TXE partition applied on many fissioning systems a general parameterization of the fragment residual temperature ratio as a function of is obtained, giving the possibility to predict prompt fission quantities as a function of fragment. Other TXE partition methods (based on models and assumptions at scission or on equal residual temperatures of complementary fragments at full acceleration) are compared to this one, revealing limits of applicability as well as the sensibility of prompt neutron emission models to the TXE partition. The behaviour of experimental with the increase of incident energy consisting in the multiplicity increase for heavy fragments only, is argued and entirely supported by the quantitative Point-by-Point model results of describing very well the experimental of 237Np(n, f) at 0.8 and 5.5 MeV incident energies. [Copyright &y& Elsevier]

Abstract: A full characterization of neutron detector properties was achieved by means of a 252Cf source with timing of fission events. The input neutron energies were separated with the time-of-flight technique. The pulse height, the pulse shape and the time-of-flight spectra were measured in coincidence mode as three-dimensional distributions. On the basis of these data, the following characteristics were determined for each detector: response function, light output versus proton (neutron) energy, energy resolution function for neutron energies from 1 to 7MeV, time shift correction, and finally the detector efficiency from threshold up to 12MeV. The experimental results were compared with Monte-Carlo simulations. Two new analytical dependencies are suggested for the light output calculation for electrons and protons. [Copyright &y& Elsevier]