Neutron angular correlations in spontaneous and neutron-induced fission

Vogt, R.; Randrup, J.

doi:10.1103/physrevc.90.064623

Cited by 26 publications

(32 citation statements)

References 29 publications

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“…A short sample of the thermal-neutron-induced fission of 235 U is listed below. It demonstrates the large coverage of fission quantities that can all be obtained in correlation with each other, as for example angular correlations of the emitted neutrons [156]. Moreover, complex experimental cuts can easily be applied.…”

Section: Outputmentioning

confidence: 99%

General Description of Fission Observables: GEF Model Code

Schmidt

Jurado

Amouroux

et al. 2016

Nuclear Data Sheets

445

421

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The GEF ("GEneral description of Fission observables") model code is documented. It describes the observables for spontaneous fission, neutron-induced fission and, more generally, for fission of a compound nucleus from any other entrance channel, with given excitation energy and angular momentum. The GEF model is applicable for a wide range of isotopes from Z = 80 to Z = 112 and beyond, up to excitation energies of about 100 MeV. The results of the GEF model are compared with fission barriers, fission probabilities, fission-fragment mass-and nuclide distributions, isomeric ratios, total kinetic energies, and prompt-neutron and prompt-gamma yields and energy spectra from neutron-induced and spontaneous fission. Derived properties of delayed neutrons and decay heat are also considered.The GEF model is based on a general approach to nuclear fission that explains a great part of the complex appearance of fission observables on the basis of fundamental laws of physics and general properties of microscopic systems and mathematical objects. The topographic theorem is used to estimate the fission-barrier heights from theoretical macroscopic saddle-point and ground-state masses and experimental ground-state masses. Motivated by the theoretically predicted early localisation of nucleonic wave functions in a necked-in shape, the properties of the relevant fragment shells are extracted. These are used to determine the depths and the widths of the fission valleys corresponding to the different fission channels and to describe the fission-fragment distributions and deformations at scission by a statistical approach. A modified composite nuclear-level-density formula is proposed. It respects some features in the superfluid regime that are in accordance with new experimental findings and with theoretical expectations. These are a constant-temperature behaviour that is consistent with a considerably increased heat capacity and an increased pairing condensation energy that is consistent with the collective enhancement of the level density. The exchange of excitation energy and nucleons between the nascent fragments on the way from saddle to scission is estimated according to statistical mechanics. As a result, excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment in the superfluid regime. This description reproduces some rather peculiar observed features of the prompt-neutron multiplicities and of the even-odd effect in fission-fragment Z distributions. For completeness, some conventional descriptions are used for calculating pre-equilibrium emission, fission probabilities and statistical emission of neutrons and gamma radiation from the excited fragments. Preference is given to simple models that can also be applied to exotic nuclei compared to more sophisticated models that need precise empirical input of nuclear properties, e.g. spectroscopic information.The approach reveals a high degree of regularity and provides a considerable insight into the physics of the fission process. Fission obs...

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Section: Outputmentioning

confidence: 99%

General Description of Fission Observables: GEF Model Code

Schmidt

Jurado

Amouroux

et al. 2016

Nuclear Data Sheets

445

421

View full text Add to dashboard Cite

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“…We note that even if scission neutrons are emitted isotropically, they may not be detected as such in the lab frame. Scission neutrons make up an unknown fraction of the total neutron emission, estimated at approximately 10 − 20% [12,28,29].…”

Section: Anisotropy In Neutron Emission Ratementioning

confidence: 99%

“…This analysis corrects for slight variations in efficiency between detectors. the light fragment [12], where x is an adjustable input parameter expected to be larger than 1.…”

Section: Anisotropy In Neutron Emission Ratementioning

confidence: 99%

“…The commonly used MCNPX-PoliMi Monte Carlo code treats such correlations using data-based evaluations [5]. The new, physics-based fission models CGMF [6,7,8] and FREYA [9,10,11,12,13,14,15] generate complete events and can thus produce correlations between emitted particles on an event-by-event basis. These codes require high fidelity experimental data for validating their models.…”

Section: Introductionmentioning

confidence: 99%

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High resolution measurement of tagged two-neutron energy and angle correlations in Cf252 (sf)

et al. 2019

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Background: Spontaneous fission events emit prompt neutrons correlated with one another in emission angle and energy. Purpose: We explore the relationship in energy and angle between correlated prompt neutrons emitted from 252 Cf spontaneous fission. Methods: Measurements with the Chi-Nu array provide experimental data for coincident neutrons tagged with a fission chamber signal with 10 o angular resolution and 1 ns timing resolution for time-of-flight energy calculations. The experimental results are compared to simulations produced by the fission event generators CGMF, FREYA, and MCNPX-POLIMI IPOL(1)=1. Results: We find that the measurements and the simulations all exhibit anisotropic neutron emission, though differences exist between fission event generators. Conclusions: This work shows that the dependence of detected neutron energy on the energy of a neutron detected in coincidence, although weak, is non-negligible,indicating that there may be correlations in energy between two neutrons emitted in the same fission event.

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“…The computational model FREYA [1][2][3][4][5][6][7] generates complete fission events, i.e. it provides the the full kinematic information on the two product nuclei as well as all the emitted neutrons and photons.…”

Section: Introduction To Freyamentioning

confidence: 99%

Neutron-neutron and neutron-photon correlations withFREYA

Vogt

Randrup

2017

EPJ Web Conf.

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Abstract. For many years, the state of the art for modeling fission in radiation transport codes has involved sampling from average distributions. However, in a true fission event, the energies, momenta and multiplicities of emitted particles are correlated. The FREYA (Fission Reaction Event Yield Algorithm) code generates complete fission events. Event-by-event techniques such as those of FREYA are particularly useful because it is possible to obtain complete kinematic information on the prompt neutrons and photons emitted during the fission process. It is therefore possible to extract any desired correlation observables. We describe FREYA and compare our results with neutron-neutron, neutron-light fragment and neutron-photon correlation data.

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Neutron angular correlations in spontaneous and neutron-induced fission

Cited by 26 publications

References 29 publications

General Description of Fission Observables: GEF Model Code

General Description of Fission Observables: GEF Model Code

High resolution measurement of tagged two-neutron energy and angle correlations in Cf252 (sf)

Neutron-neutron and neutron-photon correlations withFREYA

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