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Angular and Kinetic Properties of Scission Neutrons within Time-dependent Density Functional Theory

T0 review · 2 major / 2 minor · reviewed 2026-06-27 · grok-4.3

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Pith's one-line read Scission neutrons explain the excess high-energy yield in prompt fission neutron spectra for plutonium and californium when added to evaporation models.

desk verdict TDDFT scission neutrons fill the high-energy PFNS gap only if the low-energy Maxwellian evaporation model extrapolates accurately, which the abstract does not verify. read the letter →

arxiv 2606.09656 v1 pith:R6KZRDH6 submitted 2026-06-08 nucl-th

Antonio Bjelčić , Ibrahim Abdurrahman , Kyle Godbey This is my paper · ORCID
classification nucl-th
keywords scissionneutronspromptfissiontime-dependentdensityfunctionaltheorynuclearneutronenergyspectrumevaporationmodelangulardistributiondynamics
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper uses time-dependent density functional theory to model scission-neutron emission during fission in three systems: thermal-neutron fission of uranium-235 and plutonium-239, plus spontaneous fission of californium-252. With a larger simulation domain, it extracts angular and energy distributions showing that scission neutrons are absent below roughly 1.5 to 2 MeV at selected angles and instead populate the higher-energy region of the prompt spectrum. Adding the calculated scission spectrum to a Maxwellian evaporation model fitted only to low-energy data reproduces the measured high-energy yields for plutonium and californium, while an evaporation-only model underestimates them. This match supplies evidence that a non-negligible scission-neutron component is already visible in existing experimental spectra.

What carries the argument

Time-dependent density functional theory simulations that compute the angular and kinetic distributions of scission neutrons emitted during the fission process.

What would settle it

A high-precision measurement of the prompt neutron spectrum in 239Pu(n_th,f) that shows the high-energy tail is fully reproduced by an evaporation-only model without any additional high-energy component would falsify the claim.

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Extended reading notes

Core claim

Scission-neutron emission is investigated in 235U(n_th,f), 239Pu(n_th,f) and 252Cf(sf) within time-dependent density functional theory. Using a substantially larger simulation domain than in previous studies, the angular and energy distributions of emitted scission neutrons are extracted over a specific range of emission angles. At these angles, scission neutrons are absent below a threshold energy of roughly 1.5--2 MeV, and instead contribute predominantly to the higher energy part of the prompt fission neutron spectrum. Combining the calculated scission-neutron spectrum with a Maxwellian model for the evaporated component, constrained by low-energy experimental data, reproduces the measure

Load-bearing premise

A Maxwellian evaporation model fitted only to low-energy data continues to describe the evaporated neutron component accurately across the full energy range without further adjustments.

Editorial extensions

If this is right

  • The high-energy prompt-fission-neutron yield in 239Pu(n_th,f) and 252Cf(sf) is reproduced only when the scission-neutron spectrum is included.
  • Evaporation-only models systematically underestimate the observed high-energy prompt neutron yields.
  • A non-negligible scission-neutron component is required to explain existing high-energy prompt fission neutron spectra.
  • The angular and energy distributions extracted from the simulations identify a clear energy threshold below which scission neutrons do not appear at the studied angles.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Similar TDDFT calculations applied to other fissioning nuclei could map how the scission contribution varies with mass and excitation energy.
  • Angular-resolved neutron measurements at facilities could directly test the predicted 1.5--2 MeV threshold for scission neutrons.
  • Reactor simulations that rely on accurate high-energy neutron spectra may need to incorporate an explicit scission component derived from microscopic dynamics.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 2 minor

Summary. The manuscript uses time-dependent density functional theory (TDDFT) with an enlarged simulation domain to compute angular and kinetic distributions of scission neutrons emitted in 235U(n_th,f), 239Pu(n_th,f), and 252Cf(sf). Scission neutrons are found to be absent below a threshold of roughly 1.5–2 MeV and to contribute mainly at higher energies. The central result is obtained by superposing the TDDFT scission spectrum onto a Maxwellian evaporation component whose parameters are fixed exclusively by low-energy prompt-fission-neutron-spectrum (PFNS) data; this combined spectrum reproduces the measured high-energy PFNS for 239Pu and 252Cf, whereas the evaporation-only Maxwellian systematically underestimates the data. The authors interpret the improvement as direct evidence for a non-negligible scission-neutron component already present in existing high-energy PFNS measurements.

Significance. If the comparison to experiment is robust, the work supplies a microscopic, parameter-constrained link between TDDFT scission-neutron spectra and existing high-energy PFNS data, thereby identifying a possible experimental signature without new measurements. The adoption of a substantially larger computational domain than earlier TDDFT studies is a clear technical improvement. The significance is reduced, however, by the absence of any independent validation that the Maxwellian form remains accurate when extrapolated beyond the fitted low-energy regime.

major comments (2)
  1. [Abstract / PFNS comparison] Abstract and the PFNS-comparison section: the claim that the evaporation-only Maxwellian (parameters fixed solely by low-energy data) systematically underestimates the high-energy yield, while addition of the TDDFT scission spectrum restores agreement, is load-bearing. No test is shown that modest re-adjustment of the Maxwellian parameters or inclusion of other high-energy evaporation mechanisms (pre-equilibrium, level-density variations) could not absorb the same discrepancy, leaving the necessity of a distinct scission component unproven.
  2. [Methods and results sections on spectrum extraction] Methods / results on spectrum extraction: the manuscript provides no quantitative assessment of numerical convergence with respect to simulation-domain size, time-step, or basis truncation, nor any error bands on the extracted scission-neutron spectra that enter the final comparison. These omissions directly affect the reliability of the high-energy tail that is asserted to resolve the experimental mismatch.
minor comments (2)
  1. [Abstract] Abstract: the statement that scission neutrons are “absent below a threshold energy of roughly 1.5–2 MeV” would benefit from an explicit definition of the angular acceptance window used to extract this threshold.
  2. [Results / figures] Figure captions and text: several statements refer to “the measured high-energy prompt-fission-neutron yield” without citing the specific experimental data sets or their energy ranges.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review. We respond point-by-point to the major comments below.

read point-by-point responses

  1. Referee: [Abstract / PFNS comparison] Abstract and the PFNS-comparison section: the claim that the evaporation-only Maxwellian (parameters fixed solely by low-energy data) systematically underestimates the high-energy yield, while addition of the TDDFT scission spectrum restores agreement, is load-bearing. No test is shown that modest re-adjustment of the Maxwellian parameters or inclusion of other high-energy evaporation mechanisms (pre-equilibrium, level-density variations) could not absorb the same discrepancy, leaving the necessity of a distinct scission component unproven.

    Authors: The Maxwellian parameters are deliberately fixed only by low-energy PFNS data to prevent circular fitting to the high-energy region under discussion. This follows standard practice in the field. The systematic under-prediction at high energies is a documented limitation of pure evaporation models. Adding the TDDFT scission spectrum (with no adjustment to the evaporation component) accounts for the observed excess. While other mechanisms could in principle contribute, the microscopic, parameter-free TDDFT result provides a specific prediction that matches the discrepancy. We will revise the manuscript to explicitly note that parameters remain unchanged and to discuss why re-adjustment would violate the low-energy constraint. revision: partial

  2. Referee: [Methods and results sections on spectrum extraction] Methods / results on spectrum extraction: the manuscript provides no quantitative assessment of numerical convergence with respect to simulation-domain size, time-step, or basis truncation, nor any error bands on the extracted scission-neutron spectra that enter the final comparison. These omissions directly affect the reliability of the high-energy tail that is asserted to resolve the experimental mismatch.

    Authors: We agree that explicit convergence tests and uncertainty estimates would strengthen the results. Although the enlarged domain is presented as an improvement, quantitative assessments were omitted. In the revised manuscript we will add convergence studies varying domain size and time step, together with estimated error bands on the extracted spectra obtained from these variations. revision: yes

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: TDDFT scission spectrum is independent; Maxwellian fit to low-energy data is external benchmark

full rationale

The derivation chain rests on TDDFT computations of scission-neutron angular and energy distributions (independent first-principles simulation) combined with a standard Maxwellian evaporation model whose parameters are fixed by low-energy experimental PFNS data. The paper states scission neutrons are absent below ~1.5-2 MeV, allowing the low-energy fit to constrain evaporation without using high-energy data. The subsequent comparison (evaporation-only underestimates high-energy yield; addition of TDDFT scission restores agreement) is a direct test against external measurements rather than a self-referential reduction. No equations equate a fitted quantity to a 'prediction' by construction, no self-citations bear the central claim, and no ansatz or uniqueness theorem is smuggled in. The structure is self-contained against external benchmarks.

Assumptions & free parameters 1 free parameters · 1 assumptions · 0 invented entities

The claim rests on the separation of scission and evaporation components, the validity of TDDFT for describing scission emission, and the assumption that a Maxwellian fitted to low-energy data can be extrapolated without additional free parameters for the high-energy regime.

free parameters (1)
  • Maxwellian parameters for evaporation
    Constrained by low-energy experimental data to define the evaporated neutron component before adding the scission spectrum.
assumptions (1)
  • domain assumption TDDFT with the chosen functional and larger domain accurately captures scission neutron emission without significant boundary or numerical artifacts
    Invoked by the use of a substantially larger simulation domain than previous studies to extract angular and energy distributions.

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Cite this review

Pith. "Pith review of Angular and Kinetic Properties of Scission Neutrons within Time-dependent Density Functional Theory." pith.science (2026). https://pith.science/paper/R6KZRDH6

@misc{pith2026260609656,
  author       = {Pith},
  title        = {Pith review of: Angular and Kinetic Properties of Scission Neutrons within Time-dependent Density Functional Theory},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/R6KZRDH6}},
  note         = {Machine review of arXiv:2606.09656}
}
abstract

Scission-neutron emission is investigated in $^{235}\mathrm{U}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$, $^{239}\mathrm{Pu}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$ and $^{252}\mathrm{Cf}(\mathrm{sf})$ within time-dependent density functional theory. Using a substantially larger simulation domain than in previous studies, the angular and energy distributions of emitted scission neutrons are extracted over a specific range of emission angles. At these angles, scission neutrons are absent below a threshold energy of roughly $1.5$--$2\,\mathrm{MeV}$, and instead contribute predominantly to the higher energy part of the prompt fission neutron spectrum. Combining the calculated scission-neutron spectrum with a Maxwellian model for the evaporated component, constrained by low-energy experimental data, reproduces the measured high-energy prompt-fission-neutron yield in both $^{239}\mathrm{Pu}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$ and $^{252}\mathrm{Cf}(\mathrm{sf})$, whereas the evaporation-only model systematically underestimates it. This identifies a signature of scission neutrons already present in existing high-energy prompt fission neutron spectra and constitutes direct evidence for a non-negligible scission-neutron component in prompt fission neutron emission.

Figures

Figures reproduced from arXiv: 2606.09656 by the authors.

Figure 1
Figure 1. FIG. 1. Snapshots of the post-scission neutron density evolu [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. FIG. 2. SN kinetic energy distributions for three fissioning [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. FIG. 3. The PFNS for [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

Discussion (0). Continue with ORCID to comment.

Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Influence of the Exit Channel in $^{235}$U(n,f) and $^{239}$Pu(n,f) Reactions in Time-Dependent Density Functional Theory

    nucl-th 2026-07 conditional novelty 6.0 of 10

    Rare near-symmetric and highly-asymmetric fission in 236U and 240Pu show distinct neck dynamics, lower total kinetic energy, and different fragment excitation sharing than standard asymmetric fission.

Reference graph

Works this paper leans on

41 extracted references · 3 canonical work pages · cited by 1 Pith paper

  1. [1]

    and Bohr and Wheeler [10], experimentally investi- gated since 1962 [11], and have been studied using vari- ous models for decades [12–24]. Despite this long history, SNs remain experimentally unresolved: prompt-neutron observables alone do not distinguish whether a detected neutron was emitted at scission or later evaporated from a fragment, making any e...

    work page Pith review arXiv 1962

  2. [2]

    Hahn and F

    O. Hahn and F. Strassmann, Naturwissenschaften27, 11 (1939)

    1939

  3. [3]

    Meitner, L

    L. Meitner, L. and O. R. Frisch, Nature143, 239 (1939)

    1939

  4. [4]

    Benderet al., J

    M. Benderet al., J. Phys. G: Nucl. Part. Phys.47, 113002 (2020)

    2020

  5. [5]

    Bulgac, S

    A. Bulgac, S. Jin, and I. Stetcu, Front. Phys.8, 63 (2020)

    2020

  6. [6]

    Schunck and D

    N. Schunck and D. Regnier, Prog. Part. Nucl. Phys.125, 103963 (2022)

    2022

  7. [7]

    J. M. Verbeke, J. Randrup, and R. Vogt, Comput. Phys. Commun.222, 263 (2018)

    2018

  8. [8]

    Talou, I

    P. Talou, I. Stetcu, P. Jaffke, M. E. Rising, A. E. Lovell, and T. Kawano, Comput. Phys. Commun.269, 108087 (2021)

    2021

Show all 41 references
  1. [9]

    Koning, S

    A. Koning, S. Hilaire, and S. Goriely, Eur. Phys. J. A 59, 1 (2023)

    2023

  2. [10]

    H. L. Anderson, E. Fermi, and H. B. Hanstein, Phys. Rev.55, 797 (1939)

    1939

  3. [11]

    Bohr and J

    N. Bohr and J. A. Wheeler, Phys. Rev.56, 426 (1939)

    1939

  4. [12]

    H. R. Bowman, S. G. Thompson, J. C. D. Milton, and W. J. Swiatecki, Phys. Rev.126, 2120 (1962)

    1962

  5. [13]

    V. S. Stavinsky, JETP (Soviet Physics)9, 437 (1959)

    1959

  6. [14]

    R. W. Fuller, Phys. Rev.126, 684 (1962)

    1962

  7. [15]

    Boneh and Z

    Y. Boneh and Z. Fraenkel, Phys. Rev. C10, 893 (1974)

    1974

  8. [16]

    M¨ adler, Z

    P. M¨ adler, Z. Physik A321, 343 (1985)

    1985

  9. [17]

    Milek, R

    B. Milek, R. Reif, and J. Revai, Phys. Rev. C37, 1077 (1988)

    1988

  10. [18]

    Brosa, S

    U. Brosa, S. Grossmann, and A. M¨ uller, Physics Reports 197, 167 (1990)

    1990

  11. [19]

    Brosa and H.-H

    U. Brosa and H.-H. Knitter, Z. Physik A343, 39 (1992)

    1992

  12. [20]

    Carjan, P

    N. Carjan, P. Talou, and O. Serot, Nuclear Physics A 792, 102 (2007)

    2007

  13. [21]

    Rizea, V

    M. Rizea, V. Ledoux, M. V. Daele, G. V. Berghe, and N. Carjan, Comp. Phys. Comm.179, 466 (2008)

    2008

  14. [22]

    Carjan and M

    N. Carjan and M. Rizea, Phys. Rev. C.82, 014617 (2010)

    2010

  15. [23]

    Capote, Y.-J

    R. Capote, Y.-J. Chen, F.-J. Hambsch, N. Kornilov, J. Lestone, O. Litaize, B. Morillon, D. Neudecker, S. Oberstedt, T. Ohsawa, N. Otuka, V. Pronyaev, A. Saxena, O. Serot, O. Shcherbakov, N.-C. Shu, D. Smith, P. Talou, A. Trkov, A. Tudora, R. Vogt, and A. Vorobyev, Nuclear Data...

    2016

  16. [24]

    Carjan and M

    N. Carjan and M. Rizea, Phys. Rev. C99, 034613 (2019)

    2019

  17. [25]

    Catapult neutrons from neck snapping in fission,

    J. Randrup, R. Capote, and R. Vogt, “Catapult neutrons from neck snapping in fission,” (2026), arXiv:2604.10790 [nucl-th]

    2026 arXiv

  18. [30]

    See Supplemental Material at [URL will be inserted by publisher] for technical details regarding the computa- tional aspects, convergence and experimental data

  19. [31]

    A. D. Carlson, V. G. Pronyaev, R. Capote, G. M. Hale, Z.-P. Chen, I. Duran, F.-J. Hambsch, S. Ku- nieda, W. Mannhart, B. Marcinkevicius, R. O. Nelson, D. Neudecker, G. Noguere, M. Paris, S. P. Simakov, P. Schillebeeckx, D. L. Smith, X. Tao, A. Trkov, A. Wall- ner, and W. Wang,...

    2018

  20. [32]

    Skarsv˚ ag and K

    K. Skarsv˚ ag and K. Bergheim, Nuclear Physics45, 72 (1963)

    1963

  21. [33]

    S. S. Kapoor, R. Ramanna, and P. N. Rama Rao, Phys. Rev.131, 283 (1963)

    1963

  22. [34]

    V. N. Nefedov, Sov. Phys. JETP11, 1195 (1960)

    1960

  23. [35]

    M. V. Blinov, N. M. Kazarinov, and A. N. Protopopov, Sov. Phys. JETP15, 704 (1962)

    1962

  24. [36]

    R. L. Higdon, Math. Comp.47, 437 (1986)

    1986

  25. [37]

    Nakatsukasa and K

    T. Nakatsukasa and K. Yabana, J. Chem. Phys.114, 2550 (2001)

    2001

  26. [38]

    M. Ueda, K. Yabana, and T. Nakatsukasa, Phys. Rev. C.67, 014606 (2003)

    2003

  27. [39]

    Nakatsukasa and K

    T. Nakatsukasa and K. Yabana, Phys. Rev. C.71, 024301 (2005). Supplemental Material: Angular and kinetic properties of scission neutrons within time-dependent density functional theory Antonio Bjelˇ ci´ c,1,∗ Ibrahim Abdurrahman, 2 and Kyle Godbey 2 1Lawrence Livermore Nationa...

    2005

  28. [40]

    Saturation values and the averaging interval [t1, t2] used to compute the probability distributionP (SN) [θ1,θ2](E) are indicated. FIG. S6. The SN energy distribution for 239Pu(nth,f) for η= 3, 4, 5, is shown on linear (upper) and logarithmic (lower) scales. The distribution i...

  29. [41]

    Bjelˇ ci´ c, N

    A. Bjelˇ ci´ c, N. Schunck, and M. Verriere, Phys. Rev. C 113, 034602 (2026)

    2026

  30. [42]

    Bjelˇ ci´ c and T

    A. Bjelˇ ci´ c and T. Nikˇ si´ c, Comput. Phys. Commun.253, 7 107184 (2020)

    2020

  31. [43]

    Abdurrahman, M

    I. Abdurrahman, M. Kafker, A. Bulgac, and I. Stetcu, Phys. Rev. Lett.132, 242501 (2024)

    2024

  32. [44]

    A. S. Vorobyev, O. A. Shcherbakov, A. M. Gagarski, G. A. Petrov, G. V. Val'ski, and T. E. Kuz'mina, J. Exp. Theor. Phys.127, 659 (2018)

    2018

  33. [45]

    A. S. Vorobyev, O. A. Shcherbakov, A. M. Gagarski, G. A. Petrov, and G. V. Val’ski, Journal of Experimental and Theoretical Physics125, 619 (2017)

    2017

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