pith. sign in

arxiv: 2605.29404 · v1 · pith:U2DNRG3Dnew · submitted 2026-05-28 · ⚛️ nucl-th · nucl-ex

Narrowing the Gap Between Theory and Evaluations: Angular Momentum Distributions in Fission Fragments

Petar Marevi\'c , Nicolas Schunck , Marc Verriere This is my paper

Pith reviewed 2026-06-29 00:45 UTC · model grok-4.3

classification ⚛️ nucl-th nucl-ex
keywords angular momentum distributionsfission fragmentsmicroscopic nuclear modelneutron-induced fissionphoton multiplicitiesuranium-235plutonium-239sawtooth pattern
0
0 comments X

The pith

A microscopic nuclear model predicts angular momentum distributions across fission fragment masses that match experimental photon multiplicities without any adjustable parameters.

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

The paper introduces a microscopic framework that calculates angular momentum distributions for fission fragments over their full range of masses and charges. Applied to neutron-induced fission of uranium-235 and plutonium-239, the results display a clear sawtooth pattern in the average values together with a strong dependence on isobaric chains. These distributions reproduce measured photon multiplicities from experiment with no parameter fitting. The work indicates that first-principles nuclear theory can now reach quantitative agreement with data that previously required phenomenological adjustments.

Core claim

We present a microscopic framework for predicting angular momentum distributions over the full range of fission fragment masses and charges. For the neutron-induced fission of 235U and 239Pu, the obtained distributions exhibit a pronounced sawtooth pattern in average values, reveal a substantial isobaric dependence, and reproduce experimental photon multiplicities without adjustable parameters. These results demonstrate that microscopic theory is gradually becoming quantitatively competitive with phenomenological models.

What carries the argument

A microscopic nuclear model that generates angular momentum distributions for fission fragments from first principles across the full mass and charge range.

If this is right

  • The calculated distributions exhibit a pronounced sawtooth pattern in their average values for the studied fission reactions.
  • A substantial isobaric dependence appears in the angular momentum distributions.
  • Experimental photon multiplicities are reproduced without introducing adjustable parameters.
  • Microscopic theory reaches quantitative agreement with data previously handled only by phenomenological models.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same framework could be tested on additional fission reactions or at different incident neutron energies to check consistency.
  • If the model holds, it supplies a route to predict gamma-ray emission spectra from fission without separate tuning steps.
  • The isobaric dependence may connect to fragment shape or pairing effects that other fission observables could probe independently.

Load-bearing premise

The underlying microscopic nuclear model produces accurate angular momentum distributions directly from its equations without empirical adjustments specific to fission.

What would settle it

A clear mismatch between the predicted sawtooth pattern or isobaric dependence and new measurements of angular momentum in fission fragments from the same or similar reactions would falsify the central claim.

Figures

Figures reproduced from arXiv: 2605.29404 by Marc Verriere, Nicolas Schunck, Petar Marevi\'c.

Figure 2
Figure 2. Figure 2: Photon multiplicities from FFs in fission of 240Pu∗ , cal￾culated with the cgmf code. FFs are deexcited using either mi￾croscopic or default phenomenological angular momentum dis￾tributions, while keeping all other initial conditions equal. Ex￾perimental data are taken from Ref. [22]. In [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 1
Figure 1. Figure 1: Average angular momentum of FFs in isobaric chains as a function of the FF mass AF, for 236U ∗ (a) and 240Pu∗ (b). The error bars show 1σ spread within each chain. The inset shows distributions in three AH = 130 isobars for fission of 236U ∗ . the form p(JF) ∝ (2JF + 1) exp  − 1 2 JF(JF + 1) B2 (ZF, AF, TF)  , (5) where B 2 (ZF, AF, TF) encodes a possible dependence on FF charge, mass, and temperature, a… view at source ↗
read the original abstract

We present a microscopic framework for predicting angular momentum distributions over the full range of fission fragment masses and charges. For the neutron-induced fission of $^{235}$U and $^{239}$Pu, the obtained distributions exhibit a pronounced sawtooth pattern in average values, reveal a substantial isobaric dependence, and reproduce experimental photon multiplicities without adjustable parameters. These results demonstrate that microscopic theory is gradually becoming quantitatively competitive with phenomenological models.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript presents a microscopic framework for predicting angular momentum distributions over the full range of fission fragment masses and charges. For neutron-induced fission of 235U and 239Pu, the distributions exhibit a pronounced sawtooth pattern in average values, substantial isobaric dependence, and reproduce experimental photon multiplicities without adjustable parameters, claiming that microscopic theory is becoming quantitatively competitive with phenomenological models.

Significance. If the parameter-free claim holds under a verifiable microscopic method, the work would represent a meaningful advance by providing first-principles angular-momentum inputs for fission evaluations, potentially reducing reliance on empirical tuning in nuclear data applications.

major comments (1)
  1. [Abstract] Abstract and introduction: the central claim that results are obtained 'without adjustable parameters' and constitute a 'parameter-free' prediction cannot be assessed because the specific microscopic method (e.g., which energy-density functional, pairing treatment, or fission dynamics implementation), validation against known benchmarks, and uncertainty quantification are not described, leaving a load-bearing derivation gap for the reproducibility assertion.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the report and the opportunity to clarify our manuscript. We address the major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract and introduction: the central claim that results are obtained 'without adjustable parameters' and constitute a 'parameter-free' prediction cannot be assessed because the specific microscopic method (e.g., which energy-density functional, pairing treatment, or fission dynamics implementation), validation against known benchmarks, and uncertainty quantification are not described, leaving a load-bearing derivation gap for the reproducibility assertion.

    Authors: We agree that the abstract and introduction should explicitly reference the key elements of the microscopic method to allow readers to immediately assess the parameter-free nature of the predictions. The full manuscript describes the specific energy-density functional, pairing treatment, fission dynamics implementation, benchmark validations, and any uncertainty considerations in the methods and results sections. To address this concern directly, we will revise the abstract and introduction to include a concise statement of these methodological choices and validation steps. This change will strengthen the reproducibility assertion without altering the scientific content or results. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper presents a microscopic framework that generates angular momentum distributions and reproduces photon multiplicities without adjustable parameters, as stated in the abstract. No load-bearing steps reduce by construction to fitted inputs, self-definitions, or self-citation chains within the provided text. The central claim of parameter-free prediction from the underlying nuclear model stands as an independent derivation against external benchmarks, with no quoted equations or citations exhibiting the enumerated circular patterns. This is the expected outcome for a self-contained microscopic calculation.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Only the abstract is available, so the ledger is necessarily incomplete and based on stated claims rather than explicit derivations.

axioms (1)
  • domain assumption The chosen microscopic nuclear model accurately generates fission fragment angular momenta from the underlying nuclear structure without empirical adjustments.
    Abstract asserts parameter-free reproduction; this assumption is load-bearing for the competitiveness claim.

pith-pipeline@v0.9.1-grok · 5595 in / 1137 out tokens · 28733 ms · 2026-06-29T00:45:18.344644+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

20 extracted references · 18 canonical work pages

  1. [1]

    Talou, R

    P. Talou, R. V ogt, eds., Nuclear Fission: Theories, Experiments and Applications (Springer, 2023)

    2023

  2. [2]

    Schunck, D

    N. Schunck, D. Regnier, Theory of nuclear fission, Progress in Particle and Nuclear Physics125, 103963 (2022). https://doi.org/10.1016/j.ppnp.2022.103963

    work page doi:10.1016/j.ppnp.2022.103963 2022

  3. [3]

    Bulgac, I

    A. Bulgac, I. Abdurrahman, S. Jin, K. Godbey, N. Schunck, I. Stetcu, Fission fragment intrinsic spins and their correlations, Phys. Rev. Lett.126, 142502 (2021). 10.1103/PhysRevLett.126.142502

    work page doi:10.1103/physrevlett.126.142502 2021

  4. [4]

    Marevi ´c, N

    P. Marevi ´c, N. Schunck, J. Randrup, R. V ogt, An- gular momentum of fission fragments from micro- scopic theory, Phys. Rev. C104, L021601 (2021). 10.1103/PhysRevC.104.L021601

    work page doi:10.1103/physrevc.104.l021601 2021

  5. [6]

    Scamps, Microscopic description of the torque acting on fission fragments, Phys

    G. Scamps, Microscopic description of the torque acting on fission fragments, Phys. Rev. C106, 054614 (2022). 10.1103/PhysRevC.106.054614

    work page doi:10.1103/physrevc.106.054614 2022

  6. [8]

    Randrup, R

    J. Randrup, R. V ogt, Generation of fragment angular momentum in fission, Phys. Rev. Lett.127, 062502 (2021). 10.1103/PhysRevLett.127.062502

    work page doi:10.1103/physrevlett.127.062502 2021

  7. [9]

    Stetcu, A.E

    I. Stetcu, A.E. Lovell, P. Talou, T. Kawano, S. Marin, S.A. Pozzi, A. Bulgac, Angular Momentum Re- moval by Neutron andγ-Ray Emissions during Fis- sion Fragment Decays, Phys. Rev. Lett.127, 222502 (2021). 10.1103/PhysRevLett.127.222502

    work page doi:10.1103/physrevlett.127.222502 2021

  8. [10]

    Breschi, S

    J. Randrup, T. Døssing, R. V ogt, Probing fission frag- ment angular momenta by photon measurements, Phys. Rev. C106, 014609 (2022). 10.1103/Phys- RevC.106.014609

    work page doi:10.1103/phys- 2022

  9. [11]

    Scamps, A

    G. Scamps, A. Guilleux, D. Regnier, A. Bernard, Uncertainty principle and an- gular momentum generation in micro- scopic fission models (2025),2512.02207, https://arxiv.org/abs/2512.02207

    work page arXiv 2025

  10. [12]

    Wilson et al., Angular momentum genera- tion in nuclear fission, Nature590, 566 (2021)

    J.N. Wilson et al., Angular momentum genera- tion in nuclear fission, Nature590, 566 (2021). https://doi.org/10.1038/s41586-021-03304-w

    work page doi:10.1038/s41586-021-03304-w 2021

  11. [13]

    Talou, I

    P. Talou, I. Stetcu, P. Jaffke, M. Rising, A. Lovell, T. Kawano, Fission fragment decay simulations with the CGMF code, Computer Physics Communications269, 108087 (2021). https://doi.org/10.1016/j.cpc.2021.108087

    work page doi:10.1016/j.cpc.2021.108087 2021

  12. [14]

    Verbeke, J

    J.M. Verbeke, J. Randrup, R. V ogt, Fission Reac- tion Event Yield Algorithm FREY A 2.0.2, Com- puter Physics Communications222, 263 (2018). https://doi.org/10.1016/j.cpc.2017.09.006

    work page doi:10.1016/j.cpc.2017.09.006 2018

  13. [15]

    Litaize, O

    O. Litaize, O. Serot, L. Berge, Fission modelling with FIFRELIN, Eur. Phys. J. A51, 177 (2015). 10.1140/epja/i2015-15177-9

    work page doi:10.1140/epja/i2015-15177-9 2015

  14. [16]

    Marevi ´c, N

    P. Marevi ´c, N. Schunck, M. Verriere, Microscopic theory of angular momentum distributions across the full range of fission fragments, Phys. Rev. C113, 014612 (2026). 10.1103/yr2c-nvf3

    work page doi:10.1103/yr2c-nvf3 2026

  15. [17]

    Marevi ´c, N

    P. Marevi ´c, N. Schunck, Microscopic angular mo- mentum distributions in fragments for neutron- induced fission of U-235 and Pu-239 (2025),https: //doi.org/10.5281/zenodo.17303186

    work page doi:10.5281/zenodo.17303186 2025

  16. [18]

    Schunck, ed., Energy Density Functional Meth- ods for Atomic Nuclei., IOP Expanding Physics (IOP Publishing, Bristol, UK, 2019)

    N. Schunck, ed., Energy Density Functional Meth- ods for Atomic Nuclei., IOP Expanding Physics (IOP Publishing, Bristol, UK, 2019)

    2019

  17. [19]

    Marevi ´c, N

    P. Marevi ´c, N. Schunck, E. Ney, R. Navarro Pérez, M. Verriere, J. O’Neal, Axially-deformed solution of the Skyrme-Hartree-Fock-Bogoliubov equations us- ing the transformed harmonic oscillator basis (IV) hfbtho (v4.0): A new version of the program, Com- puter Physics Communications276, 108367 (2022). https://doi.org/10.1016/j.cpc.2022.108367

    work page doi:10.1016/j.cpc.2022.108367 2022

  18. [20]

    Verriere, D

    M. Verriere, D. Regnier, The Time-Dependent Gen- erator Coordinate Method in Nuclear Physics, Front. Phys.8, 1 (2020). 10.3389/fphy.2020.00233

    work page doi:10.3389/fphy.2020.00233 2020

  19. [21]

    Regnier, N

    D. Regnier, N. Dubray, M. Verrière, N. Schunck, FELIX-2.0: New version of the finite element solver for the time dependent generator coordinate method with the Gaussian overlap approximation, Com- puter Physics Communications225, 180 (2018). https://doi.org/10.1016/j.cpc.2017.12.007

    work page doi:10.1016/j.cpc.2017.12.007 2018

  20. [22]

    Pleasonton, Promptγ-rays emitted in the thermal-neutron induced fission of 233U and 239Pu, Nuclear Physics A213, 413 (1973)

    F. Pleasonton, Promptγ-rays emitted in the thermal-neutron induced fission of 233U and 239Pu, Nuclear Physics A213, 413 (1973). https://doi.org/10.1016/0375-9474(73)90161-9

    work page doi:10.1016/0375-9474(73)90161-9 1973