{
  "abstract": "Standard r-process models often treat the freeze-out phase as a passive, uniform smoothing of the global abundance pattern. We demonstrate, however, that the final pattern is instead actively sculpted by a dynamic ``neutron economy'' that operates well after the free neutron source is exhausted. By analyzing cold neutron star merger outflows, we identify a distinct neutron exporter-importer relationship: the second-peak region ($A \\sim 130$) transitions early into a $β$-decay dominated regime, acting as a net exporter, while the third-peak ($A \\sim 195$) and Rare Earth ($A \\sim 164$) regions remain capture-dominated neutron importers. Targeted simulations reveal that the final peak structures emerge from a competition between two opposing forces: a global ``push'' driven by neutron capture shifting mass toward heavier nuclei, and a local ``pull'' from beta delayed neutron emission returning material back toward lighter masses. We identify $^{136}\\text{Pd}$, $^{135}\\text{Ag}$, and $^{130}\\text{Ru}$ as the primary exporters driving this economy, while third-peak fine structure is governed by $N=126$ isotones (Sm to Tb). Physically, this transport reflects a fundamental drive toward shell closure, where nuclei that overshoot the $N=82$ closed shell shed mass to migrate back toward this stable configuration, while nuclei in the third peak capture these redistributed neutrons to anchor themselves at the $N=126$ shell. Crucially, our models overproduce the odd-even staggering in the third peak compared to solar data. This discrepancy suggests current models likely overestimate the $β$-delayed neutron emission probabilities ($P_n$) for these $N=126$ nuclei, highlighting them as high-priority targets for theoretical refinement and future FRIB experiments.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.31465",
  "author_total": 2,
  "authors": [
    {
      "name": "Mengke Li"
    },
    {
      "name": "Bradley Meyer"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/b6s9m3c2a9gh4.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.31465",
  "fulltext_url": null,
  "id": "b6s9m3c2a9gh4",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.31465",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "arxiv",
      "nucl-th"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.31465",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-25",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/b6s9m3c2a9gh4.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:52Z",
      "native_id": "2609.31465",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.31465"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    },
    {
      "field": "physics",
      "origin": "arxiv:nucl-th",
      "subfield": "nuclear"
    }
  ],
  "title": "Neutron Economy and Freeze-out Dynamics in the Late-Time Cold r-Process",
  "title_text": "Neutron Economy and Freeze-out Dynamics in the Late-Time Cold r-Process",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:52Z",
  "url": "https://research.draconitic.com/paper/b6s9m3c2a9gh4",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.3847/1538-4357/aea157",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}