Production Memory of the 225Ra-225Ac Clock in Neutron-Star Merger Ejecta
Abstract
Radioactive nuclei in neutron-star merger ejecta carry information about both their abundance and their production history. Using the 225Ra-225Ac sequence, we establish exact conditions linking a surviving isotope partition to the time available for parent decay. An Ac fraction of 0.1 produced solely through Ra decay requires at least 2.456 days, providing a direct consistency test for proposed source states. We show that subsequent activity retains additional production memory: two histories with the same mean birth time can produce different response crossings. This distinction is captured analytically and separates mean chronology from the influence of the production-time distribution. A controlled radiation calculation then shows how deposition and photon escape transform the nuclear contrast into a common light-curve pivot for fixed ejecta properties. The results connect nuclear production chronology to late-time merger emission and provide benchmarks for nucleosynthesis and radiation-transport calculations.
Related
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BibTeX
@misc{anwer2026production,
title = {{Production Memory of the $^225\mathrmRa$-$^225\mathrmAc$ Clock in Neutron-Star Merger Ejecta}},
author = {Hisham Anwer},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.11095},
eprint = {2610.11095},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.11095},
}
RIS
TY - UNPB
TI - Production Memory of the ^225Ra-^225Ac Clock in Neutron-Star Merger Ejecta
AU - Hisham Anwer
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.11095
UR - https://arxiv.org/abs/2610.11095
AB - Radioactive nuclei in neutron-star merger ejecta carry information about both their abundance and their production history. Using the ^225Ra-^225Ac sequence, we establish exact conditions linking a surviving isotope partition to the time available for parent decay. An Ac fraction of 0.1 produced solely through Ra decay requires at least 2.456 days, providing a direct consistency test for proposed source states. We show that subsequent activity retains additional production memory: two histories with the same mean birth time can produce different response crossings. This distinction is captured analytically and separates mean chronology from the influence of the production-time distribution. A controlled radiation calculation then shows how deposition and photon escape transform the nuclear contrast into a common light-curve pivot for fixed ejecta properties. The results connect nuclear production chronology to late-time merger emission and provide benchmarks for nucleosynthesis and radiation-transport calculations.
ER -