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Angular Momentum Removal by Neutron and γ-Ray Emissions during Fission Fragment Decays

Journal Article · · Physical Review Letters
 [1];  [2];  [2];  [2];  [3];  [3];  [4]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Texas A&M University
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of Michigan, Ann Arbor, MI (United States)
  4. Univ. of Washington, Seattle, WA (United States)
+ Show Author Affiliations
In this work, we investigate the angular momentum removal from fission fragments (FFs) through neutron and γ-ray emission, finding that about half the neutrons are emitted with angular momenta ≥ 1.5 ℏ and that the change in angular momentum after the emission of neutrons and statistical γ rays is significant, contradicting usual assumptions. Per fission event, in our simulations, the neutron and statistical γ-ray emissions change the spin of the fragment by 3.5 – 5 ℏ , with a large standard deviation comparable to the average value. Such wide angular momentum removal distributions can hide any underlying correlations in the fission fragment initial spin values. Within our model, we reproduce data on spin measurements from discrete transitions after neutron emissions, especially in the case of light FFs. The agreement further improves for the heavy fragments if one removes from the analysis the events that would produce isomeric states. Finally, we show that while in our model the initial FF spins do not follow a sawtoothlike behavior observed in recent measurements, the average FF spin computed after neutron and statistical γ emissions exhibits a shape that resembles a sawtooth. This suggests that the average FF spin measured after statistical emissions is not necessarily connected with the scission mechanism as previously implied.
Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Texas A & M Univ., College Station, TX (United States); Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
Grant/Contract Number:
89233218CNA000001; FG02-97ER41014; NA0003841; NA0003920
OSTI ID:
1839629
Alternate ID(s):
OSTI ID: 1841554
OSTI ID: 1866954
Report Number(s):
LA-UR-21-23498; 89233218CNA000001
Journal Information:
Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 22 Vol. 127; ISSN 0031-9007
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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