Wed·Jul 22, 2020Wednesday·July 22, 2020

1. 01*

   Extracting dynamics in the fusion of neutron-rich light nuclei

   R.T. deSouza🇺🇸 · Varinderjit Singh🇺🇸 · S. Hudan🇺🇸 · Z. Lin🇺🇸 · C.J. Horowitz🇺🇸

   The dependence of fusion dynamics on neutron excess for light nuclei is extracted. This is accomplished by comparing the average fusion cross-section at energies just above the fusion barrier for ${}^{12-15}$C + ${}^{12}$C with measurements of the interaction cross-section from high evergy collisions. The experimental results indicate that the fusion cross-section associated with dynamics increases with increasing neutron excess. Calculations with a time-dependent Hartree-Fock model fail to describe the observed trend.

   nucl-exnucl-th0 citations
2. 02*

   Cosmogenic activation of silicon

   R. Saldanha🇺🇸 · R. Thomas🇺🇸 · R.H.M. Tsang🇺🇸 · A.E. Chavarria🇺🇸 · R. Bunker🇺🇸 · J.L. Burnett🇺🇸 · S.R. Elliott🇺🇸 · A. Matalon🇺🇸 · P. Mitra🇺🇸 · A. Piers🇺🇸 · P. Privitera🇺🇸 · K. Ramanathan🇺🇸 · R. Smida🇺🇸

   The production of ${}^3$H, ${}^7$Be, and ${}^{22}$Na by interactions of cosmic-ray particles with silicon can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of silicon CCDs and wafers with a neutron beam that mimics the cosmic-ray neutron spectrum, followed by direct counting, we determined that the production rate from cosmic-ray neutrons at sea level is ($112\pm 24$) atoms/(kg day) for ${}^3$H, ($8.1\pm 1.9$) atoms/(kg day) for ${}^7$Be, and ($43.0\pm 7.1$) atoms/(kg day) for ${}^{22}$Na. Complementing these results with the current best estimates of activation cross sections for cosmic-ray particles other than neutrons, we obtain a total sea-level cosmic-ray production rate of ($124\pm 24$) atoms/(kg day) for ${}^3$H, ($9.4\pm 2.0$) atoms/(kg day) for ${}^7$Be, and ($49.6\pm 7.3$) atoms/(kg day) for ${}^{22}$Na. These measurements will help constrain background estimates and determine the maximum time that silicon-based detectors can remain unshielded during detector fabrication before cosmogenic backgrounds impact the sensitivity of next-generation rare-event searches.

   ↳ physics.ins-detastro-ph.COnucl-exPRD(2020)·29 citations
3. 03*

   Atom probe characterisation of segregation driven Cu and Mn-Ni-Si co-precipitation in neutron irradiated T91 tempered-martensitic steel

   T. P. Davis (1) · M. A. Auger (1 and 2) · N. Almirall (3) · P. Hosemann (4) · G. R. Odette (3) · P. A. J. Bagot (1) · M.P. Moody (1) · D. E. J. Armstrong (1) ((1) Department of Materials, University of Oxford, UK) ((2) Department of Physics, Universidad Carlos III de Madrid, Spain) ((3) Materials Department, University of California, Santa Barbara, USA) ((4) Department of Nuclear Engineering, University of California, Berkeley, USA)

   The T91 grade and similar 9Cr tempered-martensitic steels (also known as ferritic-martensitic) are leading candidate structural alloys for fast fission nuclear and fusion power reactors. At low temperatures (300 to 400 ${}^{\circ }$C) neutron irradiation hardens and embrittles these steels, therefore it is important to investigate the origin of this mode of life limiting property degradation. T91 steel specimens were separately neutron irradiated to 2.14 dpa at 327 ${}^{\circ }$C and 8.82 dpa at 377 ${}^{\circ }$C in the Idaho National Laboratory Advanced Test Reactor. Atom probe tomography was used to investigate the segregation driven formation of Mn-Ni-Si-rich (MNSPs) and Cu-rich (CRP) co-precipitates. The precipitates increase in size and, slightly, in volume fraction at the higher irradiation temperature and dose, while their corresponding compositions were very similar, falling near the Si(Mn,Ni) phase field in the Mn-Ni-Si projection of the Fe-based quaternary phase diagram. While the structure of the precipitates has not been characterized, this composition range is distinctly different than that of the typically cited G-phase. The precipitates are composed of CRP with MNSP appendages. Such features are often observed in neutron irradiated reactor pressure vessel (RPV) steels. However, the Si, Ni, Mn, P and Cu solutes concentrations are lower in the T91 than in typical RPV steels. Thus, in T91 precipitation primarily takes place in solute segregated regions of line and loop dislocations. These results are consistent with the model for radiation induced segregation driven precipitation of MNSPs proposed by Ke et al. Cr-rich alpha prime ($\alpha$') phase formation was not observed.

   ↳ cond-mat.mtrl-scinucl-ex0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.