Fri·Jul 7, 2017Friday·July 7, 2017

1. 01*

   Energy dependence of the prompt $\gamma$-ray emission from the $(d,p)$-induced fission of ${}^{234}{\mathrm{U}}^{\ast }$ and ${}^{240}{\mathrm{Pu}}^{\ast }$

   S. J. Rose🇳🇴 · F. Zeiser🇳🇴 · J. N. Wilson🇫🇷 · A. Oberstedt🇷🇴 · S. Oberstedt🇧🇪 · S. Siem🇳🇴 · G. M. Tveten🇳🇴 · L. A. Bernstein🇺🇸 · D. L. Bleuel🇺🇸 · J. A. Brown🇺🇸 · L. Crespo Campo🇳🇴 · F. Giacoppo🇳🇴 and 13 other authors

   Prompt fission $\gamma$-rays are responsible for approximately 5\% of the total energy released in fission, and therefore important to understand when modelling nuclear reactors. In this work we present prompt $\gamma$-ray emission characteristics in fission, for the first time as a function of the nuclear excitation energy of the fissioning system. Emitted $\gamma$-ray spectra were measured, and $\gamma$-ray multiplicities and average and total $\gamma$ energies per fission were determined for the ${}^{233}$U(d,pf) reaction for excitation energies between 4.8 and 10 MeV, and for the ${}^{239}$Pu(d,pf) reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra $\sim$5 MeV of energy is potentially available in the excited fragments for $\gamma$-decay. The measured results are compared to model calculations made for prompt $\gamma$-ray emission with the fission model code GEF. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

   nucl-exPRC(2017)·9 citations
2. 02*

   Measurement of the neutron lifetime using an asymmetric magneto- gravitational trap and in situ detection

   R. W. Pattie Jr. · N. B. Callahan · C. Cude-Woods · E. R. Adamek · L. J. Broussard · S. M. Clayton · S. A. Currie · E. B. Dees · X. Ding · E. M. Engel · D. E. Fellers · W. Fox and 26 other authors

   The precise value of the mean neutron lifetime, ${\tau }_n$, plays an important role in nuclear and particle physics and cosmology. It is a key input for predicting the ratio of protons to helium atoms in the primordial universe and is used to search for new physics beyond the Standard Model of particle physics. There is a 3.9 standard deviation discrepancy between ${\tau }_n$ measured by counting the decay rate of free neutrons in a beam (887.7 $\pm$ 2.2 s) and by counting surviving ultracold neutrons stored for different storage times in a material trap (878.5$\pm$0.8 s). The experiment described here eliminates loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls and neutrons in quasi-stable orbits rapidly exit the trap. As a result of this approach and the use of a new in situ neutron detector, the lifetime reported here (877.7 $\pm$ 0.7 (stat) +0.4/-0.2 (sys) s) is the first modern measurement of ${\tau }_n$ that does not require corrections larger than the quoted uncertainties.

   nucl-exhep-exnucl-thScience(2018)·180 citations
3. 03*

   A Magnetic Field Cloak For Charged Particle Beams

   K. Capobianco-Hogan🇺🇸 · R. Cervantes🇺🇸 · A. Deshpande🇺🇸 · N. Feege🇺🇸 · T. Krahulik🇺🇸 · J. LaBounty🇺🇸 · R. Sekelsky🇺🇸 · A. Adhyatman🇺🇸 · G. Arrowsmith-Kron🇺🇸 · B. Coe🇺🇸 · K. Dehmelt🇺🇸 · T. K. Hemmick🇺🇸 and 7 other authors

   Shielding charged particle beams from transverse magnetic fields is a common challenge for particle accelerators and experiments. We demonstrate that a magnetic field cloak is a viable solution. It allows for the use of dipole magnets in the forward regions of experiments at an Electron Ion Collider (EIC) and other facilities without interfering with the incoming beams. The dipoles can improve the momentum measurements of charged final state particles at angles close to the beam line and therefore increase the physics reach of these experiments. In contrast to other magnetic shielding options (such as active coils), a cloak requires no external powering. We discuss the design parameters, fabrication, and limitations of a magnetic field cloak and demonstrate that cylinders made from 45 layers of YBCO high-temperature superconductor, combined with a ferromagnetic shell made from epoxy and stainless steel powder, shield more than 99% of a transverse magnetic field of up to 0.45 T (95 % shielding at 0.5 T) at liquid nitrogen temperature. The ferromagnetic shell reduces field distortions caused by the superconductor alone by 90% at 0.45 T.

   ↳ physics.acc-phnucl-exphysics.ins-detNucl.Instrum.Meth.A(2018)·6 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.