Fri·Aug 25, 2017Friday·August 25, 2017

1. 01*

   Cosmogenic activation of materials

   Susana Cebrian🇪🇸

   Experiments looking for rare events like the direct detection of dark matter particles, neutrino interactions or the nuclear double beta decay are operated deep underground to suppress the effect of cosmic rays. But the production of radioactive isotopes in materials due to previous exposure to cosmic rays is an hazard when ultra-low background conditions are required. In this context, the generation of long-lived products by cosmic nucleons has been studied for many detector media and for other materials commonly used. Here, the main results obtained on the quantification of activation yields on the Earth's surface will be summarized, considering both measurements and calculations following different approaches. The isotope production cross sections and the cosmic ray spectrum are the two main ingredients when calculating this cosmogenic activation; the different alternatives for implementing them will be discussed. Activation that can take place deep underground mainly due to cosmic muons will be briefly commented too. Presently, the experimental results for the cosmogenic production of radioisotopes are scarce and discrepancies between different calculations are important in many cases, but the increasing interest on this background source which is becoming more and more relevant can help to change this situation.

   nucl-exastro-ph.HEhep-exphysics.ins-detInt.J.Mod.Phys.A(2017)·45 citations
2. 02*

   Determination of the ${}^{36}$Mg($n,\gamma$)${}^{37}$Mg reaction rate from Coulomb dissociation of ${}^{37}$Mg

   Sharma Shubhchintak🇺🇸 · R. Chatterjee🇮🇳 · R. Shyam🇮🇳

   We use the Coulomb dissociation (CD) method to calculate the rate of the ${}^{36}$Mg($n,\gamma$)${}^{37}$Mg radiative capture reaction. The CD cross sections of the ${}^{37}$Mg nucleus on a ${}^{208}$Pb target at the beam energy of 244 MeV/nucleon, for which new experimental data have recently become available, were calculated within the framework of a finite range distorted wave Born approximation theory that is extended to include the projectile deformation effects. Invoking the principle of detailed balance, these cross sections are used to determine the excitation function and subsequently the rate of the ${}^{36}$Mg($n,\gamma$)${}^{37}$Mg reaction. We compare these rates to those of the ${}^{36}$Mg($\alpha ,n$)${}^{39}$Si reaction calculated within a Hauser-Feshbach model. We find that for $T_9$ as large as up to 1.0 (in units of 10${}^9$ K) the ${}^{36}$Mg($n,\gamma$)${}^{37}$Mg reaction is much faster than the ${}^{36}$Mg($\alpha ,n$)${}^{39}$Si one. The inclusion of the effects of ${}^{37}$Mg projectile deformation in the breakup calculations, enhances the ($n,\gamma$) reaction rate even further. Therefore, it is highly unlikely that the $(n,\gamma )$ $\beta$-decay $r$-process flow will be broken at the ${}^{36}$Mg isotope by the $\alpha$-process.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2017)·18 citations
3. 03*

   Enhancement of the Triple Alpha Rate in a Hot Dense Medium

   Mary Beard · Sam M. Austin · Richard Cyburt🇺🇸

   In a sufficiently hot and dense astrophysical environment the rate of the triple-alpha (3alpha) reaction can increase greatly over the value appropriate for helium burning stars owing to hadronically induced de-excitation of the Hoyle state. In this paper we use a statistical model to evaluate the enhancement as a function of temperature and density. For a density of $10^{6}gmc{m}^{-3}$ enhancements can exceed a factor of one-hundred. In high temperature/density situations, the enhanced 3alpha rate is a better estimate of this rate and should be used in these circumstances. We then examine the effect of these enhancements on production of ${}^{12}$C in the neutrino wind following a supernova explosion and in an x-ray burster.

   ↳ nucl-thastro-ph.HEastro-ph.SRnucl-exPRL(2017)·22 citations
4. 04*

   Examining the model dependence of the determination of kinetic freeze-out temperature and transverse flow velocity in small collision system

   Hai-Ling Lao🇨🇳 · Fu-Hu Liu🇨🇳 · Bao-Chun Li🇨🇳 · Mai-Ying Duan🇨🇳 · Roy A. Lacey🇺🇸

   The transverse momentum distributions of the identified particles produced in small collision systems at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) have been analyzed by four models. The first two models utilize the blast-wave model with different statistics. The last two models employ certain linear correspondences based on different distributions. The four models describe the experimental data measured by the Pioneering High Energy Nuclear Interaction eXperiment (PHENIX), Solenoidal Tracker at RHIC (STAR), and A Large Ion Collider Experiment (ALICE) cCollaborations equally well. It is found that both the kinetic freeze-out temperature and transverse flow velocity in the central collisions are comparable with those in the peripheral collisions. With the increase of collision energy from that of the RHIC to that of the LHC, the considered quantities typically do not decrease. Comparing with the central collisions, the proton-proton collisions are closer to the peripheral collisions.

   ↳ nucl-thhep-exhep-phnucl-exNucl.Sci.Tech.(2018)·33 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.