Fri·Dec 2, 2016Friday·December 2, 2016

1. 01*

   Activity measurement of 60Fe through the decay of 60mCo and confirmation of its half-life

   Karen Ostdiek · Tyler Anderson🇺🇸 · William Bauder · Matthew Bowers · Adam Clark · Philippe Collon · Rugard Dressler🇨🇭 · John Greene🇺🇸 · Walter Kutschera · Wenting Lu🇨🇳 · Austin Nelson🇺🇸 · Michael Paul🇮🇱 and 3 other authors

   The half-life of the neutron-rich nuclide, {\fesixty} has been in dispute in recent years. A measurement in 2009 published a value of $(2.62\pm 0.04)\times 10^6$ years, almost twice that of the previously accepted value from 1984 of $(1.49\pm 0.27)\times 10^6$ years. This longer half-life was confirmed in 2015 by a second measurement, resulting in a value of $(2.50\pm 0.12)\times 10^6$ years. All three half-life measurements used the grow-in of the $\gamma$-ray lines in {\nisixty} from the decay of the ground state of ${}^{60}\text{Co}$ (t${}_{1/2}$=5.27 years) to determine the activity of a sample with a known number of {\fesixty} atoms. In contrast, the work presented here measured the {\fesixty} activity directly via the 58.6 keV $\gamma$-ray line from the short-lived isomeric state of ${}^{60}\text{Co}$ (t${}_{1/2}$=10.5 minutes), thus being independent of any possible contamination from long-lived ${}^{60\text{g}}\text{Co}$. A fraction of the material from the 2015 experiment with a known number of {\fesixty} atoms was used for the activity measurement, resulting in a half-life value of $(2.72\pm 0.16)\times 10^6$ years, confirming again the longer half-life. In addition, {\fesixty}/{\fe} isotopic ratios of samples with two different dilutions of this material were measured with Accelerator Mass Spectrometry (AMS) to determine the number of {\fesixty} atoms. Combining this with our activity measurement resulted in a half-life value of $(2.69\pm 0.28)\times 10^6$ years, again agreeing with the longer half-life.

   nucl-exPRC(2017)·11 citations
2. 02*

   Neutron capture cross section measurement of 238U at the n TOF CERN facility with C6D6 scintillation detectors in the energy region from 1 eV to 700 keV

   n_TOF Collaboration: F. Mingrone🇨🇭 · C. Massimi🇮🇹 · G. Vannini🇮🇹 · N. Colonna🇮🇹 · F. Gunsing🇫🇷 · P. Žugec🇭🇷 · S. Altstadt🇩🇪 · J. Andrzejewski🇵🇱 · L. Audouin🇫🇷 · M. Barbagallo🇮🇹 · V. Bécares🇪🇸 · F. Bečvář🇨🇿 and 92 other authors

   The aim of this work is to provide a precise and accurate measurement of the 238U(n,g) reaction cross section in the energy region from 1 eV to 700 keV. This reaction is of fundamental importance for the design calculations of nuclear reactors, governing the behaviour of the reactor core. In particular, fast reactors, which are experiencing a growing interest for their ability to burn radioactive waste, operate in the high energy region of the neutron spectrum. In this energy region most recent evaluations disagree due to inconsistencies in the existing measurements of up to 15%. In addition, the assessment of nuclear data uncertainty performed for innovative reactor systems shows that the uncertainty in the radiative capture cross-section of 238U should be further reduced to 1-3% in the energy region from 20 eV to 25 keV. To this purpose, addressed by the Nuclear Energy Agency as a priority nuclear data need, complementary experiments, one at the GELINA and two at the n_TOF facility, were proposed and carried out within the 7th Framework Project ANDES of the European Commission. The results of one of these 238U(n,g) measurements performed at the n_TOF CERN facility are presented in this work. The gamma-ray cascade following the radiative neutron capture has been detected exploiting a setup of two C6D6 liquid scintillators. Resonance parameters obtained from this work are on average in excellent agreement with the ones reported in evaluated libraries. In the unresolved resonance region, this work yields a cross section in agreement with evaluated libraries up to 80 keV, while for higher energies our results are significantly higher.

   nucl-exPRC(2017)·17 citations
3. 03*

   Alpha Conjugate Neck Structures in the Collisions of 35 MeV/nucleon 40Ca with 40Ca

   K. Schmidt🇵🇱 · X. Cao🇺🇸 · E. J. Kim🇰🇷 · K. Hagel🇺🇸 · M. Barbui🇺🇸 · J. Gauthier🇺🇸 · S. Wuenschel🇺🇸 · G. Giuliani🇺🇸 · M. R. D. Rodrigues🇺🇸 · H. Zheng🇮🇹 · M. Huang🇺🇸 · N. Blando🇺🇸 and 15 other authors

   The de-excitation of alpha-conjugate nuclei produced in reactions of 35 MeV/nucleon 40Ca with 40Ca has been investigated. Particular emphasis is placed on examining the dynamics of collisions leading to projectile-like fragment exit channels. A general exploration of the reaction systematics reveals the binary dissipative character of the collisions and a hierarchy effect similar to that seen for heavier systems. Investigation of the subset of events characterized by a total alpha-conjugate mass (alpha particles plus alpha-conjugate fragments) equal to 40 and atomic number equal to 20 reveals a dominance of alpha-conjugate exit channels. The hierarchy effect for these channels leads to the production of alpha-clustered neck structures with potentially exotic geometries and properties.

   nucl-exnucl-thPRC(2017)·21 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.