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Register a new userExperimental neutron capture data of $^{58}$Ni from the CERN n_TOF facility
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The $^{58}$Ni $(n,gamma)$ cross section has been measured at the neutron time of flight facility n_TOF at CERN, in the energy range from 27 meV up to 400 keV. In total, 51 resonances have been analyzed up to 122 keV. Maxwellian averaged cross sections (MACS) have been calculated for stellar temperatures of kT$=$5-100 keV with uncertainties of less than 6%, showing fair agreement with recent experimental and evaluated data up to kT = 50 keV. The MACS extracted in the present work at 30 keV is 34.2$pm$0.6$_mathrm{stat}pm$1.8$_mathrm{sys}$ mb, in agreement with latest results and evaluations, but 12% lower relative to the recent KADoNIS compilation of astrophysical cross sections. When included in models of the s-process nucleosynthesis in massive stars, this change results in a 60% increase of the abundance of $^{58}$Ni, with a negligible propagation on heavier isotopes. The reason is that, using both the old or the new MACS, 58Ni is efficiently depleted by neutron captures.
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Background:The design of new nuclear reactors and transmutation devices requires to reduce the present neutron cross section uncertainties of minor actinides. Purpose: Reduce the $^{243}$Am(n,$gamma$) cross section uncertainty. Method: The $^{243}$Am(n,$gamma$) cross section has been measured at the n_TOF facility at CERN with a BaF$_{2}$ Total Absorption Calorimeter, in the energy range between 0.7 eV and 2.5 keV. Results: The $^{243}$Am(n,$gamma$) cross section has been successfully measured in the mentioned energy range. The resolved resonance region has been extended from 250 eV up to 400 eV. In the unresolved resonance region our results are compatible with one of the two incompatible capture data sets available below 2.5 keV. The data available in EXFOR and in the literature has been used to perform a simple analysis above 2.5 keV. Conclusions: The results of this measurement contribute to reduce the $^{243}$Am(n,$gamma$) cross section uncertainty and suggest that this cross section is underestimated up to 25% in the neutron energy range between 50 eV and a few keV in the present evaluated data libraries.
The cross section of the $^{62}$Ni($n,gamma$) reaction was measured with the time-of-flight technique at the neutron time-of-flight facility n_TOF at CERN. Capture kernels of 42 resonances were analyzed up to 200~keV neutron energy and Maxwellian averaged cross sections (MACS) from $kT=5-100$ keV were calculated. With a total uncertainty of 4.5%, the stellar cross section is in excellent agreement with the the KADoNiS compilation at $kT=30$ keV, while being systematically lower up to a factor of 1.6 at higher stellar temperatures. The cross section of the $^{63}$Ni($n,gamma$) reaction was measured for the first time at n_TOF. We determined unresolved cross sections from 10 to 270 keV with a systematic uncertainty of 17%. These results provide fundamental constraints on $s$-process production of heavier species, especially the production of Cu in massive stars, which serve as the dominant source of Cu in the solar system.
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.
Proton decay from the 3$hbaromega$ isoscalar giant dipole resonance (ISGDR) in $^{58}$Ni has been measured using the ($alpha,alphap$) reaction at a bombarding energy of 386 MeV to investigate its decay properties. We have extracted the ISGDR strength under the coincidence condition between inelastically scattered $alpha$ particles at forward angles and decay protons emitted at backward angles. Branching ratios for proton decay to low-lying states of $^{57}$Co have been determined, and the results compared to predictions of recent continuum-RPA calculations. The final-state spectra of protons decaying to the low-lying states in $^{57}$Co were analyzed for a more detailed understanding of the structure of the ISGDR. It is found that there are differences in the structure of the ISGDR as a function of excitation energy.
Background: Using the chiral (Kyushu) $g$-matrix folding model with the densities calculated with Gogny-HFB (GHFB) with the angular momentum projection (AMP), we determined the central values of matter radius and neutron skin from the central values of reaction cross sections $sigma_{rm R}({rm EXP})$ of p+$^{40,48}$Ca and p+$^{208}$Pb scattering. As for p+$^{58}$Ni scattering, $sigma_{rm R}({rm EXP})$ are available as a function of incident energy $E_{rm in}$. Aim: Our aim is to determine matter radius $r_{m}$ and skin $r_{rm skin}$ for $^{58}$Ni from the $sigma_{rm R}({rm EXP})$ of p+$^{58}$Ni scattering by using the Kyushu $g$-matrix folding model with the GHFB+AMP densities. Results: For p+$^{58}$Ni scattering, the Kyushu $g$-matrix folding model with the GHFB+AMP densities reproduces $sigma_{rm R}({rm EXP})$ in $8.8 leq E_{rm in} leq 81$MeV. For $E_{rm in}=81$MeV, we define the factor $F$ as $F=sigma_{rm R}({rm EXP})/sigma_{rm R}({rm AMP})=0.9775$. The $Fsigma_{rm R}({rm AMP})$ be much the same as the center values of $sigma_{rm R}({rm EXP})$ in $8.8 leq E_{rm in} leq 81$MeV. We then determine $r_{rm m}({rm EXP})$ from the center values of $sigma_{rm R}({rm EXP})$, using $sigma_{rm R}({rm EXP})=C r_{m}^{2}({rm EXP})$ with $C=r_{m}^{2}({rm AMP})/ (Fsigma_{rm R}({rm AMP}))$. The $r_{m}({rm EXP})$ thus obtained are averaged over $E_{rm in}$. The averaged value is $r_{m}({rm EXP})=3.697$fm. Eventually, we obtain $r_{rm skin}({rm EXP})=0.023$fm from $r_{rm m}=3.697$fm and $r_p({rm EXP})=3.685$fm of electron scattering.
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