Resonance analysis of 147^{147}Sm(n,alpha) cross sections: Comparison to optical model calculations and indications of non-statistical effects

We have measured the $^{147}$Sm(\textit{n},$\alpha$) cross section from 3 eV to 500 keV and performed an $\mathcal{R}$-matrix analysis in the resolved region ($E_{n}$$<$ 700 eV) to extract $\alpha$ widths for 104 resonances. We computed strength functions from these resonance parameters and compared them to transmission coefficients calculated using optical model potentials similar to those employed as inputs to statistical model calculations. The statistical model often is used to predict cross sections and astrophysical reaction rates. Comparing resonance parameters rather than cross sections allows more direct tests of potentials used in the model and hence should offer greater insight into possible improvements. In particular, an improved $\alpha$+nucleus potential is needed for applications in nuclear astrophysics. In addition to providing a more direct test of the $\alpha$% +nucleus potential, the $\alpha$-width distributions show indications of non-statistical effects.Comment: Accepted for publication in Physical Review

Cross sections of the 144

Cross sections of the 144Sm(n,α)141Nd and 66Zn(n,α)63Ni reactions were measured at En = 4.0, 5.0 and 6.0 MeV performed at the 4.5-MV Van de Graaff Accelerator of Peking University, China. A double-section gridded ionization chamber was used to detect the alpha particles. The foil samples of 144Sm2O3 and enriched 66Zn were placed at the common cathode plate of the chamber. Monoenergetic neutrons were produced by a deuterium gas target through the 2H(d,n)3He reaction. The neutron flux was monitored by a BF3 long counter. Cross sections of the 238U(n,f) reaction were used as the standard to perform the (n,α) reaction measurement. Present results are compared with existing measurements and evaluations. They are generally in agreement with TALYS-1.6 code calculations. For the 144Sm(n,α)141Nd reaction our measurements support the data of JEF-2.2. For the 66Zn(n,α)63Ni reaction present results support the data of EAF-2010 and TENDL-2015 data

What we do and do not know about the s-process

AGB stars are the source for the main component of the $s$-process. Here we discuss both the properties which are reasonably well known and those which still suffer from substantial uncertainties. In the former case, we are fairly sure that the $s$-process contribution from AGB stars comes from masses between about 1 and 3 \msun, and the dominant neutron source is the $^{13}$C$(\alpha$,n)$^{16}$O reaction. In the latter category remains the formation mechanism for the $^{13}$C-pocket. Attempts at including rotation seem to inhibit neutron capture reactions. Explaining the observations seems to require a spread in the size of the $^{13}$C-pocket so some stochastic process, such as rotation, must be involved.Comment: To be published in Nuclear Physics A; Invited Review for "Nuclei in the Cosmos VIII", Vancouver, July 200