Measurement of direct neutron capture by neutron-rich sulfur isotopes

Thermal neutron capture cross sections for $^{34}$S(n,$\gamma$)$^{35}$S and $^{36}$S(n,$\gamma$)$^{37}$S have been measured and spectroscopic factors of the final states have been extracted. The calculated direct-capture cross sections reproduce the experimental data.Comment: 4 pages (uses espcrc1.sty), 1 postscript figure (uses psfig), accepted for publication in Nucl. Phys. A (Suppl.), uuencoded tex-files and postscript-files available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Stherm.u

New results on P -odd asymmetry of

A series of ultra-sensitive experiments has been carried out in 2001-2009 at the ILL measuring P -odd asymmetry in $\gamma$ -quanta emission in the nuclear reaction 10B (n,$\alpha$) 7Li* $\rightarrow$ $\gamma$ + $7Li$(g.s.) with polarized cold neutrons. The resulting value of the asymmetry coefficient is \ensuremath \alpha_{P\mbox{-}{\rm odd}}= +(0.0 \pm 2.6_{{\rm stat}} \pm 1.1_{{\rm syst}}) \times 10^{-8} . These experiments profited from high-intensity PF1B neutron facility and a new version of the integral measuring method: for decreasing experimental uncertainties, the frequency of neutron spin-flip was higher than a typical reactor power noise frequency. Using the new value, we constrain the weak neutral current constant in the cluster model framework to \ensuremath f_{\pi}^{^{10}\rm B} \leq 0.6 \times 10^{-7} (at 90% c.l.). This constraint agrees with that following from the nuclear reaction 6Li (n,$\alpha$) 3H : \ensuremath f_{\pi}^{^{6}\rm Li} \leq 1.1 \times 10^{-7} (at 90% c.l.). However, they both contradict the “best” value in the quark model by Desplanques, Donoughe, and Holstein \ensuremath f_{\pi}^{{\rm DDH}}=4.6\cdot 10^{-7} . We invite experts in the field to contribute to the theoretical analysis of the problem

Neutron capture of Si-30

At the Karlsruhe and Tubingen 3.75 MV Van de Graaff accelerators the cross section of the reaction Si-30(n,gamma)Si-31(2.62h) was measured by the activation technique via the beta spectrum of the Si-31-decay. Natural silicon samples of 50 to 90 mum thickness were irradiated back to back with gold foils which served as capture standard. Neutrons were generated using the Li-7(p,n) and T(p, n) reactions. The capture cross section was measured at the neutron energies 25, 30, 52, 104, 149, 180, and 215 keV, respectively. The data have been interpreted with the help of DWBA calculations. We find that the measured cross sections are strongly determined by direct capture and that resonant contributions have been overestimated previously. (C) 2002 Elsevier Science B.V. All rights reserved.Peer reviewe

First observation of P-odd asymmetry of α -particle emission in the 10^{10}B(n,α)7^{7}Li nuclear reaction

International audienceWe present measurements of P-odd asymmetry of emission of α -particles in the B10(n,α)Li7 nuclear reaction, which are carried out using beams of polarized cold neutrons at Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia) and Institut Max von Laue – Paul Langevin (ILL, Grenoble, France) nuclear reactors. The α -particle detector is an ionization chamber with insensitive gaseous layer