I. Introductory remarks and present status II. Laboratory experiments and astrophysics III. Future options scenarios status and challenges new developments neutron reactions in astrophysics – status and perspectives

neutron capture scenarios big bang stellar He burning s process in TP-AGB and in massive stars explosive nucleosynthesis p and r processes neutron capture accounts for 75% of the stable isotopes, but only for about 0.005% of the total post BB abundances

Maxwellian averaged cross sections required  measure  (E n ) by time of flight, 0.3 < E n < 500 keV, determine average for stellar spectrum correct for SEF high accuracy, wide energy range  produce thermal spectrum in laboratory, measure stellar average directly by activation correct for SEF very high sensitivity

prompt  -rays + TOF-method detection of neutron capture events * Moxon-Rae   ~1% * PH-weighting ~20% * Ge, NaI < 1% single  ´ s all  ´s * 4  BaF 2 ~100% (n,  ): activation in quasi-stellar spectrum most sensitive * small cross sections, atoms! selective * natural samples or low enrichment

compilation of stellar (n,  ) cross sections even-even nuclei Bao & Käppeler 1987 Bao et al Beer, Voss & Winters 1992 collect experimental data, renormalize, calculate MACS, recommend based on educated choices by experienced experimentalist complement by theory (SEF ) current update by Dillmann & Plag: KADONIS

status of stellar (n,  ) cross sections s process:  = 1-3% p and r process:  ~ 5% what do we have? nuclear input must be good enough that it doesn‘t punch through to calculated abundances! what do we need? beware: discrepancies often larger than uncertainties!!!

activation in quasi-stellar spectrum - neutron source 7 Li(p,n) 7 Be - neutron flux 197 Au(n,  ) 198 Au - 15 C detected via 5.3 MeV line (t 1/2 =2.45 s) most  (n,  ) of unstable nuclei measured this way: 14 C(n,  ) 15 C neutron cone Au/ 14 C/Au lithium proton beam half-life limits  0.1 s < t 1/2 < 10 yr with  -spec  no limit with AMS! sample properties  >10 14 atoms  impurities acceptable

activation in quasi-stellar spectrum possible neutron sources:  7 Li(p, n) 7 Be  kT=25 keV  2·10 9 neutrons/s, 100  A  3 H(p, n) 3 He  52 keV  1·10 8 “ “  18 O(p, n) 18 F  5 keV  2·10 5 “ “ higher beam currents needed for - activations at low energies - long-lived product nuclei - studies of double neutron captures higher beam currents require new target technology!

complete info:  (E n ) via TOF method & folding with stellar spectrum larger samples * limited sensitivity optimal efficiency higher flux limited selectivityenriched samples ** * not desirable and even excluded for unstable samples ** mandatory

   >90% up to 10 MeV  casc > 98%  E/E = 6% at 6 MeV clear signatures  t = 500 ps good TOF resolution optimal efficiency : 4  BaF 2 array sample    Pb neutron target p-beam  collimated n-beam now also at Los Alamos and CERN FZK

high neutron fluxes : spallation sources PS213 n_TOF Collaboration 0.8 proton energy (GeV) repetition rate (Hz) pulse width (ns) 5 20 flight path (m) average proton current (  A) 2 20 neutrons per proton 760 since 1987 since 2001 wide neutron energy range from thermal to 250 MeV

still higher fluxes in future  J-PARC spallation source similar features than LANSCE, but 50 times more flux  LANSCE improved by factor of 10 – 20 by upgrade of LAMPF  improved by factor of 100 by shorter flight path Low energy proton accelerators with beam currents of up to 200 mA (Soreq Nucl. Research Center, Univ. of Frankfurt/M)

unstable samples: now and then r and p process (n,  ) cross sections for a variety of selected unstable isotopes (r : 60 Fe, 106 Ru, 126 Sn, 182 Hf... (p : 91,92 Nb, 97,98 Tc...) for direct use in reaction networks to derive rates of inverse reactions to test and assist statistical models 63 Ni 79 Se 81 Kr 85 Kr 147 Nd 147 Pm 148 Pm 151 Sm 154 Eu 155 Eu 153 Gd 160 Tb 163 Ho 170 Tm 171 Tm 179 Ta 185 W 204 Tl branch point status s process future + 59 Fe, 125 Sn, 181 Hf….

summary numerous remaining quests for s process (branchings, grains, massive stars ) and many more for explosive nucleosynthesis present facilities and detectors suited for most stable isotopes new approaches required for radioactive samples spallation sources, new low energy accelerators, and RIB facilities promising, both for stellar and explosive nucleosynthesis important for quantitative picture of galactic chemical evolution