N eutron cap ture measurements (NCap)

1. Neutron capture measurements (NCap) neutron production via 7Li(p,n) proton accelerator radioactive ions Michael Heil for the NCAP collaboration Radioactive ion beam facility Extensive neutron source Improved g-detection system Measure neutron capture cross sections on radioactive targets

2. Motivation Neutron capture cross sections of unstable isotopes are important for the nucleosynthesis of the heavy elements: Neutron capture Abundance (Si=106) Fe Mass number • s-process: the analyses of branchings along the s-process path give information on physical state of stellar plasma. • r- and p-process: • capture of the remaining free neutrons during freeze out will influence the final abundance pattern. • Data necessary to test and assist model calculations.

3. Motivation / s-process 63Ni 79Se 81Kr 85Kr 147Nd 147Pm 148Pm 151Sm 154Eu 155Eu 153Gd 160Tb 163Ho 170Tm 171Tm 179Ta 185W 204Tl • Branchings determine • neutron density • temperature • mass density • convection time scales • in the star during the s process 152 154 155 156 241d Gd 151 153 9.3 h 8.8yr 5.0yr Eu 150 152 154 93 yr Sm Experimental challenge: Measure (n,g) of unstable isotopes

4. Motivation / r-process The production of 60Fe in core collapse supernovae depends strongly on the uncertain 59Fe(n,g) cross section. The observation of 60Fe (t1/2=1.5 Myr) with the INTEGRAL satellite will constrain supernovae models if the 59Fe(n,g) cross section is known. No experimental data available Calculations: 1 mb – 10 mb Detection of 60Fe with INTEGRAL or RHESSI Evidence for a nearby Supernova 2.8 Myr ago at a distance of a few 10 pc. Deep-Sea Manganese Crust

5. Production of radioactive samples • So far, milli-gram samples are necessary to perform neutron capture experiments on radioactive isotopes. • Problems: • Activity of the samples: • Assume 500 mg 85Kr: • Ig=0.43 %, Eg = 514 keV: 30 GBq • Availability of the samples • We need an experimental setup which allows to measure neutron capture cross sections of nano-gram samples • We need a possibility to produce isotopically “pure” nano-gram samples

6. Experimental setup Sample by ion implantation of radioactive beams Neutron production via 7Li(p,n) 100 5.5 En (keV) g prompt flash Neutron beam Proton beam Proton accelerator g g other reactions (n,g) on sample 4p BaF2 TOF (ns) 0 10 39 4 cm flight path for high neutron flux 4p BaF2 detector for efficient g-ray detection R. Reifarth et al., Nucl. Instr. Meth. A (in press)

7. radioactive ions Sample production • To perform neutron capture experiments • on radioactive isotopes one needs samples with about 1015 atoms: • With FAIR and other upcoming RIB facilities (Spiral2, RIA, Eurisol) intensities of >1010 ions/s are reached for a wide variety of isotopes. • Implantation of selected isotopes in thin carbon foils: • beam intensity ≥ 1010 1/s (8.64·1014 1/day) • beam size Ø < 2 cm • high purity (<10% contaminant beam) • thin backings (<1 mg/cm2 carbon backings) • -> low energy radioactive beam (< 5 MeV/u) • Expected production intensities: • 6·109 for 59Fe • 3·1010 for 85Kr 5 MeV/u 59Fe ions in carbon

8. The NUSTAR facility "Super-FRS" Low-Energy Branch Super-FRS Ring Branch High-Energy Branch

9. Production rates of exotic nuclei K.-H. Schmidt

10. Neutron source • Neutron production via 7Li(p,n) reaction • We propose to build a pulsed high-current, low-energy accelerator: • - 2 to 3 MeV proton energy • - repetition rates 1 to 100 kHz • - pulse width < 1 ns • - average current <100 mA at 10 kHz Worldwide most intense neutron source in the keV region !

11. Physics performance - example 85Kr • No experimental data available, theoretical calculations at 30 keV: 123 mb, 67 mb, 25 mb, 150 mb: Uncertain by a factor of 6 • Beam time of 2 days: • 85Kr beam of 3.25·1010 1/s (> 5.6·1015 atoms in two days, 800 ng) • Neutron flux of 1·108 neutrons/s/cm2 • Neutron capture cross section of 100 mb collection of > 35 000 counts in 1 week background from backing: 125 000 carbon Activity of target: 50 kBq Ig=0.43 %, Eg = 514 keV 85Kr This setup would also allow measurements of very small (n,g) cross sections (weak s-process, neutron poisons)

12. Schedule and milestones  • Submission of the proposal ( April 2004) • PAC: evaluation of the proposals (June 2004) • Submission of technical report (Jan. 2005) • PAC: evaluation of TR’s (March 2005) • Technical Design Report (Jan. 2006) • R&D (2004 – 2008) - Proof of principle experiment at Karlsruhe - Study different proton accelerator concepts - BaF2 pulse shape, implantation setup … • Construction phase (2008 – 2010) • Operation in 2010   

13. NCap-Collaboration • Bari, Italy, INFN (G. Tagliente) • Bologna, Italy, INFN (N. Colonna) • Bologna, Italy, ENEA (A. Mengoni) • Madrid, Spain, CIEMAT (D. Cano-Ott, E.M. Gonzalez-Romero) • Darmstadt, Germany, GSI (C. Scheidenberger, K. Sümmerer) • Dresden, Germany, Forschungszentrum Rossendorf (A. Junghans) • Karlsruhe, Germany, FZK (L. Audouin, M. Heil, F. Käppeler, R. Plag, S. Walter) • Legnaro, Italy, INFN (P. F. Mastinu) • Los Alamos, USA, LANL (R. Reifarth) • Notre Dame, USA, University of Notre Dame (M. Wiescher) • Oak Ridge, USA, ORNL (P. Koehler) • Osaka, Japan, RCNP (Y. Nagai) • Saclay, France, CEA (F. Gunsing) • Valencia, Spain, IFIC (J. L. Tain) You are welcome to join !!!