Astrophysics with spallation sources  (n,  ) cross sections for the s process  operating spallation facilities: LANSCE, J-PARC, n_TOF & examples for time-of-flight studies  comparison of spallation facilities and future options Franz Käppeler Karlsruhe Institute of Technology

status of s-process (n,  ) cross sections and remaining quests even-even nuclei current quests in s-process nucleosynthesis model tests: 16 s-only isotopes ± 1% n n,T,  via branchings ~20 unstable isotopes ± 5% presolar grains: anomalies in ~20 elements with 75 isotopes ± 1% bottle neck 15 n-magic nuclei ± 5% reactions: neutron poisons: abundant light elements neutron sources: ( ,n) reactions on 13 C and 22 Ne thermally excited el. and inel. scattering states: yields at A < 60: (n,  ) and (n,p) cross sections

status and requests needed: cross sections with uncertainties between 1 and 5% for complete set of isotopes from 12 C to 210 Po, including unstable samples

  (E n ) measured by time of flight and folded with stellar neutron spectrum √π ∫ E n exp(−E n /kT) dE n ‹  › = = ‹  v› 2 ∫  E n ) E n exp(-E n /kT) dE n vTvT Maxwellian averaged cross sections  MACS directly measured via activation

 (E n ) via TOF for 1 < E n < 300 keV s-process energies   low mass stars: kT = 8 keV and 25 keV massive stars: kT = 25 and 90 keV

E n = ½ m v 2 resolution  E n /E n = 2  t/t + 2  s/s pulsed neutron sources low energy (VdG, FRANZ)   high energy with moderator (spallation sources, e-linacs)

Los Alamos Luhan Neutron Scattering Center: pulsed, moderated spallation source for time-of-flight studies thermal < E n < 300 keV,  t = 250 ns WNR: unmoderated tungsten spallation target using the 800 MeV pulsed proton beam from the LANSCE linac 0.5 < E n < 750 MeV,  t ~150 ps 800 MeV proton linac plus PSR 17 n/p

Luhan (FP 14)  pulse width:250 ns  rep rate:20 Hz  moderator:water  neutron energy:th – 300 keV  flight path: 20 m  neutron beam diameter: 10 mm  equipment:BaF 2 calorimeter, 160 modules „designed for neutron capture reactions on small quantities, of order 1 mg, of radioactive or rare stable nuclei“ Nucl. Sci. Eng. 106 (1990) 208

DANCE array: 160 BaF 2 modules (n,  ) reactions →small samples, small cross sections the 62 Ni problem: integrated neutron flux in massive stars too small, reaction flow NOT in equilibrium → strong impact of single cross sections

the 62 Ni problem 62 Ni(n,  ) 63 Ni mass number abundance ratio (courtesy I. Dillmann)  TOF 25.8 ± 3.7 (2008) 37.0 ± 3.2 (2005) 12.5 ± 4.0 (1983) 26.8 ± 5.0 (1975)  activation 20.2 ± 2.1 (2009) 23.4 ± 4.6 (2008) 26.1 ± 2.6 (2005)

smallest sample ever used in TOF 237 Np, 400  g

J-PARC in Japan Japan Proton Accelerator Research Complex Japan Spallation Neutron Source

Ions Negative Hydrogen Energy for RCS injection400 MeV Energy for ADS 600 MeV Peak Current50 mA Beam Pulse Length500 μs Repetition Rate50 Hz Extraction Beam Energy3 GeV Repetition25 Hz Average Beam Current333 μA Extraction SchemeFast Extraction Beam Energy30 Gev (50 Gev) Average Beam Current25 μA (15 μA) Repetition0.2 Hz ~ 0.7 Hz ( 0.3 Hz) Extraction SchemeSlow, and Fast J-PARC beam parameters LINAC 3 GeV synchrotron 50 GeV synchrotron 50 n/p

J-PARC Accurate Neutron-Nucleus Reaction measurement Instrument

ANNRI – inside/outside

ANNRI specifications JKPS , 2011  proton beam power:17.5 kW → 120 kW (→ 1 MW)  pulse width:double pulse (100 ns separated by 600 ns)  rep rate:25 Hz  moderator:coupled hydrogen moderator  neutron energy: eV < E n < 50 keV  intensity at 1 MW at 21.5 m: 4.3×10 7 n/cm 2 /s (1.5 < En < 25 meV) 9.3×10 5 n/cm 2 /s (0.9 < En < 1.1 eV) 6.0×10 6 n/cm 2 /s (0.9 < En < 1.1 keV)  beam diameter: 3, 7, 22 mm  equipment:Ge spectrometer at 21.5 m NaI spectrometer at 27.9 m

ANNRI: intensity and beam profile

107 Pd(n,  ) with Ge spectrometer sample mass 137 mg

n_TOF - the CERN spallation neutron source 20 GeV protons on lead block  300 neutrons per proton  most luminous n-source worldwide  high resolution TOF facility

J-PARC in Japan Neutron creation Neutron detection 50 MeV 1.4 GeV

1 st collimator ( Ø=11 cm ) halo cleaning and first shaping  + filter station 2 nd collimator (Ø=1.8/8 cm) beam shaping neutrons from spallation target Experimental Area  185 m from the spallation target  location of samples and detectors

n_TOF coordinates CERN / INTC-O-011  proton beam power:20 GeV, 9 kW  pulse width:6 ns  rep rate:0.4 Hz  moderator:(borated) water  neutron energy: th < E n < 1 GeV  intensity at 185 m: 0.2 – 2·10 5 n/s/decade  energy 1 MeV  neutron beam diameter: 30 (70) mm  equipment:TAC, C 6 D 6 for (n,  ) FIC, PPAC for (n,f) pCVD, Mgas for (n,cp)

186 Os (2 g, 79 %) 187 Os (2 g, 70 %) 188 Os (2 g, 95 %) Al can environmental background 197 Au (1.2g) flux normalization (using Ratynski and Macklin high accuracy cross section data) nat Pb (2 g) in-beam gamma background nat C (0.5 g) neutron scattering background high resolution in neutron energy -ray detection: C 6 D 6 scintillators C6D6C6D6 C6D6C6D6 Neutron beam Sample changer

n_TOF results for 62 Ni previous TOF measurements (courtesy Iris Dillmann) n_TOF n_TOF campaign to determine (n,  ) cross sections of all stable Fe and Ni isotopes and of 63 Ni

in-beam  rays  from 1 H(n,  ) substantially reduced (borated water in saturated conditions, 1.28% H 3 BO 3 ) 2009: new target with separate moderator x13 x1.2 gravitational cut-off at 0.02 eV

borated water moderator

courtesy by Claudia Lederer 63 Ni(n,  ) – first results from n_TOF (2011)

TAC with 40 BaF 2 modules

TAC data for 241 Am(n,  ) Increase of the RRR limit above 150 eV present URR limit about 320 keV

astrophysics measurements at n_TOF campaign (n,  ) 151 Sm 204,206,207,208 Pb, 209 Bi 24,25,26 Mg 90,91,92,94,96 Zr, 93 Zr 186,187,188 Os, 139 La 19 isotopes (2 radioactive) 19 full publications campaign (n,  ) 54,56,57 Fe 58,60,62,63 Ni 33 S(n,  ) 26 Al(n,p) 59 Ni(n,p)

n_TOF target New Experimental Area (EAR-2) EAR-2 EAR-1 (at 185 m) ~ 20 m Flight-path length : ~20 m at 90° respect to p-beam direction expected neutron flux enhancement drastic reduction of the t 0 flash Flight-path length : ~20 m at 90° respect to p-beam direction expected neutron flux enhancement drastic reduction of the t 0 flash 10 m n_TOF upgrade

proposed EAR-2 n_TOF target pit Technical gallery m from pit) m from pit, above ground Existing hole To be built ISR n-flux x25, n-rate x10, lower background Dear Colleagues, I'm very proud to announce that this morning the INTC committee "strongly recommended " to the Research Board our proposal for EAR-2. Sergio Bertolucci, Director for Research and Computing, was present during the discussion and gave a positive reaction. Kind regards Enrico Feb 2, 2012

comparison of pulsed neutron sources FacilityNeutron flux at sample [cm -2 s -1 dec -1 ] Repetition rate [Hz] Flight path [m] Pulse width [ns] Neutron energy range [eV] Karlsruhe VdG1· K ·10 5 LANSCE5· th J-PARC3· x100th n_TOF5· th GELINA at Geel5· th Facilityn/p Lansce 17 J-PARC 45 n_TOF 300 Upgrades Neutron flux at sample FRANZ 1 ∙ 10 7 Lansce 5 ∙ 10 7 J-PARC 3 · 10 7 n_TOF 2 · 10 6