CERN-INTC /INTC-P-415 Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction Spokespersons: C. Guerrero (U. Sevilla) and C. Domingo-Pardo (IFIC) Close Collaborators: U. Koester (ILL), D. Schumann (PSI) and S. Heinitz (PSI) 47th Meeting of the INTC (25 th June 2014)

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Nucleosynthesis through the s-process 2 Nuclear reactions: energy generation nucleosynthesis condensation ejection, explosion interstellar gas & dust Mixing (abundance distribution) Chemical elements beyond Iron are synthesized via neutron capture reactions in stars: ~ ½ by the s-process (red giants) ~ ½ by the r-process (explosive) Fusion reactions Neutron capture reactions

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Fe Co Ni Rb Ga Ge Zn Cu Se Br As Zr Y Sr Kr (n,  ) ()() ()() 79 Se, t 1/2 =65 ky 80 Br, t 1/2 =17 min, 92 % (   ), 8 % (   ) 85 Kr, t 1/2 =11 y s-only neutron number proton number 63 Ni, t 1/2 =100 y Nucleosynthesis through the s-process Understanding abundances “around” branching points: -Half lifes -(n,g) cross sections -Neutron density and temperature

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Motivation: branching points 4 Lederer et al., PRL 110 (2013) Abbondanno et al., PRL 93 (2004)

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Branching point at A= Figure 1. The s-process flow in the mass region A= Branching points are indicated by dotted blue boxes, and the one of interest in this work ( 147 Pm) is marked in red. The s-only isotopes 148 Sm and 150 Sm are indicated by double squares. EnEn 5keV8keV10keV15keV20keV25keV30keV40keV50keV60keV80keV100keV 151 Sm Pm Stellar Enhancement Factors (SEF) according to Kadonis * Studies at thermal

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Previous measured and calculated values 6 Only one measurement to date: Reifarth et al. [APJ 582 (2003) 1251–1262] at FZK in which they irradiated 28 ng of 147 Pm with a 25 keV. Measurement at ~25 keV, but the 95% of the neutron exposure in the main s-process occurs at much lower stellar temperatures, of about 90 MK (kT = 8 keV). Sizable extrapolations with HF needed. Kadonis EAR-2 + sufficient material → first ever ToF measurement in the E n range of interest

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Sample production in three steps Branching points are radioactive! Production via (n,  ) or (n,  )  - in the ILL research reactor Neutron flux: 1.5x10 15 n/cm 2 /s (highest F n,th worldwide) Irradiation time: 60 days (1.3 cycles) [March –June 2012] Step 1: Purchase of the stable isotopes and production of [J. Neuhausen] Step 2: Irradiation at the ILL High Flux reactor [U. Koester] 147 Pm: 146 Nd(n,  ) 147 Nd (  -, 10d) 147 Pm (enrichment 0.35%) 0.29 mg of 147 Pm (2.6 y) [1.2e18 atoms] Step 3: Chemical separation and target [S. Heinitz and D. Schumann]

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Innovation and exploitation of C 6 D 6 for (n,  ) IMPROVING THE HARDWARE: R. Plag et al. (The n_TOF Collaboration), “An optimized C 6 D 6 detector for studies of resonance-dominated (n,γ) cross-sections”, Nucl. Instrum. Meth. A 496 (2003) IMPROVING THE SOFTWARE: U. Abbondanno et al. (The n_TOF Collaboration), “New experimental validation of the pulse height weighting technique for capture cross-section measurements”, Nucl. Instrum. Meth. A 521 (2004) 454– EXPLOITING THE TECHNIQUE: U. Abbondanno et al. (The n_TOF Collaboration), “Neutron capture cross section measurement of 151 Sm at the CERN neutron Time of Flight facility”, Phys. Rev. Lett. 93, (2004) and 24 PRC and PRL papers using C 6 D 6 at n_TOF between 2004 and ONE FINAL STEP HARDWARE-WISE: P. Mastinu et al. (The n_TOF Collaboration), “New C 6 D 6 detectors: reduced neutron sensitivity and improved safety”, n TOF-PUB (2013) State-of-the-art C 6 D 6 + n_TOF-EAR2: (n,  ) on sub-milligram radioactive samples! C 6 D 151 Sm (206 mg) → 63 Ni (111 mg) → 241 Am (32 mg) → 240 Pu (3 mg)

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Detectors and 147 Pm 9 neutrons 147 Pm sample

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) URR 25 bins/decade RRR 1000 bins/decade  stat =7% The measurement and beam time request - Beam line: n_TOF EAR-2 [x27 more flux than (n,  ) in EAR1] - Detectors: 4xL 6 D 6 and the PHWT - Normalization: “Saturated Resonance Method” with 197 Au - Background: not available at this moment, to be seen during commissioning Based on TENDL-2012 Effect of the (reduced) E n

Carlos GUERRERO et al., “Tackling the s-process stellar neutron density via the 147 Pm(n,  ) reaction” 47 th CERN INTC Meeting (June 25 th 2014) Summary of beam request SampleObjectiveProtons 147 PmCapture Cross section of 147 Pm1x10 18 EmptyOverall beam-on background0.2x10 18 DummySample backing related background0.6x AuNormalization0.2x Pm (beam-off)Sample activity background- Total 2x : EAR2 (new) + enough material from ILL (new/unique)→ now it’s possible! Appropriate sample mass: if more → EAR-1 or elsewhere if less → too demanding to be proposed without very well characterized EAR-2 Following the EAR-2 commissioning, best candidate for a measurement (challenging, radioactive, sub-milligram (0.3 mg), never measured, inter-laboratory (ILL, PSI, CERN) collaboration)