1. CERN-INTC-2014-047/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)

2. 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

3. 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

4. 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 (@nTOF) 4 Lederer et al., PRL 110 (2013) 022501 Abbondanno et al., PRL 93 (2004) 161103

5. 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=147-148 5 Figure 1. The s-process flow in the mass region A=144-150. 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 Sm0.931.00.900.89 0.88 0.890.90 147 Pm1.0 0.990.980.960.950.930.900.88 Stellar Enhancement Factors (SEF) according to Kadonis * Studies at thermal ongoing @ILL

6. 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 MACS @ 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

7. 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 pellets @PSI [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 preparation @PSI [S. Heinitz and D. Schumann]

8. 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,  ) 8 2003. 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) 425-436 2004. 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) 454–467 2004-2012. 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, 161103 (2004) and 24 PRC and PRL papers using C 6 D 6 at n_TOF between 2004 and 2014 2013. 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-2013-002 (2013) State-of-the-art C 6 D 6 + n_TOF-EAR2: (n,  ) on sub-milligram radioactive samples! C 6 D 6 @n_TOF-EAR1: 151 Sm (206 mg) → 63 Ni (111 mg) → 241 Am (32 mg) → 240 Pu (3 mg)

9. 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 sample @n_TOF-EAR2 9 neutrons 147 Pm sample

10. 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 resolution @EAR-2

11. 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 background0.6x10 18 197 AuNormalization0.2x10 18 147 Pm (beam-off)Sample activity background- Total 2x10 18 2014: 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)