Spokespersons: C. Guerrero (U. Sevilla) and C. Domingo- Pardo (IFIC)

1. CERN-INTC-2014-047/INTC-P-415Tackling the s-process stellar neutron density via the 147Pm(n,g) 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 (25th June 2014)

2. Mixing (abundancedistribution) interstellar gas & dust condensation ejection, explosion • Nuclear reactions: • energy generation • nucleosynthesis Nucleosynthesis through the s-process Fusion reactions Neutron capture reactions 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)

3. 80Br, t1/2=17 min, 92 % (b-),8 % (b+) proton number 85Kr, t1/2=11 y 79Se, t1/2=65 ky neutron number Nucleosynthesis through the s-process Zr s-only Y Sr (n,g) Rb Kr Br (b-) Se As (b+) Ge Ga • Understanding abundances “around” branching points: • Half lifes • (n,g) cross sections • Neutron density and temperature Zn Cu Ni Co 63Ni, t1/2=100 y Fe

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

5. Branching point at A=147-148 Studies at thermal ongoing @ILL * 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 (147Pm) is marked in red. The s-only isotopes 148Sm and 150Sm are indicated by double squares. Stellar Enhancement Factors (SEF) according to Kadonis

6. Previous measured and calculated values Only one measurement to date: Reifarth et al. [APJ 582(2003) 1251–1262] at FZK in which they irradiated 28 ng of 147Pmwith a MACS @ 25 keV. Kadonis 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. EAR-2 + sufficient material → first ever ToF measurement in the En range of interest

7. Sample production in three steps Branching points are radioactive! Production via (n,g) or (n, g)b- in the ILL research reactor Neutron flux: 1.5x1015 n/cm2/s (highest Fn,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] 147Pm: 146Nd(n,g)147Nd (b-, 10d)147Pm (enrichment 0.35%) 0.29 mg of 147Pm (2.6 y) [1.2e18 atoms] Step 3: Chemical separation and target preparation @PSI [S. Heinitz and D. Schumann]

8. Innovation and exploitation of C6D6for (n,g) • 2003. IMPROVING THE HARDWARE: R. Plag et al. (The n_TOF Collaboration), “An optimized C6D6 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 151Sm at the CERN neutron Time of Flight facility”, Phys. Rev. Lett. 93, 161103 (2004) and 24 PRC and PRL papers using C6D6 at n_TOF between 2004 and 2014 • 2013. ONE FINAL STEP HARDWARE-WISE: P. Mastinu et al. (The n_TOF Collaboration), “New C6D6 detectors: reduced neutron sensitivity and improved safety”, n TOF-PUB-2013-002 (2013) • State-of-the-art C6D6 + n_TOF-EAR2: (n,g) on sub-milligram radioactive samples! C6D6@n_TOF-EAR1:151Sm (206 mg) →63Ni (111 mg)→241Am (32 mg)→240Pu (3 mg)

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

10. The measurement and beam time request RRR 1000 bins/decade URR 25 bins/decade - Beam line: n_TOF EAR-2 [x27 more flux than (n,g) in EAR1] - Detectors: 4xL6D6 and the PHWT - Normalization: “Saturated Resonance Method” with 197Au - Background:not available at this moment, to be seen during commissioning Effect of the (reduced) En resolution @EAR-2 Based on TENDL-2012 Dstat=7%

11. Summary of beam request • 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)