The Experimental Astrophysics group at the Goethe University

The Experimental Astrophysics group at the Goethe University Frankfurt http: //exp-astro. physik. uni-frankfurt. de/ Currently: • 5 scientists • 12 Ph. D students • 8 students Experimental Astrophysics at the Goethe University Frankfurt

Activities • With strong ties to n-TOF – measurments of (n, g) cross sections (motivated by astrophysics but also applied) – Complementary measurements at FRANZ (cleaner background and higher fluxes in ke. V regime) and n-TOF (wide spectrum, superior neutron energy resolution) – (n, a), (n, p) cross sections in similar fashion – Development of high-performance DAQ (FPGA+FADC) – Development of neutron- / gamma detectors, tests (LENA, Neu. LAND) • General Portfolio: – Determination of reaction cross sections with astrophysical relevance (n-, p-, a-, g-induced) – Specialized in measurments on / with radioactive isotopes – p-induced: Experimental Astrophysics at the Goethe University Frankfurt

Neutron-induced reactions • FRANZ – TOF (10 cm, 1 m flightpath) – Activation – (n, g), (n, a), (n, f) • n-TOF – TOF (10 m, 180 m flightpath) • DANCE / Los Alamos – TOF (20 m flightpath) Experimental Astrophysics at the Goethe University Frankfurt

Detector for Advanced Neutron Capture Experiments neutrons: • spallation source • thermal. . 500 ke. V • 20 m flight path • 3 105 n/s/cm 2/decade collimated neutrons beam g-Detector: sample t 1/2 > 100 d m ~ 1 mg 34 cm • 160 Ba. F 2 crystals • 4 different shapes • Ri=17 cm, Ra=32 cm • 7 cm 6 Li. H inside • eg 90 % • ecasc 98 % Experimental Astrophysics at the Goethe University » Nuclear. Frankfurt Astrophysics with Neutron Facilities and LANL and RIA «

The Frankfurt neutron source at the Stern-Gerlach. Zentrum (FRANZ) 20 m. A DC neutron flux: 1012 s-1 2 m. A proton beam (8 A peak current) 250 k. Hz < 1 ns pulse width neutron flux at 1 m: 107 s-1 cm-2 neutron flux at 0. 1 m: 109 s-1 cm-2 Experimental Astrophysics at the Goethe University Frankfurt

Neutron spectrum Quasi-Maxwellian averaged distribution: k. T = Emax = Experimental Astrophysics at the Goethe University Frankfurt 25 ke. V 110 ke. V

Effect of proton energy uncertainty • Ep = 1912 ke. V • different proton energy distributions • 30 µm lithium • 10 mm diameter gold foils • weighting of sample thickness for different neutron angles considered Experimental Astrophysics at the Goethe University Frankfurt

Ep=2200 ke. V, 5 µmx 3 mm Li, 3 mm sample Experimental Astrophysics at the Goethe University Frankfurt

Ep=2100 ke. V, 5 µmx 3 mm Li, 3 mm sample Experimental Astrophysics at the Goethe University Frankfurt

Ep=1980 ke. V, 1 µmx 3 mm Li, 3 mm sample Experimental Astrophysics at the Goethe University Frankfurt

The 4 p Ba. F 2 array for TOF measurements Hardware: • g-calorimeter – 15 cm thick – eg, total ~ 90 % – ecasc, total ~ 98 % – ecasc, peak ~ 50 % • • 96 channels 1 GS/s FADC + FPGA 30 TB RAID array Allows: • Particle identification • deadtime-less DAQ • pile-up correction • fast data reduction Experimental Astrophysics at the Goethe University Frankfurt

Schematic TOF spectrum 200 128 En (ke. V) • 80 cm flight path • 10 cm inner detector radius • Emax = 200 ke. V • Emin = 1 ke. V prompt flash other reactions (n, g) on sample 0 130 160 Experimental Astrophysics at the Goethe University Frankfurt TOF (ns)

The Frankfurt neutron source at the Stern-Gerlach. Zentrum (FRANZ) neutron flux: 1012 s-1 2 m. A proton beam (8 A peak current) 250 k. Hz < 1 ns pulse width neutron flux at 1 m: 107 s-1 cm-2 neutron flux at 0. 1 m: 109 s-1 cm-2 sample TOF with 10 cm flightpath using fast charged particle detectors: Si-diode, C-diamond, ionization chamber Experimental Astrophysics at the Goethe University Frankfurt

Proton-induced reactions • (p, g), (p, n) – FRANZ (high currents, limited energy range) – Experimental storage ring (ESR) at GSI and maybe rex-isolde (goal: radioactive nuclei) • (p, n) – LAND/R 3 B setup, determination of Gamow. Teller strength, hence half-lifes under stellar conditions • (a, g) – Van de Graaff: Notre Dame – ESR (still to be shown) Experimental Astrophysics at the Goethe University Frankfurt

The Frankfurt neutron source at the Stern-Gerlach. Zentrum (FRANZ) 2 m. A proton beam (8 A peak current) 250 k. Hz Experimental Astrophysics at the Goethe University Frankfurt 20 m. A DC

Reaction Studies at the ESR Measurements of (p, g) or (α, g) rates in the Gamow window of the p-process in inverse kinematics. Particle detectors Advantages: • Applicable to radioactive nuclei • Detection of ions via in-ring particle detectors (low background, high efficiency) • Knowledge of line intensities of product nucleus not necessary • Applicable to gases Challenges: • UHV conditions • Low-energy beam • Detectors must be bakeable • Interaction with rest gas Experimental Astrophysics at the Goethe University Frankfurt Gas jet ESR

gamma-induced reactions • g-induced – Coulomb excitation (GSI) – direct (HIGS, ELBE) Experimental Astrophysics at the Goethe University Frankfurt

Radioactive beam experiments for the s-process Idea: Determine AX(n, g) from nat. Pb(A+1 X, AX+n) Coulomb Dissociation of A+1 X gives A+1 X(g, n) Detailed balance gives AX(n, g) Experimental Astrophysics at the Goethe University Frankfurt

Detector developments for FAIR/GSI • Neutron detection between 0. 01 and 1 Me. V – LENA • Neutron detection between 0. 1 and 1 Ge. V – Neu. LAND Experimental Astrophysics at the Goethe University Frankfurt

Neutron detection – 10 ke. V – 1 Me. V LENA ( low energy neutron detector array): Detection of low energy neutrons with high angular resolution. Plastic scintillator bars 100 x 4. 5 x 1 cm Tests needed! time resolution energy threshold FWHM=0. 8 ns Experimental Astrophysics at the Goethe University Frankfurt

Neutron detection – 100 Me. V – 1 Ge. V Neu. LAND (New Large Acceptance Neutron Detector): Detection of relativistic neutrons with high efficiency -60 layers of scintillator -each -5 cm deep , 2. 5 x 2. 5 m 2 cross section -Cosists of scintillator 40 bars (5 x 5 x 250 cm 3) Experimental Astrophysics at the Goethe University Frankfurt