A Recoil Separator for ALNA-Phase2

1. Manoël Couder University of Notre Dame Joint Institute for Nuclear Astrophysics A Recoil Separator for ALNA-Phase2 Henderson DUSEL Capstone Workshop

2. Charged particles cross section measurements at low energy • Effort to extract the signal at low energy are needed because cross section drops exponentially • Increase the number of interactions • Beam intensity increased • Gas target are more and more elaborated • Improved detection techniques • Gamma detector: 4p, segmented • Active shielding Henderson DUSEL Capstone Workshop

3. Large Gamma Arrays based on Compton Suppressed Spectrometers Tracking Arrays based on Position Sensitive Ge Detectors EUROBALL GAMMASPHERE AGATA GRETA e~ 10 — 5 % ( Mg=1 —Mg=30) e~ 40 — 20 % ( Mg=1 —Mg=30) Slide from: J. Simpson, “The AGATA project”, NPDC19, 2005

4. Charge particles Cross section measurements at low energy – Status • Effort to extract the signal at low energy (fight against background) are needed because cross section drops exponentially: • Increase the number of interactions • Beam intensity increased • Gas target are more and more elaborated • Try to extract more by improving detection techniques • Gamma detector: 4p, segmented • Active shielding • Underground laboratory Henderson DUSEL Capstone Workshop

5. Inverse kinematics: “Heavy ion” beam on light target HI beam Find additional tags to improve detection for (p,g) and (a,g) Direct kinematics: Light ion beam on heavy target g rays p, 4He beam No additional tag possible only fight to increase signal to noise ratio. Target g rays HI beam 1017 @100mA for 1 recoil/10 min Require rejection of the beam-> RMS Existing device: DRAGON @ Triumf ERNA @ Bochum … Reaction products p, 4He target Henderson DUSEL Capstone Workshop

6. DRAGON ISAC Recoil energy spectra in singles and coincidence mode for 21Ne(p,g)22Na at Ecm = 258.6 keV Gamma energy spectrum in singles and coincidence mode DRAGON @ Triumf Radioactive beam induce reaction -> Inversekinematics is the only solution. Example with stable beam induce reaction 21Ne(p,g)22Na Residual beam Spectrum and picture from S. Engels Thesis, http://dragon.triumf.ca/docs/sabine_thesis.pdf Henderson DUSEL Capstone Workshop

7. 12C(a,g)16O @ ERNA - Bochum BaF2g detector • Signal • Cosmic and room background • Beam induced background @ Ecm = 3.2 MeV Spectrum from D. Schürmann, Santa Tecla 2005 Spectrum from F. Strieder, Tuckson 2003 Henderson DUSEL Capstone Workshop

8. The dramatic cosmic background reduction leaves the environmental and beam induce background. The number of bad g – HI coincidence decrease !! Why a RMS underground ? The Notre Dame Recoil Mass separator • Design of a RMS for (a,g) reaction studies at low energy for beam with 16<A<40. Large acceptance q<40 mrad DE/E<7.4% • Required for reaction of interest: 22Ne(a,g)26Mg, 18O(a,g)22Ne • Mass separation achieved with a Wien filter • New design of the electrodes • First beam expected late 2007 • Good prototype for underground laboratory • High intensity AC accelerator is required for beam up to A=40 • Source and accelerator development @ LBNL Henderson DUSEL Capstone Workshop

9. Wien Filter – Mass separation Detection system Beam q+2 q+1 Charge selection Recoil Beam Jet gas target + post-stripper g detectors 8cm Recoil+Beam q selected The Notre Dame RMS Henderson DUSEL Capstone Workshop

10. Summary: • RMS must accept ALL the recoils • Large angular and energy acceptance • Low event rate ~1/few hours • Rejection important >1020 beam ions • Low energy No ID of the heavy ion, no additional discrimination • g ray – HI coincidence is crucial to make a TRUE EVENT ID G.P.A. Berg1, M. Couder1, J. Görres1, J. Hinnefeld2, L.O. Lamm1, P.J. Leblanc1, E. Stech1, M. Wiescher1 1 University of Notre Dame. 2 Indiana University, South Bend. Henderson DUSEL Capstone Workshop