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ANASEN - Array for Nuclear Astrophysics Studies with Exotic Nuclei

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Title: ANASEN - Array for Nuclear Astrophysics Studies with Exotic Nuclei


1
ANASEN - Array for Nuclear Astrophysics Studies
with Exotic Nuclei
Jeff Blackmon (LSU), Grigory Rogachev (FSU), Ingo
Wiedenhoever (FSU) and Ed Zganjar (LSU)
Flexible, large-area charged-particle detector
array targeting (?,p) reactions, proton
scattering, and transfer reactions using the ReA3
facility at the NSCL and RESOLUT at FSU Active
Target
To improve understanding of light rare isotopes
and (p,?) and (?,p) rates that are important in
the ?p/rp processes
Silicon-strip detector array backed with
2-cm-thick CsI Gas proportional counter for
proton-tracking capability Supported by NSF MRI
Program Here 1) Nuclear Structure studies of
light nuclei 2) Nuclear Astrophysics measurements
2
ANASEN
Annular silicon-strip array
RIB
3 Rings of 12 Super-X3 silicon-strip detectors
backed w/ 2cm thick CsI
Anode wires of cylindrical gas proportional
counter
3
Silicon Strip Detectors
X3 detectors constructed for ORRUBA by Micron
Semiconductor 4 resistive strips (10mm X 75mm)
S.D. Pain et al., NIMB261 (2007) 1122.
1 mm thick detectors
?x lt 1 mm ?E lt 100 keV
Super-X3 version 40x19 mm Ohmic
segmentation First 12 detectors ordered
Forward angle detectors currently under
design 18cm outer diameter in 4 quadrants (6
Si) Minimal (1mm) PC board on outer radius Pin
out and mounting along radial direction 8cm ID
design for use with PC
Micron QQQ2 design
Ep
4
Proton-Resonant Scattering with ANASEN
  • Thick, active target allows simultaneous
    measurement of multiple resonances
  • Proton-depth tracking allows distinction between
    elastic and inelastic excitations

Beam View
p
Beam slows downin target gas, scans over
Resonanceenergies
Same depth,different Ep ?
5
Study of light exotic nuclei through resonance
reactions with RNBs RNB8, 2009
Structure of 8B
http//cosmo.volya.net D. Morris A. Volya
P. Navratil et al., PRC 73, 065801 (2006)
6
Study of light exotic nuclei through resonance
reactions with RNBs RNB8, 2009
Structure of 8B
7Bep
3
2-
Dominant configuration for the missing states
is 7Be(1/2-)p. Should be observed in inelastic
scattering. D. Halderson, PRC 69, 014609 (2004)
G.V. Rogachev et al., Phys. Rev. C64 (2001)
061601(R)
7
RESOLUT a new radioactive beam facility at John
D. Fox Superconducting Accelerator Lab. at
Florida State University
  • In-flight production of radioactive beams in
    inverse kinematics
  • Combination of Superconducting RF-Resonator with
    high acceptance magnetic Spectrograph to create
    mass spectrometer

8
Study of light exotic nuclei through resonance
reactions with RNBs RNB8, 2009
Hybrid (thick/thin) target technique
E1
E3
CH
RESOLUT beam composition 75 of 7Be, 25 of 7Li
p
2
7Be
7Li(p,n)7Be I7Be2x105 pps
7Be
  • Target is thick enough for 7Be to lose
    significant fraction of its energy.
  • But thin enough for 7Be recoils to make it out of
    the target.

9
Study of light exotic nuclei through resonance
reactions with RNBs RNB8, 2009
140o
Excitation function of inelastic p7Be scattering
compared to R-matrix calculations with no new
states in 8B.
Elastic
U. Greife, et al., NIM B 261 (2007) 1089
Inelastic
Inelastic
10
Study of light exotic nuclei through resonance
reactions with RNBs RNB8, 2009
7Be(p,p) 148o
7Be(p,p)7Be 146o
Red curve is an R-matrix fit with the following
resonances 1 - 0.77 MeV known 1 0 - 1.8
MeV new 3 - 2.32 MeV known 1 2 - 2.4 MeV
new 2- - 3.5 MeV known 2,3 1 - 3.5 MeV
new
7Be(p,p)7Be 138o
7Be(p,p) 140o
7Be(p,p) 132o
7Be(p,p)7Be 130o
11
(?,p) with ANASEN as active target
  • Example 36 MeV 18Ne
  • 22 MeV 18Ne after window (4 MeVcm)
  • ?Elab0.68 MeV/cm in 200 Torr
  • ?Ecm120 keV/cm
  • Chamber filled with 200-400 Torr He gas
  • Beam enters through 2?m Ti foil

Top View
Beam View
p
p
HV
  • Protons produced with energies from few? 20 MeV
    in extreme cases
  • 4He(18Ne,p) Ep3-11 MeV
  • For 10 MeV protons, ?E 5 keV in PC region ? 105
    e
  • Resistive wire ? good determination of position
    in PC

12
(?,p) - count rates, resolution, issues
  • Entire excitation function measured with 1
    bombarding energy
  • Should be able to measure (a,p) cross section
    over a significant fraction of the Gamow window -
    though more difficult for heavier Z
  • Ecm can be reconstructed with good (lt100 keVcm)
    resolution, but
  • More difficult for forward/backward angles
  • Dependent on emittance of beam
  • Thickness required of PC for accurate position
    reconstuction?
  • Leakage of charge from high ionization region of
    beam into PC

13
Proton scattering and (p,?) with ANASEN
?p-process
Red Most interesting cases
  • Our understanding of (p,?) and (?,p) reactions
    can be improved by studying nuclear structure via
  • proton elastic scattering
  • proton inelastic scattering
  • (p,?) reactions

14
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15
Neutron-Detector Development 6Li-Glass Sandwich
  • (d,n) in inverse kinematics Detect low-energy,
    30-100 keV neutrons in backward directions
    ?-p branching ratios and angular distributions
  • Plan use 6Li-glass scintillator-stack (5 cm
    depth10 efficient.)
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