a recoil separator at notre dame for radiative capture … recoil separator at notre dame for...
TRANSCRIPT
A Recoil Separator at Notre Damefor radiative capture studies
Manoël CouderUniversity of Notre Dame
Joint Institute for Nuclear Astrophysics
Frontier 2007 August 21Manoël Couder 2
Direct radiative capture measurements
• Suffer from:– Very low cross section →Need high efficiency– Beam induced and room background→ Need clear signature
• Direct kinematics– Signature is the γ’s– Efficiency depend on the detectors (small
compared to charge particles detectors)→Inverse kinematics
Frontier 2007 March 19, 2007Manoël Couder 3
Recoil separators: basic principles
projectiles projectiles
target
+recoils
focussing
separationDetection
Identificationrecoils
projectiles
ray detection
⎟⎟⎠
⎞⎜⎜⎝
⎛=
bbEmcE
2arctanmax
γθ
γpppr ±= *
Drawings from D. SchürmannDrawings from D. Schürmann
Velocity/energy selection
Rejection required for 100 μA > 1012
assuming 1k in the detector.
Coincidence/time of flight
Frontier 2007 March 19, 2007Manoël Couder 4
The Notre Dame recoil separator:Design parameters
17 mrad3.5 %2.7 MeV36Ar(α,γ)40Ca
32 mrad6.5 %3. MeV22Ne(α,γ)26Mg
40 mrad7.4%2. MeV18O(α,γ)22Ne
Δθ (mrad)ΔE/E (%)Ebeam(MeV)Reaction
Stable beam from the KN (4MV) Van de Graaff acceleratorBeam intensity up to 100 μA
Beam mass up to ~40Acceptance
Minimum counting rate 1 per hour
Frontier 2007 March 19, 2007Manoël Couder 5
St. George
Exis
iting
bea
m li
ne
Charge Selection
Mass Selection
Detection - ID
Jet gas target
KN accelerator
Frontier 2007 March 19, 2007Manoël Couder 6
Charge selection
• Multiple charge state after gas target– Mass selection device are
charge state dependant– Selection of the most
abundant one (~40%)– Clean rejection of the other
beam charge state– ΔQ/Q0 can be large →
Selection in two step
36S(α,γ)40Ar @8MeV
Frontier 2007 March 19, 2007Manoël Couder 7
-5.0000E-01
0.0000E+00
5.0000E-01
1.0000E+00
1.5000E+00
-600 -500 -400 -300 -200 -100 0 100 200 300 400
Z (mm)
Magnetic fieldElectric fieldE/B ratioFigure of merit
+30%
Mass separation:Wien filter fringe fields - longitudinal
Typical Wien filter fringe field
-5.0000E-01
0.0000E+00
5.0000E-01
1.0000E+00
1.5000E+00
-600 -500 -400 -300 -200 -100 0 100 200 300 400
Z (mm)
Magnetic fieldElectric field
Frontier 2007 March 19, 2007Manoël Couder 8
Mass separation:Wien filter fringe fields - longitudinal
-5.0000E-01
0.0000E+00
5.0000E-01
1.0000E+00
1.5000E+00
-600 -500 -400 -300 -200 -100 0 100 200 300 400
Magnetic fieldElectric fieldE/B ratioFigure of merit
Modified Wien filter fringe field
Frontier 2007 March 19, 2007Manoël Couder 9
Wien filter
3D calculation to validate 2D result and decide on the end shapeSimion + Geant4
Frontier 2007 March 19, 2007Manoël Couder 10
St. George
Bruker drawing
Detection system:MCP (tof) + Si detector
24Mg(α,γ)28Si5+ @ 8MeV
Frontier 2007 March 19, 2007Manoël Couder 11
Aberrations correction
Calculation up to 4th orderCorrections up to 3rd orderembedded in the magneticdipoles pole faces.
Frontier 2007 March 19, 2007Manoël Couder 12
Status and perspective
• Elements ordered with Bruker Biospin– First shipment expected for end of 2007
• Scattering/background study– Slits position optimization
• Detector and gas target development• Charge state distribution through gas target
study• Commissioning should start in summer 2008
Frontier 2007 March 19, 2007Manoël Couder 13
Collaborators
Georg Berg, Joachim Görres, Ed Stech, Larry Lamm, P.J. Leblanc,Wanpeng Tan, Michael Wiescher
University of Notre Dame
Jerry Hinnefeld
Indiana University South Bend