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

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St. George

Exis

iting

bea

m li

ne

Charge Selection

Mass Selection

Detection - ID

Jet gas target

KN accelerator

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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.

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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

Frontier 2007 March 19, 2007Manoël Couder 14

Source of background