HiRA: Science and Design Considerations

• Scientific Program:– Astrophysics:

• Transfer reactions• Resonance spectroscopy

– Nuclear Structure:• Inelastic scattering• Transfer reactions• Resonance spectroscopy• Breakup reactions

– Complex Reactions:• Fragmentation• Correlations

• Design Considerations:– Resolution issues

• Angular resolution• Energy resolution• Mass and charge

resolution• Timing resolution

– Angular coverage– Dynamic range– Flexibility– Matching to other devices– Cost

beamTarget

HiRAHigh Resolution Array

1.5 mm

4 cm• 20 Telescopes • 62.3 x 62.3 mm2 Active Area• δθ < δθ < δθ < δθ < ±±±±0.160.160.160.16οοοο deg (35 cm)• δΕ < 50 δΕ < 50 δΕ < 50 δΕ < 50 keV

Design supports many configurations

1024 pixels per telescope

LASSA: HiRA prototype

• LASSA- HiRA comparisons:

characteristic LASSA HiRA # telescopes 9 20 area/telescope 25 cm2 38 cm2 design distance 20 cm 35-100 cm pitch 3 mm (16) 1.9 mm (32) total # strips 432 1920 electronics CAMAC ASIC ∆E thickness 75 µm 75 µm E thickness 0.5 mm 1.5 mm CsI(Tl) thickness 6 cm 4 cm

HiRA project

• IU: Silicon development:– de Souza, Caraley, Davin, Viola

• WU/SIU: Electronics development:– Sobotka, Elson, Engel

• MSU/Milano/IU: Mechanical design – van Goethem, Morris, Moroni, Wallace

• MSU: CsI(Tl) – van Goethem, Wallace, Nett

• DAQ: MSU/IU– Fox, Elson

• Budget: 0.54MD– 0.2MD silicon

First studies: masses relevant to the rp-process

The rapid proton capture process is a process believed to occur on the surface of an accreting neutron star in a binary system

With X-ray telescopes we observe x-ray bursts that are believed to be produced by the rp-process.

X-ray burst

Separation energy defines path

Sp=(M(Z,N)-M(Z-1,N)-Mp)c2

Sα=(M(Z,N)-M(Z-2,N-2)-Mα)c2

The rp-process

Single nucleon transfer reactions (p,d),(d,3He)

• Kinematics are forward peaked– Measurements are only

possible for θ

Producing a beam

Stable Beams are produced in the Ion Source and accelerated in the K500&K1200 Superconducting Cyclotrons

The Primary beam is then incident on a production target producing secondary beams. These beams are then separated using the A1900 Fragment Separator

Secondary beams from Kr primary beamIf we require a beam intensity of 1 x 104 then we could make mass measurements of all the nuclei in yellow here without changing the setting of the fragment separator.

This can work to our advantage as we will be able to use some with known masses as calibrations.

Possible geometryPossible geometry• HiRA covers the solid angle

with about 70% efficiency.• S800 spectrometer is used to

detect binary reaction partner. – e.g. for p(66As,d)65As, 65As

would be detected with 100% efficiency in S800 focal plane.

– suppresses background from breakup reactions on 12C in CH2 target.

– Experiment can be finished in several days - week using 104ions/s.

– Device must be able to fit into the S800 chamber.

S800 Spectrograph with Strip array having ∆Θ∆Θ∆Θ∆Θ

Experimental Challenges for (p,d) mass meas.

• Need good energy resolution: – δδδδEcm≈≈≈≈2 δ δ δ δElab– Stop particles in silicons, CsI(Tl) serves mainly to veto fast

particles.

• Need good angular resolution if you want to take advantage of the full solid HiRA solid angle.– kinematic broadening increases with angle, move backward

angle telescopes away from the target.– ~1.9 mm pitch is compromise between wanting good resolution

and also low interstrip hit probabilities.

• Major challenges are good calibrations of the silicon energy and the beam energy.

• Particle identification via ∆∆∆∆E-E is easy for (p,d). (For elastic, inelastic, you may need TOF.)

Silicon energy calibration

• Calibration with a 228Th ααααsource (8.7 MeV) and a precision pulser.

• Source can be mounted between the 75 µµµµm and 1.5 mm silicon detectors.

• Scheme has been tested with LASSA silicon detectors.

• It merely requires that that the columns of detectors of the array can be moved apart, one side of each silicon mount be removed and the source inserted.

228Th source

Silicon detectors CsI(Tl) crystals

Secondary beam characteristics

The Beam spot on the production target also has a finite width.

The Beam energy is defined by the momentum acceptance of your fragment separator. Typically on the order of 1-3% ∆p/p

Beam position, energy & angle determination

Two 2-dimensionalPPAC’s in the dispersive intermediate image of the the S800 beam line determine the ion’s angle and energy.

Two removeable PPAC’s at the target can check the trajectory reconstruction using the upstreamPPAC’s

One 2 dim. PPAC at the object determines the beam ion’s position at the target image

Final uncertainties

Uncertainties needed to be considered

•Beam Energy

•Incident angle of beam on target

•Target thickness

•Distance to HiRA (angular resolution)

•Detector resolution

Resonance spectroscopy Resonance spectroscopy -- RadiativeRadiativeCapture viaCapture via CoulexCoulex

• Resonances relevant to hot stellar environments.− 20Na, 23Al, 24Si, etc.

• Branching ratios, Spins• E.g. 20Na resonances

– Energies to 10 keV accuracy.

High Resolution Strip detector Array

77LiLi

pp( )2212

1 vv vv −µ≈relE

Yield ∝ (2J+1)

Correlation Technique• Experimental correlation function:

• Correlation function in thermodynamic limit (Boal, Jennings)

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• Excellent angular resolution.− governs δE*, 40 keV FWHM

has been achieved.

• Moderate energy resolution• Excellent isotopic resolution• Good multi-hit capability.

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Resolution

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Erel (MeV)• Uses same geometry• Isolated resonances which

decay to the g.s. are easiest cases. − 14O { e.g. 13N(p,γ) }− 23Al {e.g. 22Mg (p,γ) }

• Direct capture, e.g. 7Be(p,γ) is harder.

Resolution Resolution requirementsrequirements

Need:

Complex Reactions

• Correlation functions:– Imaging of nuclear collisions

• Resolution requirements identical to that for resonance spectroscopy

• Need multi-hit capability• Fragmentation and L.G.P.T.

– Investigations of caloric curve– Isospin dependence of

fragmentation, L.G.P.T., EOS– Science of rare isotope

production• Need excellent broad-

range PID

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Excellent PID possibleWith non-planar 75 µm ∆E

Scaling behavior

• Appears to be respected by all statistical production mechanisms.

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β+α= ZNZNCYZNY