r 3 b gamma calorimeter h. alvarez pol – r 3 b gamma calorimeter nustar calorimeter wg –...

R3B Gamma Calorimeter

H. Alvarez Pol – R3B Gamma Calorimeter NUSTAR Calorimeter WG – Valencia 17/06/05

H. Alvarez Pol, D. Cortina, I. Durán GENP – Univ. Santiago de Compostela

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R3B Requirements for a Calorimeter

Technical Proposal reference Foreseen problems / Main challenges

Total absorption efficiency Very large crystals

Gamma energy resolution Strong request on scintillator properties and

Gamma multiplicity

Gamma sum energy See problems on energy resolution

Proton energy resolution Huge dynamic range in electronics

Affordable cost !

Constrains in space (inner detector and available space)

80% (up to E=15 MeV Lab system)

2-3% E/E

(N)/<N> < 10%

(Esum)/<Esum> < 10%

<1% Ep/Ep ( Ep = 300 MeV)


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Experimental constrains (Kinematics)

Gammas are emitted with energies up to

Elab

= 3.2 ECM

(for β = 0.82)

✗ To correct for the Lorentz boost it is

mandatory a high granularity.

✗ A huge crystal length is required for full

energy absorption

Due to the boost, gammas are basically emitted in the forward direction.

A large open zone in the backwards region reduces dramatically the crystal bulk needed.

ECM

= 10 MeV(β = 0.82)


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Polar angle resolution

From the relation between the lab and CM gamma

energies and assuming we know the gamma polar

angle (θ) in LAB with a resolution σ(θ), then

= σ(θ)β sin θ

1 - β cosθ

σ(ECMγ)

ECMγ

Requesting a constant relative resolution

= k1

then

σ(θ) = k1 β sin

θ

1 - β cosθ

σ(ECMγ)

ECMγ

Most critical region: θ ~ 0.6 rad ~35o


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Optimum detector profile

Requesting the same energy resolution for each crystal element, with a constant inner-

face length,

r(θ) = cte β sin

θ1 - β cosθ


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Simplified detector profile

Design parameters:✗Low number of channels✗Sufficient granularity (θ)✗Low radius to reduce the crystal volume✗Simplicity

A detector divided in 3 large assemblies:✔Barrel (50º < θ < 90º)✔Backward End Cap (90º < θ < 133º)✔Forward End Cap (7º < θ < 50º)

The proposed segmentation results in a CM

energy resolution of 1.5% (σ) / 3.5% FWHM

due only to polar angle uncertainties.Note: this resolution depends on pattern rec. algorithms

Barrel

Barrel

Backward End

CapForward End

Cap

Forward End Cap

Backward

End Cap


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A proposal for the calorimeter


Total of 6570 crystals in 73 different crystal

types covering the full azimuthal volume and

polar angles between 7º and 133º✔Trapezium-like shaped✔Inner and outer faces are parallel✔Typical volume 10x20xlength mm3

✔Individual crystal designs (3D and workshop

drawings) available

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FORWARD END CAP (7º < θ < 50º)✔Cone-like shaped ✔32 different crystal types✔90x32 = 2880 crystals ✔Inner-side crystal faces dimension:

from 8x20 mm2 to 25x20 mm2

BACKWARD END CAP (90º < θ < 133º)✔Cone-like shaped ✔15 different crystal types✔90x15 = 1350 crystals ✔Inner-side crystal faces dimension:

from 12x20 mm2 to 18x20 mm2

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BARREL (50º < θ < 90º)✔Cylinder-like shaped ✔26 different crystal types✔90x26 = 2340 crystals ✔Inner-side crystal faces dimension:

9x20 mm2 or 10x20 mm2

Some final numbers (for CsI):✗Total weight: ~ 1600 Kg✗Total volume: ~ 360 dm3

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Proposal setup simulation


Details on simulation on a separate talk

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Summary

➢A first proposal is available. Requests for criticism! ➢Documentation available

✔Technical note on the proposal: R3B_CAL_01/05✔Access to the geometry datafile and other technical notes:

http://www.usc.es/genp/r3b


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