Simulation of Protons in CEPA1:a Pyramide-like Phoswich ArrayE. Nacher

Parameters of the simulation

Geometry:Array of 3× 3 pyramid-like phoswich detectors. Each of them with a square at the entrance face(side: 49.9 cm) and a square at the exit side (side: 80 cm). The diagonal side of each pyramid is10.2 cm long (the simmetry axis is 10 cm long). Each individual detector is comprised of a LaBr3crystal 4 cm long opticaly coupled to a LaCl3 crystal 6 cm long.

Primary Generator:Protons of energies ranging from 20 to 360 MeV have been generated at a distance of 20 cm fromthe entrance face. They are direceted towards the detector along the z-axis but with an apertureof 0.754o so that they cover a circle of � = 1 cm)

(a) (b)

Figure 1: Detail of the geometry simulated and the tracks of the protons (180 MeV ) in the centralcrystal.

1CALIFA Endcap Prototype Array

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Physics:Livermore low energy electromagnetic processes for gamma-rays and electrons. Standar Physicsfor positrons and protons.

Results

Energy deposited per unit length as a function of the depth in the detector: The Bragg Curve.

Depth (mm)0 10 20 30 40 50 60 70 80 90 100

DE

/DX

(M

eV/m

m)

0

1

2

3

4

5

6

7

(a)

Depth (mm)0 10 20 30 40 50 60 70 80 90 100

DE

/DX

(M

eV/m

m)

1

2

3

4

5

6

(b)

Figure 2: (a) Proton Energy: 180 MeV. (b) Proton Energy: 200 MeV

Depth (mm)0 10 20 30 40 50 60 70 80 90 100

DE

/DX

(M

eV/m

m)

1.2

1.3

1.4

1.5

1.6

1.7

(a)

Depth (mm)0 10 20 30 40 50 60 70 80 90 100

DE

/DX

(M

eV/m

m)

1.05

1.1

1.15

1.2

1.25

(b)

Figure 3: (a) Proton Energy: 240 MeV . (b) Proton Energy: 280 MeV .

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Fig. 4 shows the nergy deposited in the 4 cm of LaBr3 by individual protons of one specificenergy from 100 to 320 MeV in steps of 20 MeV . Up to 120 MeV the proton is totally stopped inthe LaBr3 and all the counts are in the photopeak at 100 MeV and 120 MeV . For 140 MeV andbeyond the LaBr3 crystal acts as a ∆E detector, the proton scapes and all the counts are now inthe broad peaks below 100 MeV . Protons of 140 MeV leave about 90 MeV in the LaBr3 crystal,protons of 160 MeV leave about 75 MeV and so on.

Energy (keV)40 50 60 70 80 90 100 110 120 130

310×

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Figure 4: Proton energies from 180 MeV to 320 MeV in steps of 20 MeV .

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Fig. 5 represents the same as Fig. 4 but with all counts coming from all different energies addedup. It looks like it is not possible to distinguish protons of 220 MeV from the ones with higherenergy.

Energy (keV)40 50 60 70 80 90 100 110 120 130

310×

0

200

400

600

800

1000

Figure 5: Proton energies from 180 MeV to 320 MeV in steps of 20 MeV .

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A different approach to separate different proton energies is to represent the energy deposited inthe first crystal (4 cm of LaBr3) as a function of the total energy deposited in the whole detector.This is shown in Fig. 6.

E (MeV)0 50 100 150 200 250 300

Del

ta E

(M

eV)

0

20

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140

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DE(1st block) vs E(total)

100 MeV

120 MeV

140 MeV

160 MeV

180 MeV

200 MeV

220 MeV240 MeV

260 MeV280-320 MeV

Figure 6: ∆E - E scatter plot for protons with energies from 180 MeV to 320 MeV in steps of20 MeV .

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The same figure but in a 3-dimensional view:

E (MeV)0 50 100 150 200 250 300 Delta

E (MeV)

0 20406080100120140

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20000

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DE(1st block) vs E(total)

Figure 7: ∆E - E 3D plot for protons with energies from 180 MeV to 320 MeV in steps of 20 MeV .

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