Motivation

In order to checking our simulation results for the coarse grid run on the SwiMM, we evaluated the number of 122 keV photons into the BAT detector by a solid angle calculation method.

Results

We show the results as follows. The predicted counts go great with the detected counts on the simulation.

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 Predicted Counts: 221159
 Detected  Counts: 222651 +/- 472
 ------------------------------------
 Predicted/Detected = 99.3 +/- 0.2 %
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How to estimate the Predicted Counts

(1) Calculate a solid angle for the detector.

We used the following formula for the solid angle.

Fig. 1: solid angle fomula for like an oblong detector

We show the character definitions of this formula, and calculate each solid angle like a right figure.
Then we sum up the all solid angle.

Fig. 2: Character definitions of the solid angle formula

Fig. 3: Sum up each solid angle

(2) Incoming photons "N" at 122 keV

N_soildangle =  Generated photons(SwiMM)/(4*PI) * SumSolidAngle
             =  1.516816e8 /(4*PI) * 0.09795
             =  1.182301e6

N = 0.5*N_soildangle + 0.5*N_soildangle*Transmission effect(Pb:0.0221)
       [Open Mask]          [Close Mask]

Hence,  N = 6.04240e5

(3) Detection efficiency for CZT

PredictedPhoton = N * (32768*0.16cm^2)/(120.12cm*72.66cm) *  Detection effect(CZT:0.6093)
                = 221159