Study of PoGO background
dependence on the collimator
material/slow scintillator threshold
April 21, 2004
Tsunefumi Mizuno
[email protected]
History of changes;
updated on April 15, 2004
modified on April 21, 2004
PoGO_collimator_2004-04-21.ppt
1
Simulated Geometry
•Thickness of fast scint. = 2.63cm
(D = 2.23cm)
•W (thickness of slow scint.) = 0.2cm
•L1 (slow scint. length) = 60cm
•L2 (fast scint. length) = 20cm
•Thickness of W collimator = 25um
•Thickness of Sn collimator = 100um
•Thickness of btm BGO = 2.68cm
•Length of btm BGO = 3cm
(not tapered in simulator for simplicity)
•Gap between BGOs = 0.5cm
(including BaSo4 eflector)
•Thickness of side Anti BGO = 3cm
•Length of side Anti BGO = 60cm
•# of units = 217 (geometrical area of fast
scint. not covered by slow scint. = 934.4 cm2)
PoGO_collimator_2004-04-21.ppt
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Simulation Condition
•The same Crab spectrum as that used in Hiro’s EGS4 simulation was
simulated here. That is,
•E-2.1 spectrum with 100mCrab intensity, 20-200keV (300.8 c/s/m2)
•100% polarized, 6h exposure
•Attenuation by air of 4g/cm2 (atmospheric depth in zenith
direction is ~3g/cm2 and that in line-of-sight direction is 4g/cm2)
•Atmospheric downward/upward gamma spectra for GLAST BFEM
simulation were used as background.
•Use Geant4 ver5.1. Possible minor bug of polarization vector after
Compton scattering was fixed by user (found by Y. Fukazawa @
Hiroshima Univ.).
PoGO_collimator_2004-04-21.ppt
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Detector Resopnses
•The same detector responses as those used in Hiro’s EGS4
simulation
•If there is a hit in slow/anti/btm scintillators, event is rejected.
(Threshold is 3 keV for anti/btm BGO and 10, 30, 100, 300, and
1000 keV for slow scintillator. Note that the position dependence
has not taken into account yet.). Energy smearing and poisson
fluctuation are not taken into account yet for veto scintillators.
•Assumed detector resposes:
• 0.5 photo-electron/keV
• fluctuated by poisson distribution
• smeared by gaussian of sigma=0.5 keV (PMT energy
resolution)
• minimum hit threshold after three steps above is 3 keV
PoGO_collimator_2004-04-21.ppt
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Event Analysis
•The same as those of Hiro’s EGS4 Simulation
•Use events in which two or three fast scintillators detected a hit.
•The largest energy deposit is considered to be photo absorption
•The second largest energy deposit is considered to be Compton
scattering.
•Smallest energy deposit (in case of three scintillators with hit) is
ignored.
•Smear azimuth angle distribution with Hiro’s resolution function.
•No event selection on compton kinematics
PoGO_collimator_2004-04-21.ppt
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Expected Background (1)
Flux(c/s/cm2/keV)
atmospheric downward gamma, W collimator of 25um
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
If we can reduce the slow scint. threshold below 100 keV,
PoGO will have sensitivity up to ~90 keV.
PoGO_collimator_2004-04-21.ppt
6
Expected Background (2)
Flux(c/s/cm2/keV)
atmospheric downward gamma, Sn collimator of 100um
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
BG level of Sn 100 um due to atmospheric downward gamma is ~1.5 x (BG
level of W 25um; see page 6.). PoGO will have sensitivity up to ~80 keV for
slow scint. treshold of 100 keV.
PoGO_collimator_2004-04-21.ppt
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Expected Background (3)
Flux(c/s/cm2/keV)
atmospheric upward gamma, W collimator of 25um
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
If we can reduce the slow scint. threshold below 100 keV,
PoGO will have sensitivity up to ~90 keV.
PoGO_collimator_2004-04-21.ppt
8
Expected Background (4)
Flux(c/s/cm2/keV)
atmospheric upward gamma, Sn collimator of 100um
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
BG level of Sn 100 um due to atmospheric downward gamma is ~1.5 x (BG
level of W 25um; see page 8.). PoGO will have sensitivity up to ~80 keV for
slow scint. treshold of 100 keV.
PoGO_collimator_2004-04-21.ppt
9
Expected Background (5)
Flux(c/s/cm2/keV)
atmospheric downward gamma, W collimator of 25um, lowE process
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
If we take into account the fluorescent X-rays, BG level below
100 keV increases by a factor of ~2 (see page 6).
PoGO_collimator_2004-04-21.ppt
10
Expected Background (6)
Flux(c/s/cm2/keV)
atmospheric downward gamma, Sn collimator of 100um, lowE process
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
Even if we take into account the fluorescent X-rays, BG level
below 100 keV does not change very much (see page 7).
PoGO_collimator_2004-04-21.ppt
11
Expected Background (7)
Flux(c/s/cm2/keV)
atmospheric upward gamma, W collimator of 25um, lowE process
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
If we take into account the fluorescent X-rays, BG level below
100 keV increases by a factor of ~2 (see page 8).
PoGO_collimator_2004-04-21.ppt
12
Expected Background (8)
Flux(c/s/cm2/keV)
atmospheric upward gamma, Sn collimator of 100um, lowE process
100mCrab (incident)
100mCrab (detected)
Background due to atmospheric gamma
Eth=10keV, 30keV, 100keV, 300keV and 1MeV
20
100
gamma energy (keV)
If we take into account the fluorescent X-rays, BG level below 30 keV
increases by a factor of 2. BG level in 30-100 keV does not change very much
(see page 8).
PoGO_collimator_2004-04-21.ppt
13