1. PoGO_collimator_2004-04-21.ppt1 Study of PoGO background dependence on the collimator material/slow scintillator threshold April 21, 2004 Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU History of changes; updated on April 15, 2004 modified on April 21, 2004

2. PoGO_collimator_2004-04-21.ppt2 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 cm 2 )

3. PoGO_collimator_2004-04-21.ppt3 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/m 2 ) 100% polarized, 6h exposure Attenuation by air of 4g/cm 2 (atmospheric depth in zenith direction is ~3g/cm 2 and that in line-of-sight direction is 4g/cm 2 ) 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.).

4. PoGO_collimator_2004-04-21.ppt4 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

5. PoGO_collimator_2004-04-21.ppt5 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

6. PoGO_collimator_2004-04-21.ppt6 Expected Background (1) atmospheric downward gamma, W collimator of 25um 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV If we can reduce the slow scint. threshold below 100 keV, PoGO will have sensitivity up to ~90 keV.

7. PoGO_collimator_2004-04-21.ppt7 Expected Background (2) atmospheric downward gamma, Sn collimator of 100um 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV 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.

8. PoGO_collimator_2004-04-21.ppt8 Expected Background (3) atmospheric upward gamma, W collimator of 25um 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV If we can reduce the slow scint. threshold below 100 keV, PoGO will have sensitivity up to ~90 keV.

9. PoGO_collimator_2004-04-21.ppt9 Expected Background (4) atmospheric upward gamma, Sn collimator of 100um 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV 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.

10. PoGO_collimator_2004-04-21.ppt10 Expected Background (5) atmospheric downward gamma, W collimator of 25um, lowE process 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV If we take into account the fluorescent X-rays, BG level below 100 keV increases by a factor of ~2 (see page 6).

11. PoGO_collimator_2004-04-21.ppt11 Expected Background (6) atmospheric downward gamma, Sn collimator of 100um, lowE process 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV Even if we take into account the fluorescent X-rays, BG level below 100 keV does not change very much (see page 7).

12. PoGO_collimator_2004-04-21.ppt12 Expected Background (7) atmospheric upward gamma, W collimator of 25um, lowE process 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV If we take into account the fluorescent X-rays, BG level below 100 keV increases by a factor of ~2 (see page 8).

13. PoGO_collimator_2004-04-21.ppt13 Expected Background (8) atmospheric upward gamma, Sn collimator of 100um, lowE process 100mCrab (incident) 100mCrab (detected) gamma energy (keV) Flux(c/s/cm2/keV) 20 100 Background due to atmospheric gamma Eth=10keV, 30keV, 100keV, 300keV and 1MeV 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).