GRAPE A Balloon-Borne Gamma-Ray Polarimeter (5-3 kev) Mark L. McConnell, James R. Ledoux, John R. Macri, Matt Orr, and James M. Ryan Space Science Center University of New Hampshire Durham, NH X-Ray Polarimetry Workshop SLAC / Stanford 9-11 February 24
GRAPE Science Model (SM1) Gamma-RAy Polarimeter Experiment Scattering Elements 28 element array of plastic each 5 mm square by 5 cm long optically isolated read out by a 5-inch PSPMT Hamamatsu R3292 PSMT Calorimeter Elements 4 element array of CsI(Tl) each 1cm square by 5 cm long read out by a MAPMT Hamamatsu R59 MAPMT CsI(Tl) Array Plastic Elements BC-44 Position-Sensitive PMT Hamamatsu R3292
On-Axis Performance Effective Area (cm 2 ) 4 3 2 1 Effective Area vs. Depth 11.6 mm 88.9 mm 76.2 mm 63.5 mm 5.8 mm 25.4 mm 3 4 5 6 7 8 9 1 Energy (kev) 2 3 4 5 Simulations (based on a modified version of GEANT3) have been used to characterize the design.
On-Axis Performance Figure of Merit (relative) 7 6 5 4 3 2 1 Figure-of-Merit vs. Depth 76.2 mm 5.8 mm 25.4 mm 63.5 mm 88.9 mm 11.6 mm The figure-of-merit incorporates an estimate of the increased background as a function of detector volume. FoM = µ 1 ɛa Vdet 3 4 5 6 7 8 9 1 2 3 4 5 Energy (kev) Optimum Depth for this design is ~3 inches
Off-Axis Performance 7.62 cm depth @ 2 kev 1. 3. Modulation Factor.8.6.4.2. Modulation Factor Effective Area 1 2 3 4 Angle (Degs) 5 6 7 2.5 2. 1.5 1..5. Effective Area (cm 2 ) The GRAPE design offers significant response even at large off-axis angles. This makes GRAPE an attractive design for polarization studies of transient sources (Gamma-Ray Bursts).
Science Model Components This photo shows the 5-inch PSPMT, the array of plastic scattering elements and the MAPMT/CsI assembly.
GRAPE SM1 Lab Set-Up (drawing not to scale) POLARIZER POLARIMETER PMT 288 kev, partially polarized MAPMT PSPMT 662 kev, unpolarized 137 Cs CsI array plastic scintillator array Polarization Fraction.8.6.4.2. 2 4 6 8 1 12 14 Scatter Angle (degs) 6 kev 662 kev 12 kev 16 18 Photons partially polarized by scattering off a plastic scintillator. Also provides electronic tagging of each photon.
Correction of SM1 Data 1.4 1.2 GRAPE - SM1 14 12 GRAPE - SM1 1. 1 Counts.8.6 Counts 8 6.4.2. Unpolarized Data (normalized) 5 1 15 2 25 356 kev 3 35 4 2 Polarized Data (raw data) 5 1 15 2 288 kev 25 3 35 Azimuthal Scatter Angle (degs) Azimuthal Scatter Angle (degs) The response to an unpolarized beam is used to correct for geometric effects. Counts 14 12 1 8 6 4 2 Polarized Data (corrected) 5 1 15 2 GRAPE - SM1 25 3 35 Azimuthal Scatter Angle (degs)
SM1 Results at Incidence Runs taken with the incident beam having a polarization angle that differs by ~9. 1 7 Corrected Counts 8 6 4 2 GRAPE Science Model (SM1) Incidence φ = 4 ± 2 Corrected Counts 6 5 4 3 2 1 GRAPE Science Model (SM1) Incidence φ = 134 ± 3 6 12 18 24 3 36 6 12 18 24 3 Azimuthal Scatter Angle (degs) Azimuthal Scatter Angle (degs) Polarization = 62 (±3)% Polarization = 73 (±6)% 36
SM1 Results at 3 Incidence Runs taken with the incident beam having a polarization angle that differs by ~9. Corrected Counts 14 12 1 8 6 4 GRAPE Science Model (SM1) 3 Incidence φ = Corrected Counts 12 1 8 6 4 GRAPE Science Model (SM1) 3 Incidence φ = 9 2 2 5 1 15 2 25 3 Azimuthal Scatter Angle (degs) 35 5 1 15 2 25 3 Azimuthal Scatter Angle (degs) 35 Polarization = 63 (±4)% Polarization = 73 (±7)%
GRB Sensitivity We have estimated the polarization sensitivity of a longduration balloon payload consisting of a planar array of 36 GRAPE modules, covering less than 1 m2 of area. Frequency based on BATSE 4B catalog.
Solar Flare Sensitivity The solar flare polarization sensitivity for various energy bands. These data assume a balloon-borne array of 16 GRAPE modules. 3 Minimum Detectable Polarization (%) 25 2 15 1 5 X1-Class Flare X1-Class Flare 1 2 3 4 Energy (kev) 5 6
GRAPE Science Model (SM2) Gamma-RAy Polarimeter Experiment Scattering Elements 6 element array of plastic each 5-mm square by 5-cm long optically isolated read out by a flat-panel MAPMT Hamamatsu H85 MAPMT Calorimeter Elements 4 element array of CsI(Tl) each 5-mm square by 5-cm long read out by same flat-panel MAPMT Hamamatsu H85 MAPMT CsI plastic elements flat-panel PMT FEE Single module with MAPMT and FEE electronics.
SM2 Module Logic plastic scintillator bars (photon scattering) inorganic scintillator (CsI or LaBr 3, calorimeter) or from other MAPMTs or coincidence Text gate The single MAPMT provides independent signals for both the scattering and calorimeter elements. flat panel MAPMT pulse heights & hit IDs front-end electronics ADCs event builder sparse event data Eliminates additional mass in front for calorimeter readout.
Large Area Arrays Large area arrays can easily be fabricated. Inter-module events will increase the effective area. Large areas could be used as an imaging detector plane.
Lab Testing of SM2 Module Now in Progress The H85 provides an 8 x 8 array of anodes on a 6-mm pitch.
SM1 vs. SM2 Array Effective Area (cm 2 ) 3.5 3. 2.5 2. 1.5 1..5 Effective Area SM1 vs. SM2 Array SM1 (PSPMT) SM2 (MAPMT) Modulation Factor (µ 1 ) 1..8.6.4.2 Modulation Factor SM1 vs. SM2 Array SM1 (PSPMT) SM2 (MAPMT).3 4 5 6 7 2 3 4 5 6 7 2 1 1 Energy (kev).3 4 5 6 7 2 3 4 5 6 7 2 1 1 Energy (kev) These simulation results compare a single SM1 module with a 4-element array of SM2 modules.
SM1 vs. SM2 Array Figure of Merit 1 8 6 4 2 Figure of Merit SM1 vs. SM2 Array 3 4 5 6 7 2 3 4 5 6 7 2 1 1 Energy (kev) SM1 (PSPMT) SM2 (MAPMT) Despite the lower modulation factor, the FoM of the SM2 array exceeds that of the SM1 module. The SM2 array provides : ~25% greater sensitivity ~3% smaller footprint ~75% smaller volume close-packing
LaBr 3 Scintillator Another important advance, in terms of energy resolution, will come from the use of Lanthanum Bromide in place of the CsI. Counts 14 12 1 8 6 4 2 GRAPE Energy Resolution (simulated) LaBr 3 ( E/E = 9.5%) CsI ( E/E = 25%) 5 1 15 2 Total Energy Loss (kev)
Project Status First science model successfully tested. Now testing an improved design based on flat panel multi-anode PMT. Engineering balloon flight of SM2 array in 26. Development of a full balloon payload for ULDB...... a bunch of GRAPEs