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GEANT4 Simulations of TIGRESS

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Presentation on theme: "GEANT4 Simulations of TIGRESS"— Presentation transcript:

1 GEANT4 Simulations of TIGRESS
TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer M.A. Schumaker University of Guelph, Ontario, Canada For the TIGRESS Collaboration GEANT4 User’s Workshop, CERN, Geneva November 11 – 15, 2002

2 What is TIGRESS? TIGRESS is a Gamma-Ray Spectrometer
Assembled over 6 years, ending in 2008 Will be one of the most advanced, most efficient gamma-ray spectrometer in the world High gamma detection efficiency and large photopeak-to-background ratio Will perform nuclear astrophysics, nuclear structure, nuclear reactions experiments, and beyond TIGRESS is a sophisticated gamma ray spectrometer scheduled to begin assembly next year. The complete array will be assembled by 2008. When it is complete, TIGRESS will be the most advanced, most efficient gamma-ray spectrometer in the world. This is due to a very high gamma ray detection efficiency

3 TIGRESS Location TIGRESS will be an experimental facility for the ISAC-II radioactive ion beam accelerator at the TRIUMF Laboratory in Vancouver, Canada

4 ISAC Isotope Separator and Accelerator
Advanced radioactive ion beam accelerator facility For ISAC, radioactive nuclei are produced by bombarding targets with up to 100 uA of 500 MeV protons from the TRIUMF main cyclotron Can then be separated and accelerated for a variety of experiments Accelerated masses up to 30 amu Energies up to 1.5 MeV per nucleon ISAC exists, and runs. Make a point of this. But don’t say too much more

5 ISAC-II Upgrade Scheduled for completion in 2007
The ISAC-II upgrade to ISAC will increase the mass and energy limits Accelerated nuclei up to 150 amu Energies up to 6.5 MeV per nucleon Up to 15 MeV for light nuclei Allows Coulomb Excitation and Fusion experiments due to higher energies TIGRESS will take maximum advantage of the new capabilities ISAC-II provides Nuclear evaporation experiments (clarification if someone asks)

6 Production Accelerator
ISAC II ISAC II 0.15 – 6.5 MeV/A ISAC II High b SCRF SC LINAC ISAC I 0.15 – 1.5 MeV/A Med b SCRF Tigress Low b SCRF DTL1 Thick/Hot Target high-energy proton beam DTL2 CSB is charge state booster (knocks more electrons off ion) when they come out of the target they are 1+ RFQ is radio frequency quadrupole DTL drift tube linac SC linac is superconducting (niobium) Highest current used is 40 uA from TRIUMF (melt target) Ion Source RFQ Production Accelerator TRIUMF 500 MeV Cyclotron 100 mA Ion Beam A/q < 30 Low-Energy Experiments Isotope Separator CSB

7 TIGRESS Design Composed of sixteen separate detectors
Modular design is versatile Detectors can be replaced with other detection devices Detectors can be used with other experiments Allows the full array to be assembled over time

8 Geometry Forward Configuration Provides Maximum Efficiency
Back Configuration Provides Maximum Peak-to-Background Ratio This should really discuss the flexibility of design, not really the flexibility of TIGRESS

9 TIGRESS Simulation Using GEANT4
Goal was to create a detailed simulation to determine the expected efficiency and peak-to-background response of the detectors, and to aid in design optimization studies

10 TIGRESS: Reality vs. Simulation
Beam of radioactive nuclei passes through detector, collides with target in the centre of the array Low Energy Beam particles become embedded in target material, and decay High Energy Coulomb excitation or fusion with target particles, creating exotic nuclei Gamma rays emitted in random directions Detected by Ge Crystals Compton Suppression Shield detect scattered gamma rays Simulation (Current Implementation) Particle Gun set at centre of the array Emits gamma rays of a certain energy Random directions Germanium crystals and Suppression shields set as Sensitive Detectors Energy deposition in each is recorded and analyzed EM Physics List Only processes for photons, electrons and positrons needed

11 TIGRESS HPGe Crystals TIGRESS uses High-Purity Germanium Crystals for gamma detection HPGe provides excellent energy resolution Crystals are designed to maximize the solid angle coverage inside the detector Leads to high gamma-ray detection efficiency Good HPGe gives 2 keV FWHM at 1.33 MeV (Co-60 second photopeak) Best for energy above 100 keV (silicon also works… but lots of compton scattering) 11 cm across somehow point this out

12 Compton Suppression Compton Suppression shields detect events which scattered in the germanium crystal When an event is detected in both the germanium crystal and the suppression shield, the event is not included in the data Detecting scattered events decreases the magnitude of the spectral background, so it is important to optimize the shield design Compton Escape Suppression BGO Compton Scattered Gamma Ray Say that we’re interested in optimizing this feature of the detector

13 These come together to form…
60 cm long A TIGRESS Detector

14 Testing the Simulation
Energy (keV) Counts (total=1 million) Comparison of GEANT4 Simulation to Previous Monte Carlo Program

15 TIGRESS Efficiency Slide after geometry – put in spectrum and explain that we wanted to test the output of the code (and explain gamma ray spectra) And scanning test Say what was in the previous slide

16 Geometry Detector geometry is determined by a small number of variables set in a configuration file Configuration file is read at run time Geometry was designed to be extremely malleable From run to run, the detector measurements can be changed very easily All components, but most notably the Compton suppression shield measurements can be changed for different runs, and the results compared Nothing is hardcoded. That’s a better way to say it

17 Suppression Shield Optimization
The suppressor shields should detect as many events as possible, though cost is an issue The thicknesses of the sides, back, and front extensions were examined Runs were performed to investigate the optimal design Performed in both the forward and backward configuration

18 Suppression Shield Optimization

19 Suppression Shield Optimization
Go with 10 mm Show the other results

20 Suppression Shield Optimization


22 Summary A simulation of TIGRESS was created to determine the expected efficiency at various energies, and the behaviour of the Compton suppression shield This was used to maximize the peak-to-background ratio by simulating different Compton suppressor designs We have made significant progress with GEANT4, but there is much more to do

23 Future Goals Make the simulation closer to reality
Simulate electrode dead layers in Germanium crystals Aluminum shell around the suppression shield, beamline vacuum chamber, etc. Suppression shield scintillation? Compare the simulation to the first TIGRESS detector prototype HPGe detector expected November 2002 Suppressor expected spring 2003

24 Acknowledgements University of Guelph (Guelph, Ontario, Canada)
Carl Svensson Paul Finlay Geoff Grinyer TRIUMF (Vancouver, British Columbia, Canada) Helen Scraggs and Kelly Cheung Greg Hackman and Gordon Ball McMaster University (Hamilton, Ontario, Canada) Jim Waddington The Full TIGRESS Collaboration

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