scintillation detectors john neuhaus - university of iowa fall 2010
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John Neuhaus - University of Iowa Fall 2010
Scintillation Detectors
John Neuhaus - University of Iowa Fall 2010
Basics
• Ionizing radiation excites matter, but doesn’t ionize
• De-excitation by heat, phosphorescence or fluorescence
• Fluorescence (ns timescale) in response to radiation is called scintillation
John Neuhaus - University of Iowa Fall 2010
Details
• Light created proportional to energy deposited
• Fluorescence is fast!• Pulse shape discrimination possible• Basic two-part exponential decay
sftt
eBeA **
John Neuhaus - University of Iowa Fall 2010
Types of Scintillators
• Organic Crystals• Organic Liquids• Plastics• Inorganic Crystals• Gaseous Scintillators• Glasses
John Neuhaus - University of Iowa Fall 2010
Organic Crystals
• Aromatic hydrocarbons, typically containing benzene rings
• Sometimes pure crystals (anthracene, stilbene)
• Decay time of few ns• Light from free valence electrons (π orbitals)
John Neuhaus - University of Iowa Fall 2010
Inorganic Crystals• NaI(Tl), BGO, LYSO,
PbWO4• High light, slower
response (250 ns for NaI), high density (~7 g/ml for BGO, LYSO)
• Usually hygroscopic, expensive
• Make good gamma detectors
John Neuhaus - University of Iowa Fall 2010
Organic Liquids
• Liquid solution of organic scintillators in organic solvent
• P-Terphenyl, PPO, etc. in xylene, toluene, cyclohexane, etc.
• Easily doped (e.g. with 10B for neutron detection)
John Neuhaus - University of Iowa Fall 2010
Plastics
• Polymerizable solvent, like polystyrene or polyvinyltoluene
• High light, fast response, easily machineable and cheap
• Sensitive to body acids and organic solvents• In fiber form -> wavelength shifting
John Neuhaus - University of Iowa Fall 2010
Wavelength Shifting
• Solvents liquid and solid fluoresce, typically in UV
• Primary fluor (pTP, etc.) absorbs UV and re-emits at longer wavelength
• Secondary (3HF, POPOP) shifts further and inhibits self-absorption
John Neuhaus - University of Iowa Fall 2010
John Neuhaus - University of Iowa Fall 2010
John Neuhaus - University of Iowa Fall 2010
Radiation Damage Mechanisms• Damage of dopants• Reduction in transmittance of base (“hidden
damage”)
BC505 Sample Undoped base
John Neuhaus - University of Iowa Fall 2010
Methods of Improving Radiation Hardness
• Rad-hard dyes• Large Stokes’ shift
dyes to move past damaged region
• Rad-hard bases• Combos (e.g. 3HF
and PDMS)
John Neuhaus - University of Iowa Fall 2010
Applications – Triggers and Vetos
• Halo veto rejects poorly collimated beam
John Neuhaus - University of Iowa Fall 2010
Applications – Cont’d
• Beam size trigger, selectable beam size
John Neuhaus - University of Iowa Fall 2010
Applications – Cont’d
• Muon veto rejects beam events that contain muons
High-z absorber
Experiment
John Neuhaus - University of Iowa Fall 2010
Applications – Cont’d
• Hodoscope, “path viewer”
• Track charged particles
• Onel, et al. 1998
John Neuhaus - University of Iowa Fall 2010
Test Beam
• Well characterized beam for detector R&D• Single elements (e.g. scintillator plate)• Full calorimeters• FNAL (Mtest) and CERN (H2)
John Neuhaus - University of Iowa Fall 2010
FNAL MTest
John Neuhaus - University of Iowa Fall 2010
FNAL MTest
John Neuhaus - University of Iowa Fall 2010
MTest Details
• Low Energy electrons (1-2 GeV)• High Energy Protons (120 GeV)• Pions (1-66 GeV)• Muons (1-120 GeV)• Multiple spill modes– One 4s spill/min– Two 1s spills/min– Several ms spills/min
John Neuhaus - University of Iowa Fall 2010
Beam Composition
John Neuhaus - University of Iowa Fall 2010
Calorimeter Experiments
Iowa Quartz Plate Calorimeter 2006 at FNAL, p-Terphenyl deposited quartz plates
John Neuhaus - University of Iowa Fall 2010
Calorimeter Exp Cont’d
QPCAL at CERN H2 Facility
John Neuhaus - University of Iowa Fall 2010
Data from H2