Scintillation Detectors

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