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Applications of Caesium Iodide in High Energy Physics

Applications of Caesium Iodide in High Energy Physics. Applications of Caesium Iodide in High Energy Physics. What is Caesium Iodide?. Alkali Halide Scintillator Grown from crystal seed Fantastic light output Properties enhanced by dopants (Thallium or Sodium) - CsI(Tl).

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Applications of Caesium Iodide in High Energy Physics

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  1. Applications of Caesium Iodide in High Energy Physics

  2. Applications of Caesium Iodidein High Energy Physics What is Caesium Iodide? • Alkali Halide Scintillator • Grown from crystal seed • Fantastic light output • Properties enhanced by dopants (Thallium or Sodium) - CsI(Tl) Unfortunately CsI(Tl) is... • Prone to radiation damage • A Poison A Caesium Iodide crystal from the BaBar calorimeter

  3. Applications of Caesium Iodidein High Energy Physics What is Poison? • Piss-poor US rock/metal • Big hair (4 counts) • Still living in the 80’s • Leather and Denim fetishists We proved in tests… …music has same artistic value as a Polo mint

  4. Applications of Caesium Iodidein High Energy Physics Poison’s artistic merit Jimi Hendrix Comfortably mediocre Artistic Merit (log scale) Krankies Nowt Arsecockfuck

  5. Applications of Caesium Iodide in High Energy Physics What is a scintillator? All solids give off energy as thermal radiation, normally in the infrared range. Some solids have the special capability of emitting ultra-violet and visible radiation - when the excitation of the crystal is by charged particles or photons, the luminescent material is called a scintillator. Energy loss in scintillators is through the usual shower deposition process. g e- e- g e+ g e+ g e- e- e- e+ g Radiation Lengthsc0 e- 0 1 2 3

  6. Applications of Caesium Iodide in High Energy Physics The process of scintillation Energy absorption from shower is by sensitiser. Photon emission is by activator. In some scintillators, a dopant is added to the lattice as a second activator to hinder re-absorption of photons - this is the role of the Thallium in CsI(Tl). Electrons Conduction Band EC Exciton Band EE Excitation Photon emission Photon absorption Exciton creation Exciton remains bound until de-excited De-excitation Valence Band EV Holes

  7. Applications of Caesium Iodide in High Energy Physics Caesium Iodide - the John Shaft of scintillators Not only is CsI(Tl) the black private dick that’s a sex machine to all the chicks, it is also the cat that won’t cop out when there’s danger all about. =

  8. Applications of Caesium Iodide in High Energy Physics Applications of CsI(Tl) 3 main areas that utilise CsI(Tl) scintillator: • Electromagnetic Calorimetry • Medical: PET and CAT scanners • Industrial applications: x-ray scanners (scintillator on CCD, PMT or pin-diode)

  9. Applications of Caesium Iodide in High Energy Physics CsI(Tl) for Calorimetry CsI(Tl) very good for calorimetry at BaBar energies. CsI(Tl) is also used for the electromagnetic calorimeter of the Belle experiment in Japan - also looking at B-physics. The BaBar Detector Cross-section of BaBar Calorimeter

  10. Applications of Caesium Iodide in High Energy Physics Medical Applications 2 main types: Positron Emission Tomography (PET) and Computed Axial Tomography (CAT). PET scans use positron emission from radioactive isotopes; CAT scans rely on direct x-ray detection. PET image CAT image

  11. Applications of Caesium Iodide in High Energy Physics Commercial Uses of CsI(Tl) Primary commercial use of scintillators is x-ray scanners, such as those used in airport baggage scanners e.g. Hilger Crystals produce CsI(Tl) arrays for Rapiscan baggage scanners. CsI(Tl) strip mounted on a pin-diode array Some freak’s luggage

  12. Applications of Caesium Iodide in High Energy Physics What’s so pimp about CsI(Tl)? • High light output and efficiency • Light output peak at 565nm (good for PMT’s) • Light output enhanced by second activator (Thallium) - less re-absorption • Moderately dense (4.5 g/cm3 - PbWO4 is just over 8 g/cm3) but fine for MeV-GeV energies • Slightly hygroscopic so crystals are water tuneable

  13. Applications of Caesium Iodide in High Energy Physics Why CsI(Tl) doesn’t ask for trouble, but ends up getting glassed 2 main phenomena which affect performance of CsI(Tl): • Radiation Damage • Afterglow Both phenomena are affected by doping concentration and crystal growing conditions; both hinder performance of crystal.

  14. Applications of Caesium Iodide in High Energy Physics Radiation Damage: what’s the beef? Continuous exposure to ionising radiation leads to the formation of colour centres (F-centres) - these colour centres absorb light in the blue/green, hence the reddish-brown hue of damaged/old crystals. Cs+ I- F-centre formation in CsI(Tl) Scattered g Incidentg e Captured electron Scattered I- ion

  15. 100ms Applications of Caesium Iodide in High Energy Physics Afterglow in CsI(Tl) Afterglow in CsI(Tl) is not properly understood. Short term (ms) afterglow is important: high afterglow leads to smearing of measurements and degrades energy resolution. Light output from a CsI(Tl) crystal with significant afterglow

  16. Applications of Caesium Iodide in High Energy Physics Understanding Afterglow System currently under construction for measuring afterglow in 1-inch CsI(Tl) plugs. PC running LabVIEW Incident x-rays 1.25 MHz ADC Card BNC Adapter Box Crystal and holder PMT

  17. Applications of Caesium Iodide in High Energy Physics And to conclude... Caesium Iodide: not as accurate as it could be...

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