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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What is Caesium Iodide?
Unfortunately CsI(Tl) is...
A Caesium Iodide crystal from the BaBar calorimeter
What is Poison?
We proved in tests…
…music has same artistic value as a Polo mint
Poison’s artistic merit
Artistic Merit (log scale)
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.
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).
Conduction Band EC
Exciton Band EE
Exciton remains bound until
Valence Band EV
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.
Applications of CsI(Tl)
3 main areas that utilise CsI(Tl) scintillator:
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.
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.
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.
mounted on a
Some freak’s luggage
What’s so pimp about CsI(Tl)?
Why CsI(Tl) doesn’t ask for trouble, but ends up getting glassed
2 main phenomena which affect performance of CsI(Tl):
Both phenomena are affected by doping concentration and crystal growing conditions; both hinder performance of crystal.
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.
F-centre formation in CsI(Tl)
Scattered I- ion
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
System currently under construction for measuring afterglow in 1-inch CsI(Tl) plugs.
PC running LabVIEW
1.25 MHz ADC Card
BNC Adapter Box
Crystal and holder
And to conclude...
Caesium Iodide: not as accurate as it could be...