Powder and Single Crystal
P-47 Powder Scintillators
Research and development has resulted in production of a P-47 coated scintillator on a glass disc for secondary electron detection. The use of P-47 (Y1Si2O7:Ce3) produces a scintillator which lasts longer, and the use of glass as a support material gives a signal output 2-4 times higher than that of plastic. The P-47 coated scintillator offers the following advantages:
- Constant high quality
- High signal output
- Long durability
- No vacuum contamination
- No Al-coating
- Bakeable up to 265?C
- Indefinite shelf-life
YAP Single Crystal Scintillators
YAP (Ytrium Aluminum Perouskite) is more efficient in terms of light output than YAG, while sharing the same insensitivity to radiation damage and efficiency at fast scan rates. In addition, the emission spectrum peaks at about 378nm, which corresponds closely to the maximum sensitivity of the S11 photo multiplier used in most scanning electron microscopes. Also, the decay time of YAP is faster than YAG (40ns rather than 80ns), producing substantially superior overall performance.
All YAP scintillators are polished on one side and mat ground on the other side. YAP crystals should be coated with 50nm of aluminum before use.
YAG Single Crystal Scintillator Discs
YAG (Ytrium Aluminum Garnet) single crystal scintillators are chosen by many scanning electron microscopists because they have a very fast response time of 50-60ns and they do not degrade when bombarded by electrons or ions unlike plastic or most phosphor scintillators. They are therefore particularly suited for high current operations.
Light emission peaks at about 560nm which means that S20 photo cathodes are most suitable for detecting the emission. The response is better than for the Plano P-47 disc below 5kV and again at higher accelerating voltages, where the performance of powder scintillators falls off while the response of the YAG continues to rise linearly.
The crystal should be coated with 50nm of aluminum before use. If the layer becomes damaged it can be removed with sodium hydroxide without damage to the crystal. The crystals are mounted with the mat surface in contact with the lightpipe as this has been shown to increase the efficiency. Uncoated YAG scintillators may be baked at temperatures up to 1000?C.