"Bret Cannon" wrote in message news:GSa7l.2646$ email@example.com... | | "John Larkin" wrote in message | news: firstname.lastname@example.org... | > On Thu, 01 Jan 2009 02:58:33 GMT, "Martin Riddle" | > wrote: | >
| >>Anyone have any tips. Good reference links. | >>I'm toying with the idea, seems like a nice hardware/software project. | >>
| >>Cheers | >
| > Scintillator and PHA? | >
| > John | >
| Using a scintillator lets you use a PMT to do the low level amplification of | the signal, but you lose energy resolution. For covering large areas, | scintillators are much cheaper than semiconductor ionizing radiation | detectors, which is why they are used in radiation portal monitors at border | crossings. For this application, a properly packaged scintillator and a PMT | is probably more expensive than a silicon detector and preamp. The most | common inorganic scintillator is thallium doped sodium iodide (NaI:Tl), | which is hygroscopic and the toxicity of thallium is also a concern. | Plastic scintillators are cheaper but they don't offer any energy | resolution. | | | Energy resolution is a significant difference between scintillator and | semiconductor x-ray detectors. A good scintillator generates about one | scintillation photon per 20 eV of absorbed x-ray energy, but with light | collection efficiency and quantum efficiency the signal "current" (ignoring | PMT amplification) is at best about one electron per 400 eV of x-ray photon | energy. This signal has full shot noise plus the excess statistical noise | of the PMT, so the energy resolution of characteristic x-ray lines in | severely degraded. | | In contrast, using a silicon diode detector gives 1 electron-hole pair per | 3.76 eV, they can all be collected, and this signal has much less than full | shot-noise. This means that the energy resolution the measurement will be | determined by the electronics used, especially the charge integrating | pre-amp. The sub-shot noise behavior of semiconductor radiation detectors | is quantified by the Fano factor, which is the ratio of the observed | variance of the signal to the average number of electrons in pulses due to a | fixed x-ray energy. In room temperature silicon detectors the Fano factor | has been measured to be less than 0.1. | | Makers of radiation detection electronics have application notes on pre-amps | for radiation detectors including AMETEK/Ortec and Cremat, | | Bret Cannon | | |
Thanks, Yes this would be for Identifying various elements in a particular sample. I was planning on a Si-diode detector, Hamamatsu or some other. I did find the Amptek site which has similar info to Cremat and the others. Right now I am collecting information, particularly on the PA.