1. Important EDS Parameters EDAX Detector Geometry Deadtime & Time Constants

2. Optimum Count Rate u High Energy Peaks –Use a Longer time constant –CPS to give 20 - 40% Deadtime u Low Energy Peaks –Use Longest time constant –500 - 1000 counts/sec u Throughput (faster time constant, cps to give 30 - 60% Deadtime)

3. Accelerating Voltage u Overvoltage = Voltage/Peak Energy u Typically, the accelerating voltage should be 2x the highest energy line and no more than 10 to 20 times the lowest energy line of interest. u 10 times for Quantitative Analysis u 20 times for Qualitative Analysis

4. Why should the overvoltage be at least 2 for the highest energy element? Low overvoltage means a small, poorly excited peak and poor statistical quality in the spectrum Electron Volume X-Ray Vol.

5. Why should the overvoltage be less than 10 to 20 times the lowest energy peak? High overvoltage means a high absorption condition and a small peak and poor statsitics (again) Electron Int. Vol. X-Ray Generated Volume X-Ray Escape Volume

6. Take-Off Angle u The take-off angle is the angle between the x-ray trajectory and the sample surface. u The angle is a combination of detector angle, its position, sample working distance, and sample tilt. u Typical angles will range from 25 - 40 degrees

7. Detector Geometry Elevation Angle scale setting Intersection Distance/ Working Distance u Elevation Angle = The angle between the horizontal and the detector normal. u Intersection Distance = The distance in mm between the pole piece to where the electron beam intersects the detector normal. u Working Distance = The distace from the pole piece to the sample surface.

8. EDAX Detector Geometry EA ID WD < ID TOA < EA WD > ID TOA > EA Tilt > 0 TOA > EA

9. Real Time “Clock Time” u Real Time = Live Time + Dead Time (Real Time = Clock Time) u Live Time - time when detector is alive and able to receive an x-ray event u Dead Time - time when the detector or preamplifier is unable to accept a pulse because it is busy processing or rejecting an event(s).

10. Stored Counts in 10 Clock Seconds (peak = 67% DT) The higher count rate does not necessarily produce more counts in the spectrum.

11. Stored Counts in 10 Clock Seconds --using fast and slow time constants Sometimes using a faster time constant is a way to get more data in the same time. Usually a good idea when collecting maps.

12. Deadtimes on a DX Prime System

13. Deadtimes on a Phoenix System