Multichannel Analyzer (MCA)

1. Multichannel Analyzer (MCA) • Raphael Cherney • Dan Elg • Sam Sun • Chen Wang

2. Background: X-ray Detection X-ray photons Vsignal X-ray Detector Amplifier • NASA’s detectors can “see” individual X-ray photons • Photon  Vpulse • Height proportional to energy • Our MCA measures the pulse heights and their times of arrival MCA

3. MCA Functionality

4. Applications • Radiation detection • Nuclear power • Food industry • *X-ray spectroscopy • Non-destructive testing • Environmental analysis and monitoring

5. Our Task • Build a $25 multichannel analyzer • Handle pulses ranging from 100 ns to 100 us (Require 1-50 us) • 100,000 counts per second (Require 1000 pulses) • Handle pulse height from 0V to 10V • Output ASCII file with time and pulse height • Create histogram of pulse heights V vpulse tpulse t

6. Attack of the Killer Circuit!

7. Building an MCA Baby steps… Circuits can be fun!

8. Signal In (10 V Analog)

9. Signal In (10 V Analog) Variable Gain Amplifier

10. Signal In (10 V Analog) Variable Gain Amplifier

11. Fast Signal Bypass Signal In (10 V Analog) Variable Gain Amplifier

12. Fast Signal Bypass Threshold Signal In (10 V Analog) Variable Gain Amplifier Adjustable Threshold Fast Comparator

13. Fast Signal Bypass Threshold Signal In (10 V Analog) Variable Gain Amplifier Adjustable Threshold Fast Comparator

14. Fast Signal Bypass Signal In (10 V Analog) Adjustable Threshold Variable Gain Amplifier Fast Comparator Peak and Hold

15. Fast Signal Bypass Signal In (10 V Analog) Adjustable Threshold Variable Gain Amplifier Fast Comparator Analog to Digital Converter Peak and Hold

16. Fast Signal Bypass PIC Signal In (10 V Analog) Pulse Counter Adjustable Threshold Peak Value Variable Gain Amplifier Fast Comparator Analog to Digital Converter Peak and Hold

17. PIC Clock Cycles • Missed pulse??

18. PIC Clock Cycles • Missed pulse?? • Actually, no. • Hardware counter • Limit processing time by using analog circuitry

19. Signal In (10 V Analog) PIC Processor D-type Flip-Flop Adjustable Threshold Signal Latch Pulse Counter Peak Value Fast Comparator Analog to Digital Converter Peak and Hold

20. Coincidence / Anticoincidence Primary Signal Secondary Signal • Always need to reset peak and hold Coincidence Anticoincidence

21. Full System

22. Threshold Baseline Reset Reset Zoom-in After detecting rising-edge of comparator, count x (in this case 5) clock pulses, then enable ADC Assuming 800 kcps, the ADC takes 1.25 μs to sample Timing Diagram 1 horizontal unit = 5 clock cycles = 250 ns

23. Onboard Histogram • Stores data on PIC • Detection system  ADC  Histogram • Allows us to count quickly without having to send data quickly

24. USB • Wait  send data  wait • Sends ~1 kB every time • Full-speed bulk transfer Packet Formation Buffer Descriptors USB SIE Histograms Endpoint Buffers Ready?

25. Host Application Histogram Incoming data Flux Plot File I/O

26. GUI

27. UV Flux Monitor • Photodiode outputs current according to flux • Converted into voltage, read by PIC • Uses onboard PIC ADC UV Light Isignal Vsignal Current-to- Voltage Converter UV Photodiode PIC

28. Final Deliverables • An MCA • A UV Flux Monitor • Software to control these two devices, and display data

29. What Now? • Test firmware • Finish GUI • Rev 2 of PCB • System integration and final testing • Write documentation

30. Special thanks to: • Steve Holt • Keith Gendreau • Brad Minch • Gill Pratt • Mihir Ravel • 2008 MCA team Questions?