Pulse Analysis

Advanced Reading

Measurement and Detection of Radiation, N. Tsoulfanidis, Ch. 1.
Radiation Detection and Measurement, G.F. Knoll , Chapter 17, pp. 610 – 632, Chapter 18, pp. 685 – 700.

Equipment

Oscilloscope Oscilloscope Information
NIM Bin Nim Bin Information
Pulse Generator Tail Puse Generator Information
Coaxial Cables Coaxial Cable Information
Single Channel Analyzer (SCA) SCA Information
Amplifier Amplifier Information
Computer With MCA card and Genie 2000 Software Genie 2000 Software Information

Procedure:

Part A: Single Channel Analyzer SCA Setup Diagram

PURPOSE:
The main objective of this excersize is to become familiar with the Amplifier and Single Channel Analyzer (SCA).

NOTE – During the following steps, your particular SCA or amplifier (such as a PDA if you are using one) may have slightly different terms, especially with SCA terminology. Make sure to ask your Lab instructor if you have any questions.

Connect the tail pulse generator output (provided by the lab assistants) to the input of the oscilloscope. Using the oscilloscope, measure amplitude, fall time and frequency of the pulse. Confirm these parameters with your Lab instructor before proceeding.
Remove the cable providing the pulse generator output from the oscilloscope and connect it to the amplifier.
[Note – not all amplifiers will have this option. Ask your Lab instructor for information if using a PDA or Amplifier without the following capability] Adjust the amplifier to “negative” (flip switch + or -) and “unipolar” (inverted polarity, unipolar shaping – by selecting the correct out connection) to produce a monopolar linear pulse of positive amplitude and between 0 and 10 volt size.
Remove the cable from the oscilloscope and connect this output to the SCA input. Run a cable from the SCA output to the oscilloscope.
Set the SCA on “integral” so that it acts as a simple discriminator, and set the discrimination level to a low value so that an output logic pulse is produced. Discuss the response of SCA with your Lab instructor and what this means to the incoming signal.
Display the logic output pulse from the SCA on the oscilloscope.
With the SCA set at “integral,” find the lower level discriminator setting at which the input pulse amplitude is just discriminated.
By varying the Pulser output amplitude, plot the SCA input amplitude (Pulse from Linear Amplifier) vs. the corresponding LLD setting.

Is the relationship linear?
If Not, What are the possible Sources of Non-Linearity?

Switch the SCA to “window” (i.e., Differential). At some arbitrary LLD and ULD setting, determine the range of input-pulse heights, which will produce an SCA output pulse for a given upper level discriminator setting.
Now vary the ULD setting (keeping LLD fixed) and determine if the window width is linear.
Check at least one window setting at another LLD dial setting to see whether the width changes.
Set the SCA to “Integral” and determine the relationship between the ULD and LLD dial settings for normal operation.

Part B: Multi-channel Analyzer Calibration MCA Calibration Setup Diagram

PURPOSE:

The purpose of this exercise is to learn the basic operations of one of the multi-channel analyzers (MCA's), which will be available for general use throughout the semester. Familiarize yourself with the procedures necessary to produce and display a multi-channel spectrum.

STEPS: You will need to have the Lynx window open and the Webex window as well. On the Webex window you will have an oscilloscope and the video window visable. (The Lynx consists of a MCA and oscilloscope as well as many other fun toys.)

Open the Lynx window on your computer
Note the specifications on the size, polarity, and shape of the input pulse expected by the MCA. Set the pulse generator amplitude and amplifier gain to produce a shaped pulse that meets these specifications.
Since the pulse generator amplitude is fixed, all these pulses should now be stored in a single channel (or a small group of channels neighboring each others).
For those using a PAD module for an amplifier, note that you will have a bipolar pulse. Use the ADC settings to filter the second pulse.
Using the pulse generator with about 1 kHz frequency, measure the integral linearity of the MCA by successively recording for several seconds with several different pulse amplitudes. By not erasing the memory between steps,

Record the Pulse Voltage by using Scope.
Plot Volts vs. Channels Number.

Repeat Number 3 for a different Gain (Amplifier Gain)
After every pulse, which the MCA accepts and analyzes, it is “dead” for a certain time, i.e., it will not accept additional pulses during that time interval. The pulse generators can be used to measure the MCA dead time by making use of the “double pulse” feature.
With the pulser initially set on “single pulse,” vary the pulse amplitude until the recorded events lie somewhere near the middle of the MCA channel range.
Now switch the pulser to “double pulse” and observe the amplifier output on the oscilloscope while also supplying it to the MCA.
Note that the spacing between double pulses can be varied using the “delay” control.
Starting with a delay of zero (<10 ms) slowly increase delay until the MCA begins recording a second peak corresponding to the smaller delayed second pulse.
Measure the corresponding time spacing on the oscilloscope, which is now the corresponding MCA dead time.
Repeat using several different pulse amplitudes and plot the MCA dead time vs. channel number.

Is there any relationship between Channel Number and Dead time?
What type of ADC is in use?
Plot a chart of Pulse Amplitude vs. Dead Time.