Steps to be taken in making and testing a small scintillator counter.

                                                        Kari van Brunt
                                                        June 10, 2003

These are based upon Kari's experience in making a small scintillator
counter in the past week.

I. Calculations:

1. Estimate No. of Cosmic Rays
   (see PPB/PDG,pp. 180)
    If detector is 1/2 m**2, flat, how many
    soft, hard, total?
    [This is how many we expect!]

2. Delay time by adding cable?
     How far does light travel in 1 second?
     How many feet is that?
     How long does it take to travel 1 ft.?
     What if n = 1.6?

3. How much charge is delivered?
     If signal is 1 V, and it travels down a 50 ohm cable,
     what is the current?  If the signal lasts 5 ns, how much charge?
     If gain is 10**7, how many  photoelectrons?

4. What does photoelectron mean?

5. How many photoelectrons are delivered to the photocathode?

     How many photons does 1 cm thick scintillator yield?
     How many have appropriate angle of incidence for TIR?
     What is quantum efficiency of photocathode?
     Suppose we lose 1% each time they hit the edge of the 
      scintillator.  How many do we lose?  [lost = 1-e**N_bounces]
     How many bounces are there?

     Liouville Theorem says you can't put the same  number of photons
      in a smaller phase space (where phase space is the product of the 
      available delta x * delta y * delta theta_x * delta theta_y).
      If our ligh guide goes from 20 cm -> 2 cm in diameter, by what 
      factor do  we keep photoelectrons?

6. We have a signal of 10,000 cts/s. If noise is due only to 
      Poisson statistics, how much uncertainty is there? (sqrt(N))

7. How many data points fall within your uncertainty?
    (1 sigma; 2 sigma; 3 sigma?) ( > 3 sigma).
   (For good data, expect to be no more than 3 sigma away..)

8.  A signal shows up in bin No. 75.  If each bin is 0.25 pc, how much 
    charge was deposited by that signal?

9) A 1 pe signal is found in bin # 22?  What is the gain?

10)  Accidental occurrence rate:
      R1 * R2 * delta time.



II. Procedures.

1. Build counter.
  a) Clean light guide and scintillator (we didn't do this)
  b) Prepare light guide for gluing  by taping plastic flush with the edge 
of the surface to be glued, so you catch excess glue.
  c) stand lightguide on ring stand with part to be glued up.  Tape it to 
ring stand.
  d) Mix epoxy  on foil. 
  e) line edge of light guide with epoxy.
  f) set scintillator on top of light guide and hold.
    DO NOT HANDLE SCINTILLATOR DIRECTLY!
  g) allow it to set.
  h) wrap foil around combo, leaving a layer of air.  This way you don't 
change n for the scintillator.
  i) put cookied on PMT
  j) add PMT
  k) push tightly against block, secure with metal ring.

2. Test the counter
 I) a) know how to sue scope
    b) take anode signal and put in ch 1.
    c) triggering on 1, vary the trigger  and look at different
       signals.
    d) find the 1PE signal.
    e) trigger more negative to find cosmic ray signal
    f) hook oscilloscope to counter.
    g) see how many cts/sec do you see? (Ea. time  scope is triggered the 
       scaler counts)

II. At this point, can do 2 things:
    a) put small ctr in coincidence with large counter, and look at 
       coincidences on oscilloscope, or hook small counter to logic.
    b) place counters in coincidence (want rays to only pass through 
        scintillator)
    c) use scope to count rates in S1,L1, or both.  How do coincidences 
       change with threshold?  Investigate 1 p.e. signal and cosmic
       ray signal. How can you see a coincidence on scope?  How likely is 
it you'll see a 1pe signal coincidence? (Calc. 9)

   d) make a threshold plot. change the threshold and record cts.

III.  Test Counter Cont'd.
     Now that you have convinced yourself you can see signal, let's do 
some of the same investigations with logic instead of scope.
   a) send dynode signal from S1 to discriminator, and L1 to 
discriminator;
      output to coincidence.
     count rates in S1. (is it what you'd expect?)
     count rates in L1. (is it what you'd expect?)
     count rates in coincidence (is it what you'd expect?)

  b) test uniformity of counters.
     take a number of rates for each ctr. (10 or so)
     calc. mean
     find uncertainty
     find out how much each differs from mean (1 sigma, 2 sigma, 3 sigma, 
etc)
     (expect 32% within 1 sigma
             5% within 2 sigma
             0.27% within 3 sigma (PDG p. 242)
       create a scatter  plot that show cts vs time taken. note any 
trends. 
does the number depend on time?

  	
.  Add CAMAC
    cd c:/dtake
    dt
    3 returns
  At menu,    
          type sta to start
          choose n (# events)
          choose s

     at the end of run:
           save data with:  DDUMP
           save histogramst with : HDUMP
     (choose a run not already in use, and use the same run number for the 
      data and histograms.)
    
     hit return twice

   at menu, go to dos.
    del wat.dat
    load your data
           ("dlo")
    look at data ("dis")
          1 for ctr 1 ADC
          2 for ctr 2 ADC
          3 for ctr 1 TDC
          4 for ctr 2 TDC

          (note above could be changed by the dtake setup, but this
        is how they are setup now.)

Here you can try to resolve the 1PE signal, pedestal, peak charge 
deposited,  # cts within a bin range;

How do light leaks affect your data?
 How well does the ctr perform wrt light leaks?
  (try measureing cts w. lights on,off, oreplastic blankets, lights on, 
off, etc.)


III.  Theory
1) How does the oscilloscope work?
     how does CRT work?
     discovery of e-?

2) how does the PMT work?

3) how does scintillator  work?

4) how does light guide work?

5) what does discriminator do?

6) how does coincidence gate work?

7) why invert signal from dynode?

8) why factor 2/3 difference from dynode than anode?