From naranjo Fri Nov  5 07:21:49 2004
Date: Fri, 5 Nov 2004 07:21:49 +0000
To: mjloughlin@natural.demon.co.uk, APX077@coventry.ac.uk,
        nigel.hawkes@npl.co.uk, colin.murray.01@bbc.co.uk
Cc: puherman@ritva.physics.ucla.edu, camara@physics.ucla.edu,
        shopkins@uiuc.edu
Subject: BBC 03 final analysis walkthrough
Reply-To: Brian Naranjo <naranjo@physics.ucla.edu>

Dudes,


BBC 03 FINAL ANALYSIS
=====================

A total of 3050 4-channel 1 GS/s 8 ms triggers were written
to disk.  A PZT "pill" microphone was used to trigger the digitizer.
There was some noise picked up by the pill causing spurious
triggers.  These bad triggers are removed in software, leaving
2262 valid triggers.  The timing in the 8 ms window is fixed
by discriminating, in software, on the leading edge of the shock wave.

  PAGE 1 - Sonoluminescence PMT
  -----------------------------
  - The SL PMT bias was set to -1050 V so that one photoelectron
    gave approximately 1 pC anode charge (see 'sl_single_pe.pdf')
  - The analysis threshold is 1 photoelectron.
  - There are 1683 counts between -3.0 ms and -0.5 ms during
    the 2262 triggers.  So, the dark rate was 300 Hz.  This
    was due to a bad PMT and was remedied in subsequent runs.
    Subtracting the dark counts, we get about 2 light pulses
    per cavitation.
  - The first collapse's light is around -40 us to -30 us.
    Seth should have provided Carlos's nice data showing
    the sequence of events: cavitation, first collapse, and
    then arrival of the shock wave.

  PAGE 2 - Neutron Detector
  -------------------------
  - Apart from the peaks at -60 us, both the proton recoil and
    electron recoil distributions are statistically flat over
    the 8 ms window.
  - There are 20 neutrons in the window [-100 us, 100 us].
    Just to be sure, these events will be examined in detail
    later in the analysis.  We believe the neutrons at -60 us
    are due to the seed neutron scattering.  After seeding,
    it takes another 20 us for the first collapse (as seen on
    the previous page at -40 us).  Then the shock propagates
    at ~1200 m/s, reaching the pill 40 us later.
  - There are also gammas at around -60 us.  These are due
    to the 4.4 MeV gamma emitted simultaneously with every
    AmBe neutron.
 
  PAGE 3 - Coincident Hits
  ------------------------
  All SL events within +/- 250 ns of a neutron detector event are plotted.

  - Trigger 106 is an interesting event.  It occurs at -48 us,
    near the end of the seed peak.  My guess is that both the
    4.4 MeV gamma and AmBe neutron scattered in the deuterated
    acetone.  The 4.4 MeV gamma scatters an electron which
    gave Cerenkov light, and the AmBe neutron seeded the
    bubble.  The scattered gamma then scattered again in
    the neutron detector.
   - Trigger 166 is a random coincidence.
   - Trigger 1145 is an event where a high energy cosmic,
     probably a muon, passed through both the neutron detector and
     the deuterated acetone.  Passing through the neutron detector,
     it looks like a high energy electron recoil.  Passing through
     the deuterated acetone, it gives off a little Cerenkov light.
     We can even say which direction the cosmic was going!
     Look at my earlier timing calibration between ND 2 and SL 1,
     the neutron signal lags the SL signal by (10.1 +/ 0.9) ns.
     In this case, the neutron signal only lags by 8 ns.  Since
     the neutron detector and scintillator are separated by ~1 ns
     on average, we conclude that the muon passed through the
     liquid scintillator before the deuterated acetone.

  Seed Events
  -----------
  For your enjoyment, all 20 neutron events in the range [-100 us, 100 us]
  are plotted in the same range with all four channels.

   - The same leading edge fit technique is used to find the leading edge
     of the shock.  Curiously, the shocks are often preceded by up
     to 10 us of small amplitude pre-shock.  This is probably due
     to the shock propagating in the quartz resonator which has
     a large speed of sound v = 5500 m/s. 
   - Event 2528 featured a seed neutron scattering from one neutron
     detector cell to next.  It hit channel two first.
   - We were all hoping we would see at least one event containing
     all three signposts: the scattered neutron seed, a first
     collapse photon, and the shock.  Unfortunately, the light
     in the zero pressure system is not bright enough to guarantee
     light with every collapse.


If you have any questions, call me on my cell (714) 457-9249.

Brian
