To help make the analysis discussion clear, please examine the
chamber structure diagram. It is a side-view
of the chamber, showing the
composition of lead, X-ray films, and emulsions, plus a rough diagram of
the three types of particles interacting in the chamber.
Pre-Analysis
When a chamber is flown and the films are all disassembled and developed,
there is first an intense session of initial mapping. A detailed illustrated
description of this process can be found here.
Energy Analysis
After a particle interacts in the chamber, it produces a cascade of
secondary particles (electrons and gamma rays)
whose number grows until it reaches a maximum, and then disperses. The energy
of the primary particle can be determined from this effect.
The cascade leaves two signatures: First, the individual electrons may be seen
(and counted) in the emulsion plates, if viewed under a microscope.
(A human being must manually count every track seen in a 100 micron circle,
on five or more layers, for this method to be effective.) Second,
the shower leaves a visible splotch in the X-ray films, the density of which
correlates with the number of photons. A photo-densitometer can measure
this semi-automatically.
Charge Analysis
The charge is determined by tracing the shower back to its initial interaction
in the chamber. Above the interaction, the primary particle is also visible
in the emulsion as a single track whose density is a function of chage.
Protons and Helium nuclei leave a signature where individual grains of ionized
silver may be counted. Heavier nuclei are too dense to observe this, however;
we must examine the behavior of either the width of the track, or more
commonly, the density of delta-rays (electrons in the emulsion that
are knocked out of their home silver atoms, producing a series of "whiskers"
off the main primary trail). Gamma rays and neutrons are uncharged, and
leave no trail at all; Thus, they are the hardest of all to identify.
The hardware and software that we use for this analysis is described
elsewhere.
E.O.