Although one can build arrays of scintillation counters that act like ``pixels'' in computer graphics and can tell where particles go within an uncertainty of the size of the individual counters, this is very expensive and not usually very precise. Moreover, it was not how the business of ``tracking'' elementary particles got started.
The earliest ``position-sensitive detectors'' took advantage of the tendency of liquid droplets to form (or ``nucleate'') on ions when a gas (like air) is ``supersaturated'' with a vapour (like water or alcohol) that would like to precipitate but can't quite make up its mind where to start. The result, once the process is finished, is a cloud of liquid droplets, hence the name `` cloud chamber.'' But this final state is not very useful. It is the situation just after a fast ionizing particle passes through the saturated gas that is interesting - the left-behind ions nucleate a trail of liquid droplets like a string of beads, and one can see (and/or take a picture of) that trail at that moment, to ``see the track'' of the particle. If it is passing through a magnetic field, the curvature of the track reveals its momentum and the density of the track reveals its charge and its speed, from which one learns its mass and just about everything about it that can be measured directly. This device was used for many of the early cosmic ray experiments.
The trouble with cloud chambers is that they don't have very fine resolution and the droplets start falling as soon as they form. Moreover, even a saturated gas has a rather low density, so if one is looking for interactions of a beam particle with other nuclei the events are spread out over too large a volume to photograph efficiently. Another method still used today is to place a stack of photographic emulsions in the path of the beam and to examine the resulting tracks of silver particles created by the ionizing particle. The problem with this technique is that the emulsion is not reusable --- one ``takes an exposure'' and then the emulsions must be dissected and painstakingly examined with a microscope. Too much work. What was really needed was a sort of ``high density cloud chamber'' that ``healed'' soon after each track had been photographed.
The apocryphal story is that a 
experimenter sat staring
glumly into his beer glass one night after wishing for such a
device, and noticed that the bubbles always seemed to form in
the same places. He sprinkled in a few grains of salt and,
sure enough, the bubbles formed on the salt grains.
``Eureka!'' he cried, leaping up, ``the bubbles form on ions!''
And off he went to build the first bubble chamber.
The idea of the bubble chamber is that a liquid (usually
liquid hydrogen) can be abruptly decompressed, causing it
to ``want'' to boil, but (like the supersaturated vapour) it
can't make up its mind where to start first.
If the decompression is done just as ionizing particles
pass through the liquid, the ions in their tracks will
nucleate the first bubbles of vapour and a clear, sharp
track can be seen and photographed; then the liquid is
quickly recompressed, the bubbles go away, and the chamber
is ready for another ``event.''
Such liquid hydrogen bubble chambers are still in use today, but they had their heyday back in the 1950's and 1960's when higher energy accelerators introduced particle physicists to the ``hadron zoo'' of strongly-interacting particles. The most gratifying aspect of a bubble chamber picture is that you can make a big copy of it and put it on your wall, where anyone can point to the different tracks and say, ``There goes a pion,'' or, ``This short gap here is a Lambda.'' The picture appeals to the all-important Visual Cortex, leading to such familiar phrases as, ``Seeing is believing,'' and, ``A picture is worth a thousand words.'' [I won't attack these comforting myths this time; I like bubble chamber pictures too!]
The trouble came when experimenters set out to measure
the curvatures and densities of millions of tracks in bubble chamber
pictures. This involves more than just patience; in the 1960's
an army of ``scanners'' was hired by the big 
labs to filter
hundreds of thousands of bubble chamber pictures looking for
certain topological configurations of tracks that were of interest
to the experimenter; a lexicon of ``vees'' and ``three-prongs''
was built up and eventually these people could recognize events
containing different types of elementary particles more efficiently
than any physicist --- for, almost without exception, the scanners
were nonscientists selected for their rare talents of patience
and pattern recognition. It was a fascinating sociological
phenonenon, but it cost enormous sums for the salaries of these
people and physicists would always rather buy fancy equipment
than create mere jobs. So, as electronics and computers grew
in power and shrank in price, it was inevitable that the
experiments pressing the limits of 
technology would
seek an ``electronic bubble chamber'' that could be read out,
analyzed and tabulated all by computers.
The result was the wire chamber, which again uses the ionization caused by charged particles but this time detects the ion's charges directly with sensitive electronics. There are many versions of this technology, but almost all involve thousands of tiny wires strung through a target volume at extremely precise positions and maintained at high voltage so that any ions formed will drift toward one or more of the wires and form a pulse that can be read out at the ends of the wire and interpreted. Such devices can ``track'' particles through huge volumes to a fraction of a mm and can analyze hundreds or even thousands of events per second, with one ``event'' containing dozens or even hundreds of particle tracks.
Today's large 
experiments all involve scintillation counters,
wire chamber arrays and other components, each especially sensistive
to one or another type of particles, and require on-line computers
that must be built specially to handle the enormous flow of
information;
an ubiquitous feature of really high energy particle physics
is that there are enormous numbers of particles in the ``final state''
after two extremely high energy projectiles collide head-on.
It is easy to see why this is: the more energy you have, the more
mass you can create. It also follows that the heavier the particle,
the more ways it has to decay, so the heaviest particles
should have the shortest lifetimes. When this rule is not
obeyed, we have cause to get suspicious.