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290 Radiochemistry and Nuclear Chemistry

A ~+p'~'K~ ++x O
H ~.~ L ~x++p-m,..n++p
E K'+ p'P'A ~176
F I~n-+ p
B K~ "=" 1r ~-
C h" ll++v
D t~. e + +v+~
DII*C /

if§

FIG. 10.4. The reaction products of an annihilated antiproton as seen in the CERH liquid
hydrogen bubble chamber. (Annual report 1961, CERN).

10.5. Formation and properties of some elementary particles

The track formed by a moving particle in the magnetic field of a bubble chamber is
characterized by its width, length and curvature. From a kinematic analyses of the tracks
it is possible to determine the mass and charge of the particles involved. Further, as seen
at points A-B and E-F in Figure 10.4, the interruption of a track can indicate an
uncharged particle, as they do not form visible tracks. From a knowledge of the tracks
formed by known particles, "strange tracks" can be analyzed to identify new particles in
bubble chamber pictures and to assign their properties. All these properties have to be
quantize~, so new quantum states have been introduced, like baryon number, statistics,
symmetry, parity, hypercharge, isospin, strangeness, color, etc. in addition to spin. It is
found that many of the particles observed are sensitive to only one or two of the forces of
nature (w which serves as an additional aid in their classification. Nevertheless, the
array of properties assigned to the hundreds of "elementary particles" which have been
discovered resembles the situation when 40 radioelements were reported between uranium
and lead, as described in chapter 1.
Before we proceed to the order which has evolved from this picture we must describe
some of the concepts used to define these particles. It has been practical to divide the
particles according to their masses: (i) baryons are the "heavy" ones (protons, neutrons,