440
18.
THE DETECTION OF PARTICIQES
appearing in doubles or triples. The primary ionization at one
atmosphere is about 20 ion pairs per centimeter ofpath. Secondary
electrons are produced with ranges from 0.01 to 0.1 millimeter,
giving the dotted or beaded appearance
of the track.
There are
about 40 ion pairs, total per
centimeter of path. When electrons
with energies in excess of approximately 2 Mev pass through a
gas
at a pressure
of 2 or more atmospheres, they suffer an occa—
sional small angle deection.
The probability of such a deection
is directly proportional to the pressure.
Since, also, the number
of individual nuclear deections is invefsely proportional to the
square of the energy of the electrons, 200—300 Kev electron
tracks are found to have many curves.
The curves are gen—
erally gradual, since they are made up of many small deections
(which are more probably than large angle deections).
For elec—
trons
of energies of 100 Kev or less, the tortuous tracks are
heavier, are thick near the ends, and show more beads at the
points of curving.
Sharp bends are common.
X amd 'y
ionization is largely due to secondary
(photo—) electrons ejected by the primary rays.
Consequently,
the individual tracks, for the most part, have the bearded, tortuous
appearance of slow electron tracks.
The space ionized by the
secondary electrons is much larger than that occupied by
primary rays.
REFERENCES
1. C. E. WynmWilliams and F. A. B. Ward, Proc. Roy. Soc., A131, 391
1931
.
2. ].
(R. Dànning, Rev. Sci. Inst., 5, 387 (1934).
3. Rutherford, Ward and WynmWilliams, Proc. Roy. Soc., A129, 211
(1930 .
4. Street a)nd ]ohnson, ]r. Frank. Inst., 214, 155 (1932).
R. D. Evans, Rev. Sci. Inst., 5, 371 (1934).
5. C. E. Wynn—Williams, Proc. Roy. Soc., A136, 312 (1932).
6. W. G. Shepherd and R. O. Haxby, Rev. Sci. Inst., 7, 425 (1936).
6'. E.C.Stevenson and I. A. Getting, Rev. Sci. Inst., 8, 414 (1937).
H.
Lifschutz and ]. L. Lawson, Bul. Amer. Phys. Soc., 12, 7
(Nov. 1937).
7. H. Geiger and W. Müller, Phys. Zeit, 29, 839 (1928); 30, 489, 523
_
(1929); Naturwiss, 16, 617 (1928).
.
8. Geiger and Klemperer, Zeits. f. Physik, 36, 364 (1926); 49, 753 (1928).
9. Gingrich, Evans and Edgerton, Rev. Sci. Inst., 7, 450 (1936).
18.
THE DETECTION OF PARTICIQES
appearing in doubles or triples. The primary ionization at one
atmosphere is about 20 ion pairs per centimeter ofpath. Secondary
electrons are produced with ranges from 0.01 to 0.1 millimeter,
giving the dotted or beaded appearance
of the track.
There are
about 40 ion pairs, total per
centimeter of path. When electrons
with energies in excess of approximately 2 Mev pass through a
gas
at a pressure
of 2 or more atmospheres, they suffer an occa—
sional small angle deection.
The probability of such a deection
is directly proportional to the pressure.
Since, also, the number
of individual nuclear deections is invefsely proportional to the
square of the energy of the electrons, 200—300 Kev electron
tracks are found to have many curves.
The curves are gen—
erally gradual, since they are made up of many small deections
(which are more probably than large angle deections).
For elec—
trons
of energies of 100 Kev or less, the tortuous tracks are
heavier, are thick near the ends, and show more beads at the
points of curving.
Sharp bends are common.
X amd 'y
ionization is largely due to secondary
(photo—) electrons ejected by the primary rays.
Consequently,
the individual tracks, for the most part, have the bearded, tortuous
appearance of slow electron tracks.
The space ionized by the
secondary electrons is much larger than that occupied by
primary rays.
REFERENCES
1. C. E. WynmWilliams and F. A. B. Ward, Proc. Roy. Soc., A131, 391
1931
.
2. ].
(R. Dànning, Rev. Sci. Inst., 5, 387 (1934).
3. Rutherford, Ward and WynmWilliams, Proc. Roy. Soc., A129, 211
(1930 .
4. Street a)nd ]ohnson, ]r. Frank. Inst., 214, 155 (1932).
R. D. Evans, Rev. Sci. Inst., 5, 371 (1934).
5. C. E. Wynn—Williams, Proc. Roy. Soc., A136, 312 (1932).
6. W. G. Shepherd and R. O. Haxby, Rev. Sci. Inst., 7, 425 (1936).
6'. E.C.Stevenson and I. A. Getting, Rev. Sci. Inst., 8, 414 (1937).
H.
Lifschutz and ]. L. Lawson, Bul. Amer. Phys. Soc., 12, 7
(Nov. 1937).
7. H. Geiger and W. Müller, Phys. Zeit, 29, 839 (1928); 30, 489, 523
_
(1929); Naturwiss, 16, 617 (1928).
.
8. Geiger and Klemperer, Zeits. f. Physik, 36, 364 (1926); 49, 753 (1928).
9. Gingrich, Evans and Edgerton, Rev. Sci. Inst., 7, 450 (1936).