12—6.
IONIZATION BY ALPHA PARTICLES
271
.
'
.
where the subscript (a) refers to the standard. Average values of:
.
will be found in table 6.
Bragg and Kleeman have shown that
the atomic stopping power is approximately proportionaltothè
,
square
root of the atomic weight of the substance, This has been
justied by theoretical work, particularly by
Relative
molecular stopping powers may be obtained by the addition of the
_
separate values of 5 of the constituent atoms.
12—6.
Ionization by Alpha Particles.—Alpha particles are very
'
good ionizers; The ionization is so intense along a straightpath
that, in an expansion chamber, the individual water drops coalesce
_
to give a straight line, as in gure 12—3. Ordinarily the alpha
particle is able to plunge through the outer electrons of an atom,
losing energy and speed as it ionizes or excites the atom, without
suffering any deection itself. But,
it passes sui,
ciently close to a nucleus to be deviated sharply from the straight
'
path and the drop track shows a sharp bend.
'
The total number of ion pairs which can be produced by a
alpha particle in dry air at 15°“C. and 76 centimeters pressure;
i.e.,the total ionizatz‘on (), is directly proportional to the
energy
with which the particles
leave the source.
Thus,
=
1.80 '>< 1010 é‘ô.
(12—12)
fis given as the saturation iohizatibn current divided bythe
,
'
total number of particles emitted each second and (% is-measured
'
by observations on the deeCtion of
and
magnetic elds. As an example, the long
_
from radium C’ (R
= 6.92 cm.,—
.Mev.)
‘
can produce a total of_2.20 X 105
;“ Values
_
_
1.2 >< 105 to 25 X 105 f01"
subStànçes.
“(See table 4, at {the end
of the total
'
number of ion pairs
" 109neon130arg0n145alfl
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NatallofthewnsrmduœdbYanalPhaPartldearedueto
.
_
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"
IONIZATION BY ALPHA PARTICLES
271
.
'
.
where the subscript (a) refers to the standard. Average values of:
.
will be found in table 6.
Bragg and Kleeman have shown that
the atomic stopping power is approximately proportionaltothè
,
square
root of the atomic weight of the substance, This has been
justied by theoretical work, particularly by
Relative
molecular stopping powers may be obtained by the addition of the
_
separate values of 5 of the constituent atoms.
12—6.
Ionization by Alpha Particles.—Alpha particles are very
'
good ionizers; The ionization is so intense along a straightpath
that, in an expansion chamber, the individual water drops coalesce
_
to give a straight line, as in gure 12—3. Ordinarily the alpha
particle is able to plunge through the outer electrons of an atom,
losing energy and speed as it ionizes or excites the atom, without
suffering any deection itself. But,
it passes sui,
ciently close to a nucleus to be deviated sharply from the straight
'
path and the drop track shows a sharp bend.
'
The total number of ion pairs which can be produced by a
alpha particle in dry air at 15°“C. and 76 centimeters pressure;
i.e.,the total ionizatz‘on (), is directly proportional to the
energy
with which the particles
leave the source.
Thus,
=
1.80 '>< 1010 é‘ô.
(12—12)
fis given as the saturation iohizatibn current divided bythe
,
'
total number of particles emitted each second and (% is-measured
'
by observations on the deeCtion of
and
magnetic elds. As an example, the long
_
from radium C’ (R
= 6.92 cm.,—
.Mev.)
‘
can produce a total of_2.20 X 105
;“ Values
_
_
1.2 >< 105 to 25 X 105 f01"
subStànçes.
“(See table 4, at {the end
of the total
'
number of ion pairs
" 109neon130arg0n145alfl
=r“
NatallofthewnsrmduœdbYanalPhaPartldearedueto
.
_
,
ltsd1rectactwn@nthegasatomsÏfdf0Ptfa°ksareexammed
f
"