282
12.
ALPHA, BETA AND GAMMA RAYS
in direction.
Furthermore, several beta rays with different veloci'.
ties leave any one substance so that a homogeneous beam cannot
be had without the use of magnetic or electric elds and consequent_
diminution in intensity.
When a homogeneous beam of beta
'
particles passes through a layer of matter, it emerges with a Wide
distribution of velocities.
The range of âez‘a particles is dened as in the case of alpha
particles. Values for aluminum and air are given in table 11.
Average values of the specic ionization by electrons will be
found in table11.
Beta particles of energies between 1.36 and
0.081 Mev(Hr = 6000 to 1000) produce from 45 to 200 ion pairs
per centimeter in air at 76 centimeters and 15° C.,* the specic ,
'
ionization varying inversely as the square of the velocity.
energy required to produce each ion pair in air is about 35 volts,
the same as for alpha particles. Thus, the slower electrons lose
'
energy by the process
of ejection of photo-electrons from the gas
,
atoms.
FaSter electrons than those just mentioned lose energy not
only by the photo—ionization process but also by a radiation process. …
The latter consists of the radiation of energy when the particles
suddenly change their velocity in an atomic impact, as in the
production of the continuous X-ray spectrum by the abrupt
impact of electrons on the
of an X—ray tube.
For the faster
electrons, the stopping power is proportional to the logar1thmof
their energy;
,
For exceedingly fast electrons,
> 13 7mc2), the pair produc—
tion process discussed in chapter 14 most probably occurs.
_
The drop tracks produced by gamma ray: (see gure 12—18)
.
are similar to those of X-rays.
The ion‘ization is much less, ab0Ut‘
._
ône-hundredth of that produced by the beta rays from the same
source and the ions are more diHusely spread throughout the gas
It is largely a
result of the secondary electrons which the. gamma
mY$ ;eject from the atoms»
-
',
,
The absorption of gamma rays in matter is the result ofthree
_
‘
;p;ïocessesîwhOSerelatiîzeimportance depends on the energy 1neaCh
_
Ph9ËOHÇ andthe atomic weight of the absorber. Thepredomlnant
_
“f
gamma rays and for heavœrelements
_- ç
the beta particles: themselves
12.
ALPHA, BETA AND GAMMA RAYS
in direction.
Furthermore, several beta rays with different veloci'.
ties leave any one substance so that a homogeneous beam cannot
be had without the use of magnetic or electric elds and consequent_
diminution in intensity.
When a homogeneous beam of beta
'
particles passes through a layer of matter, it emerges with a Wide
distribution of velocities.
The range of âez‘a particles is dened as in the case of alpha
particles. Values for aluminum and air are given in table 11.
Average values of the specic ionization by electrons will be
found in table11.
Beta particles of energies between 1.36 and
0.081 Mev(Hr = 6000 to 1000) produce from 45 to 200 ion pairs
per centimeter in air at 76 centimeters and 15° C.,* the specic ,
'
ionization varying inversely as the square of the velocity.
energy required to produce each ion pair in air is about 35 volts,
the same as for alpha particles. Thus, the slower electrons lose
'
energy by the process
of ejection of photo-electrons from the gas
,
atoms.
FaSter electrons than those just mentioned lose energy not
only by the photo—ionization process but also by a radiation process. …
The latter consists of the radiation of energy when the particles
suddenly change their velocity in an atomic impact, as in the
production of the continuous X-ray spectrum by the abrupt
impact of electrons on the
of an X—ray tube.
For the faster
electrons, the stopping power is proportional to the logar1thmof
their energy;
,
For exceedingly fast electrons,
> 13 7mc2), the pair produc—
tion process discussed in chapter 14 most probably occurs.
_
The drop tracks produced by gamma ray: (see gure 12—18)
.
are similar to those of X-rays.
The ion‘ization is much less, ab0Ut‘
._
ône-hundredth of that produced by the beta rays from the same
source and the ions are more diHusely spread throughout the gas
It is largely a
result of the secondary electrons which the. gamma
mY$ ;eject from the atoms»
-
',
,
The absorption of gamma rays in matter is the result ofthree
_
‘
;p;ïocessesîwhOSerelatiîzeimportance depends on the energy 1neaCh
_
Ph9ËOHÇ andthe atomic weight of the absorber. Thepredomlnant
_
“f
gamma rays and for heavœrelements
_- ç
the beta particles: themselves