336
14.
ARTIFICIAL TRANSMUTATION
It has been shown, both experimentally and theoretically, that
the effective-cross-section 0 for the capture of slow neutrons is inversely proportional to the velocity @ of the neutrons; i.e.,
'
0' =
k/v,
(14—44)
where k is the constant of proportionality. This law is valid except
in the resonance regions.
.
,
14—24.
Uranium and Thorium Bombarded by Neutrons.—
Fermi found that when uranium was bombarded with neutrons,
radio—active nuclei weie produced. Several half—lives were observed
and chemical tests proved that elements had been produced
with atomic numbers greater than 92.
These are called tmm—
_
uranic elements.
Thus,
—
92U + on -—> 92U* —> 93Eka Re* —à 94Eka Os* —> etc., (14—45)
with the emission of negative electrons (beta rays) from each active
substance (*). The half—lives are 10", 2.2’, 59’, and 66 hours, suc- ’
cessively, in this series. Other series With uranium have also been
identied.34
When thorium is bombarded with neutrons, a new radio-active
family is produced35. The actinium series is characterized by
elements whose mass numbers are equal to 472 + 3, where 71 is an
integer: the uranium-radium series by 471 + 2 and the thorium
series by 471. The new family has mass numbers equal to 472 + 1.
14—25.
Theories of the Nucleus.—See sections 10—11 and
10—12.
The size of the nucleus (distance where normal scattering
no longer holds) proves
to be consistent With the dimension de—
.
'
rived from quantum mechanical computation of the uncertainty
position of the components of the nucleus. The assumption of
_
electrons as components would lead to an entirely different dimen- '
,
_
sion.
Hence, electrons do not exist in nuclei; they are created at
’
the moment of their emission and are accompanied by the transi—
_
tion of*a proton into a neutron or Vice versa, according to Whether
_
,
a positron or a negative electron is emitted.
-
-
Ÿ'
,
Because of the c6mparatively wide separation of the extra- Ï :
"
'
nuclear electrons, processes which deal only with the outer parts
of the atom may be treated With Simple collision considerations,
__
,
-
between free individual particles;.and the outer part itself may
be“
,
14.
ARTIFICIAL TRANSMUTATION
It has been shown, both experimentally and theoretically, that
the effective-cross-section 0 for the capture of slow neutrons is inversely proportional to the velocity @ of the neutrons; i.e.,
'
0' =
k/v,
(14—44)
where k is the constant of proportionality. This law is valid except
in the resonance regions.
.
,
14—24.
Uranium and Thorium Bombarded by Neutrons.—
Fermi found that when uranium was bombarded with neutrons,
radio—active nuclei weie produced. Several half—lives were observed
and chemical tests proved that elements had been produced
with atomic numbers greater than 92.
These are called tmm—
_
uranic elements.
Thus,
—
92U + on -—> 92U* —> 93Eka Re* —à 94Eka Os* —> etc., (14—45)
with the emission of negative electrons (beta rays) from each active
substance (*). The half—lives are 10", 2.2’, 59’, and 66 hours, suc- ’
cessively, in this series. Other series With uranium have also been
identied.34
When thorium is bombarded with neutrons, a new radio-active
family is produced35. The actinium series is characterized by
elements whose mass numbers are equal to 472 + 3, where 71 is an
integer: the uranium-radium series by 471 + 2 and the thorium
series by 471. The new family has mass numbers equal to 472 + 1.
14—25.
Theories of the Nucleus.—See sections 10—11 and
10—12.
The size of the nucleus (distance where normal scattering
no longer holds) proves
to be consistent With the dimension de—
.
'
rived from quantum mechanical computation of the uncertainty
position of the components of the nucleus. The assumption of
_
electrons as components would lead to an entirely different dimen- '
,
_
sion.
Hence, electrons do not exist in nuclei; they are created at
’
the moment of their emission and are accompanied by the transi—
_
tion of*a proton into a neutron or Vice versa, according to Whether
_
,
a positron or a negative electron is emitted.
-
-
Ÿ'
,
Because of the c6mparatively wide separation of the extra- Ï :
"
'
nuclear electrons, processes which deal only with the outer parts
of the atom may be treated With Simple collision considerations,
__
,
-
between free individual particles;.and the outer part itself may
be“
,