316
14.
ARTIFICIAL TRANSMUTATION
to the excitation energy EI.
In general, the reaction energy will
have a series Of values E,, where i = 0, 1, 2, 3, etc., corresponding
to the various excited states in the nucleus.
_
In the case of phosphorus 7, the values of E,— have been found to
be, EO = 0.0, El = —1.2, E2 = —2.6 and E3 = —4.6 Mev. In
the case of chlorine, EO = +0.1, El = ——2.5 and E2 : -—4.2 Mev.
The maximum reaction energy of + 0.1 MeV is equivalent to
(0.1 >< 106) (1.07 >< 10—9) = 0000107 mass units.
14—10.
Calculation
of
Nuclear
Masses—The
maximum
reaction energy may be determined experimentally. Then, equa-'
tion 14—10 may be used to compute one of the nuclear masses,
provided the others are known. For example, using mass units
from the mass spectrograph, or from other nuclear reactions, in the
equation
'
17Cl35 + ;;He4 = 18A38 + 1111 + EO
(14—12)
we have
,
349796 + 40037 = A38 + 10081 + 0.000107.
(14—13)
.
Thus 7, the isotopic weight of the argon thirty—eight isotope (A38) is
379753 mass units, correct to three decimal places (ie, + 00016).
14—11.
Discovery of Neutrons (n).——In 1930, Bothe and
Becker8 bombarded lithium, beryllium and boron with alpha rays
from polonium. By means of a point counter (D) as in gure 14-662,
.
they observed a radiation whose penetrating power, through an
absorber Â, was three times that of the hard gamma rays from
radium C
.
They assumed that the radiation was of the gamma ray
type because of its tremendous penetration. From the measured
.
.
absorption coefcients of the rays and the Klein-Nishina formula j
.
(x—ray chapter),the wave—length >\ was deduced. Then, from the
relation'that V = 12336/À, each photon of the postulated gamma
rays was found to have an energy of 15
'
_
The _Îoliots*
9 studied the new radiations with a deep ioniza—
tion chamber (D) capable of detecting heavy charged particles, as
.
.
in guré 14—65. They found that the rays from beryllium, which
'
could penetrate to great distances in heavy materials such as’
,
lead (at H), were readily absorbed by light materials such as paraf—
which contain many hydrogen
In the latter case many
* Dr. F. ]oliot and hisWife, Dr. Irene Curie. ]oliot,_daughter of Madame Curie.— -
‘
14.
ARTIFICIAL TRANSMUTATION
to the excitation energy EI.
In general, the reaction energy will
have a series Of values E,, where i = 0, 1, 2, 3, etc., corresponding
to the various excited states in the nucleus.
_
In the case of phosphorus 7, the values of E,— have been found to
be, EO = 0.0, El = —1.2, E2 = —2.6 and E3 = —4.6 Mev. In
the case of chlorine, EO = +0.1, El = ——2.5 and E2 : -—4.2 Mev.
The maximum reaction energy of + 0.1 MeV is equivalent to
(0.1 >< 106) (1.07 >< 10—9) = 0000107 mass units.
14—10.
Calculation
of
Nuclear
Masses—The
maximum
reaction energy may be determined experimentally. Then, equa-'
tion 14—10 may be used to compute one of the nuclear masses,
provided the others are known. For example, using mass units
from the mass spectrograph, or from other nuclear reactions, in the
equation
'
17Cl35 + ;;He4 = 18A38 + 1111 + EO
(14—12)
we have
,
349796 + 40037 = A38 + 10081 + 0.000107.
(14—13)
.
Thus 7, the isotopic weight of the argon thirty—eight isotope (A38) is
379753 mass units, correct to three decimal places (ie, + 00016).
14—11.
Discovery of Neutrons (n).——In 1930, Bothe and
Becker8 bombarded lithium, beryllium and boron with alpha rays
from polonium. By means of a point counter (D) as in gure 14-662,
.
they observed a radiation whose penetrating power, through an
absorber Â, was three times that of the hard gamma rays from
radium C
.
They assumed that the radiation was of the gamma ray
type because of its tremendous penetration. From the measured
.
.
absorption coefcients of the rays and the Klein-Nishina formula j
.
(x—ray chapter),the wave—length >\ was deduced. Then, from the
relation'that V = 12336/À, each photon of the postulated gamma
rays was found to have an energy of 15
'
_
The _Îoliots*
9 studied the new radiations with a deep ioniza—
tion chamber (D) capable of detecting heavy charged particles, as
.
.
in guré 14—65. They found that the rays from beryllium, which
'
could penetrate to great distances in heavy materials such as’
,
lead (at H), were readily absorbed by light materials such as paraf—
which contain many hydrogen
In the latter case many
* Dr. F. ]oliot and hisWife, Dr. Irene Curie. ]oliot,_daughter of Madame Curie.— -
‘