,
'
,
11—3.
UNITS OF RADIOACTIVITY
_
241
'
be shown by allowing them to pass through a magnetic eld. — In & '
_
gure 11—1, the eld is perpendicular to the papefand the active
5
‘
'
'
is located at x.
The deection of the alpha ray is
'
_
eiaggerated in comparison with that of the beta ray. From
'
direction of the deectionsand of the eld it is found that the
' _ — alpha rays are positively charged and the beta rays are negatively
_
charged whereas the gamma rays are uncharged.
_
It Will be shown in the next chapter that the alpha rays are
up of a stream of alpha particles each-of which has a positive
.
'ch'arge, numerically equal to twice that of the electron, andan "
'
atomic weight nearly equal to'4. It will also be shown that beta
'
ï
'
particles are high speed electrons and that gamma rays are elec—
radiations similar in nature to X—rays.
'
"
_
L.Ï,'
11—3,
Units "of Radioactivity. 1—In order to specifyf the
'
amount of a substance at hand, one may state its mass. Thèùnit,’
,
'
for radioactive substances, consists of a certain number of grams of
_
called radium emanation or radon.
This mass unit, called
"
"
the curie, after the Curies, was dened by the Radiology Congress
'
in Brussels in_ 1910 as
“
The amount of emanation in equilibrium -
…:With bne gram of pure r‘adium.”
It has a mass
of 6.51 X 10“6
“,,.grarns and occupies 0.66 cubic nllimeters at 76 centimeters
_
0° C.
The international radium standardconsists
of the ràdon in equilibrium with 21.99 milligrams ofspecially puri‘
" ed radium chloride prepared by Madame Cü'r'ie and preservedat
'
-
'
the Bureau Internationale des.Poids et Measures at Sèvres hear
'
Paris, France. Secondary standards havebeen prepared
and
"
.
tributed throughout the various countries.
_
"
'
When alpha, beta or gamma rays are emitted_.from the atoms
of “
'
a radioactive substance, it is'obviou‘s
_atôms;
must
_a .change.' They' are said to
""
therefore, … ;
.
=
,
possible to,specify the amount
of a radioactive
_»_.
.
'
of the number of atoms Which disintegrate'eacfhf_sec'orïd; called
__
.' activity, A substanœ has an
c_ur_.i€ when
371 X 1010: “
__
atoms disi‘ntegrate each second;
—'Mâz‘u7n_.- “A'unit Ïon_e' 'thousand,times
'
more oftèn udnpt
'
5
..
=
"
.
"
' - The Mache 'ùnit’of—'_radon
Of .'
1_Q' _—3
fe.s.u. When all the radiation
_
_.
'
'
,
11—3.
UNITS OF RADIOACTIVITY
_
241
'
be shown by allowing them to pass through a magnetic eld. — In & '
_
gure 11—1, the eld is perpendicular to the papefand the active
5
‘
'
'
is located at x.
The deection of the alpha ray is
'
_
eiaggerated in comparison with that of the beta ray. From
'
direction of the deectionsand of the eld it is found that the
' _ — alpha rays are positively charged and the beta rays are negatively
_
charged whereas the gamma rays are uncharged.
_
It Will be shown in the next chapter that the alpha rays are
up of a stream of alpha particles each-of which has a positive
.
'ch'arge, numerically equal to twice that of the electron, andan "
'
atomic weight nearly equal to'4. It will also be shown that beta
'
ï
'
particles are high speed electrons and that gamma rays are elec—
radiations similar in nature to X—rays.
'
"
_
L.Ï,'
11—3,
Units "of Radioactivity. 1—In order to specifyf the
'
amount of a substance at hand, one may state its mass. Thèùnit,’
,
'
for radioactive substances, consists of a certain number of grams of
_
called radium emanation or radon.
This mass unit, called
"
"
the curie, after the Curies, was dened by the Radiology Congress
'
in Brussels in_ 1910 as
“
The amount of emanation in equilibrium -
…:With bne gram of pure r‘adium.”
It has a mass
of 6.51 X 10“6
“,,.grarns and occupies 0.66 cubic nllimeters at 76 centimeters
_
0° C.
The international radium standardconsists
of the ràdon in equilibrium with 21.99 milligrams ofspecially puri‘
" ed radium chloride prepared by Madame Cü'r'ie and preservedat
'
-
'
the Bureau Internationale des.Poids et Measures at Sèvres hear
'
Paris, France. Secondary standards havebeen prepared
and
"
.
tributed throughout the various countries.
_
"
'
When alpha, beta or gamma rays are emitted_.from the atoms
of “
'
a radioactive substance, it is'obviou‘s
_atôms;
must
_a .change.' They' are said to
""
therefore, … ;
.
=
,
possible to,specify the amount
of a radioactive
_»_.
.
'
of the number of atoms Which disintegrate'eacfhf_sec'orïd; called
__
.' activity, A substanœ has an
c_ur_.i€ when
371 X 1010: “
__
atoms disi‘ntegrate each second;
—'Mâz‘u7n_.- “A'unit Ïon_e' 'thousand,times
'
more oftèn udnpt
'
5
..
=
"
.
"
' - The Mache 'ùnit’of—'_radon
Of .'
1_Q' _—3
fe.s.u. When all the radiation
_
_.
'