10—6.
VELOCÏTY SELECTION
229
"
77.4, 11.5 and 11.1, respectively. The mean atomic weight, when
g
24, 25 and 26 are taken in these proportions is 24.34. This is in
good agreement with the chemical atomic
of maghesium,
24.32.
It is of interest that the isotopes of a—given element are so
mixed together in nature that samples from widely different
regions of the earth have the same atomic weight.
10—6.
Velocity Seiection.8—Positive rays, collimated by the
slits & and S2 of gure 10—7, pass through a velocity selector S'
where they are subjected to the action… of electric and magnetic
elds arranged perpendicularlyto each other as in the case of the
'
beta rays in gure 2—9. The ions which can then pass through the
slit
83
are
all
of nearly
'
the same velocity. Actually.
_
_
“_
.
=
there is an exceedingly small s' ww
…
‘
.
range of velocities.
The ions
.
'
'
are deected by a second mag.
netic— eld, also perpendicular
s
_
_
-
to the paper, and come to a
,
.'
focus
on
the
photographie 33@
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plate P.
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10—7. Simultaneous Veloc—
_
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ity and Direction Focus.»—Jn
,
…
order to increase stillmore
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resolving p0Wer. and hencethe
.
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accuracy in- mass
.
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tions, the sharpnessoftheBambndge’searlymass spectrograph.
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images on…,chephüîogfaph1C
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