/
l
'
310
14.
ARTIFICIAL TRANSMUTATION
chamber and it was further assumed that the long thin trackB
was due to a proton, as in the H particle work described in the
-
preceding sections.
14—4.
Conservation of Momentum.—The three tracks (gure
lil—3) were found to lie in the same plane. Thus, the momentum
before the collision was equal to that after the transmutation. To
.
test this, the angle 0 between the proton track and the forward
difection of the alpha track, and the corresponding angle @ for the
residual nucleus were determined from the stereoscopic photo—
graphs.
(q5 is negative if 6 is positive). In the forward direction,
we have
'
maya = m,v,… cos @ + m,,vP cos 0
(14—1)
and in the normal direction
‘
O = m,vr sin qä + mpvz, sin 6,
(lé—2)
where
mr and m,, are the respective masses of the alpha particle,
residual nucleus and proton while U… 01 and 010 are their velocities.
,
The masses of the alpha particle and of the proton were known and
,
the velocity of the alpha particle could be deduced from the
distance which it had traveled from the source to the collision (see
'
gure 12—9). With less certainty, the velocity of the proton was
ï
calculated from the range of track B
.
…,
The momentum m,w of the .
residual nucleus was then calculated from equation 14—2 and found —
to satisfy equation, 14—1. Thus, momentum was conserved during
_
‘;“;
:
the transmutation.
,
14—5.
The Reaction Scheme.—The identity of the particle
causing track C (gure 14—3) was deduéed from the law of conser—
‘
.
v—atidn’ of electric charge. Thus, the nitrogen nucleus of charge7
,
(= Z, the atomic number) added to the alpha particle of
]
nucleus of charge 9 from which a
charge11se5ected to leave a‘residual nucleus of charge 8,1f3,an
fatî
who1”ejenam5ers tothewe1ghts
7N14+2He4—>9F18—>80” +1H1<14-3>
_…L_… uw
\
u"
___
;
..
*……_________………_