326
14.
ARTIFICIAL TRANSMUTATION
incident particle of denite energy,
and a known ejected particle.
If several reactions are possible, with a given target and incident
.
particle, there will be a corresponding set of a ’s. If the energy of
the incident particle is varied, a Will also vary; the curves of a vs. E
have the same shape as the excitation curves, for thin targets. In
a resonance region, Y, 0 and the probability of the transmutation '
are comparatively large.
'
Theoretical equations have been developed for (7. The 0 225. E
theoretical relationship for charged particles is known as the
Gamow function. Experimental and theoretical values are in good
agreement and range from zero to 10—24 cm.2 in the usual cases. In
certain slow-neutron reactions, values of 0 as great as 10“20 have
been observed.
14—17.
Simple Capture of Protons.—Gamma rays have been
observed when a thin target of lithium was bombarded With
protons.
It has been shown23 that the number of gamma rays
varies with proton energy, as shown in gure 14—13. The first
*
sharp peak occurs at 440 Kev
11 Kev).
The reaction is
_
3Ll7 + 1H1
41368
4B68 + 7.
(14—21)
30
There are,
course, other cases of
the simple capture of protons. The
_
'
.
MODERATELY
react1on
,
ÎH/GK
à
”RG”
6612 + l
7N13*
7N13 + + :
‘Ë
20
7N13* _…c18 + …;
(14—22)
’
Î
.
has been well established24 by obser—
‘
,
ë’
_
vation of the gamma rays and the
g '
/0
duction of the active nitrogen. Two
È
,
‘
resonances
are
noted; for protons
of
.
-
energ1es 0.40 and 0.48 Mev.
In gen— .
_
,
eral, this type of transmutation has.
400
500
1200
/000
2000
a
lOW probability ELS
With
F
_
—
""?VÛL75
_
those in which a particle is ejected. …
‘
IG' 14_13'
Yleld fromammple In all cases the phenomenon of reso,
-
capture process.
_
__
’
_
,
»
,_
_
,
nance is promment.
:
-
,
14—18. Multiple _Reactions.—The alpha particles .ejected
,
‘ombor0n, bombarded by protons, are found to have an unusual
:
,
'
is- (1) a mono-energetic group of
.
;
_
'
_
)
—