14-7. RESONANCE PENETRATION
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313
of protons (1Hl) were emitted when a thick target of aluminum
(13Al27) was bombarded with alpha particles (2He4). The use of
a
means that alpha particles of all energies from the
.
maximum (5.3 MeV, for polonium) down to zero are in
due to
their retardation as they enter the aluminum. InasInuCh as the
,
protons did not leave the nuclei (at a given angle of emission)
_
with a continuous distribution of ener‘
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gies similar to that of the incident
—,
particle, there must be certain favored
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—
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energy groups of the incident particles % -
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which cause copious emission of pro— @"
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tons; i-.e., there is a resonance p/ze- ?:
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nommon between the protons and the 2
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.
_
alpha particles. This is brought ont %’
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clearly in gure 14—5. This is called
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the excitation curve of the transmu:
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5
5
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tation.
The yield 13 the number of…
OF ALPHA pAR7‘/ÇLES
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protons per alpha particle and the
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MLsu_
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peaks show the resonance excitation FIG-_l4—5_- ResP}îäCê PhÇn0menaof the protons for alpha particles,of
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denite energies. The curve was.obtair_red_._6 with a thin aluminum
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target bombardedbymono-energet1calphapart1cles The various
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'ènergy values of the alphaparücles
»by sl°Wîng
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own fast alpha =P@€ËiÇlÊS Withthmf°sor …Wäthia laY@f î'°f
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As & matteroffactalphapaft1desofsu1tableîçïgy
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thé emission; notonlyofonegrwpbutofseV6raîgmups Of Pf0t0ns
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s1multaneouslyAnexamplewhenanalummum
was
1447ResonancePeeaüon—Instudles0fthescattengüfï»
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