ANGLE DEPENDENT ENERGY LOSSES OF AMORPHOUS MATERIALSFOR MEV PROTONS
N. Sakamoto, N. Shiorni and R. Ishiwari
Department of Physics, Nara Women's University, Nara
Abstract
Thin foils of Be, Al, Ag, Mylar and Cellophane were bombarded
Energyby a very sharply collimated proton beam at 6.9 MeV.
losses and multiple scattering yield have been measured as a funcAngular distribution of emergence angles between 0° and l. 7°.
tions of multiple scattered protons were well reproduced byRelative energy losses, ~E(6)/~E(O), have
Moliere's theory.
been found to increase by l-4% with increase of emergence angles.
These results constitute the first evidence that measurements ofan average quantity such as stopping power may yield information
about the dependence of energy loss on the impact parameter of a
proton relative to a lattice atom.
It is well established that particles incident at small angles to atomic rows and planes in single crystals exhibit anomalThis is a channeling effect on energy
ous energy loss rates 1 ) .
Energy losses of channeled particles are smaller thanloss.
those of particles which traverse in random direction because
channeled particles are kept away from atoms and go through a
In usual stopping power measregion of lower electron density.
urement polycrystaline or amorphous thin foils· are used instead of
In this case we can select a particle trajecsingle crystals.
tory and an average impact parameter of a particle relative to alattice atom by defining very sharply the emergence angle of a
We have studyed the dependence of energy loss on theparticle.
Results
emergence angle of a proton with several solid targets.
show a small but significant connection between energy loss andangular deflection of protons that have passed through thin solidfoils.
The energy losses of 6.9 MeV protons in Be, Al, Ag, Mylar andCellophane foils have been measured at six or seven emergence angTarget thicknesses were from 4.4 toles between 0° and 1.7°.
6.5 rng/crn 2 and energy losses of protons in these targets were fromIncident proton beam was collimated very sharp130 to 350 keV.
ly by a double slit system; a maxrnurn angular divergence was 0.048°A silicon surface barrier detector with 0.7 rnrn
at full width.
diameter slit was mounted 171 ern apart from the target and wasmovable perpendicularly to the beam direction in a range of 5 ern.
Experimental results of Be foil are shown in figure 1 as a
In the upper half, angular distribution of
typical example.
Predictions ofmultiple scattered protons is presented.
Moliere's theory are given in a solid curve and an excellent agreeIn thement between the experiment and the theory is obtained.
lower half, relative energy losses, 6E(6)/6E(O), are shown as a
As seen in the figure
function of deflection angle of protons.

-265-energy loss becomes larger
with increasing emergence angle and the increase of energy
loss amounts to about 3%.
In other targets angular distributions of multiple scattered protons are well reproduced by Moliere's theory andrelative energy losses increase by l-2% with the increase of emergence angle.

o1.0

6.437 mg/cm 26.922 MeV

~~

0.8

Moliere~~

0.6
0.4
0.2

The measured increase of
relative energy losses is toolarge to be explained by the~ 1.03
following three corrections;l) the increase of path length~ 1.02
caused by multiple scattering 2 ) ~, 2) the increase of target
thickness with increasing pro'[;;' l. 01
ton emergence angle, 3) the<Idecrease of proton energy
1.ooe---~~--~--------------~
caused by a single Rutherford
Another effectscattering.
to be examined is a target
x-ray photographs
texture.
32l0
showed that Be, Al and Ag tar2
radxloj
angle
Deflection
gets had a little texture buttargets
Mylar and Cellophane
Angular distribution andFig. lwere perfectly amorphous.
energy losses of multiple
relative
From the fact that Mylar andprotons as a function of
scattered
Cellophane also show the ener- deflection angle.
gy loss increase with emergence angles, we can conclude
that the origin of this phenomenon is not target texture effect
Therefore these results
but geometric effect of measurements.
indicate a significant connection between stopping power and deflection angle of a proton; in other words an average impact paramUnfortunately, up
eter of a proton relative to a lattice atom.
till now, the atempt of theoretical explanation of this phenomenon
is unsuccessful.

+~+Referencesl)
2)

G. Clark, D. Morgan and J. Poate., in Atomic Collision
Phenomena in Solids ( eds. D. Palmar et al.; North Holland,Amsterdam, 1970 ) p.388.
B. Rossi and K. Greisen, Rev. Mod. Phys. 13(1941) 240.
C.N. Yang, Phys. Rev. ~(1951) 599.

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