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Particles having energies above $10^{18}$ eV are the so-called ultr...
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Today the upper limit on the energy of Cosmic Rays is called **Grei...
VOLUME
16,
NUMBER
17
PHYSICAL
REVIEW
LETTERS
25
APRiL
1966
tons.
When
the
complete
potential
is
deformed,
the
optical
parameters (Table
I)
found
so
far
to
give
the best
fit
to the
elastic
polarization
also
produce
the best
prediction
of inelastic
asymmetry.
All
the
curves in
Fig.
2
use
a
central-well
deformation
parameter
of
P,
=0.
39 for
~si
and
P,
=
0.
22
for
~Ni.
The deformation
parameter
of the spin-orbit term
is
1.
5
times the
central-
well
value,
which
produces
slightly
better
agree-
ment with the
asymmetry
data
for
"Si.
Both
real and
imaginary
parts
of
the
spin-orbit
in-
teraction are
included,
but since
i
W~I
«VS,
the
imaginary part
makes
little difference.
The
curves
also include Coulomb-excitation
amplitudes,
'
which make little
difference in
either the
asymmetry
or
the cross section.
We
find that for
all
of the
calculations
made,
the predictions
of inelastic
asymmetry
and
inelastic
polarization are
very
nearly
identi-
cal.
In
summary
we
find
that,
provided
the
imag-
inary
and
spin-orbit terms
are included,
the
collective-model
generalization
of the
optical
potential
gives
a
good
account of the
present
inelastic
asymmetry
data at all but
the
most
forward
angles.
It
is
quite
possible
that
a
more
comprehensive
treatment of
the
spin-de-
pendent
interaction will
improve
matters in
this
region,
and
such
calculations are in
pro-
gress.
It
is a
pleasure to
acknowledge
many
useful
conversations concerning
this work with G. R.
Satchler and N.
M.
Hi.ntz. We
are much indebted
to
the
indefatigable
ORIC
cyclotron
operators,
and
to
M. B.
Marshall,
W.
H.
White,
I.
B.
Schneider,
and A. W.
Riikola of the
ORIC
staff,
for their
essential
contributions to the
experi-
mental
effort.
*Research
sponsored
by
the
U. S.Atomic
Energy
Com-
mission
under
contract
with
the Union Carbide Corpora-
tion.
)Oak Ridge
Graduate
Fellow
from
the
University
of
Minnesota under
appointment
from
Oak
Ridge
Asso-
ciated
Universities.
f.
Graduate
Fellow from the
University
of Tennessee
under
appointment
from
the National Science
Founda-
tion.
~R.
H.
Bassel, G. R. Satchler, R. M. Drisko,
and
E.
Rost, Phys.
Rev.
128,
2693
(1962).
The
present
DW
calculations include the spin-orbit
term in the
elag+ic
distortion.
M.
P. Fricke and
G.
R. Satchler,
Phys.
Rev.
139,
B567
(1965).
3T.
Stovall
and
N. M.
Hintz,
Phys.
Rev.
135,
B330
(1964).
See,
for
example, W.
S.
Gray,
R.
A.
Kenefick,
J.
J.
Kraushaar,
and
G.
R.
Satchler,
Phys.
Rev.
142,
735
(1966);
G. R.
Satchler,
to
be
published.
5E.
R.
Flynn
and
R. H.
Bassel,
Phys.
Rev.
Letters
15,
168
(1965),
and
other
references
given
there.
6L.
N.
Blumberg,
E. E.
Gross, A.
van
der
Woude,
and
A.
Zucker,
Nucl. Instr.
5
Methods
~39
125
(1966);
L.
N.
Blumberg,
E. E.
Gross,
A. van
der
Woude,
A. Zucker,
and
R.
H. Bassel,
to
be
published.
END TO
THE
COSMIC-RAY
SPECTRUM'~
Kenneth Greisen
Cornell
University, Ithaca,
New York
(Received
1
April
1966)
The
primary
cosmic-ray
spectrum
has been
measured
up
to
an
energy
of
10'
eV,
'
and
sev-
eral
groups
have
described
projects
under
de-
velopment
or in
mind'
to
investigate
the
spec-
trum
further,
into
the
energy
range
10"-10"
eV.
This note
predicts
that above
10'
eV
the
pri-
mary
spectrum
will
steepen
abruptly,
and
the
experiments
in
preparation
will at
last
observe
it
to
have
a
cosmologically
meaningful
termi.
-
nation.
The cause of
the
catastrophic
cutoff is
the
intense
isotropic
radiation first
detected
by
Penzias
and
Wilson'
at
4080
Mc/sec
(7.
35
cm)
and
now
confirmed as
thermal in
character
by
measurements of
Roll and
Wilkinson4
at
3.
2
cm wavelength.
It is not
essential
to the
pres-
ent
argument
that
the
origin
of this
radiation
conform
exactly
to the
primeval-fireball
mod-
el
outlined
by
Dicke,
Peebles,
Roll,
and
Vfil-
kinson',
what
matters
is
only
that
the
radia-
tion
exists and
pervades
the
observable
uni-
verse.
The
transparency
of
space
at
the
per-
tinent
wavelengths,
and
the
consistency
of
in-
tensity
observations in
numerous directions,
748