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I'
X-661-76-132
PREPanva
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ENERGY SPECTRA OF COSMIC
RAY NUCLEI: 4<Z<26
AND .3<E<2 GeV/amu
(NASA-Tr4-X-71133) ENERGY SPECTRA OF COSMIC
N76-26139
RAY NUCLEI: 4<Z<26 AND .3<E<2 GEV/AMU
(NASA) 45 P FIC $4.00
CSCL 03B
UNCL AS
G3/93 43640
R.
C.
MAEHL
J.
F.
ORMES
A.
J.
FISHER
F.
A.
HAGEN
JUNE 1976'
-----
GODDARD SPACE
i
"LIGHT CENTER
GREENBELT, MARYLAND
Abstract
Energy spectra of cosmic ray nuclei in the charge range 5x7426 have
been derived from the response of an acrylic plastic Cerenkov detector.
Data were obtained using a balloon borne detector and cover the energy
range 3204E42200 MeV/amu. Spectra are derived from a formal deconvolution
using the method of Lezniak (1975). Relative spectra of different elements
are compared by observing charge ratios. Secondary primary ratios are
observed to decrease with increasing energy, consistent with the effect
previously observed at higher energy.
p
rimary to primary ratios are constant
for 657x10 and 14576 26 but vary for 1057414. This data is found to be
consistent with existing data where comparable and .lends strong support to
the idea of two separate source populations contributing to the cosmic ray
composition.
i
I
ENERGY SPECTRA OF COSMIC RAY NUCLEI:
4s7s26 and .3s
p
s2 GeV/amu
I. INTRODUCTION
One of the most important aspects of the chemical composition
of the cosmic rays is the variation of that composition with energy. If
we are to understand the nature of the cuemic ray source (or sources) and
how the cosmic rays propagate through the galaxy we must measure the
details of the energy spectra on an element by element basis. In the past
several years it has been established that the ratio of cosmic ray
secondary (i.e, nuclear spallation products produced in propagation) to primary
nuclei (i.e. nuclei found in the cosmic ray source) decreases as a function
of energy for very high energies, T > 10 GeV/amu (Juliusson, et al, 1972,
Smith et al., 1973; Ormes et al., 1973; Webber et al., 1973).
In addition, it also appears that the ratios of at least some primary
nuclei are energy dependent at such energies (Ormes et al, 1973;
Juliusson, 1974, Lund et al, 1975). It has been postulated that
the secondary to primary ratio variations may be due to an energy
dependent leakage from the galaxy at high energies (Webber et al.,
1973, Juliusson, (1974). This phenomenon necessarily results in a
somewhat smaller effect in the primary ratios also. However, if
we find the energy dependence of the ratios of primaries to be in
quantitative disagreement with predictions based on the secondary/primary
ratios it becomes necessary to evoke some additional, different phenomenon
such as multiplicity of source types (Ramaty et al., 1973) or confinement
volumes (Cartwright, 1973).
It is now generally accepted that such energy dependences
do exist
Lund (1973) has summarized the most current observations„
In order to differentiate between source and propagation effects it is
L.
^
1
-2-
Specifically, at the present time we do not know how low in energy these
variations occur and it is to this question we address ourselves in this
paper.
Using data obtained from a high altitude balloon borne detector,
we have determined the differential kinetic energy spectra of various
cosmic ray nuclei in the charge range kZE28. The data are derived from
kT
the response of an acrylic plastic Cerenkov counter and cover the kinetic
energy range 400 MeV
/
amu s T 5 2100 MeV/amu. Although this is a reasonably
narrow energy range it is a crucial region. It will allow us to understand
if and how the variations in energy spectra observed at higher energies
extend to lower regions of the energy scale. These data are not the
first observations in this energy range but our high statistical accuracy,
good charge resolution and rigorous mathematical treatment of the
Cerenkov counter response allow some interesting new conclusions.
II. DETECTOR SYSTEM & BALLOON FLIGHT
The data we report on here are from a high altitude balloon flight
from Thompson, Canada in August, 1-
'
3. The detector system, shown in
Fig. 1, has been described in detail elsewhere
(
Fisher et al., 1973). The
details of the balloon flight are given by Hagen
(
1976).
For this analysis we make use of only the top two scintillators, S1 and
S2; the Cerenkov counter and the spark chamber. The remainder of the system, a
stack of scintillators below S2 not shown in Figure 1, was intended for use in the
isotope mode and the results from that analysis are published elsewhere
(Hagen et al., 1975; Fisher et al., 1976). The live time for the flight was
3.14x10
4
sec and the geometric
faC.^Or
for this analysis was 2740 cm2sr.