Large areas of nuclear emulsions and plastic detectors were exposed to the primary cosmic radiation during high altitude balloon flights. From the analysis of 141 particle tracks recorded during a total exposure of 1.3 x 10 to the 7th power sq m ster.sec., a charge spectrum of the VVH particles has been derived

Blanford, G. E., Jr.

Friedlander, M. W.

Hoppe, M.

Klarmann, J.

Walker, R. M.

Wefel, J. P.

English

NASA Technical Reports Server

i
161
PRIMARY COSMIC RAY PARTICLES WITH Z > 35 (VVH PARTICLES)
G. E. Blanford Jr.,* M. W. Friedlander, M. Hoppe , J. Klarmann,
R. M. Walker and J. P. Wefel**
Laboratory for Space Physics, Washington University
St. Louis, Missouri 63130, U.S.A.
Large areas of nuclear emulsions and plastic detectors
were exposed to the primary cosmic radiation during
high altitude balloon flights. From the analysis of
141 particle tracks recorded during a total exposure
of 1.3 x 107 m2.ster.sec., a charge spectrum of the
VVH particles has been derived.
1. Introduction. In a collaboration between the University of
Bristol, the General Electric Research and Development Center,
the University of California at Berkeley and Washington University,
several high altitude balloon flights were undertaken in order to
investigate the primary cosmic ray particles with Z > 30 (i.e. the
VVH particles). After the flights, the packages were divided,
with each group analysing its portion independently. The data
reported in this paper were obtained from a total exposure of
1.3 x 107 m2.ster.sec., approximately equal to the total exposure
of previously p u b l i s h e d experiments. The most recent review of
the observations of VVH particles was given by Price (1971) at
the last International Cosmic Ray Conference; the present results
together with extensive discussion of experimental details are
being published elsewhere (Blanford et al, 1973 a, b).
2. Detectors and Scanning. Four balloon flights provide the
observational basis of the present data. All flights were launched
from Palestine, Texas and floated over a region where the geomag-
netic cutoff averaged around 4.3 6V. Typical flight altitudes
were at 3-4 gm/cm2. The four flights, referred to as Barndoor
II and III and Texas III and IV, carried multiple detector layers.
All had Ilford G5 emulsions, and a variety of plastic detectors.
In order of decreasing sensitivity, these plastics are cellulose
nitrate (Daicel); cellulose triacetate (Kodacel and Bayer TN),
cellulose acetate butyrate (Bayer BN-CAB) and Lexan (polycarbonate)
Each package also employed a shifter whereby one layer of the
detector was moved relative to the rest when the balloon attained
float altitude. By matching tracks, we unambiguously identified
each event as either ascent of altitude. In Barndoor III, four
separate shift positions were used as the balloon drifted in alti-
tude and geomagnetic cutoff during the flight. Only altitude
tracks have been included in the further analysis.
*Now at NASA-Johnson Space Center, Houston, Texas, 77058.
**Now at Naval Research Laboratory, Washington; D. C. 20375
https://ntrs.nasa.gov/search.jsp?R=19740014222 2020-03-23T09:14:48+00:00Z
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completely
spark scanned,
in another
Scanning of the etched plastic sheets was carried out both
with the semi-automatic spark scanning technique and with an
optical microscope. Layers of Dai eel '.and CTA were etched for
long periods in order to produce etched holes that
penetrated tire plastic, and these sheets were then
In addition, all tracks found in one layer but not
(via the spark scanning) were followed in an optical microscope
into the other layers to locate incompletely etched tracks.
This procedure, of starting with the most sensitive plastic
and working through to the least sensitive .-(Texan) should yield
the highest efficiencies. Spark scanning alone for CTA plastic
on Barndoor III was found to be 88% efficient, but in combination
with optical tracing the efficiency was estimated to be >98%.
90
From the CTA, each track was traced
to an etched layer of CAB, and from there
to the Lexan. This procedure ensured
that each event would be located in the
maximum number of layers and it also
provides an immediate rough d i v i s i o n
of the data into broad charge groups,
defined by the sensitivities of the
plastics, as shown in Fig. 1.
80
a 70
o
60
O
uJ
u
50
Among the al t i tude VVH t racks , we
have found a group that were due to
non-VVH par t i c les wi th k inet ic energ ies
below the geomagne t i c th reshold . Un-
less care is taken to identify and
exclude these l igh t ly -charged par t ic les
they may be con fused w i th the faster
VVH pr imar ies . These obse rva t i ons
have been descr ibed by B lanford et
al , ( 1972 ) . All resul ts reported
in the present paper refer only to
fast parti cl es .
40
20
LEXAN
BN-CAB
TN-CTA .
10° 30° 50' 70°
ZENITH ANGLE
90»
Fig. 1. Charge thresh-
olds for track registra-
ti on. The two TN-CTA
curves refer to spark
and optical scann ing .
3. Charge Determinat ion. Each of the " fas t " VVH events was
located in addi t ional layers of p las t ic that were e tched in
r igourously cont ro l led cond i t ions , and the track etching rate
Vt was computed from measurements on the resul t ing e tched cones ,
The track etching rate is connected to the charge and energy of
the par t ic le v ia the ion izat ion. Wi th ca l ib ra t ion being based
upon low energy Fe pr imar ies recorded and a l s o wi th ions f r o m 1 ,
the HILAC acce le ra to r . Th is ca l ib ra t ion d i f fers from that em-
ployed by other workers , and has been d i s c u s s e d by B lanford et
al , ( 1 9 7 3 a ) , who a lso treat the ass ignment of e f fec t i ve k inet ic
energy. (This is needed for the ion izat ion depends on energy
which is not measured but only poor ly def ined by the cu t -o f f . )
On several
emu ls ions using
flights, events were also measured in nuclear
a photodensi tometer and methods as descr ibed
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161
by Fowler et al , (1970). In the figure below (Fig. 3a & b) there
are shown the results of the comparison of charge assignments
based on independent measurements in different detectors.
X
UJ
Ul
o
z
U
100
60
70
60
SO
40 50 60 70 80 90
CHARGE IN CAB
100
100
z 90
O
3 80
3
JE
Ul 70
U 60
0
K
< 50
X
o
40
o - C A B + L E X A N / ,
* - C A B \S
...«„ yf
X
/
o
/r • :
*A**
£ \
2> .*»•
/ A . ,
^4-"
40
Fig. 3
50 60 70 60 90
CHARGE IN PLASTIC
assignments in Lexan and
100
Comparison between charge  CAB
plastics, and between emulsion and plastics. Typical
error bars are shown for only a few representative points
The overall statistical accuracy of charge assignments is
estimated to be AZ = +|%.
-b
4-. Experimental Results and Discussion. Despite the large de-
tector areas and l
limited. In view
we have divided th
charge units wide.
Z > 86 ; this d i v i s i
tion, it was felt
probably represent
ong exposure times, the
of this, and the experi
e charge spectrum into
The heaviest group is
on was used because, wi
that an apparent charge
a genuine Z = 82 or 83
The final charge assignment for each
of all plastic and emulsion measurements,
layers. This was true for all except for
which no plastic charge measurements were
were located via the Dai eel.scanning , and
rest entirely on emulsion measurements.
statistics are quite
mental charge resolution,
groups each normally 5
defined as those with
thin our charge resolu-
of 84 or 85 would most
rather than Z > 90.
event was the average
made in the various
Z < 40 parti cles for
available; these events
their charge values
The lower boundary of
the lowest charge group is set by the threshold of the Daicel.
This threshold is not well defined, and there appears to be a
varying efficiency near threshold. As discussed elsewhere
(Blanford et al , 1973a), we consider here only those events with
Z >35, where we are confident we have close to 100% detection
efficiency. Measurements on these particles are confined to Barn-
door III, while for particles with Z^ 50 all flights were used.
The observed spectrum, at detector flight level, is given in
Table I.
Above Z = 50, the agreement with earlier work is generally
good. For charges between 40 and 50, we find a greater flux
than do Fowler et al , (1970). It must be emphasised that the
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161
Table I
Charge Spectrum at Flight Level
Charge
 i35 36-40 41-45 46-50 51-55 56-60 61-65 66-70 71-75 76-80 81-85 *86
Events 20 19 22 13 21 22 10
U±05
10 5 3
02 ±02
the data in the Tab le represent combined
in wh ich there were d i f ferent a rea-so l id
di f ferent charge g roups .
data from four fl ights
angle factors for the
To determine the f lux of each group of particles, the fl ight'
level spect rum for each f l ight ( i .e. the component data of Table
I) was ex t rapo la ted to the top of the atmosphere and only then
was the total spec t rum obta ined. B e c a u s e of uncer ta in t ies in the
fragmentation parameters for VVH-par t i c le col l is ions in the atmos-
phere, we prefer to quote f lux va lues in broader charge g roups ,
and these are l is ted in Table II, a long wi th the rat ios of ob-
served and solar sys tem abundances to the 20 < Z < 30 group.
TABLE II
FLUX OF VVH PARTICLES AT TOP OF THE ATI10SPHERES
Charge Group Number of Tracks
Used.for Flux
Computation
Flux1
2 •(m -ster-sec)
(x 105}
Ratio* of Flux to
that of Fe-group
(x 106)
Ratio of Solar
System Abundances(Cameron)
(x 106)
35
41
51
61
71
- 40
- 50
. 60
- 70
- 85
> 86
19
35
47
13
24
3
16 i 4
28 t 6
7 ± 1
2.3 ± 0.6
3.5 ± 0.7
0.8 ± 0.5
33 ± 8 '
57 ± 12
14 ± 2
4.7 ± 1.2
7.1 i 1.4
1.6 t 0.9
176
14
22
2
7
Notes: 1. Geomagnetic cutoff specifies the minimum rigidity; the corresponding cut-off kinetic
energy thus varies with (Z/A). Flux values have therefore been normalized to a
standard kinetic energy of 1.0 GeV/nucleon, the cut-off value for the highest
charge group. An Integral energy spectrum with slope -1.5 has been assumed for
this normalization.
22. The flux of the Fe-group 1s usually quoted at 0.4 part1.cles/ra -ster-sec. This Is
appropriate for the usual cut-off rigidity over Texas; for computing the ratio of
the VVH particle fluxes to the Fe-group, the Fe-group has also been normalized
(as above) to a kinetic energy of 1.0 GeV/nucleon, leading to a flux of 0.49
particles/m'-ster-sec. . .
 %
The apparently low abundance of the 36-40 group cannot be
due to the cho ice of the lower boundary for this group. We find
(and have l is ted in Table I) only 20 par t ic les wi th measured
charges Z < 3 5 , and even i f a large proport ion of these shou ld
properly have been c l a s s e d wi th the (36-40) group, there wou ld
still remain a s ign i f i can t d i sc repancy . Con tamina t ion of the
(41-50) group by un recogn ised s low (but l ighter) par t ic les is
cons idered unl ikely, as many have already been removed in the
earlier analysis .
5
161
5. C o n c l u s i o n s . We have found three events w i th Z >86 , wi th
actual a s s i g n e d va lues of Z = 90, or, wi th in the exper imenta l
uncer ta int ies, poss ib l y Z = 92. No t ransuranic nuclei were found.
Because of charge resolut ion l imitat ions it is di f f icul t to sep-
arate Z = 93 or 94 from Z = 90-92, but the observa t ion of trans-
bismuth par t ic les prov ides e v i d e n c e , yet again, that r -process
nuc leosyn thes is must be invo lved in the source of VVH cosmic rays.
The s ign i f icant underabundance of the (36-40) group reported
here might seem to s u g g e s t that the r -process dominates throughout
the spec t rum, s ince the product ion of the (36-40) group via the
r -process is much less (about 1/3) than in the s - p r o c e s s . How-
ever , both r and s p r o c e s s e s contr ibute about equal ly in the
(41-50) group, and the presumpt ion of r -process dominance cannot
exp la in the obse rved overabundance in this (41 -50 ) group.
We thus f ind that the deta i ls of the charge spec t rum, even
wi th the modes t charge reso lu t ion and s ta t i s t i cs so far a t ta ined,
cannot be fully exp la i ned by one nuc leosyn thes i s p r o c e s s , and
more de ta i led mode ls are required. Paper 163 at this meet ing
(B lanford et a l . ) is add ressed to a more de ta i led examina t ion
of the impl icat ions of the charge spec t rum o b s e r v e d for Z > 50.
6. A c k n o w l e d g e m e n t s . We are grateful to our co l l eagues for
their help at the ear l ier s tages of our co l labora t ion , and to
the f l ight c rews at the N . C . A . R . Ba l loon Fac i l i ty in Pa les t i ne ,
Texas , for their unfai l ing competence . Thanks are a lso due to
our scanners for al l of their w o r k . This research has been
suppor ted under N . A . S . A . Grant NGR-26-008-1 and N . S . F . Sc ience
Development Grant GU-1147 .
Re fe rences
B L A N F O R D , G. E . Jr., M. W.
R. M. W a l k e r and J. P
6037.
Fr iedlander, J.
. W e f e l , ( 1972 ) ,
Klarmann, S . S.
J . Geophys. Res
Pomeroy,
. 77,
BLANFORD, G. E. Jr., M. W. Friedlander, J. Klarmann, S. S. Pomeroy,
R. M. Walker, J. P. Wefel, P. H. Fowler, J. M. Kidd, E. J.
Kobetich, R. T. Moses and R. T. Thome (1973a), Phys. Rev.
(in course of publications).
BLANFORD, G. E. Jr., M. W. Friedlander, J. Klarmann, R. M. Walker
and J. P. Wefel (1973b), Phys. Rev. (in the course of
publication) .
FOWLER, P. H., V. M. Clapham, V. G. Cowan, J. M. Kidd and R. T.
Moses, (1970), Proc. Roy. Soc. London A318, 1.
PRICE, P. B., (1971), Rapporteur Paper, 12th International Con-
ference on Cosmic Rays, Hobart, Tasmania.


Primary cosmic ray particles with z 35 (VVH particles)

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