The Ariel VI satellite was launched by NASA on a Scout rocket on 3rd June 1979 from Wallops Island, Virginia, USA, into a near circular 625 km orbit inclined at 55 deg. It carried a spherical cosmic ray detector designed by a group from Bristol University. A spherical aluminum vessel of diameter 75 cm contains a gas scintillation mixture and a thin spherical shell of Pilot 425 plastic, and forms a single optical cavity viewed by 16 photomultipliers. Particle tracks through the detector may be characterized by their impact parameter p and by whether or not they pass through the cup of plastic scintillator placed between the sphere and the spacecraft body (referred to below as the Anti-Coincidence Detector or ACD). Individual particle charges are determined by separately measuring the gas scintillation and the Cerenkov emission from the plastic shell. This is possible because of the quite different distribution in time of these emissions

Fowler, P. H.

Gay, A. M.

Masheder, M. R. W.

Moses, R. T.

Walker, R. N. F.

Worley, A.

English

NASA Technical Reports Server

115
OG4.4-3
ARIEL VI MEASUREMENTS OF ULTRA-HEAVY COSMIC RAY FLUXES
IN THE REGION 34 < Z < 48m
P.H. Fowler, M.R.W. Masheder, R.T. Moses,
R.N.F. Walker, A. Worley and A.M. Gay
H.H. Wills Physics Laboratory, University of Bristol,
Tyndall Avenue, Bristol BS8 ITL, England.
i. Introduction. The Ariel VI satellite was launched by NASA on a Scout
rocket on 3rd June 1979 from Wallops Island, Virginia, USA, into a near-
circular 625 km orbit inclined at 55 ° . It carried a spherical cosmic ray
detector designed by a group from Bristol University. The salient
features of this detector are shown in Fig. I.
"---T"ack of ionising Pa*'ticle
16 4cm dia.photomultipliers
800 torr gas mixture(56% neon,
31% argon, 0.6% nitrogen,
2% helium)
• 6ram Pilot 425 spherical shell
lastic scintillator shower
_ detector
I f__-'------_f I----Main spacecraft body
Fig. 1 Schematic cross-section of Ariel VI Cosmic ray detector
A spherical aluminium vessel of diameter 75 cm contains a gas
scintillation mixture and a thin spherical shell of Pilot 425 plastic,
and forms a single optical cavity viewed by 16 photomultipliers. Particle
tracks through the detector may be characterised by their impact para-
meter p and by whether or not they pass through the cup of plastic
scintillator placed between the sphere and the spacecraft body (referred
to below as the Anti-Coincidence Detector or ACD). Individual particle
charges are determined by separately measuring the gas scintillation and
the Cerenkov emission from the plastic shell. This is possible because of
the quite different distribution in time of these emissions. See also (i).
The last data from Ariel VI was received in February 1982, but
spacecraft power supply problems had restricted data collection to only
427 of the days in orbit, with actual experiment live-time equivalent
to 352 complete days at 1OO% efficiency.
2. Data Selection. Results from a first analysis of part of the Ariel VI
data set have already been reported (2). The present analysis covers all
available high charge data collected by Ariel VI. It includes improvements
to the cut-off map used to apply cut-off labels to individual events and
new event timings which allow for imperfections in the spacecraft clock
by using measured cosmic ray fluxes as clock calibrations. Event timing,
- and the subsequent allocation of an inferred local vertical cut-off to an
individual event, is important for the Ariel VI data analysis because a
small number of low energy iron nuclei, which can stop in the detector at
15 
RIEL I EASUR MENTS F LTRA-HEAVY OSMIC Y XES 
 E EGION      
. . owler, .R.W. asheder, .T. oses, 
.N.F. alker, . orley d _ . ay 
H.H. ills Physics Laboratory, niversity of ristol, 
Tyndall Avenue, ristol BS8 lTL, England. 
G .4--3 
1. troduction. he riel I atellite as nched y ASA n  cout 
rocket on 3rd June 1979 fro  allops Island, irginia, SA, into a near-
ircular 5 k  rbit i clined t 0 . t arried a pherical cosmic r y 
etector designed by a group fro  ristol niversity. The salient 
f atures f t is etector re s wn i  ig. 1. 
ig. 1 
----··--·-Track of ionising particle 
---16 4cm dia. photomultipliers 
.....-="'"800 torr gas m ixture(56% neon, 
31 % argon, 0.6% nitrogen, 
12% helium) It---I-__ 
4.6mm Pilot 425 spherical shell 
__ Plastic scintillator shower 
detector 
r1---Main spacecraft body 
Schematic cross-~ection of Ariel VI Cosmic ray detector 
A spherical aluminium vessel of diameter 75 cm contains a gas 
cintillation ixture a d a t in s herical hell f ilot 425 lastic, 
and for s a single optical cavity viewed by 16 photomultipliers. article 
tracks t rough t e etector ay be characterised by t eir i pact ara-
eter p and by hether or not they pass through the cup of plastic 
scintillator placed between the sphere and the s acecraft body (referred 
t  elow as t e nti-Coincidence etector r CD). I dividual article 
charges are determined by separately easuring the gas scintillation and 
t e erenkov e ission fro  t e lastic shell. his i  ossible ecause f 
t e uite ifferent istribution i  ti e f t ese e issions. See also (1). 
he st ata fr  riel I as ceived  ebruary 982, ut 
spacecraft power supply problems had restricted data collection to only 
427 f t e days i  rbit, ith actual experiment li e-time equivalent 
to 352 complete days t 100  efficiency. 
2. ata election. esults fro  a first analysis of part of the .Ariel I 
ata set ave already een reported ( ). he resent nalysis covers ll 
available high charge data collected by riel I. It includes i provements 
t  t e cut-off ap used t  apply cut-off labels t  i dividual events and 
new event ti ings hich allow for i perfections in the spacecraft clock 
by using easured cosmic ray fluxes as clock calibrations. vent ti ing, 
a d t e s bsequent llocation f an i ferred l cal ertical t-off t  an 
individual event, is i portant for the riel I data analysis because a 
s all number f lo  energy ir n uclei, hich can st p i  t e etector t 
https://ntrs.nasa.gov/search.jsp?R=19850025723 2020-03-20T18:02:38+00:00Z
I I 6 OG4.4-3
high impact p_rameters, can simulate b%ghe_ ch_ge$ up to a limit of
apparent charge 47. Hence, for abundance measurements, in the charge
region 34 < Z < 48, data can only be accepted from those regions where
the earth's magnetic field excludes such low energy iron nuclei. This is
empirically determined to be for vertical cut-offs greater than 3.4 GV.
Finally, with the improved statistics from the complete mission,
it is seen that events which produce a signal in the ACD (hits) have a
cut-off distribution indicative of pollution from electron showers to the
highest charges, though hardly statistically significant for z > 70_ The
hit spectrum also shows evidence of additional fragmentation due to pass-
age through the body of the spacecraft. Consequently these ACD hits
require separate analysis and are not included in the results quoted in
this paper or in the companion paper 0G4.4-4.
3. Results. Fig. 2 shows the distribution of accepted data for this
charge region. Numbers given are actual numbers of detected events, with
two provisos: i) a correction has been made for the exponential tail
associated with the relativistic rise in energy loss for charges 30,31,32
using measured abundances from HEA03-C2 (3); this affects the first five
bins: ii) some events in the lower part of this charge region have been
collected as events of second highest priority (i), at lower efficiency,
and in this case scaling has been made event by event to an equivalent
100% efficiency; this effect has become small by bin 8 onwards.
%
60"
_ 4o- _ ,,,_
35 &0 45 50
APPARENT CHARGE
Fig. 2 Distribution of accepted data for deter n/nation of 33 _ Z _ 48
abundances.Dotted insert shows distribution of 34Se content
from Table i.
During data re-analysis small improvements have been made to
charge allocation as a function of gain setting and an energy dependent
non-Z 2 correction has been applied to all data. This is discussed further
in 0G4.4-4. Its effects are in any case small for Z < 48.
in order to allot events to individual charge species the effects
of the resolution function of the experiment must be removed from the data
in a deconvolution procedure. The resolution function is well determined
11  
high i pact Parqmete;r;s, Can s;i..mul,<;J,te higher cha;r:ge~ up t  Po li it f 
apparent charge 47. ence, for abundance easurements' in the charge 
re ion 34    48, ata can onl,y be accepted fro  t ose reg~ons here 
t e arth's agnetic fi ld cludes s ch l  ergy ir n uclei. his i  
e pirically etermined t  be f r ertical t-offs reater t an .  . 
inally, ith t e i proved tatistics fr  t e mplete i sion, 
it i  seen t at e ents hich roduce a si nal i  t e D ( its) ave a 
c t-off istribution i dicative f ollution fro  electron showers t  the 
highest charges, though hardly statistically significant for Z .:. 70. The 
it spectrum also shows evidence f a ditional fragmentation due t  ass-
e t r ugh t e dy f t e acecraft. onsequently t ese CD its 
require separate analysis and are not included i  the results quoted ;in 
t is aper r i  t e panion aper OG . -4. 
3. esults. ig. 2 shows t e istribution f accepted ata f r t is 
charge region. Numbers given are actual numbers of detected events, with 
t o rovisos: i) a orrection as en~ de f r t e po ential t il 
associated with the relativistic rtse ;i.n energy loss for charges 30,31,32 
sing easured undances  EA03-C2 ); is fects e irst i e 
ins: ii  s e vents i  t e l er art f t is arge r gion ave en 
collected as events of second highest riority (1), at lo er effic;i.ency, 
a d i  t is ase s aling as een ade vent y ent t  an quivalent 
 fficiency; is fect as come all y in  nwards. 
60 
Vl 
i: 40 
w 
> w 
u. 
o 
20 
0 
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· 
· 
· , 
· 
· 
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, 
, 
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--f'--.---r- r '" "," "1 -'-'-( -I'---'I~I-T-I"-,-r-r 
 4    
RENT GE 
Fig. 2 istribution of accepted data for determtnation of 33 < Z < 48 
abundances.Dotted i sert shows istribution f 34Se content 
 able 1. 
uring ata re-analysis s al,l i provements ave en ade t  
charge allocation as a function of gain setting and an energy dependent 
non-Z2 correction has been applied to all data. This is discussed further 
i  OG4.4-4. Its effects are i  any case s all for Z  48. 
in order to allot events to individual charge species the effects 
f t e r solution f nction f t e experiment ust e re oved fr  t e ata 
i   econvolution rocedure. he resolution f nction i  ell etermined 
117
OG4.4- 3
Table 1 Elemental Abundances for 33 < Z < 48
Ariel VI Comparison Data
Deconvolved Corrected to Charge I HEA03-C3 SS + FIPD propagations
Z Numbers outside expt pairs Brewster Letaw
et al. et al.
26 3.46 x 10 6 10 6 10 6 10 6 10 6
33 (81 + 21) (21 + 6) 72 + 5 [9]<19 ii 68
34 180 -+ 29 51 -+ 8 ._ 43 +i0 55
- 6
3584 + 2524 + 7 _ 43 + 4 [7]<14 10 ] 316 71 3 19 6 23 + 8 24
- 5
3722 + 20 6 + 5 ] 38 + 4 [9]<16 20 _8 ii0 4 32 7 35 +i0 47
- 6 46
- 4
41 33 + 22 9 + 6 ] 19 + 4 [3]< 6 2.5 __ i02 5+13 10_+4 8_+2 6
44 12 + 8
4645 13 -+149_ 12 ] 6 -+ 2 ] 6.0
4847 14 +139_+13 ] 6 + 2 ] 4.9
for 26Fe and is found to fit well to a Gaussian part and an exponential
tail to high charge (2). In addition the shapes of the abundance peaks at
12Mg, 14Si and 2oCa allow the variance of the Gaussian to be separated
into a Poisson part and a part varying as Z2. A resolution function may
then be constructed for any higher charge by extrapolation. The resolu-
tion function for 34Se is shown as a dotted insert in Fig. 2. Using these
- functions the observed data may be deconvolved into a best-fit set of
abundances, giving the numbers shown in column 2 of Table i. These numbers
yield the curve shown in Fig. 2 when operated on by the appropriate
resolution functions. The fit is seen to be reasonably good, though the
Z = 38 peak appears offset. The decrease in numbers of detected events
around Z = 43 is too steep for the measured resolution function of the
experiment. This fluctuation results in a best-fit abundance for Z = 43
which is approximately lh s.d. below zero. This value was set at zero and
not varied in subsequent fitting procedures.
4. Discussion. The limited charge resolution achieved by the Ariel VI
detector reveals only one clear charge peak in this region, at Z = 38,
and only one odd charge, Z = 35, is strictly necessary to obtain a good
- fit to the data. Nevertheless the best-fit abundances in column 3, which
have been corrected for fragmentation in the experiment, form the most
convenient comparison with other work. The errors shown are the excur-
7 4.4-3 
a le 1 l ental undances f  3     4  
Ariel VI o parison ata 
Deconvolved Corrected to Charge I HEA03-C3 SS + FIPD propagations 
 bers tsi e t irs r ster L  
 
6 6 1 6 
 .   
26 .  1 6 6 
33 (81 ± 21) (21 ± 6) ]  ±  [9]<19 11 ] 43 +10   1  ±   ±   
-  
35 84 ± 25 24 ± 7 ] ± [7]<14 10 J 43 4 31   ±   ±  23 + 8   
37 22 ± 20 6 ± 5 ] ± [9]<16 20 ] 38 4 47 3  11  ± 2   ±  35 +10 46  
39 54 ± 25 14 ± 7 ] ± f5]<12 8 ] 26 4 24 40 42 ± 20 12 ± 6 13+ 5 16  
41 33 ± 22 9 ± 6 ] ± [3]< 6 2.5 ] 19 4 10 2 5 ± 13  ± 4 8 ± 2  
43 0 ] 3 ± 2 ] 7.0   ±  
45 13 ± 14 ] 6 2 J ± 6.0 46 9 ± 12 
47 14 ± 13 ] 6 ± 2 ] 4.9 48 9 ± 13 
for 26Fe and is found to fit well to a Gaussian part and an exponential 
tail to high charge (2). In addition the shapes of the abundance peaks at 
12Mg, 148i and 20Ca allow the variance of the Gaussian to be separated 
into a Poisson part and a part varying as z2. A resolution function ay 
t en e onstructed f r a y i her c arge y trapolation. he r solu-
tion function for 348e is shown as a dotted insert in Fig. 2. using these 
nctions t  bserved ata ay e econvolved t   est-fit et f 
abundances, i ing t  umbers sho n i  c l n 2 f able 1. hese umbers 
yield the curve shown in Fig. 2 hen operated on by the appropriate 
resolution functions. The fit is seen to be reasonably good, though the 
  8 eak pears fset. he ecrease  bers f etected ents 
ar und   43 i  t o st ep f r t e easured r solution f nction f t e 
xperiment. his l ctuation sults   est-fit bundance r    
hich i  pproximately l~ . . elow ero. his alue as t t ro d 
not varied in subsequent fitti g procedures. 
4. Discussion. 
detector reveals 
and only one odd 
fit to the data. 
The li ited charge resolution achieved by the Ariel VI 
only one clear charge peak in this region, at Z = 38, 
charge, Z = 35, is strictly necessary to obtain a good 
evertheless the est-fit abundances in colu n 3, hich 
have been corrected for fragmentation i  the experiment, for  the ost 
convenient comparison ith ther ork. he rrors shown are t e ex cur-
1 1 8 OG4.4-3
sions needed in a given abundance to produce a change of one unit of
X 2, the two neighbouring abundances being adjusted to keep the total area
constant. They may be regarded as approximations to 1 s.d. errors for
individual charges. With this procedure, fluctuations are strongly anti-
-correlated between neighbouring abundances and a significant decrease in
the errors results when abundances for charge pairs are constructed as in
column 4.
The best-fit values and upper limits presented by the HEAO3-C3
group at Bangalore (4) are shown in column 5, and agreement between the
two experiments for individual charges is seen to be uniformly good,
though the integrated total is rather higher for the Ariel VI data.
Columns 6 and 7 of the table quote results from two propagations of
Cameron (1982) solar system abundances (5) through about 6 gmcm -2 of
ISM with slightly different assumed First Ionisation Potential Dependence
(Brewster et al. (6) and Letaw et al. (7)). Agreement between observed
cosmic ray abundances and propagated SS is seen to be reasonably good in
this area, with the FIPD of ref. (7), which saturates at potentials less
than 7 eV, producing better agreement around charge 38.
5. Acknowledgements. The Ariel VI project has been supported throughout
its lifetime by the UK Science and Engineering Research Council. A team
from the Appleton Laboratory was responsible for project management and
raw data handling when in orbit. Main spacecraft contractor was MSDS,
Portsmouth. The Bristol experiment was built partially by support
personnel within the Bristol Physics Department and partially by
Eritish Aerospace, Filton. The electronics for the Bristol experiment was
built by Pye Telecommunications Ltd., Cambridge. We are indebted to all
of the above for a successful mission.
6. References.
i. P.H. Fowler et al., 1979, Proc. 16th ICRC, Kyoto, 12, 338
2. P.H. Fowler et al., 1981, Nature, 291, 45
3. B. Byrnak et al., 1983, Proc. 18th ICRC, Bangalore, _, 29
4. W.R. Binns et al., 1983, Proc. 18th ICRC, Bangalore, OGI-16
5. A.G.W. Cameron, 1982, in "Essays in Nuclear Astrophysics"
ed. C.A. Barnes et al.
6. N.R. Brewster et al., 1983, Ap. J. 264, 324
7. J.R. Letaw et al., 1984, Ap. J. 279, 144
118 
G4.4-  
sions needed in a given abundance to produce a change of one unit of 
2
, the t o neighbouring abundances being adjusted t  keep the t tal area 
onstant. hey ay e r gar ed s pproximations t   .d. rrors f r 
i dividual charges. ith t is procedure, fl ctuations are strongly anti-
- orrelated etween eighbouring bundances nd a ignificant ecrease i  
the errors results hen abundances for charge pairs are constructed as in 
olumn . 
The est-fit values and upper li its presented by the EA03-C3 
group at Bangalore (4) are shown in column 5, and agreement between the 
t o experiments for individual charges is seen to be uniformly good, 
though the i tegrated t tal is rather higher for the riel I ata. 
olumns 6 and 7 f t e t ble uote r sults fro  t o rop gations f 
Cameron (1982) solar system abundances (5) through about 6 g cm-2 of 
IS  ith slighDly different assumed First Ionisation Potential Dependence 
( rewster et al. (6) and Letaw et al. ( ». greement between observed 
cosmic ray abundances and propagated SS is seen to be reasonably good in 
is rea, ith t e IPD f f. ), hich aturates t otentials s 
than 7 eV, producing better agreement around charge 38. 
. cknowledgements. he riel I roject as een s ported t roughout 
its lif time y t e K cience d ngineering esearch ouncil.  t  
fro  t e pleton aboratory as r sponsible f r roject anagement and 
r  ata andling hen i  rbit. ain a ecraft ontractor as SDS, 
Portsmouth. The ristol experiment as uilt artially by support 
ersonnel ithin t e ristol hysics epartment and artially by 
ritish erospace, Filton. The electronics for the ristol experiment was 
built by Pye Telecommunications td., Cambridge. e are indebted to all 
f t e ove r  cessful ission. 
. eferences. 
1. P.H. Fowler et al., 1979, Proc. 16th ICRC, Kyoto, 12, 338 
. . . owler t l., 981, ature, 91, 45 
3. . yrnak et al., 1983, Proc. 18th ICRC, angalore, ~, 29 
4. .R. inns t l., 1983, roc. 18th I RC, angalore, Gl-16 
5. A.G.W. Cameron, 1982, in "Essays in uclear strophysics" 
d. .A. arnes t l. 
6. .R. rewster t l., 1983, p. J. 264, 324 
7. J. . Letaw et al., 1984, Ap. J. 279, 144 


Ariel 6 measurements of ultra-heavy cosmic ray fluxes in the region 34 or = Z or = 48

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