IONS (ANURADHA), the experimental payload designed specifically to determine the ionization states, flux, composition, energy spectra and arrival directions of low energy (10 to 100 MeV/amu) anomalous cosmic ray ions of helium to iron in near-Earth space, had a highly successful flight and operation Spacelab-3 mission. The experiment combines the accuracy of a highly sensitive CR-39 nuclear track detector with active components included in the payload to achieve the experimental objectives. Post-flight analysis of detector calibration pieces placed within the payload indicated no measurable changes in detector response due to its exposure in spacelab environment. Nuclear tracks produced by alpha-particles, oxygen group and Fe ions in low energy anomalous cosmic rays were identified. It is calculated that the main detector has recorded high quality events of about 10,000 alpha-particles and similar number of oxygen group and heavier ions of low energy cosmic rays

Biswas, S.

Chakraborti, R.

Cowsik, R.

Durgaprasad, N.

Dutt, N.

Goswami, J. N.

Kajarekar, P. J.

Singh, R. K.

Vahia, M. N.

Yadav, J. S.

English

NASA Technical Reports Server

N8 ‘2’- 221 11  
IONS (ANURADHA): IONIZATION STATES OF LOW ENERGY COSMIC RAYS 
S. Biswas, R. Chakraborti, R. Cowsik, N. Durgaprasad, P. J. Kajarekar, 
R. K. Singh, M. N. Vahia, and J. S. Yadav 
Tata Institute of Fundamental Research, Bombay 400005, India 
N. Dutt, J. N. Goswami, D. Lal, H. S. Mazumdar, and D. V. Subhedar 
Physical Research Laboratory, Ahmedabad 380009, India 
M. K. Padmanabhan 
ISRO Satellite Centre, Bangalore 560 017, India 
ABSTRACT 
IONS (ANURADHA) (1 ), the experimental payload designed specifically to  determine the ioniza- 
tion states, flux, composition, energy spectra and arrival directions of low energy (10 to 100 MeV/amu) 
anomalous cosmic ray ions of helium to iron in near-Earth space, had a highly successful flight and 
operation in Spacelab-3 mission. The experiment combines the accuracy of a highly sensitive CR-39 
nuclear track detector with active components included in the payload to  achieve the experimental 
objectives. Post-flight analysis of detector calibration pieces placed within the payload indicated no 
measurable changes in detector response due to  its exposure in spacelab environment. Nuclear tracks 
produced by @particles, oxygen group and Fe ions in low energy anomalous cosmic rays have been iden- 
tified. It is calculated that the main detector has recorded high quality events of about 10,000 a-particles 
and similar number of oxygen group and heavier ions of low energy cosmic rays. 
D I SCUSSl ON 
The low energy (5 to  100 MeV/amu) anomalous component of cosmic rays discovered in the early 
seventies has been studied in great detail over the last decade. Comprehensive information on composi- 
tion, energy spectra, radial gradient and time variation of the anomalous cosmic rays (ACR) in the inter- 
planetary medium have been obtained using instruments on board the IMP, Pioneer and Voyager space- 
crafts [2,3]. The near-Earth component of the ACR was first identified in a Skylab experiment [41; 
this has, however, not been studied in detail. The spacelab mission offered a unique opportunity for 
such a study and the Indian experiment “IONS” (or Anuradha) on board Spacelab-3 was primarily 
intended for this purpose. 
Several suggestions have so far been made about the origin of the anomalous cosmic rays [5] .  
The major distinguishing features of these models are the predicted charge states of ACR and its radial 
gradient and time variation. Further, the models of Fisk et al. [SI and Fowler et al. [ 5 ]  suggest pro- 
duction of the anomalous component within the solar system, whereas Biswas et  al. [SI suggested a 
stellar origin for these low energy particles. Extensive studies of the interplanetary ACR component 
[3,6] have yielded valuable information on their radial gradient and time variation for the period 1973- 
1984 which indicate an extra solar system origin for these particles. However, no direct measurement of 
ionization states of ACR is presently available, The primary objective of the IONS experiment was to 
obtain this crucial information for the near-Earth component of ACR. Additional information on com- 
position and intensity of this component will also be obtained from this experiment. In this report we 
present the salient features of the IONS payload, the experimental approach, flight operations and per- 
formance of the instrument and also preliminary results on anomalous particle fluences based on analysis 
of auxiliary detector elements placed inside the payload. The processing and analysis of the main 
detector stacks are currently in progress. 
64 
https://ntrs.nasa.gov/search.jsp?R=19870012678 2020-03-20T11:38:04+00:00Z
Instrument and Experimental Approach 
The IONS payload flown in Spacelab-3 is shown in Figure 1. It is 48 cm in diameter, has a 
height of 53 cm, and weighs 45 kg. The payload houses two detector modules, the main detector 
module (bottom stack) being about 40 cm in diameter and 4.5 cm thick. It is composed of 174 sheets, 
mostly of CR-39, All Diglycol Carbonate (DOP), nuclear track detectors along with a few sheets of Lexan 
Polycarbonate each of thickness of 250 pm. On the top of this stack, separated by a gap of 500 pm is a 
single sheet of CR-39 of thickness 250 pm which is held rigidly to the instrument frame by a stainless 
steel ring structure. During experiment operation the main stack is rotated using a high resolution 
stepper motor and a gear assembly in discrete steps of 40 sec of arc once every 10 sec., so as to make 
one complete revolution in 90 hrs. The movement of the stack is monitored by a 15 bit absolute shaft 
encoder coupled to it. A thin 75 pm aluminum alloy dome acts as the top enclosure of the sealed pay- 
load which is maintained at a pressure of 0.1 atmosphere during its space exposure. The payload was 
mounted directly on a cold plate fixed to a specially prepared experimental support structure to maintain 
the instrument temperature at a nominal value of 25"-40"C. The IONS instrument is mounted on space- 
lab with its Z-axis tilted by 25 deg so as to reduce the Earth shadow on the viewing cone during the 
flight. The gravity gradient stabilized attitude of the shuttle provided very favourable celestial viewing 
of IONS with a viewing cone of about 110 deg. Inside the payload a temperature sensor was placed 
close to the detector module to  monitor its temperature during the duration of the exposure. Small 
samples of test CR-39 detector elements, irradiated to energetic heavy ion beams from accelerators, are 
also included in the payload for monitoring any possible changes in the detector response due to its 
exposure in pressure and temperature conditions within the payload. The entire operation of the IONS 
instrument was controlled by onboard computer and the relevant data regarding instrument functions 
(e.g. BMT, stack movement, temperature, etc.) are telemetered down link once every second for record 
and monitoring by experimenters. The instrument operation could be initiated and interrupted, if 
required, by crew interface or via ground command. 
The experimental approach for obtaining ionization states of ACR involves several major steps. 
The atomic number, energy and arrival direction of each energetic particle incident on the detector 
modules are determined from an analysis of the track records left by the ions in the two CR-39 detector 
stacks. The revelation of latent tracks for optical viewing in these detectors is achieved by etching the 
detector sheets in a 6.25 N NaOH solution at 70°C for suitable durations of several hours. Track parame- 
ters like length, diameter, and residual range are measured and used in conjunction with energetic accel- 
erator ion calibration data, for the same CR-39 detector samples to determine atomic number and energy 
of the tracks forming ions using standard procedures [ 71. The arrival time information will be obtained 
from the angular displacement of each track in the bottom detector stack compared to its location on 
the top CR-39 sheet. This information will be coupled with space shuttle's trajectory data. Thus, the 
arrival direction of each ion in space is determined. The threshold magnetic rigidities (i.e., momentum/ 
charge) of ions are then derived from the computation of charged particle trajectories in geomagnetic 
field for the known latitude, longitude, altitude, and arrival directions. By combining the data of mag- 
netic rigidities with momentum of ions measured in the main detector, the ionization states of the heavy 
ions are determined. 
Flight Performance 
The Spacelab-3 with IONS on board was successfully launched on day 119 at 16:02: 18 GMT from 
Kennedy Space Center, Florida. Several factors contributed to make the Spacelab-3 mission ideally suited 
for the study of low energy cosmic rays. First, the flight period was characterized by very low level of 
65 
solar activity free from any flare events. This is illustrated in Figure 2, where we show two specific 
parameters characterizing the solar activity during the flight period and also their levels during solar 
minimum and maximum. Second, the instrument operation period was also free from any significant 
geomagnetic activity. Further, recent studies of anomalous cosmic rays in interplanetary space [ 31 have 
indicated that during the last solar magnetic field reversal in 1980-81 the intensity of ACR was at its 
minimum value, and the ACR flux for 10 MeV/N oxygen ions showed a steady rise from its 1981 value 
by a factor of about 10 during early 1985. 
The IONS instrument was activated on the third day into the mission via ground command. 
Following the activation, a snag was noticed as the payload was not responding to  some of the commands 
sent by the onboard computer. The cause was finally traced to a faulty cable connecting the 
computer to the remote acquisition unit through which commands were fed to the instrument. The fault 
was rectified by the crew following procedures drawn up by NASA ground support personnel, and IONS 
started operation from day 123, 12:44:08 GMT. The performance of the instrument was excellent during the 
entire period of operation of 64 hours, which was 71 percent of the planned operation duration. The 
thermal control system also worked perfectly and the temperature within the instrument was maintained 
in the range of 22"-4OoC during the entire period of operation. We show in Figures 3(a) a sample of 
encoder readings showing the actual and commanded positions of the rotating bottom detector stack 
versus GMT. Each encoder step corresponds to about 40 sec of arc once every 10 sec. An offset of 10 
divisions in commanded position is introduced for the sake of clarity. Figure 3(b) shows the instrument 
temperature for the same time slice, monitored by the temperature sensor kept inside the payload close 
to the detector module. Following the successful completion of the mission, the IONS payload was 
examined and all subsystems including the two detector modules were found to be in perfect condition, 
with no sign of any physical stress or strain suffered during its space exposure. 
Detector Response and Preliminary Results 
The CR-39 (DOP) (Allyl Diglycol Carbonate) plastic used in the present experiment is an 
extremely sensitive nuclear track detector, and was specially manufactured by Pershore Co. (UK) adopting 
a long curing cycle and doping treatment with 1 percent dioctyl phthalate. Prior to the flight, sample 
pieces of this CR-39 (DOP) plastics were exposed to accelerator beams of low energy, upto 10 MeV/N 
a-particles, 12C, l6O, 20,22Ne, 28Si, 52Cr, 58Ni and high energy, 1.88 GeV/N 56Fe and 200 MeV/N 
238U ions to determine its nuclear track recording characteristics. The results obtained from measure- 
ment of track parameters in these calibration samples are shown in Figure 4, where we plot the ratio of 
track etch rate to bulk etch rate, Vt/Vb, as a function of energy loss, dE/dx, for different ions. It can 
be seen that in the low energy loss region the etch rate ratio is a linear function of energy loss, whereas 
at higher energy loss region it can be approximated as a power function of energy loss. A least square 
fit to the data yielded the following response function for the detector over the energy loss region of 
interest. 
v t / v b  = 1 + 5.67 x (dE/dx) + 1.22 x 10-l' ( ~ E / D x ) ~ * ~  (1) 
The results of the calibration studies also showed that the CR-39 (DOP) detector used in this experiment 
efficiently records tracks of all energetic particles with Z/p 2 8, where Z is the nuclear charge and pc is 
the velocity of the ions and it should be possible to achieve a charge resolution of 0.2 charge unit. 
Sample pieces of CR-39 exposed to alpha particles, neon, iron, and uranium beams were also kept inside 
the IONS payload to monitor any change in its response function due to the ambient pressure (0.1 atm) 
and temperature (25-4OoC) within the payload. Post flight analysis of these calibration pieces indicates 
66 
that response characteristics of these CR-39 detectors remained the same during its exposure in spacelab 
environment. This can be clearly visualized from Figure 4 where we have plotted the track etch ratio 
for neon and uranium ion tracks obtained from measurements made in calibration detector pieces flown 
in the payload. Hence the response curve [equation ( l ) ]  is adequate for identifying atomic number of 
the track forming nuclei in the IONS detector stack. 
For zero time marking of the fixed top detector and the moving bottom detector module, the 
detector assembly was exposed to  a narrow collimated beam of 50 MeV alpha particles in the Variable 
Energy Cyclotron, Calcutta. We first completed the analysis of a set of small area auxiliary detectors of 
CR-39 flown in the IONS detector module in order t o  obtain initial information on the types of low 
energy cosmic ray particles and their fluxes. These CR-39 samples were etched in 6.25 N NaOH at  7OoC 
for 6 hrs. Figure 5 shows photomicrographs of some samples of tracks produced by low energy cosmic 
ray alpha particles, oxygen group (Z = 6-10) and Fe nuclei recorded during the flight. The sharp defini- 
tion of the tracks is clearly evident in these photomicrographs. Based on the measured number of tracks 
of different ions the fluxes of low energy cosmic ray alpha particles, oxygen group and iron nuclei were 
determined. The time-average differential flux of alpha particles at 8 MeV/N is obtained as (1.3 f 0.23) 
x 10-5 particles cm-2 sr-l sec-l (MeV/N)-l. Assuming that the energy spectrum of alpha particles is flat 
in the region 8-50 MeV/N as in interplanetary space. We expect to  obtain about 10,000 times annotated 
alpha particles in 8-40 MeV/N energy interval in the main detector. The time-average differential flux of 
oxygen group particles at 17 MeV/N is obtained as (1.7 f 0.5) x lom6 particles cm-2 sr-l sec-l (MeV/N)-l. 
This value is in the range expected from the interplanetary flux measured in early 1985 in Voyager-2, 
which is about 1 x p/(cm2.sr.sec.MeV/N) at  15 MeV/N, considering the radial gradient of ACR and 
the transmission factor in the geomagnetic field. At 26 MeV/N, the time average oxygen group flux is 
obtained as (5.8 f 2.0) x p/(cm2.sr.sec.MeV/N). This shows the steady recovery of ACR since solar 
maximum in 1980-81, and by April-May 1985 it  has increased by a large factor and has reached a level, 
being only 5-10 times lower from maximum flux of 1974 level. The expected number of anomalous 
cosmic rays of the oxygen group in the IONS detector in the energy interval of 15-30 MeV/N with arrival 
time information is estimated to  be about 8000 events. The expected number of other components of 
anomalous cosmic rays can be estimated from the above number of events. In addition to  anomalous 
cosmic rays we expect to obtain more than 10,000 galactic cosmic ray nuclei of oxygen and heavier 
nuclei in the IONS detector. Several important types of measurements such as isotopic composition of 
iron group nuclei can be carried out with high degree of reliability. The top CR-39 sheet and several 
upper sheets of the bottom stack of the main detector of the IONS have been processed and the 
measurements and analysis of tracks in these are currently in progress. The results obtained from these 
data will provide us the information on the ionization states and also on the composition, intensity and 
energy spectra of low energy anomalous cosmic rays in near-Earth space which will provide new clues 
to the origin of this enigmatic component of energetic particles in our solar system. 
REFERENCES AND NOTES 
1. “ANURADHA” is the Sanskrit name of the star 6-Scorpii or a part of the constallation Scorpius. 
As cosmic rays originate from some type of stars in some phase of their evolution, the stellar 
name is given to the experiment. 
2. Hovestadt, D., Vollmer, O., Gloeckler, G., and Fan, C. Y.: Phys. Rev. Lett., Vol. 31, 1973, p. 
65. Ap. J. (Letters), Vol. 182, 1973, 
p. L81; Apl. J., Vol. 202, 1975, p. 265. McDonald, F. B., Teegarden, B. J., Trainor, J. H., and 
Webber, W. R.: Ap. J. ,  Vol. 187, 1974, p. L105. Klecker, B., Hovestadt, D., Gloeckler, G., and 
Fan, C. Y.: Ap. J., Vol. 212, 1977, p. 290, and references therein. 
Garcia-Munoz, M., Mason, G. M., and Simpson, J. A.: 
67 
3. 
4. 
5. 
6, 
7. 
Cummings, A. C., Stone, E. C., and Webber, W. R.: Proc. 19th Int. Cosmic Ray Conf., Vol. 5,  
1985, p. 163. Mewaldt, R. E. and Stone, E. C.: Ibid, Vol. 5, 1985, p. 167. Mason, G. A., 
Klecker, B., Galvin, A. B., Hovestadt, D., and Ipavich, F. M.: Ibid, Vol. 5, 1985, p. 168. 
Webber, W. R., Cummings, A. C., and Stone, E. C.: Ibid, Vol. 5 ,  1985, p. 172. McKibben, R. B., 
Pyle, K. R., and Simpson, J. A.: Ibid, Vol. 5, 1985, p. 198. 
Biswas, S., Durgaprasad, N., Nevatia, J., Venkatavaradan, V. S., Goswami, J .  N., Jayanthi, U. B., 
Lal, D., and Mattoo, S. K.:  Astrophys. Sp. Sci., Vol. 35, 1975, p. 337. 
Biswas, S. and Durgaprasad, N.: 
N., and Trivedi, S.: 
and Ramaty, R.: 
Swordy, S. P.: Nature, Vol. 279, 1979, p. 622. 
Sp. Sci. Rev., Vol. 25, 1980, p. 285. Biswas, S., Durgaprasad, 
Fisk, L. A., Kozlovosky, B., 
Fowler, P. H., Redfern, R. M., and 
Proc. Ind. Acad. Sci., Vol. 90, 1981, p. 337. 
Ap. J. (Letters), Vol. 190, 1974, p. L35. 
McKibben, R. B., Pyle, K. R., and Simpson, J. A.: Ap. J., Vol. 227, 1979, p. L147. Hovestadt, 
D., Klecker, B., Gloeckler, G., Ipavich, F. M., Fan, C. Y., and Fisk, L. A.: Proc. 16th Int. Cosmic 
Ray Conf., Kyoto, Vol. 3, 1979, p. 255. 
Fleischer, R. L., Price, P. B., and Walker, R. M.: Nuclear Tracks in Solids: Principles and Appli- 
cations. Univ. of California Press, 1975. Henke, R. P., and Benton, E. V.: Nuclear Inst. and 
Methods, Vol. 97, 1971, p. 483. 
ACKNOWLEDGMENTS 
We are extremely thankful to  Indian Space Research Organization Satellite Centre (ISAC), 
Bangalore, for their excellent support in conducting various integrations and testings of IONS; to Bhabha 
Atomic Research Centre (BARC), Bombay, for fabrication of the flight and flight spare IONS structure; 
Laser Laboratory of BARC for providing laser operations; and Variable Energy Cyclotron Centre (VEC), 
Calcutta, for providing support for the alpha beam exposures. We are grateful to  NASA for providing 
us with the Spacelab-3 flight aboard the Shuttle Challenger and the Mission Specialists, Dr. Don Lind and 
Dr. Norman Thaggard, for inflight replacement of a faulty cable, as well as NASA ground engineers for 
ground support and help in reactivation of IONS during the flight. 
68 
ORIGINAL PA6E 1s 
OF POOR  QUA^ 
Figure 1. IONS payload flown in Space Shuttle Spacelab-3. In actual flight the payload was 
wrapped on its side by a thermal blanket for maintaining appropriate thermal environment 
and was placed on the open cargo bay on a specially mounted experiment support 
structure. The pressure inside the payload was maintained at 0.1 atm. during the 
flight with the help of pressure senitive venting valves fixed on the wall of the 
payload. 
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IONS (ANURADHA): Ionization states of low energy cosmic rays

IONS (ANURADHA): Ionization states of low energy cosmic rays

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