TIGER is a balloon-borne cosmic-ray experiment designed to measure the elemental abundances of Galactic

Cosmic Rays (GCRs) in the charge range 26<Z<40 with better than 0.25 charge unit( cu) resolution. The

experiment consists of a combination of plastic scintillators, plastic and aerogel Cherenkov detectors, and scintillating

fiber hodoscopes. TIGER was flown from Fort Sumner, NM aboard a high-altitude balloon on September

24, 1997 at geomagnetic cutoffs between 4.2GV and 3.2GV, and atmospheric depths between 3g/cm^2 and 6g/cm^2. The 23.5-hour balloon flight provided a statistically significant sample of GCR nuclei up through Ni and achieved charge resolution capable of resolving Co from the much more abundant Fe

Barbier, L. M.

Binns, W. R.

Christian, E. R.

Cummings, J. R.

deNolfo, G. A.

Hink, P. L.

Israel, M. H.

Mewaldt, R. A.

Mitchell, J. W.

Schindler, S. M.

Sposato, S. H.

Streitmatter, R. E.

Waddington, C. J.

Caltech Authors - Main

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OG.4.1.08 
The Trans-Iron Galactic Element Recorder(TIGER): 
A Balloon-borne Cosmic-Ray Experiment 
S.H. Sposato1 , L.M. Barbier2 , W.R. Binns1 , E.R. Christian2 , J.R. Cummings1 , G.A. de Nolfo3 , 
P.L. Hink1 , M.H. Israel1 , R.A. Mewaldt3 , J.W. Mitchell2 , S.M. Schindler3 , R.E. Streitmatter2 , 
C.J. Waddington4 
1 Physics Department and McDonnell Center for Space Sciences, 
Washington University, St. Louis, MO 63130, USA 
2 Laboratory for High Energy Astrophysics, Goddard Spaceflight Center, Greenbelt, MD 20771, USA 
3 Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USA 
4 Department of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA 
Abstract 
TIGER is a balloon-borne cosmic-ray experiment designed to measure the elemental abundances of Galac-
tic Cosmic Rays (GCRs) in the charge range 26::; Z ::;40 with better than 0.25 charge unit( cu) resolution. The 
experiment consists of a combination of plastic scintillators, plastic and aerogel Cherenkov detectors, and scin-
tillating fiber hodoscopes. TIGER was flown from Fort Sumner, NM aboard a high-altitude balloon on Septem-
ber 24, 1997 at geomagnetic cutoffs between 4.2GV and 3.2GV, and atmospheric depths between 3g/cm2 and 
6g/cm2 • The 23.5-hour balloon flight provided a statistically significant sample of GCR nuclei up through Ni 
and achieved charge resolution capable of resolving Co from the much more abundant Fe. 
1 Introduction: 
The Trans-Iron Galactic Element Recorder (TIGER) is a balloon-borne cosmic-ray experiment that uti-
lizes plastic scintillation counters, plastic and aerogel Cherenkov counters , and scintillating optical fiber ho-
doscopes. It was designed to show that the elemental abundances of Ultra-Heavy GCRs, cosmic rays in the 
charge range 26::; Z ::;40, could be measured with resolution better than 0.25 cu over a large energy range. 
This version of TIGER is a prototype for the Charge Identification Module (ZIM) on the Advanced Cosmic 
Ray Composition Experiment for the Space Station (ACCESS) (Binns et al. 1997, 1999) and for the experi-
ment selected for the Ultra-Long Duration Balloon Flight Demo2000 (Link et al. 1999) which will fly for 100 
days in the year 2001. TIGER was flown from Fort Sumner, NM on September 24, 1997 at atmospheric depths 
between 3g/cm2 and 6g/cm2 for approximately 23.5 hours. The vertical geomagnetic cut-off varied from about 
4.2 GV to 3.2 GV. 
We have been able to measure the Co/Ni abundance ratio using data from this flight. This is an interesting 
and important measurement because it can put limits on the time between the nucleosynthesis and acceleration 
of cosmic rays. The Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer( ACE) 
has measured isotopes of Co and Ni at energies < 500 Me V /nucleon. That measurement found that 59Ni, which 
decays only by electron capture, has all decayed to 59Co, implying that acceleration occurred more than 105 
years after nucleosynthesis (Weidenbeck et al. 1998). At higher energies, isotopic data are not available, but 
elemental abundances can put constraints on the decay of 59Ni. Englemann et al. ( 1990) measured a Co/Ni ratio 
of~ .12 at about 1 Ge V /nucleon. Balloon measurements of this ratio, extrapolated to the top of the atmosphere, 
have been0.17±0.05 (Dwyer & Meyer, 1985), and0.26±0.11 (Esposito et al. 1992). The measurement TIGER 
makes of the Co/Ni ratio will help resolve this discrepancy. 
2 The TIGER Instrument: 
The TIGER instrument contains three scintillation counters with wave-length-shifter-bar readout and three 
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Cherenkov detectors: 1 acrylic (n = 
1.5) radiator in a light box , 1 aero-
gel (n = 1.04) radiator in a light box, 
and 1 wavelength-shifter-bar readout 
Cherenkov detector with an acrylic 
radiator. (See Figure 1.) The latter 
detector is a new model being tested 
for possible use on ZIM . The scintil-
lation counters and the two light-box 
Cherenkov counters together provide 
charge and velocity measurements of 
the cosmic rays, provided that path-
length through the instrument can be 
determined. The 68 Photomultiplier 
Tubes (PMTs) from the scintillators 
and Cherenkov detectors are each in-
dividually pulse-height analyzed. 
The trajectory of each cosmic ray 
-------- 12g't.'tn ---------
l 
PMT 
through the instrument is measured . . . 
to within a few millimeters using a Figure 1: Cross-sect10n of the TIGER mstrument 
Coarse Hodoscope and a coded Fine Hodoscope. Each consists of two planes of 1.5mm x l .5mm square scin-
tillating optical fibers, one at the top of the stack and one at the bottom. Each plane has two layers of fibers, 
one each in the X and Y directions. The Coarse Hodoscope determines position to within 8cm and the Fine 
Hodoscope determines position to within 6mm. (Lawrence, 1996; Sposato et al. 1997) 
3 Data Analysis: 
We first corrected the data from from the 1997 balloon flight for variations in pathlength using the ho-
doscopes. The angle (B) with which the particles traverse the instrument was determined, and then each of 
the scintillator and Cherenkov signals was divided by sec(B). Next we corrected the data for areal response 
variations. After the initial sec(B) correction was applied, the data still showed a residual sec(B) dependence. 
This effect was greatest in the scintillator at the top of the stack, while the data from the scintillator at the bot-
tom of the stack did not show this effect. This residual dependence is probably related to the change in energy 
deposition of knock-on electrons with depth in the detector stack. We removed this effect by empirically fitting 
the angle dependence of the Fe peaks in the top two scintillators. 
We then made cuts to reject particles that interacted in the detector stack. Two criteria were used for se-
lection. First, the charge measured in SO and S 1 must agree to within 0.7 cu. Then the average of (SO + S 1) 
must agree with S2 to within 0.7 cu. Figure 2 shows the data after the aforementioned cuts and corrections 
were made. On the ordinates of A and B, we plot s0 ·59 where S = (SO +S 1 + S2). We obtained the exponent 
empirically: s0 ·59 ex: Z. The exponent is not 0.50 because of scintillator saturation. On the abscissa of A, we 
plot (C1 .5 ) 0 ·50/ s0 ·59 , which is a function of energy, independent of charge. On B, we plot (C1 .04 ) 0 ·50/ s0 ·59 for 
the same reason. There is no saturation in either of the Cherenkov detectors, so c0 ·50 ex: Z. A small number of 
events with (Cl.5)0 ·50;s0 ·59 < 0.28 (energy< 0.8 GeV/nucleon) were removed from the data-set. 
For events with (C1.04 ) 0 ·5 I s0 ·59 <0.13, energy below the Aero gel threshold of~ 2.5 Ge V /nucleon, (region 
1, Figure 2B.), we fit the S0 ·59 vs. (Cl.5)0 ·5 I s0 ·59 Fe with the following 2nd degree polynomial to correct for 
variations of s0 ·59 with energy: 
The charge resolution in energy region 1 is 0.25 cu. (See Figure 3.) 
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Cl',) 
Ln 
0 
~ 
A 
600 
500 
400 
300 
200~~~~~~~~ 
0.2 0.3 0.4 0.5 
(C )0_5 / So_ae 
1.5 
(1l 
L!l 
0 
rt::: 
B 
600 
1 2 3 
500 
400 
300 
200 ~~~~~~~~ 
0.0 0.2 0.4 0.6 
(C )0.5 I S0.59 
1.{]4 
Figure 2: A: Data from the acrylic Cherenkov detector and the scintillators. B: Data from the aerogel 
Cherenkov detector and the scintillators. (See text for more details.) 
For events with 0.13 <(Ci.04 ) 0 ·5/ s0 ·59 <0.37, energies of 2.5 - 7.5 GeV/nucleon, (region 2, Figure 2B.) we 
fit the s0 ·59 vs. (C1.04 ) 0 ·5 I s0 ·59 Fe with the following 2nd degree polynomial to correct for s0 ·59 variations: 
The charge resolution in energy region 2 is 0.3 cu. (See Figure 4.) Analysis of energy region 3 is in progress 
and will be presented at the conference. 
The Co/Ni ratio measured at the instrument (TIGER) and at the Top of the Atmosphere(TOA) are shown in 
Table 1. We have used empirical curves from Israel et al.(1979) for Mn/Fe versus atmospheric depth, assum-
ing that Mn/Fe and Co/Ni have the same atmospheric dependence. The Mn/Fe ratio grows with atmospheric 
depth(x) as exp(x/A), where A- 1 = 0.0343 ±0.0052. 
Energy(Ge V /nucleon) TIGER TOA 
0.8 - 2.5 0.17±0.06* 0.13±0.05 
2.5 - 7.5 < 0.15** < 0.12** 
0.8 - 7.5 0.13±0.04* 0.10±0.03 
Table 1: Co/Ni ratio measured at TIGER and at the TOA. (*Statistical error only. ** 1 a upper limit.) 
4 Discussion: 
Our Co/Ni measurement is consistent with that made by Englemann et al. at similiar energies and is marginally 
consistent with those made by Esposito et al. and Dwyer & Meyer at similar energies. Webber & Gupta(l 990) 
calculate that if none of the 59Ni has decayed, the Co/Ni ratio at these energies would be about 0.1 O; the ratio 
would be about 0.15 if the 59Ni had all decayed to 59Co. Our (and Englemann's)resultcould thus be interpreted 
to suggest that cosmic rays observed at a few GeV/nucleon were accelerated in a time :=::; the 59Ni electron-
capture half-life (8x 104 yrs). This is in disagreement with the clear ACE/CRIS result for lower-energy cosmic 
rays where complete decay of 59Ni is observed, indicating an acceleration delay > 105yrs. This disagreement 
suggests that either the cross-sections are incorrect, or the propagation model is incorrect, or differences ex-
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400 30 
Fe 
300 
(fl 00 20 Ni +> +> 
~ 200 ~ ::l = 0 0 
u u 10 
100 
Ni 
a 0 
350 400 450 500 480 500 520 
So.59 * F(C i o.5 /S{J_5g) So_59 * F(Ci 0_5 /So 59) 
Figure 3: Histogram of Fe region data for energies between 0.8 - 2.5 Gev/n_ 
80 30 
Fe 
60 
Y.l 00 20 
+> +> 
~ 40 ~ ::l Ca = 0 0 
u u 10 
20 Ni 
0 0 
350 400 450 500 550 480 500 520 
So 59 * F(COo 5 /S{J_5g) So_59 * F(C00_5 /So 59) 
Figure 4: Histogram of Fe region data for energies between 2.5 - 7 .5 Gev/n_ 
ist in the time delay between nucleosynthesis and acceleration for GCRs observed at 500 MeV/nucleon and 
1 GeV/nucleon. 
References 
Binns, W.R., et al., 1997, Proc. 25st Internat. Cosmic Ray Conf.(Durban) 5, 65 _ 
Binns, W.R., et al., 1999, Proc. 26st Internat. Cosmic Ray Conf.(Salt Lake), 004.2.22. 
Dwyer, R. and Meyer, P., 1985, ApJ, 294, 411. 
Englemann, J.J., et al., 1990, A & A, 233, 96. 
Esposito, J.A. et al., 1992, Astropart. Phys., 1, 33. 
Israel, M. H., et al., 1979, Proc. 16th Internat. Cosmic Ray Conf.(Kyoto), 1, 323. 
Lawrence, D.J., 1996, Washington University Ph. D. Thesis. 
Link, J ., et al., 1999, Proc. 26st Internat. Cosmic Ray Conf.(Salt Lake), OG4. l .15. 
Sposato, et al., 1997, Proc. Conf. Scintillating and Fiber Detectors, 527. 
Webber, W.R. and Gupta, M., 1990, ApJ, 348, 608. 
Weidenbeck, et al.,1999, ApJL, Submitted for publication. 
© University of Utah • Provided by the NASA Astrophysics Data System 


The Trans-Iron Galactic Element Recorder (TIGER): A Balloon-borne Cosmic-Ray Experiment

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The Trans-Iron Galactic Element Recorder (TIGER): A Balloon-borne Cosmic-Ray Experiment

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