TIGER Questions and Answers

about the TIGER Instrument

1. Why is this program so important to the NASA and NOAA administrations?

   It is important to NASA because the scientific community (through independent reviews of our TIGER proposals for funding) has decided that understanding the origin of galactic cosmic rays is scientifically interesting and fits with NASA Office of Space Science's goals for research. NOAA isn't very interested in TIGER.

2. If galactic cosmic rays leave the galaxy where do they go, and do they ever return? How vital are these rays to the survival of our Galaxy?

   Galactic cosmic rays continually leak out of the Galaxy. They then wander around the Universe, occasionally passing through other galaxies. Some cosmic rays here at Earth are from galaxies other than the Milky Way. Estimates are that about one in a million is extragalactic at these energies, so during the last flight, we may have gotten one. There is no way to distinguish it from any of the others, however.

   Cosmic rays don't really affect the "survival" of the Galaxy. But they do affect how the Galaxy evolves. They contain as much energy, on average, as starlight, the galactic magnetic field, and the interstellar gas. So they can affect how the gas moves in the Galaxy, which affects the star-forming regions that create the next generation of stars.

3. Does the extreme cold of the area affect the equipment?

   As TIGER goes up through the atmosphere, it can see temperatures as low as -70 Fahrenheit, so it is designed for low temperatures. For the most part, we are running in an insulated and heated building, so there is no problem. The biggest cold affect on equipment I've dealt with directly is with batteries. They don't last very long when they're cold. Flashlights (which we used in Scott's Hut) and cameras need either recharging or battery replacement pretty often.

4. How is aerogel made?

   I've never made it myself, but I found a good website on how to make it at Berkeley Lab.

5. Was the material made for TIGER's scintillator, poly-vinyl toluene, invented specifically for this mission? Was it in existence before? Can this PVT and/or the scintillator be recycled for different missions and projects dealing with GCRs?

   Poly-vinyl toluene is a very common type of plastic. The sheets we used had two extra "dyes" mixed in. One of them (p-Terphenol), makes the plastic give off much more light (scintillation) as the cosmic ray passes through it. The scintillation light is mostly in the ultraviolet, so the second dye is a wavelength shifter that turns the UV light into a bluer light that the photomultiplier tubes are more sensitive to. That dye is probably something called Bis-MSB, but the company (Bicron) that we bought the scintillator from considers the exact formulation proprietary. Bis-MSB is short for 1,4-bis[2-methlystyryl]benzene, if you're interested.

   This type of scintillator is used in many cosmic ray and particle physics experiments, and each sheet costs about $1000, so we will re-use them, if possible. Over time, the sheets get "crazed", meaning the surface distorts, and you get less light out to the photomultipliers (which is not as good).

6. Are there any considerations for turning to outside Earth orbit observations, such as solar-focused satellites (such as SOHO and GOES), ISS, or Chandra to gather further or possibly better data on cosmic rays?

   The scientific community that studies cosmic rays proposes all the time to get satellites built that will study cosmic rays (see for example HNX), but many propose and few are accepted. Satellites are expensive (the cheapest are currently $120 million).

7. Is the resolution of the 2003 version of TIGER superior to that of the 2001 version - enough that we can gather much more data on particles with atomic number > 32?

   TIGER2003 does not really have better resolution than TIGER2001. We will get a little improvement in our measurements because we've "thinned down" TIGER and will be flying higher (with a bigger balloon), so we'll lose less heavy GCRs to fragmentation. But basically we're just trying to double the number of atomic number > 32 particles we've measured (we only got about 300 in the last flight).

8. How will this benefit mankind?

   This is "pure science" that tells us about the creation and evolution of the matter that makes up us, the Earth, the Solar System, and the Galaxy. It won't have any immediate practical results, but this sort of research helps us understand the Universe better and may have practical applications eventually. Exploration is often useful just for it's own sake.

9. What makes the galactic cosmic rays so difficult to measure?

   The cosmic rays that TIGER measures are subatomic particles (bare atomic nuclei) moving at almost the speed of light. They also tend to break apart in the instruments you use to try and measure them. But the methods that TIGER uses are actually technology that has been around for many years. The biggest difficulty is actually the rarity of the cosmic rays that TIGER is interested in. In our record breaking 31.5 day flight in 2001-2002, we only collected about 300 particles of the elements between 30 and 40 (the main ones we're interested in). That's only about 10 per element, which doesn't give us a great measure of the relative abundance, which is necessary for our science. For some of the elements, we still did better than any earlier experiments, but we really need to collect more data. Which is why we're back in Antarctica.

10. Is there any way to tell what kind of interference a GCR may have experienced on its way to TIGER?

    There is no way to tell the history of an individual GCR. It is possible to tell on a statistical (average) way some things about the travels of galactic cosmic rays, i.e. their average age, how much matter they've passed through, etc. These have been determined with other cosmic ray instruments, not TIGER.

11. What is your research like? How much time do you spend on it each day?

    I spent 8 or more hours a day working on TIGER (and other research). I'll cover the science of TIGER (which is an extended topic) on the web pages.

12. Is Antarctica the only place the research can be done?

    Antarctica is the best place, but not the only one. It is best because we get 24 hours of daylight and can fly around the world while staying over land, and without crossing any political borders.

13. What are the instruments that you use for measuring cosmic rays, and how do they work?

    The TIGER instrument is one experiment with a stack of different detectors, which are all measuring the same particles. We have four detectors that measure the position of the cosmic rays (x and y position at the top and bottom of the experiment) and that gives us the exact path of the particle through the stack of detectors. We have four identical detectors, called scintillators, that measure the energy of the cosmic rays. Four independent measurements combine to give us one good one, plus we can see the particle actually slowing down (losing energy) as it passes through TIGER. And we have two detectors called Cherenkov detectors that measure the velocity of the cosmic rays (the two are "tuned" for different ranges of cosmic ray velocity).

    All of the detectors work by giving off small amounts of light when the particles pass through. Devices called photomultiplier tubes (there are almost 200 photomultipliers on TIGER) convert the light into electrical signals and, with these signals, we can get a measurement of the amount of light. These measurements are fed into an onboard computer, which transmits the data to the ground. After the flight we will take all the measurement and try and reconstruct what type of particle gave off those amounts of light.

14. What is the Mechanical Technician (Dana Braun for the 2003-2004 campaign) in charge of doing concerning the program?

    He's done a lot of the actual assembly of the instrument - bolting together structure, attaching photomultiplier tubes, making and installing the thermal shields, etc.

15. Why is the TIGER experiment only designed to measure galactic cosmic rays with atomic numbers between 26 and 40?

    Below charge 26, the CRIS instrument on ACE has already done more observation than we could possibly do with TIGER. Elements above atomic number 40 are so rare that TIGER will measure too few particles to do any science with. For these, we will need a spacecraft flying for years, which we are proposing to build (it's called HNX).

16. What is the proposed budget for this project?

    The total budget is difficult to estimate, because the money is coming from a bunch of different sources. I've heard that it costs the NSF more than $2000 per person per day to have someone down here at McMurdo, and TIGER and NSBF combined have more than 20 people. By the time you add in the cost of equipment, shipping, and salaries, it's probably over a million dollars. This is still considerably cheaper than a spacecraft, the cheapest of which currently cost about $75 million. I realize that these seem like big numbers, but a lot of the cost is salaries. When you have a large team of highly-skilled, and pretty highly-paid people working on something for a number of years, the costs add up.

17. Who is funding the program and is it enough to meet your needs?

    NASA is funding the program (with the National Science Foundation covering some of the costs of being in Antarctica). We have not had a lot of money to make improvements that would be nice, and we've had to reuse a lot of old detectors to save money, but since the program has been very successful, we've obviously had sufficient funds to do good science.

18. Do the wind patterns and or temperature patterns affect your experiment?

    Other than the ground winds needed for launch, we also need the winds at 120,000 feet (the altitude we'll fly at) to be stable and "circumpolar". This is another way of saying that they just circle around the pole, so our instrument will circle the continent and come back to almost directly overhead. This circular wind pattern will start about December 10, and this is what sets the first possible day we can launch. And, while we have to watch the temperature of our instrument so that it doesn't get too hot or too cold, the ground temperatures don't affect it at all.

19. Do you collect or monitor any data about other parts of the EM spectrum and does this relate in any way to the size of the ozone hole?

    Our instrument doesn't do anything but detect cosmic rays, which are particles and not part of the EM spectrum.

20. Does the solar wind / solar flares have any effect on your experiment?

    The solar wind is very low energy and doesn't get through the Earth's magnetic field, which extends out 60,000 miles. Solar flares can occasionally accelerate particles up to the energy that TIGER measures, but we'll know (from spacecraft like ACE), if that is happening.

21. Has global warming had any effect on your experiment or on animals that live there?

    Our instrument measures cosmic rays above the atmosphere and is completely unaffected by global warming. I know that several species (Emperor Penguins for example) are now breeding farther south than they were 30 years ago.