My academic work falls into two primary categories - research centered around the natural radiation environment , and work addressing various aspects of radiological and nuclear terrorism. In addition to these primary topics of interest, I have also published a number of papers on several practical aspects of radiation safety, primarily in areas related to administering radiation safety programs.
Natural Radiation Environment
Every living organism on earth is exposed to natural radiation; from natural radioactivity in the rocks and soils, radiation from cosmic sources, even natural radioactivity in our own bodies. Not only do these sources of radiation change from place to place on the Earth, but they have also changed over the history of life on our planet. Not only that, but as we climb mountains, climb into airplanes, or (for those lucky few) launch ourselves into space, radiation levels increase still more. Where this natural radiation comes from, the manner in which it changes from place to place on Earth, and how it affects us are all areas of intense interest. Of particular interest to me is the natural high background radiation area in Ramsar Iran, where I was lucky enough to visit in 2000. I am also fascinated by the natural nuclear reactor that formed in what is now Oklo (a part of the nation of Gabon, in western Africa), although I have not yet had the opportunity to visit.
This is also a topic of some importance - do airline passengers and crew face an elevated risk of cancer from flying? Are miners exposed to unsafe levels of radiation? Will radiation kill astronauts before they can reach Mars? Can a nearby supernova exterminate life on Earth? Or, for that matter, will interstellar radiation levels prevent living micro-organisms from traveling between planets? Should people living in areas of unusual geology be relocated to reduce their risk of cancer? We cannot even begin to answer these questions unless we understand the natural radiation environment; and studying them could well help us to better understand the risks we face from radiation from both natural and artificial sources.
My primary focus in studying the natural radiation environment has been to study the history of life's exposure to radiation. I have been working to develop mathematical models that describe changes in terrestrial, cosmic, and biological sources of radiation over the history of life on Earth. It seems likely that radiation levels today are lower than ever in the history of life on earth; not only that, but the mix of radiation to which we are exposed has changed as well - the earliest life was likely exposed to ultraviolet, beta, and gamma radiation while today over half of natural radiation exposure consists of inhaled alpha particles. Perhaps understanding these changes and their effects on life might help us better understand why we respond as we do to various types of DNA damage.
Another of my areas of interest is that of radiation and life in the universe. As one example, supernovae erupt in our galaxy a few times each century, and from time to time, they are bound to be fairly close to the Earth. In fact, researchers have found evidence of "live" radioactive debris from one such supernova in deep-sea sediments. Supernovae are among the most energetic events in the universe - astronomers have been able to identify supernovae across the visible universe - and many people have wondered if such events might have caused some of the mass extinctions we see on Earth. Even more energetic than supernovae are gamma ray bursts, and these have raised similar speculations. Luckily, our atmosphere provides a lot of radiation shielding, and it turns out that these events are not likely to affect life on our planet unless they are very close.
On the other hand, it is possible that events such as these might make it difficult for living organisms to travel through space; either between planets in our own solar system, or between solar systems. It is possible that interplanetary or interstellar radiation levels (from supernovae and gamma ray bursts) may be the major factor limiting the ability of life to spread through universe through space; this is an area that I continue to investigate as time permits.
Radiological and Nuclear Terrorism
Radiological weapons, while they have never been used, have the potential to cause large-scale disruption to a city that is attacked. Although radiological weapons are unlikely to cause massive numbers of casualties, the use of such devices may lead to social unrest and fear, and recovering from such an attack is likely to be lengthy and costly, possibly rendering large areas off-limits until clean-up is completed. In addition, many of our emergency responders and medical caregivers are unfamiliar with radiological emergencies, and it is possible that this lack of familiarity may complicate the response to a radiological emergency. For this reason, the threat of a radiological attack must be taken seriously.
Of particular concern is the availability of radioactive materials that might be used in such an attack. This was highlighted by a recent GAO investigation, in which a phony company received a radioactive materials license, which could have been used to purchase radioactive materials for illicit purposes. There have also been concerns raised that radioactive materials might be sold to a phony company overseas, only to be smuggled back into the US to be used in a terrorist attack.
If terrorists are successful in obtaining radioactive materials, they may choose to launch either an overt attack (a "dirty bomb") or a covert attack (sometimes called a "smoky bomb"). Much has been written about the former, and somewhat less about the latter. There are also several sites with information for emergency responders and medical professionals who are responding to a radiological attack. In addition to these web sites, there is a large literature on the impact of radiological terrorism.
As potentially bad as a radiological attack may be, a terrorist attack using nuclear weapons would be disastrous. We know what such weapons would do, having seen the results in Japan at the end of the Second World War. A nuclear attack in a major city could leave hundreds of thousands dead and hundreds of thousands more injured - in addition to the financial, economic, psychological, and social impact.
Making a radiological device is very little more difficult than is making any other terrorist bomb. Making a nuclear device is far more complex; physics alone places many constraints on the potential nuclear bomb-maker, and obtaining sufficient quantities of fissionable materials is even more difficult; but not impossible. There is a great deal of information available that describes the basics of nuclear weapons design and, even if making a miniaturized high-yield weapon is beyond the reach of even most nations, making a weapon comparable to the ones used in Japan is entirely possible. (http://nuclearweaponarchive.org/). In addition, the proliferation of nuclear weapons technology (and the instability of some existing nuclear weapons states) raises other possibilities for the spread of nuclear weapons to terrorist organizations.
There is a tremendous literature on the effects of nuclear weapons. Perhaps the best single reference is, appropriately enough, The Effects of Nuclear Weapons, by Glasstone and Dolan. Another good book that discusses the thermal effects of nuclear weapons (e.g. mass fires, or "fire storms") is "Whole World on Fire" by Lynn Eden.
We have no way of knowing the likelihood of a radiological or nuclear attack, so it is difficult to decide how much time and effort to devote to preparing for a response to such an attack. However, we can expect that some effects from such an attack might be similar to what we might see from some other disasters, natural and otherwise.