Additional Study Information: The purpose of this study is to use blood from healthy people to develop a test to see if people have been exposed to radiation. Between 2 and 3 tablespoons of blood will be drawn from your arm. The blood will be tested with radiation in our laboratory at the Center for Radiological Research at the Columbia University Irving Medical Center. We will measure the cellular damage that results and any changes in the genes that are expressed. Also, we may use your blood sample to develop high throughput assays and technologies to obtain these results from much smaller amounts of blood. This is so that these tests can be done with only a drop of blood. This research is aimed at developing future biomarkers of radiation exposure but cannot currently provide any meaningful information about you or your health status. Participants will receive $20 compensation. Non-CUIMC volunteers may qualify for a travel reimbursement of $30.