The following chapters detail MED and LASL participation in Project TRINITY. Chapter 1 provides background information, including a description of the TRINITY test site. Chapter 2 describes the activities of MED and LASL participants before, during, and after the detonation. Chapter 3 discusses the radiological safety criteria and procedures in effect for Project TRINITY, and chapter 4 presents the results of the radiation monitoring program, including information on film badge readings for participants in the project. The information in this report is supplemented by the Reference Manual: Background Materials for the CONUS Volumes." The manual summarizes information on radiation physics, radiation health concepts, exposure criteria, and measurement techniques. It also lists acronyms and includes a glossary of terms used in the DOD reports addressing test events in the continental United States. CHAPTER 1 INTRODUCTION Project TRINITY was the name given to the war-time effort to produce the first nuclear detonation. A plutonium-fueled implosion device was detonated on 16 July 1945 at the Alamogordo Bombing Range in south-central New Mexico. Three weeks later, on 6 August, the first uranium-fueled nuclear bomb, a gun-type weapon code-named LITTLE BOY, was detonated over the Japanese city of Hiroshima. On 9 August, the FAT MAN nuclear bomb, a plutonium-fueled implosion weapon identical to the TRINITY device, was detonated over another Japanese city, Nagasaki. Two days later, the Japanese Government informed the United States of its decision to end the war. On 2 September 1945, the Japanese Empire officially surrendered to the Allied Governments, bringing World War II to an end. In the years devoted to the development and construction of a nuclear weapon, scientists and technicians expanded their knowledge of nuclear fission and developed both the gun-type and the implosion mechanisms to release the energy of a nuclear chain reaction. Their knowledge, however, was only theoretical. They could be certain neither of the extent and effects of such a nuclear chain reaction, nor of the hazards of the resulting blast and radiation. Protective measures could be based only on estimates and calculations. Furthermore, scientists were reasonably confident that the gun-type uranium-fueled device could be successfully detonated, but they did not know if the more complex firing technology required in an implosion device would work. Successful detonation of the TRINITY device showed that implosion would work, that a nuclear chain reaction would result in a powerful detonation, and that effective means exist to guard against the blast and radiation produced. 1.1 HISTORICAL BACKGROUND OF PROJECT TRINITY