DOI: 10.1007/s10967-008-0513-1 Journal of Radioanalytical and Nuclear Chemistry, Vol. 276, No.2 (2008) 363–367 0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2007 Akadémiai Kiadó, Budapest Springer, Dordrecht Prompt determination of evacuee radiation dose from a nuclear event P. P. Bachelor,* J. I. Friese, C. E. Aalseth, J. I. McIntyre, H. S. Miley, R. W. Perkins, G. A. Warren Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, USA (Received March 2, 2007) In anticipation of a nuclear detonation, techniques to quickly assess the radiation exposure of evacuees should be developed. Based on experience relating neutron radiation exposures to activation products, measurement of activation products can be performed in a few minutes. Personal items exposed to significant levels of radiation allows neutron dose assessment via the activation products. This approach allows prompt collection of important data on human exposure following a nuclear attack. Data collected will facilitate triage decisions for emergency medical treatment to ameliorate the radiation effects on exposed individuals. Activation experiments with everyday items exposed to a neutron source are presented. Introduction Methods should be developed to quickly assess radiation exposure of evacuees and the types of radiation involved in the event of a nuclear terrorist attack. Survivors exiting the vicinity of a nuclear detonation will need prompt radiation dose assessment, and this must be done in a manner that will not slow access to medical attention. The detonation of a nuclear weapon will instantly produce activation products from neutron and photon reactions at kilometer distances. The neutron activation products produced in individuals, personal items, vehicles, and other objects that exit the area can be measured via gamma-spectroscopy. Fieldable gamma-spectroscopy instrumentation may be deployed near the event center for measurement of short-lived radionuclides, but this equipment would likely be overwhelmed by the sheer volume of samples needing analysis; items would likely be collected for laboratory- based analysis of longer-lived nuclides. From these measurements, the associated radiation dose to which individuals have been exposed can be determined. Previous work relating neutron radiation exposures to activation products in individuals indicates it should be possible to make short measurements of activation products in individuals and personal items exposed to significant levels of radiation. 1–7 This approach allows prompt collection of critically important data on human exposure, and facilitates timely emergency medical treatment or decontamination to ameliorate the radiation effects on exposed individuals. Experimental The items studied include commonly used personal items and a medical isotonic solution containing elements present in human body fluids. The integrated fission neutron exposure to the samples was approximately 6 . 10 9 n . cm –2 from a 252 Cf neutron source (3.6 . 10 9 n/s), at a distance of 50 cm from the source, for * E-mail: paula.bachelor@pnl.gov a fission neutron flux of 10 5 n . cm –2. s –1 , and a neutron equivalent exposure of 2.3 rad. 8 A Lucite block (15 cm 40 cm 40 cm) was located behind the samples to approximate the moderation resulting from the human torso. Two types of gamma-ray spectrometry radiation detector systems were used in measuring the neutron activation products: (1) high purity germanium (HPGe); and (2) dual sodium iodide [NaI(Tl)] detectors. 9 The HPGe detectors used were 40% and 60% efficient relative to a 3” 3” cm NaI(Tl) detector, contained in a passive shield of 10 cm lead; the NaI(Tl) detectors used were two 30 cm diameter 20 cm thick NaI(Tl) crystals surrounded by an anticoincidence shield of plastic scintillator 30 cm thick, a neutron shield of 15 cm thick borated polyethylene, and passive shielding of 10 cm lead. Because of their large size, each of the NaI(TI) detectors provides about an order of magnitude higher photopeak counting rates versus the HPGe detectors for small area samples and would provide about two orders of magnitude higher counting rates for very large samples, including the human body. When operating in coincidence, the dual NaI(Tl) detector system provides an extremely selective measurement of those radionuclides that decay by coincidence gamma-ray emission. 9 Coincidence techniques are highly useful for pulling a very weak signal out of a high background, and were studied to determine the applicability to these activation measurements. Results In this preliminary study, the items were irradiated and the activation products observed as indicated in Table 1. The observed counting rates are approximately one-tenth the expected rate for a neutron radiation dose equivalent of 2.3 rad if the neutron energy spectrum was similar to those shown in Fig. 1 for a medium-yield fission detonation at distances of 0.5 km and beyond.