QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL Qual. Reliab. Engng. Int. 2009; 25:899–911 Published online 9 February 2009 inWiley InterScience (www.interscience.wiley.com). DOI: 10.1002/qre.1003 Research Augmenting Real Data with Synthetic Data: An Application in Assessing Radio-Isotope Identification Algorithms ‡ T. Burr 1, ∗, † , M. S. Hamada 1 , T. L. Graves 1 and S. Myers 2 1 Statistical Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. 2 Advanced Nuclear Technology, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. The performance of Radio-Isotope IDentification (RIID) algorithms using gamma spectroscopy is increasingly becoming important. For example, sensors at loca- tions that screen for illicit nuclear material rely on isotope identification to resolve innocent nuisance alarms arising from naturally occurring radioactive material. Recent data collections for RIID testing consist of repeat measurements for each of several scenarios to test RIID algorithms. Efficient allocation of measurement resources requires an appropriate number of repeats for each scenario. To help allo- cate measurement resources in such data collections for RIID algorithm testing, we consider using only a few real repeats per scenario. In order to reduce uncertainty in the estimated RIID algorithm performance for each scenario, the potential merit of augmenting these real repeats with realistic synthetic repeats is also considered. Our results suggest that for the scenarios and algorithms considered, approximately 10 real repeats augmented with simulated repeats will result in an estimate having comparable uncertainty to the estimate based on using 60 real repeats. Published in 2009 by John Wiley & Sons, Ltd. KEY WORDS: bias-variance tradeoff; isotope identification algorithm; Lehman–Scheff´ e theorem; NaI detector; synthetic data 1. INTRODUCTION S ecuring the U.S. border against terrorist threats, such as dirty bombs, regularly makes the news (Redeker 1 ), as deployed sensors at various locations screen for illicit nuclear material. Many of these sensors rely on Radio-Isotope IDentification (RIID) algorithms using gamma spectroscopy to resolve innocent nuisance alarms. Current alarm rates among all ports of entry into the U.S. are approximately 1% (see, for example, Stromswold et al. 2 ), and these alarms are essentially all nuisance alarms due to innocent naturally occurring radioactive material such as can occur in cat litter or ceramics. Consequently, assessing ∗ Correspondence to: T. Burr, Statistical Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. † E-mail: tburr@lanl.gov ‡ This article is a U.S. Government work and is in the public domain in the U.S.A. Contract/grant sponsor: Department of Homeland Security; contract/grant number: DE-AC52-06NA25396 Published in 2009 by John Wiley & Sons, Ltd.