A methodology for improving throughput using portal monitors

Abstract

The National Internal Radiation Assessment Section (NIRAS), which operates the Canadian National Calibration Reference Centre for Bioassay and In Vivo Monitoring, has field deployable equipment for emergency response. A substantial part of this tool kit is a set of portal monitors that can be used to quickly screen people into the 'uncontaminated' and the 'contaminated'. The former term refers to a person who has <60 kBq (empirical practical detection limit) of activation/fission products and the latter group is contaminated by that amount or more. Recent field work has shown that one type of the NIRAS's portal monitors can be alarmed at significant distances if the level of contamination is high enough. The other types, which do not initiate a count until either an infra-red beam is broken or a proximity detector is activated, do not alarm but their background will be raised and this causes other problems. This paper proposes a method of group monitoring to help speed up the process of screening a large number of potentially contaminated persons using portal monitors. In short, the group of potentially contaminated persons will be kept isolated from the portal stations. Depending on a real-time estimate of the percentage of contaminated persons in the crowd, groups of persons will be selected for screening. The hypergeometric distribution has been used to decide on the sampling group size with an expectation that 90% of the time no contaminated person will be present in the group. Once removed from the main waiting area, the group will be pre-screened and then, depending on the result, sent to the appropriate portal. It is anticipated that this will greatly speed up processing as it substantially reduces the transit time. Transits times have also been estimated in addition to the number of personnel required to run all of NIRAS's field deployable equipment.

Psychosocial considerations for mass decontamination

“…In both cases, these requests were not refused, and in doing so, these vulnerable subgroups received the reassurance they needed from public officials. Pre-screening such groups using sensitive portal monitors (30) may assist in separating those who fear they are contaminated from those who are actually contaminated and provide greater speed and efficiency. Psychosocial guidance should also be on hand to provide the targeted reassurance and advice about coping strategies (31) .…”

Radiation Screening

“…However, during a large‐scale incident this may be impractical, and hospitals should plan to screen large numbers of patients using fixed and hand‐held survey meters 2 . While operator fatigue and the time required to perform a thorough examination are the major limitations of hand‐held survey meters, logistical challenges with portal detectors include limitations of sensitivity at very low levels of contamination and potential alarming by sources other than contamination of the individuals being screened 3 …”

Modeling Population Screening Process for Maximizing Throughputs

“…The HML has a small stockpile of handheld radiation monitors, portal monitors, and high resolution portable whole body counters. Over the past years, the HML has carried out underlying research in support of this emergency response function (Kramer et al 2006(Kramer et al , 2007a(Kramer et al , 2007b(Kramer et al , 2009a(Kramer et al , 2009b(Kramer et al , 2012Kramer and Hauck 2011) as have others (Engdahi and Bharwani 2005;Miller et al 2011;Palmer et al 2012) looking at maximizing sensitivity of the screening techniques and the effect of persons carrying substantial contamination (either externally or internally) on the screening equipment. In addition, the HML has also had the opportunity to participate in several large scale exercises that have provided both experience and ideas for improving its field deployable capabilities (Cornett et al 2009;Cornett and Kramer 2010;Kramer et al 2005Kramer et al , 2007cKramer et al , 2009c.…”