Real Time in Situ Gamma Radiation Measurements of the Plume Evolution from the Full-Scale Radiological Dispersal Device Field Trials

Abstract

During the Full-Scale Radiological Dispersal Device Field Trials carried out in Suffield in 2012, several suites of detection and sampling equipment were used to measure and characterize the explosive dispersal of the short half-life radioactive tracer Lanthanum-140 ((140)La). The equipment deployed included networks of in situ real-time radiation monitoring detectors providing measurements of different sensitivities and characteristics. A dense array of lower sensitivity detectors was established near field, ranging from 10 to 450 m from the detonation location. A sparser array of more sensitive detectors was established in the far field (150 m to 3.5 km from the detonation location). Each was used to collect and report the dose rate data from the radioactive plume passage with a sample time resolution of 1 s. The two systems went through independent calibrations and were compared and shown to be consistent with each other. The in situ gamma radiation measurements have allowed the movement and evolution of the plume to be described and to identify deposition rates and non-uniformities in the temporal shape of the plume. This knowledge could be applied for emergency planning guidance for the case of release of radioactive material by a radiological dispersive device.

Deposition Measurements From the Full-Scale Radiological Dispersal Device Field Trials

“…Twenty-four fixed-point surveillance (FPS) detector field systems were also deployed, as described in Korpach et al (2016). These detectors, which use 3" Â 3" NaI(Tl) crystals with 1,024-channel spectroscopic measurement over a 0 to 3 MeV energy range, have been used by Health Canada for autonomous outdoor measurement as part of their radiological monitoring network since 2002 and are calibrated for reporting of dose rate.…”

“…The response of the RadEye PRDs in this configuration was characterized by comparing pre-shot count rate data to detailed GEANT4 Monte Carlo models, as described by Korpach et al (2016) and detailed by Liu and Erhardt (2016). The RadEye PRD reports count rates using several different energy thresholds as inputs to its proprietary natural background rejection algorithms; based on experimental evaluation of the detector response to 140 La, the "Z2" threshold count rate was selected.…”

“…The array collected data for about an hour before each shot, during the plume passage, and for 1 to 2 h after the shot. After the event, the data were post-processed to compensate for any drift in gain of the NaI(Tl) system, allowing a more accurate energy-dependent dose rate calibration, as described in Korpach et al (2016).…”

“…These measurements were performed using an array of 250 pre-positioned RadEyes, mounted in 1-m-high stands, which were co-located with a subset of the witness plates. The positions of the detectors and the way they were deployed and used were also reported by Korpach et al (2016). For the purposes of comparison to the witness plate measurements, the deposition count rate was converted into surface activity density (in Bq m −2 ) using a combination of measurements in the field produced by the 140 La source before detonation and Monte Carlo simulations to calibrate the detector response.…”

Challenges for Physics-Based Models of a Radionuclide Dispersal Device

“…Various aspects of an RDD attack have been already studied both computationally [5,6,[11][12][13] and experimentally [14][15][16]. As pointed out by Magill et al [8], to estimate the consequences of an RDD attack, "one needs to quantify the type of radioactive material (the source term) and to model the dispersion under the meteorological conditions at the time of the detonation".…”