WAM-E - Instrumentation 1 Baltimore 1-2 10:00 - 12:00
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| Chair(s): Aaron Specht
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WAM-E.1
10:00 Experimental design and testing of a portable x-ray tube based KXRF system to measure lead in bone M Khan, Purdue University
; CJ Burgos, Purdue University; TR Grier, Purdue University; MG Weisskopf, Harvard T.H. Chan School of Public Health; KM Taylor, United States Army Institute of Environmental Medicine; AJ Specht*, Purdue University
Abstract: X-ray Fluorescence (XRF) is commonly used to measure cumulative exposure to lead. For many years, a method called K-shell x-ray fluorescence (KXRF) had been utilized to detect the adverse effects of metal exposure on human health. Although the equipment had undergone numerous advancements, it still has some limits. Due to its bulkiness, the liquid nitrogen cooled germanium detectors, and radioisotope it is not very portable. The technology also has concerns with long measuring times and strict licensing and maintenance requirements. In this study, we developed a new portable K-shell XRF for bone lead measurement utilizing a 140kV x-ray tube with two CdTe detectors in a 90o geometry with a ten-minute measurement time. Lead concentrated standard bone phantoms, cadaver bones, and goat bones were measured to test the limitations of the system. Aluminum and molybdenum sheets were used for the shielding and optimization of the beam. A multinuclide radioisotope calibration source was used to standardize the detector setup. We identified a peak fitting method with a normalization based on the total spectral scattering. Using two CdZnTe detectors with 1cm3 active area during a measurement gave us a limit of detection (LOD) of 0.6ug/g bone mineral for our new bone measurement system. This can be compared to the LOD for previous KXRF was 2-3ug/g and pXRF was 2-10ug/g. Thus, our new measurement system can detect lead at a factor of 3 greater efficiency than previous approaches enabling it for measurements of nearly all environmentally exposed population. This XRF was also tested with measurements of various biomarkers (blood, nails, hairs etc.) including other metals of concern (cadmium, arsenic, mercury, etc). Thus, with this iteration of XRF technology, it is possible to design a device that included the benefits of KXRF on the portable scale for bone measurement methods while excluding their primary drawbacks by leveraging advancements in detector and x-ray tube technology.
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WAM-E.2
10:15 Improvements in Energy-Dependent Exposure Calculations using 3-D Pixelated CdZnTe DI Goodman*, H3D, Inc.
Abstract: 3-D pixelated CdZnTe crystals are commonly used in RadioIsotope Identification (RIIDs) and Passive Imaging Radiation Devices (PIRDs). The required exposure rate accuracy of RIIDs and PIRDs are dictated by the ANSI n42.34-2021 standards. Changes in Section 6.5 of ANSI n42.34-2015/2021 standards have expanded dose rate accuracy requirements from 137Cs only to 241Am, 137Cs, and 60Co energies [1][2]. A CdZnTe-spectral based exposure rate estimation algorithm was modified to accurately estimate dose rates across 60-1408 keV on H420, H400, and A401 gamma-ray imaging spectrometers using a constrained least-squares optimizer. Deviations between true and measured dose rates were less than 20% for 241Am, 133Ba, 137Cs, 60Co, 57Co, 152Eu, and 54Mn sources for each of the three detectors. Issues from non-uniform angular response, stemming from non-spherical detectors, is discussed and addressed using Compton and attenuation imaging information. Combined, these results suggest that dose rate measurements from CdZnTe imaging spectrometers are adequate to pass associated RIID exposure rate standards.
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WAM-E.3
10:30 Neutron Detection Sensitivity and H*10 Dosimetry - Tensioned Metastable Fluid Detectors vs He-3 (Ludlum 42-49B) and ROSPEC S Ozerov*, Purdue University
; N Boyle, Oak Ridge Institute of Science and Education; C Harabagiu, Purdue University; D DiPrete, Savannah River National Laboratory; T Whiteside, Savannah River National Laboratory; A Boone, Savannah River Nuclear Solutions; D Hadlock, Savannah River Nuclear Solutions; W Noll, Savannah River Nuclear Solutions; D Roberts, Savannah River Nuclear Solutions; RP Taleyarkhan, Savannah River Nuclear Solutions
Abstract: This paper presents results of experimental studies conducted at Purdue University and Savannah River Site (SRS) pertaining to comparisons of: (1) One-on-one neutron detection rate (cpm/mrem/h) sensitivity between ~2.5 kg (15 cc) centrifugally tensioned metastable fluid detector (CTMFD) compared against a 4.5 kg pressurized He-3 Ludlum-45-49B detector of similarl form factor; and, (2) Ultra-low (~5 micRem/h) through moderate (15 mRem/h) intensity spectrometric (H*10) neutron dosimetry with spectrometry enabled panel of four CTMFDs and compared against state-of-art spectrometric and survey mode systems – ROSPEC, Ludlum-42-49BTM and Eberliine ASP2ETM.
The first study was conducted using a collimated 1 Ci Pu-Be (,n) neutron source emitting 2e6 n/s, and variety of shielding materials: water, concrete and lead of thicknesses varying from 0 to 0.3 m. The CTMFD as deployed (non-borated) was configured for non-spectroscopic detection only of fast energy (> 0.1 MeV) neutrons whereas, the moderated Ludlum He-3 detector monitored fast to thermal energy neutrons. MCNP simulations were deployed to account for 3-D scattering-absorption effects and for computing the industry-standard cpm/mrem/h metric. It was found that with the tensioned negative pressure (Pneg) state of 0.6 MPa, the CTMFD offered up to ~5+ times higher cpm/mrem/h sensitivity vs the Ludlum meter. At Pneg = 1.1 MPa, the sensitivity gain exponentially rises to over 100x greater than that for the He-3 based Ludlum detector. For a borated CTMFD and inclusion of 0.02 eV to 10 MeV energy neutron detection, CTMFD sensitivity gain is estimated to rise to ~700x over that of the Ludlum.
The second study focused on spectroscopic (H*10) neutron detection; H*10 neutron dosimetry (unlike for gamma dosimetry), requires consideration of neutron energy spectra due to the 20x variation of the weight factor over the thermal-to-fast energy range, as well as the neutron radiation field dose rates ranging from cosmic (~micRem/h) levels to commonly encountered ~10-20 mRem/h in nuclear laboratories /processing plants, and upwards of 106 Rem/h in nuclear reactor environments. The H*-TMFD was first validated for gamma blindness using a 0.67 Ci Cs-137 source and the background dose rate in SRS’s low-scatter facility (LCF) with all neutron sources withdrawn was estimated at ~ 0.5 micRem/h. Thereafter, moderate and ultra-low radiation field neutron dose assessments were conducted for spectroscopic and survey mode neutron dosimetry with H*-TMFD, ROSPEC, Eberline and Ludlum devices.
From moderately high radiation fields tests conducted with the high intensity (1.6x109 n/s) Cf-252 source and a total data collection time of ~0.15 h the predicted dose rates from Eberline (non-spectroscopic), Ludlum (non-spectroscopic) and spectroscopic H*-TMFD instruments were found to be: ~17 mRem/h, ~20 mRem/h, and ~12 mRem/h, respectively. The equivalent spectroscopic (SRS measured) H*10 dose rate from ROSPEC value is ~ 13 mRem/h which is within 10% of H*10-TMFD measurement. Unfolded neutron energy spectra comparisons indicated good agreement of the ROSPEC and H*10-TMFD predictions against that for a bare Cf-252 spectrum with some down scattering effects. Tests conducted for ultra-low intensity radiation field used a ~1.6x103 n/s Cf-252 bare neutron source for which over a collection time of ~18 h, the Eberline meter measured an instantaneous dose/count rate of 0 mRem/h ( 0 cpm), and a pulse- integrated dose rate of ~3.4 Rem/h at ~1 m. In contrast, The H*-TMFD panel located 0.22 m in direct line of sight of the Cf-252 source spectroscopically measured ~40 Rem/h (within +/- 5%) over 1.8 h collection live time -for which spectrum matched perfectly to that of a bare Cf-252 source. The H*TMFD predicted value of 40 Rem/h was cross-checked; it is within 10% of Lawrence Livermore National Laboratory’s published value of ~37 micRem/h (intensity / distance corrected via 1/r2 law of: 2.55 mRem/h at 1 m for a 1 g Cf-252 source); as well, predicted from use of ICRP-74 conversion coefficients, and MCNP code simulation of experiment. Epithermal neutron energy related dose rates were measured by H*TMFD to be well below 1% of the total dose rates. For micRem/h neutron radiation fields, ROSPEC measurements for H*10 dose rates are estimated to take 7+ days, versus under 2 hours with the H*TMFD.
The feasibility to utilize a single CTMFD in survey mode for H*10 dose rate (micRem/h to mRem/h) measurements (tied to pre-programmed energy spectra) within 2-3 minutes was demonstrated.
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WAM-E.4
10:45 3D Dose-Rate Mapping of Commercial Nuclear Power Plant Radiological Area Surveys using Spatially 3D CdZnTe Imaging Spectrometers DI Goodman, H3D, Inc.
; D Nestle*, H3D, Inc.; R Sobota, H3D, Inc.; B Kitchen, H3D, Inc.
Abstract: Traditional power plant radiological surveys are conducted with ionization chambers, paper, and pens. Spatial awareness survey equipment, combining simultaneous localization and mapping (SLAM) hardware and radiation detectors, enable the detailed, paper-free generation of radiological dose-rate surveys. A spatially-aware 3D pixelated CdZnTe survey tool has been demonstrated in radiologically controlled areas of a nuclear power plant undergoing decommissioning. Survey maps generated using the 3D CdZnTe solution, with dose rates ranging from 0.5 to >100 mrem/h, are compared against traditional survey maps made using ionization chambers. Isotopic-specific dose rates, computed using relative photopeak areas, are documented and superimposed with 3-D Compton images of the source distribution within the room. Estimates of source activity creating localized “hotspots” are made by combining 3D radiation maps and a 3D point kernel model inside the SourceTerm software. Detailed discussion of measurement uncertainties through bootstrapping, which includes the combined effects of spectral, device positioning, and 3D Compton imaging reconstruction uncertainties, is provided.
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WAM-E.5
11:00 Converting Plutonium Canister Survey Data to Dose Rates MG Hogue*, SRNS
; MD Ratliff, Mirion
Abstract: At the Savannah River Site (SRS), glovebox operations were preparing work to optimize a process for treating surplus plutonium for disposal. This involved impure, aged plutonium, which included largely unquantifiable levels of impurities that contribute to photon and neutron dose rates.
Survey data was available from readings on type-3013 containers taken at shipping facilities. This data was predominantly taken with ion chambers and rem ball style portable instruments.
To develop a best estimate for true dose rates, MCNP models and calibration facility testing was performed. Thermo RO-20 ion chambers were tested in the SRS Health Physics Instrumentation Calibration Facility on both the low scatter irradiator with 137Cs source and in the Americium Beam Irradiator with an 241Am source.
Conversion coefficients for RO-20 readings included correcting indicated exposure rate to true exposure rate, correcting for source-to-detector geometry, and converting true exposure rates to true dose rates. Conversion coefficients for rem balls included geometry correction and calibration coefficient update.
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WAM-E.6
11:15 Radiation Hardness Assurance Testing of Raspberry Pi Boards SC Hanson*, North Carolina State University
; SM McDonell; RJ Charrette; RB Hayes
Abstract: The electronics industry relies on radiation hardness (rad-hard) assurance testing such as Total Ionizing Dose (TID) testing to verify a board’s resilience to extreme radiation environments such as on satellites. These tests traditionally subject the simplest possible sensitive components (such as transistors or operational amplifiers) to individual tests to determine whether any change in performance occurred for a relevant circuit. Once a considerable amount of testing is performed on a part, it is labelled as having some amount of rad-hardness. Due to the length of rad-hard part lead times and the general lack of computational power in rad-hard boards versus commercial off the shelf (COTS) counterparts, there can be consideration to switch to less rad-hardened boards or COTS boards with external shielding. As a demonstration of the feasibility of commercial computer operations in extreme environments, a series of Raspberry Pi computers are irradiated in the PULSTAR Research Reactor to assess pre and post irradiation effects. Central processing unit and random access memory computational tests are executed before and after irradiation in pursuit of finding a relationship between observable computer performance degradation and neutron displacement damage. Eventually this will be compared with shielded configurations where the shielding material would be metal oxide infused conformal coating. This composite material features a hydrogenous polymer base infused with gadolinium oxide powder, and provides all of the traditional material benefits of conformal coating. The combination of gadolinium and low Z polymer elements provide notable neutron shielding worth per added mass.
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WAM-E.7
11:30 Design and fabrication of human tissue substitutes suitable for a continuous low photon energy spectrum between 10 and 120 keV H Spitz*, University of Cincinnati
; J Stringer, University of Cincinnati; E Howell, University of Cincinnati
Abstract: The conventional process involved in designing and fabricating human tissue substitute materials incorporates small quantities of additives into a base material to obtain a product that exhibits the desired effective Z, electron density, and mass attenuation coefficient () relevant to a discrete or narrow range photon energy. The suitability of a tissue substitute is determined by comparing the measured value of with the published value in the technical literature, such as ICRU Report #44. For example, the Livermore Thoracic Phantom, which contains tissue substitutes for human muscle, bone, and lung, was expressly designed to calibrate in vivo measurements of low energy plutonium x-rays. Each of the tissue substitutes used in this phantom is fabricated by adding a prescribed quantity of CaCO3 to a two-part polyurethane resin. Radiation attenuation at low photon energy is primarily due to a combination of photoelectric and Compton interactions such that the value of changes by an order of magnitude between 10 keV and 120 keV. New formulations of adipose, muscle, bone, and lung tissues will be described that are suitable for this unique low energy spectrum. These tissue substitutes can be used in phantoms to calibrate in vivo measurements of occupational exposure involving mixtures of low energy photons and in computerized tomography (CT), where the polychromatic continuum between 40 and 120 keV does not produce the same number of photons for all energies.
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WAM-E.8
11:45 Characterization of the Spectroscopic Mobile Unshielded Radiation Field (SMURF) Detector JM Hurtado*, U.S. Environmental Protection Agency
; ZX Zhang, U.S. Environmental Protection Agency; DO Stuenkel, U.S. Environmental Protection Agency
Abstract: Developed and finalized as a U.S. Environmental Protection Agency National Center for Radiation Field Operations (NCRFO) asset in August 2021, the Spectroscopic Mobile Unshielded Radiation Field (SMURF) Detector consists of four separate sodium iodide (NaI) scintillation crystals, housed in a carbon fiber case, each 10 centimeters by 10 centimeters by 40 centimeters, mounted approximately 1.2 meters above grade in the bed of a Ford F350 pickup truck. In November 2021, the SMURF Detector was characterized to environmental measurements of Potassium-40 (K-40), Radium-226 (Ra-226), and Thorium-232 (Th-232) at the Department of Energy (DOE) large-area slab calibration pads at Walker Airfield (referred to as Walker Pads) in Grand Junction, Colorado. Completed in 1976, the Walker Pads consists of five separate concrete pads doped with varying known concentrations of K-40, Ra-226, and Th-232 each measuring about 9 meters by 12 meters by 46 centimeters deep and interconnected by an asphalt runway. Stationary 300 second surveys were performed on each pad along with ambulatory scans at varying speeds to assess losses in detector sensitivity and spatial resolution. Further assessments of the system included evaluation of the directional radionuclide source search functionality. Analysis on all measurements was performed using a region of interest for K-40, Ra-226, and Th-232 and evaluated for each of the four crystals individually in the detector array and combined as one virtual detector. The goal is to launch the SMURF as a radioisotope identifier and contamination assessment tool for both natural and industrial radionuclides in a wide range of environments.
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