The assessment of plutonium and americium in contaminated wounds with high energy resolution semiconductor detectors

Estimation of 241Am and 239Pu activity embedded in the tissue using portable planar HPGe detector

This paper describes a procedure for the estimation of 241Am and 239Pu activity present in the human tissue by measuring the depth of contaminant using a portable Planar High Purity Germanium detector (HPGe). The ratios of photopeak counts of X-rays or gammas obtained with the detector coupled to collimator are calculated for the estimation of depth of the contaminant and the optimum one is determined. Since Minimum Detectable Activities (MDA) for the detector coupled to a collimator are higher than that of bare detector, activity must be estimated using bare detector, after locating the contaminant. Two methods are described for the estimation of plutonium coexisting with 241Am: (i) Abundance and isotopic correction for 239Pu (ii) and 239Pu:241Am ratio. The procedure to estimate 239Pu when plutonium isotopes alone are present is also established. An optimum monitoring period to detect the minimum value of intake for both radionuclides corresponding to chelation therapy and excision is also derived.

Rapid detection of heavy elements in blood extracted from wounds using x-ray fluorescence analysis

In radiation emergency situations involving persons having plutonium (Pu)-contaminated wounds, rapid assessment of the degree of Pu contamination is required to determine the appropriate course of treatment. Currently, rapid on-site detection of Pu is usually performed by analysis of α-particles emitted from the adhesive tape peeled off the wound. However, the detection of α-particles is difficult, especially in traumatic skin lesions with oozing blood, because of the low permeability of α-particles in blood. Therefore, we focused on x-ray fluorescence (XRF) analysis because x-rays easily pass through several millimetres of blood. In this study, we developed a new methodology for the rapid detection of heavy elements in wounds based on XRF analysis of the contaminated blood collected by gauze patch and filter paper, using stable lead (Pb) as a model contaminant substitute for Pu. Mouse blood samples contaminated with Pb were dropped on gauze patches or absorbed by filter papers and were subjected to XRF measurement. Small pieces of filter paper served as more suitable extraction materials than gauze patches because the entire amount of blood absorbed could be measured. When we used filter paper, the signal intensity of the Pb Lα peak was proportional to the Pb concentration in the blood. With a measurement time of 30 s, the minimum detection limit of Pb in blood collected by filter paper was 2.4 ppm.

Methodology using a portable X-ray fluorescence device for on-site and rapid evaluation of heavy-atom contamination in wounds: a model study for application to plutonium contamination

Workers decommissioning the Fukushima-Daiichi nuclear power plant damaged from the Great East Japan Earthquake and resulting tsunami are at risk of injury with possible contamination from radioactive heavy atoms including actinides, such as plutonium. We propose a new methodology for on-site and rapid evaluation of heavy-atom contamination in wounds using a portable X-ray fluorescence (XRF) device. In the present study, stable lead was used as the model contaminant substitute for radioactive heavy atoms. First, the wound model was developed by placing a liquid blood phantom on an epoxy resin wound phantom contaminated with lead. Next, the correlation between the concentration of contaminant and the XRF peak intensity was formulated considering the thickness of blood exiting the wound. Methods to determine the minimum detection limit (MDL) of contaminants at any maximal equivalent dose to the wound by XRF measurement were also established. For example, in this system, at a maximal equivalent dose of 16.5 mSv to the wound and blood thickness of 0.5 mm, the MDL value for lead was 1.2 ppm (3.1 nmol). The radioactivity of 239Pu corresponding to 3.1 nmol is 1.7 kBq, which is lower than the radioactivity of 239Pu contaminating puncture wounds in previous severe accidents. In conclusion, the established methodology could be beneficial for future development of a method to evaluate plutonium contamination in wounds. Highlights: Methodology for evaluation of heavy-atom contamination in a wound was established. A portable X-ray fluorescence device enables on-site, rapid and direct evaluation. This method is expected to be used for evaluation of plutonium contamination in wounds.

Monte Carlo simulation of embedded 241Am activity in injured palm

This paper describes a methodology to estimate embedded activity of (241)Am and Pu isotopes in a wound at an unknown depth. Theoretical calibration of an array of high-purity germanium detectors is carried out using the Monte Carlo code 'FLUKA' for a (241)Am source embedded at different depths in a soft tissue phantom of dimension 10 × 10 × 4 cm(3) simulating the palm of a worker. It is observed that, in the case of contamination due to pure (241)Am, the ratio of counts in 59.5 and 17.8 keV (Ratio 1) should be used to evaluate the depth, whereas the ratio of counts in 59.5 and 26.3 keV (Ratio 2) should be used when the contamination is due to a mixture of Pu and (241)Am compounds. Variations in the calibration factors (CFs) as well as in the Ratio 1 and Ratio 2 values are insignificant when source dimensions are varied from a point source to a 15-mm diameter circle. It is observed that tissue-equivalent polymethyl methacrylate material can be used in the phantom to estimate the embedded activity, when the activity is located at a depth of <1 cm, as the corresponding CFs do not show much variation with respect to those estimated using the phantom containing soft tissue material. In all other cases, an appropriate soft tissue-equivalent material should be used in the phantom for the estimation of CFs and ratios. The CFs thus obtained will be helpful in an accurate estimation of the depth of the wound and the activity embedded therein in the palm of a radiation worker.

Error analysis for the in-vivo measurement of radionuclides in wounds: Monte Carlo study

This paper describes calculation of error associated with the direct in-vivo measurements of radionuclides in a wound. A typical radiation injury to a hand with Am radionuclide is illustrated for error analysis. A Monte Carlo model was developed and the detector pulse spectrum studied with a custom-designed HPGe detector. A pinhole collimator was designed, and its performance with a wide area detector was studied. The results show that significant errors might propagate if the lowest energy peaks of Am are used during in vivo measurements of the wound. In comparison to that, less uncertainty was found for 26.3 and 59.5 keV gamma peaks, and those levels are recommended for estimation of wound depth and activity.

New technique using room temperature diodes for the direct assessment of internal contamination by low energy gamma-ray emitters

Silicon PIN diodes were tested as direct detection elements for in vivo counting. They have a low sensitivity to background radiation in the energy range below 80 keV so that they can be used outside a shielding room for the measurement of weakly absorbing organs or tissues in cases of incorporation of fuel particles and medical radionuclides. Results are reported on the spectral characteristics of these detectors. Comparison with other techniques is examined. This paper describes a novel technique of in vivo counting which needs no shielded room and which is applicable to other types of room temperature detectors. The concept of wearable counting devices is presented with description of their design.