Timothy A. DeVol

Theoretical organically bound tritium dose estimates

Abstract— This paper illustrates a theoretical approach to estimating the dose associated with the ingestion of both organically bound tritium and tissue free water tritium relative to the ingestion of only tissue free water tritium. Organically bound tritium, specifically non-exchangeable OBT, can result in an increased dose relative to that from exchangeable organically bound tritium and tissue free water tritium because of the longer biological half-life of the former resulting in a dose conversion factor that is twice that of the latter. Non-exchangeable organically bound tritium is tritium that is bound to carbon whereas exchangeable organically bound tritium is tritium bound to oxygen, nitrogen, or sulfur. Tissue free water ranges from 85+% in most fruits and vegetables down to approximately 10% in grains. The remaining edible food mass consists, in part, of exchangeable and non-exchangeable hydrogen that is incorporated into carbohydrates, proteins and fat. The potential organically bound tritium content of several common food items was calculated knowing the amount of bound and unbound hydrogen that exists in these foods and by assuming that the hydrogen to tritium ratio is the same for the “free water” and bound hydrogen compartments. The theoretical ratio of dose from ingestion of organically bound tritium and tissue free water tritium to dose from ingestion of only tissue free water tritium was calculated to be on average within 12%, 30%, and 261% of experimentally based values for fruits and vegetables, meats and eggs, and grains, respectively. The difference is attributed to the T:H ratio being a function of the kinetics associated with the assimilation of tritium into the tissues.

Scintillation of rare earth doped fluoride nanoparticles

The scintillation response of rare earth (RE) doped core/undoped (multi-)shell fluoride nanoparticles was investigated under x-ray and alpha particle irradiation. A significant enhancement of the scintillation response was observed with increasing shells due: (i) to the passivation of surface quenching defects together with the activation of the REs on the surface of the core nanoparticle after the growth of a shell, and (ii) to the increase of the volume of the nanoparticles. These results are expected to reflect a general aspect of the scintillation process in nanoparticles, and to impact radiation sensing technologies that make use of nanoparticles.

Uranium in hot water tanks

Uranium deposits were detected inside hot water tanks using gamma-ray spectroscopic techniques and corroborated by the difference in the uranium concentration of the groundwater entering and leaving the hot water tanks. In-situ gamma-ray spectroscopy was performed using a transportable high-purity germanium (HPGe) gamma-ray spectrometer to estimate the mass of uranium in the hot water tanks. Gamma-ray spectroscopic analyses of hot water tanks in four residences with groundwater uranium concentration between 732 and 7,667 μg L−1 revealed an estimated 3.5 to 69 g of uranium in each hot water tank. The uranium deposit within the tanks was indicated by the 143.8, 163.4, and 185.7 keV gamma rays of 235U and confirmed with the 63.3, 92.3, and 92.8 keV gamma rays of 234Th as well as the 1,001 keV peak of 234mPa. An average decrease in uranium concentration of 23% was observed in the groundwater that passed through the hot water tanks. Additionally, once “uranium free” water entered the hot water tanks, the uranium deposits within the tanks resulted in an increase in the uranium concentration in the effluent water. The groundwater had an alkalinity in the range of 46–96 mg L−1 as CaCO3 and a pH range of 7.3–8.1. The accumulation of uranium in these hot water tanks results in them being classified as technologically enhanced naturally occurring radioactive materials (TENORM).

Correlating the Luminosity Parameters to Pulse Shape Discrimination

Monte Carlo simulations were used to investigate the correlation between luminosity parameters and pulse shape discrimination (PSD) and subsequently compared with experimental results from CsI:Tl. Luminosity intensity parameters A_f, As (fast and slow initial luminosities) and temporal luminosity parameters τ_f, τ_s (fast and slow decay time constants) of a dual decay mode scintillator were applied to create a dynamic model with Crystal Ball simulation system. The simulated pulses were analyzed with charge comparison (CC) and constant time discrimination (CTD) PSD methods followed by quantification of the histogrammed pulse data with Figure of Merit (FoM) and spillover (pulse misclassification). Performance in terms of FoM and spillover is compared with that of fixed reference pulses set at (A_f τ_f/A_s τ_s)_γ = 1 and (A_f τ_f/A_s τ_s)_γ = 0.1. For the CC method, independent of the reference pulse characteristics [(A_f τ_f/A_s τ_s)_γ = 1 or = 0.1], τ_s is the most influential parameter for PSD as compared with A_f, A_s, and τ_f. For the CTD method, A_f and As are seen to have less influence over the PSD compared to τ_f and τ_s when (A_f τ_f/A_s τ_s)_γ = 1 and τ_f is the most influential parameter for both reference pulses. Using both methods with either reference pulse applied, the scintillator having luminosity parameters such that is classified as having poor PSD. Excellent correlation is observed between the simulation and the experimental results with CsI:Tl, which is known for very good α/β(γ) pulse shape discrimination. This study is useful for describing how the luminosity parameters affects PSD.

Scintillation of nanoparticles: Case study of rare earth doped fluorides

An investigation of the scintillation response of rare earth doped fluoride nanoparticles was carried out taking advantage of core/multi-shell structures. A significant enhancement of the scintillation response was observed and attributed to the increase of the volume of the nanoparticles. Larger nanoparticles contain larger fractions of the irradiation cascade, their dimensions approach the electron-hole mean recombination length increasing the probability of radiative recombination, and separates the luminescence centers in the core from quenching defects on the surface of the nanoparticles.

Radionuclide Sensors for Subsurface Water Monitoring

Contamination of the subsurface by radionuclides is a persistent and vexing problem for the Department of Energy. These radionuclides must be measured in field studies and monitoed in the long term when they cannot be removed. However, no radionuclide sensors existed for groundwater monitoring prior to this teams research under the EMSP program Detection of a and b decays from radionuclides in water is difficult due to their short ranges in condensed media.

Radionuclide Sensors for Water Monitoring

Radionuclide contamination in the soil and groundwater at U.S. Department of Energy (DOE) sites is a severe problem that requires monitoring and remediation. Radionuclide measurement techniques are needed to monitor surface waters, groundwater, and process waters. Typically, water samples are collected and transported to an analytical laboratory, where costly radiochemical analyses are performed. To date, there has been very little development of selective radionuclide sensors for alpha- and beta-emitting radionuclides such as 90Sr, 99Tc, and various actinides of interest.