Computational and experimental optimization of 135Xe production in calibration sources.

Here we present a new method of irradiating 134Xe capsules to produce 135Xe gas standards which maximize the ratio of 135Xe to 133Xe production due to (n,g) and (n,2n) reactions, respectively. We performed "Spectral tuning" of the University of Utah TRIGA Reactor (UUTR) neutron spectrum to increase the length of time that 135Xe dominates undesirable 135Xe in the sample, so that the capsules - used for calibration and quality control testing of Xe gas detection equipment in support of the Comprehensive Test Ban Treaty (CTBT) - will remain viable for longer periods post-irradiation. Moreover, optimized methods of computation and analysis were developed yielding improved computational efficiency over standard Monte Carlo approaches. These methods provided valuable insight into the final design and manufacture of new, ex-core Teflon irradiation chambers tested in the UUTR. The methods of computation and analysis, as well as the physical irradiation chamber designs, were derived such that they could be readily applied to any reactor for spectral tuning of a specific reactor's flux profile. Results of the physical experiments employing the optimized irradiation chamber designs demonstrated sample viability time improvements of over 60% when compared to conventional, un-optimized methods of gas sample generation. Thus, use of these methods enhance both the CTBT-related calibrations and performance testing, and the continued stability of the CTBT monitoring network overall.

Carbon-14 content in surface soils near atmospheric and below ground nuclear detonations.

Global and regional releases of 14C have resulted from nuclear weapons testing activities; assessment of the chemical behavior and mechanisms of environmental transport and deposition of this radionuclide can assist remediation strategy development efforts and provide insights into global carbon cycling processes. This work reports a systematic evaluation of 14C in surface soils taken from the Nevada National Security Site. Surface soil samples are derived from above- and underground test locations, with underground test sites representing a range from near complete containment to uncontrolled radioactive releases. Only one surface soil taken from a underground test location (i.e. the Baneberry shot) shows elevated 14C concentrations (319 ±â€¯9 pMC) in addition to elevated concentrations of 137Cs, 60Co and 152Eu above regional backgrounds. Surface soils from above-ground test locations show extremely high 14C content (~1000 to 10,000 pMC); elevated concentrations of 152Eu and 60Co for these soils are also observed, with 137Cs at or below background levels. Taken together, these data suggest that 14C in surface soils from above-ground tests is primarily derived from in-situ neutron activation of the native soil material, whereas 14C in surface soils from underground tests may be from either recondensed particulate material or soil activation.

Low Molecular Weight Supramolecular Hydrogels for Sustained and Localized In Vivo Drug Delivery.

Supramolecular hydrogels are emerging as next-generation alternatives to synthetic polymers for drug delivery applications. Self-assembling peptides are a promising class of supramolecular gelator for in vivo drug delivery that have been slow to be adopted despite advantages in biocompatibility due to the relatively high cost of producing synthetic peptide hydrogels compared to synthetic polymer gels. Herein we describe the development and use of inexpensive low molecular weight cationic derivatives of phenylalanine (Phe) as injectable hydrogels for in vivo delivery of an anti-inflammatory drug, diclofenac, for pain mitigation in a mouse model. N-Fluorenylmethoxycarbonyl phenylalanine (Fmoc-Phe) derivatives were modified at the carboxylic acid with diaminopropane (DAP) to provide Fmoc-Phe-DAP molecules that spontaneously and rapidly self-assemble in aqueous solutions upon addition of physiologically relevant sodium chloride concentrations to give hydrogels. When self-assembly occurs in the presence of diclofenac, the drug molecule is efficiently encapsulated within the hydrogel network. These hydrogels exhibit robust shear-thinning behavior, mechanical stability, and drug release profiles to enable application as injectable hydrogels for in vivo drug delivery. Delivery of diclofenac in vivo was demonstrated by a localized injection of an Fmoc-F5-Phe-DAP/diclofenac hydrogel into the ankle joint of mice with induced ankle injury and associated inflammation-induced pain. Remediation of pain in the ankle joint was observed immediately after initial injection and was sustained for a period of nearly two weeks while diclofenac controls remediated pain for less than one day. This data demonstrates the promise of these supramolecular hydrogels as inexpensive next-generation materials for sustained and localized drug delivery in vivo.

237Np analytical method using 239Np tracers and application to a contaminated nuclear disposal facility.

Environmental 237Np analyses are challenged by low 237Np concentrations and lack of an available yield tracer; we report a rapid, inexpensive 237Np analytical approach employing the short lived 239Np (t1/2 = 2.3 days) as a chemical yield tracer followed by 237Np quantification using inductively coupled plasma-mass spectrometry. 239Np tracer is obtained via separation from a 243Am stock solution and standardized using gamma spectrometry immediately prior to sample processing. Rapid digestions using a commercial, 900 W "Walmart" microwave and Parr microwave vessels result in 99.8 ± 0.1% digestion yields, while chromatographic separations enable Np/U separation factors on the order of 106 and total Np yields of 95 ± 4% (2σ). Application of this method to legacy soil samples surrounding a radioactive disposal facility (the Subsurface Disposal Area at Idaho National Laboratory) reveal the presence of low level 237Np contamination within 600 m of this site, with maximum 237Np concentrations on the order of 103 times greater than nuclear weapons testing fallout levels.

A comparative study of 129I content in environmental standard materials IAEA-375, NIST SRM 4354 and NIST SRM 4357 by Thermal Ionization Mass Spectrometry and Accelerator Mass Spectrometry.

Iodine environmental measurements have consistently been validated in the literature using the standard material IAEA-375, soil collected approximately 160 miles northeast of Chernobyl, which is currently the only soil/sediment material with a certified 129I activity. IAEA-375 has not been available for purchase since approximately 2010. Two other standard materials that are available (NIST SRM 4354, freshwater lake sediment and NIST SRM 4357, ocean sediment) have certified activities for a variety of radionuclides but not for 129I. This paper reports a comparison of TIMS and AMS data for all three standards.

Improved pressurized Marinelli beaker measurements of radioactive xenon in air.

INL has shown that a Marinelli beaker geometry can be used for the measurement of radioactive xenon in air using an aluminum Marinelli. A carbon fiber Marinelli was designed and constructed to improve overall performance. This composite Marinelli can withstand sample pressures of 276bar and achieve approximately a 4x performance improvement in the minimum detectable concentrations (MDCs) and concentration uncertainties. The MDCs obtained during a 24h assay for 133Xe, 131mXe, and 135Xe are: 1.4, 13, and 0.35Bq/m3.

Radioxenon spiked air.

Four of the radioactive xenon isotopes ((131m)Xe, (133m)Xe, (133)Xe and (135)Xe) with half-lives ranging from 9 h to 12 days are produced from nuclear fission and can be detected from days to weeks following their production and release. Being inert gases, they are readily transported through the atmosphere. Sources for release of radioactive xenon isotopes include operating nuclear reactors via leaks in fuel rods, medical isotope production facilities, and nuclear weapons' detonations. They are not normally released from fuel reprocessing due to the short half-lives. The Comprehensive Nuclear-Test-Ban Treaty has led to creation of the International Monitoring System. The International Monitoring System, when fully implemented, will consist of one component with 40 stations monitoring radioactive xenon around the globe. Monitoring these radioactive xenon isotopes is important to the Comprehensive Nuclear-Test-Ban Treaty in determining whether a seismically detected event is or is not a nuclear detonation. A variety of radioactive xenon quality control check standards, quantitatively spiked into various gas matrices, could be used to demonstrate that these stations are operating on the same basis in order to bolster defensibility of data across the International Monitoring System. This paper focuses on Idaho National Laboratory's capability to produce three of the xenon isotopes in pure form and the use of the four xenon isotopes in various combinations to produce radioactive xenon spiked air samples that could be subsequently distributed to participating facilities.

Mechanical environmental transport of actinides and ¹³7Cs from an arid radioactive waste disposal site.

Aeolian and pluvial processes represent important mechanisms for the movement of actinides and fission products at the Earth's surface. Soil samples taken in the early 1970's near a Department of Energy radioactive waste disposal site (the Subsurface Disposal Area, SDA, located in southeastern Idaho) provide a case study for studying the mechanisms and characteristics of environmental actinide and (137)Cs transport in an arid environment. Multi-component mixing models suggest actinide contamination within 2.5 km of the SDA can be described by mixing between 2 distinct SDA end members and regional nuclear weapons fallout. The absence of chemical fractionation between (241)Am and (239+240)Pu with depth for samples beyond the northeastern corner and lack of (241)Am in-growth over time (due to (241)Pu decay) suggest mechanical transport and mixing of discrete contaminated particles under arid conditions. Occasional samples northeast of the SDA (the direction of the prevailing winds) contain anomalously high concentrations of Pu with (240)Pu/(239)Pu isotopic ratios statistically identical to those in the northeastern corner. Taken together, these data suggest flooding resulted in mechanical transport of contaminated particles into the area between the SDA and a flood containment dike in the northeastern corner, following which subsequent contamination spreading in the northeastern direction resulted from wind transport of discrete particles.