Straightforward Cell Patterning with Ultra-Low Background Using Polydimethylsiloxane Through-Hole Membranes.

Micropatterning is becoming an increasingly popular tool to realize microscale cell positioning and decipher cell activities and functions under specific microenvironments. However, a facile methodology for building a highly precise cell pattern still remains challenging. In this study, A simple and straightforward method for stable and efficient cell patterning with ultra-low background using polydimethylsiloxane through-hole membranes is developed. The patterning process is conveniently on the basis of membrane peeling and routine pipetting. Cell patterning in high quality involving over 97% patterning coincidence and zero residue on the background is achieved. The high repeatability and stability of the established method for multiple types of cell arrangements with different spatial profiles is demonstrated. The customizable cell patterning with ultra-low background and high diversity is confirmed to be quite feasible and reliable. Furthermore, the applicability of the patterning method for investigating the fundamental cell activities is also verified experimentally. The authors believe this microengineering advancement has valuable applications in many microscale cell manipulation-associated research fields including cell biology, cell engineering, cell imaging, and cell sensing.

Underground radioactivity measurements of meteorites: Development of methods suitable to determine precise terrestrial age of recent falls.

The L6 chondritic meteorite, HaH-346, fell in Libya. However, neither the exact date of the fall nor the exact size of the original meteoroid or asteroid is known. A specimen of the meteorite, weighing 488 g, was measured using ultra low-background gamma-ray spectrometry in the 225 m deep underground facility HADES. Activation products 22Na, 26Al, 60Co, 57Co, 54Mn and 44Ti were detected. The detection efficiency was determined by 3D scanning the meteorite and introducing this in the computer model of the detector and sample implemented in the MCNP6.2 Monte Carlo code. The activities of 22Na and 26Al support the hypothesis that the fall took place on 26 August 2018. Furthermore, the 60Co and 26Al activities indicate that the original radius of meteoroid was between 50 and 80 cm, which suggests the mass prior to atmospheric entry was between 2400 and 7300 kg.

Ultra-low-level measurements of airborne fission products from the Fukushima Daiichi reactor accident using high volume collection systems at Savannah River National Laboratory.

Ultra-low-level measurements of radionuclides in air have been conducted at the Savannah River National Laboratory (SRNL) to determine the atmospheric concentration of fission products released following the Fukushima Daiichi reactor accident on March 11, 2011. Air filter samples were acquired from two high-volume collection systems (a traditional filter-based system and an electrostatic precipitator-based system) to monitor airborne radionuclide concentrations in the period covering from 2 weeks to 3 years after the disaster. The world-wide spread of low-level concentrations of airborne fission products from the Fukushima event provided a unique opportunity to demonstrate SRNL's electrostatic particle collection technology and other improvements in environmental monitoring developed at the Savannah River Site (SRS). Detecting and analyzing the release allowed a comprehensive test of SRS systems for monitoring environmental radioactivity. Gamma-ray-emitting fission products (131,132I, 134,136,137Cs, and 129,132Te) and cosmogenic isotopes (7Be and 22Na) in air were detected and quantified by high-resolution gamma-ray spectroscopy at concentrations as low as 0.07 µBq per standard cubic meter (SCM) (50 mBq total 137Cs), while plutonium content was quantified by thermal ionization mass spectrometry (TIMS) at concentrations as low as 6.5 × 10-21 g/SCM (3.0 fg 239+240Pu). Isotope concentrations measured at SRNL from gamma-ray spectroscopy were compared to independent measurements from Chapel Hill, NC, located approximately 370 km (230 mi) NE of SRNL. Meteorological modeling was also used to predict radionuclide transport from the location of release to both measurement locations.

[Dominant Research Contribution of Dr. Eiichi Tanaka in the Field of Very Weak Radioactivity Measurements].

This article gives dominant research contributions of the late Dr. Eiichi Tanaka in the field of very weak radioactivity measurements with a new type of an extremely low background ß-ray scintillation spectrometer, which consists of a large plastic scintillator and a gas-flow GM counter located in the small hollow in the bottom part of the plastic scintillator. The pulse signals from plastic scintillator are coincidence-gated by the pulses from the GM counter. Dominant background signals due to the energetic muons still appear in the higher region than 3.5 MeV even with coincidence gating mode, but extreme reduction of background can be attained in the 0～3 MeV region which is essentially important in the ß-ray spectrometry for most of radionuclides.

A label-free photoelectrochemical biosensor with ultra-low-background noise for lead ion assay based on the Cu2O-CuO-TiO2 heterojunction.

Herein, a label-free and ultra-low-background-noise PEC biosensor was developed for lead ion (Pb2+) assay based on the Cu2O-CuO-TiO2 heterojunction. By calcination of cupric ion (Cu2+) doped-titanium based metal organic framework (MOF) material (NH2-MIL-125), the Cu2O-CuO-TiO2 heterojunction was synthesized. With Pb2+, lots of DNA single strands (S1) could be released based on the Pb2+ assisted cyclic amplification strategy and hybridized with hairpin DNA (HP1) on the modified electrode. The exposed phosphate groups on S1 can adsorb Cu2O-CuO-TiO2 heterojunction, which results in a large cathode photocurrent. Due to the good photoelectric property of Cu2O-CuO-TiO2 and Pb2+-triggering cyclic amplification strategy, the constructed PEC biosensor achieves a wide linear detection range (10 fM - 1 µM) and a low detection limit (6.8 fM), which provides potential applications in ultrasensitive determination of Pb2+ in environmental water samples and organisms.

Development of a low-level 39Ar calibration standard - Analysis by absolute gas counting measurements augmented with simulation.

This paper describes the generation of 39Ar, via reactor irradiation of potassium carbonate, followed by quantitative analysis (length-compensated proportional counting) to yield two calibration standards that are respectively 50 and 3 times atmospheric background levels. Measurements were performed in Pacific Northwest National Laboratory's shallow underground counting laboratory studying the effect of gas density on beta-transport; these results are compared with simulation. The total expanded uncertainty of the specific activity for the ~50× 39Ar in P10 standard is 3.6% (k=2).

Methods for using argon-39 to age-date groundwater using ultra-low-background proportional counting.

Argon-39 can be used as a tracer for age-dating glaciers, oceans, and more recently, groundwater. With a half-life of 269 years, 39Ar fills an intermediate age range gap (50-1,000 years) not currently covered by other common groundwater tracers. Therefore, adding this tracer to the data suite for groundwater studies provides an important tool for improving our understanding of groundwater systems. We present the methods employed for arriving at an age-date for a given sample of argon degassed from groundwater.

Simultaneous measurement of tritium and radiocarbon by ultra-low-background proportional counting.

Use of ultra-low-background capabilities at Pacific Northwest National Laboratory provide enhanced sensitivity for measurement of low-activity sources of tritium and radiocarbon using proportional counters. Tritium levels are nearly back to pre-nuclear test backgrounds (~2-8 TU in rainwater), which can complicate their dual measurement with radiocarbon due to overlap in the beta decay spectra. We present results of single-isotope proportional counter measurements used to analyze a dual-isotope methane sample synthesized from ~120mg of H2O and present sensitivity results.

First results of a simultaneous measurement of tritium and (14)C in an ultra-low-background proportional counter for environmental sources of methane.

Simultaneous measurement of tritium and (14)C would provide an added tool for tracing organic compounds through environmental systems and is possible via beta energy spectroscopy of sample-derived methane in internal-source gas proportional counters. Since the mid-1960's atmospheric tritium and (14)C have fallen dramatically as the isotopic injections from aboveground nuclear testing have been diluted into the ocean and biosphere. In this work, the feasibility of simultaneous tritium and (14)C measurements via proportional counters is revisited in light of significant changes in both the atmospheric and biosphere isotopics and the development of new ultra-low-background gas proportional counting capabilities for small samples (roughly 50 cc methane). A Geant4 Monte Carlo model of a Pacific Northwest National Laboratory (PNNL) proportional counter response to tritium and (14)C is used to analyze small samples of two different methane sources to illustrate the range of applicability of contemporary simultaneous measurements and their limitations. Because the two methane sources examined were not sample size limited, we could compare the small-sample measurements performed at PNNL with analysis of larger samples performed at a commercial laboratory. These first results show that the dual-isotope simultaneous measurement is well matched for methane samples that are atmospheric or have an elevated source of tritium (i.e. landfill gas). However, for samples with low/modern tritium isotopics (rainwater), commercial separation and counting is a better fit.

Development of a low-level (37)Ar calibration standard.

Argon-37 is an environmental signature of an underground nuclear explosion. Producing and quantifying low-level (37)Ar standards is an important step in the development of sensitive field measurement instruments. This paper describes progress at Pacific Northwest National Laboratory in developing a process to generate and quantify low-level (37)Ar standards, which can be used to calibrate sensitive field systems at activities consistent with soil background levels. This paper presents a discussion of the measurement analysis, along with assumptions and uncertainty estimates.

Detection of (133)Xe from the Fukushima nuclear power plant in the upper troposphere above Germany.

After the accident in the Japanese Fukushima Dai-ichi nuclear power plant in March 2011 large amounts of radioactivity were released and distributed in the atmosphere. Among them were also radioactive noble gas isotopes which can be used as tracers to test global atmospheric circulation models. This work presents unique measurements of the radionuclide (133)Xe from Fukushima in the upper troposphere above Germany. The measurements involve air sampling in a research jet aircraft followed by chromatographic xenon extraction and ultra-low background gas counting with miniaturized proportional counters. With this technique a detection limit of the order of 100 (133)Xe atoms in liter-scale air samples (corresponding to about 100 mBq/m(3)) is achievable. Our results provide proof that the (133)Xe-rich ground level air layer from Fukushima was lifted up to the tropopause and distributed hemispherically. Moreover, comparisons with ground level air measurements indicate that the arrival of the radioactive plume at high altitude over Germany occurred several days before the ground level plume.

Development of an absolute gas-counting capability for low to medium activities.

Pacific Northwest National Laboratory (PNNL) is developing a capability to measure the absolute activity concentration of gaseous radionuclides using length-compensated proportional-counting. This capability will enable the validation of low-level calibration standards for use in PNNL's new shallow underground laboratory. Two sets of unequal length proportional counters have been fabricated; one set has been fabricated using ultra-low background (ULB) electroformed copper and a second set fabricated from Oxygen-Free High-Conductivity Copper (OFHC).