Development of ultra low background gas proportional counters has made the contribution from naturally occurring radioactive isotopes – primarily α and β activity in the uranium and thorium decay ...chains – inconsequential to instrumental sensitivity levels when measurements are performed in above ground surface laboratories. Simple lead shielding is enough to mitigate against gamma rays as gas proportional counters are already relatively insensitive to naturally occurring gamma radiation. The dominant background in these surface laboratory measurements using ultra low background gas proportional counters is due to cosmic ray generated muons, neutrons, and protons. Studies of measurements with ultra low background gas proportional counters in surface and underground laboratories as well as radiation transport Monte Carlo simulations suggest a preferred conceptual design to achieve the highest possible sensitivity from an array of low background gas proportional counters when operated in a surface laboratory. The basis for a low background gas proportional counter array and the preferred shielding configuration is reported, especially in relation to measurements of radioactive gases having low energy decays such as 37Ar.
•Optimization of a cosmic ray shield to measure environmental radioactive gases.•Proportional counter sensitivity may reach ambient environmental 37Ar concentrations.•Variable length counter method evaluated for low concentration absolute gas counting.•Feasibility of several hour duration preparation of gas samples for 37Ar measurement.
A Noble Gas Migration Experiment injected
127
Xe,
37
Ar, and sulfur hexafluoride into a former underground nuclear explosion shot cavity. These tracer gases were allowed to migrate from the cavity to ...near-surface and surface sampling locations and were detected in soil gas samples collected using various on-site inspection sampling approaches. Based on this experiment we came to the following conclusions: (1) SF
6
was enriched in all of the samples relative to both
37
Ar and
127
Xe. (2) There were no significant differences in the
127
Xe to
37
Ar ratio in the samples relative to the ratio injected into the cavity. (3) The migratory behavior of the chemical and radiotracers did not fit typical diffusion modeling scenarios.
No controlled trial of treatment of generalised social phobia has been conducted in general practice.
To examine the efficacy of sertraline or exposure therapy, administered alone or in combination ...in this setting.
Study was of a randomised, double-blind design. Patients (n = 387) received sertraline 50-150 mg or placebo for 24 weeks. Patients were additionally randomised to exposure therapy or general medical care.
Sertraline-treated patients were significantly more improved than non-sertraline-treated patients (chi(2)=12.53, P<0.001; odds ratio=0.534; 95% Cl 0.347-0.835). No significant difference was observed between exposure- and non-exposure-treated patients (chi(2)=2.18, P=0.140; odds ratio=0.732; 95% Cl 0.475-1.134). In the pairwise comparisons, combined sertraline and exposure (chi(2)=12.32; P<0.001) and sertraline (chi(2)=10.13; P=0.002) were significantly superior to placebo.
Sertraline is an effective treatment for generalised social phobia. Combined treatment with sertraline and exposure therapy, conducted by the general practitioner, may enhance the treatment efficacy in primary care.
Attaining high energy efficiency with adsorption heat pumps is challenging due to thermodynamic losses that occur when the sorbent beds are thermally cycled without effective heat recuperation. The ...multi-bed concept described here enables high efficiency by effectively transferring heat from beds being cooled to beds being heated. A simplified lumped-parameter model and detailed finite element analysis are used to simulate a sorption compressor, which is used to project the overall heat pump coefficient of performance. Results are presented for ammonia refrigerant and a nano-structured monolithic carbon sorbent specifically modified for the application. The effects of bed geometry and number of beds on system performance are explored, and the majority of the performance benefit is obtained with four beds. Results indicate that a COP of 1.24 based on heat input is feasible at AHRI standard test conditions for residential HVAC equipment. When compared on a basis of primary energy input, performance equivalent to SEER 13 or 14 are theoretically attainable with this system.
► A multi-bed concept for adsorption heat pumps is capable of high efficiency. ► Modeling is used to simulate sorption compressor and overall heat pump performance. ► Results are presented for ammonia refrigerant and a nano-structured monolithic carbon sorbent. ► The majority of the efficiency benefit is obtained with four beds. ► Predicted COP as high as 1.24 for cooling is comparable to SEER 13 or 14 for electric heat pumps.
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.
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).
•39Ar is generated via reactor irradiation of potassium carbonate.•Low-level standards are produced to assist in ground water age-dating studies.•Quantification using length compensated proportional counting is performed.•Wall- and threshold-effects are studied and discussed in terms of uncertainty.
We report that large detectors employing xenon are a leading technology in existing and planned searches for new physics, including searches for neutrinoless double beta decay (0νββ) and dark matter. ...While upcoming detectors will employ target masses of a ton or more, further extending gas- or liquid-phase Xe detectors to the kton scale would enable extremely sensitive next-generation searches for rare phenomena. The key challenge to extending this technology to detectors well beyond the ton scale is the acquisition of the Xe itself. We describe the motivation for extending Xe time-projection chambers to the kton scale and possible avenues for Xe acquisition that avoid existing supply chains. If acquisition of Xe in the required quantities is successful, kton-scale detectors of this type could enable a new generation of experiments, including searches for 0νββ at half-life sensitivities as long as 1030 yr.
We report that large detectors employing xenon are a leading technology in existing and planned searches for new physics, including searches for neutrinoless double beta decay (0νββ) and dark matter. ...While upcoming detectors will employ target masses of a ton or more, further extending gas- or liquid-phase Xe detectors to the kton scale would enable extremely sensitive next-generation searches for rare phenomena. The key challenge to extending this technology to detectors well beyond the ton scale is the acquisition of the Xe itself. We describe the motivation for extending Xe time-projection chambers to the kton scale and possible avenues for Xe acquisition that avoid existing supply chains. If acquisition of Xe in the required quantities is successful, kton-scale detectors of this type could enable a new generation of experiments, including searches for 0νββ at half-life sensitivities as long as 1030 yr.
The measurement of 37Ar has been proposed as a method of detecting underground nuclear testing. The isotope 37Ar is generated by neutron activation of calcium by the reaction, 40Ca(n, a)37Ar, and, as ...a noble gas, is able to migrate more freely underground. Pacific Northwest National Laboratory has developed a high throughput 37Ar collection and measurement system using modified Ultra-Low Background Proportional Counters (ULBPCs). This system is capable of collecting, purifying, and measuring radioactivity in argon from either atmospheric or soil gas samples. This process is automated, with minimal operator intervention. This paper describes quantification of 37Ar and how we account for varying background conditions. An example is provided in which 39Ar has been shown to be a significant background in some sample sets, created by process 39K(n,p)39Ar during an underground nuclear explosion that would also create 37Ar. To account for the large background of 39Ar, we fit the data with a constant plus exponential background model with Gaussian signal model and use the results of a constrained fit to calculate 37Ar activity. We discuss the methods used to purify and count samples. We discuss the impact of increased 39Ar backgrounds on the measurement of 37Ar.
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