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Abstract  

Recent attention to international safeguards has stimulated interest in nondestructive analysis techniques. These NDA techniques include high- and low-resolution gamma-ray spectrometry, active and passive neutron counting, and physical measurements. Often, the NDA measurements are made abroad under field conditions, and in these cases, portability is important. In other cases, the measurements are made under laboratory conditions but no calibration materials are available. This paper describes several NDA applications in support of international safeguards projects, all involving international cooperation.

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Mixed population of different biotypes of C. arvense can be found in the cereal fields in Eastern Europe. Three biotypes were identified taxonomically: var. arvense; var. horridum, and var. vestitum. Out of the three identified biotypes, only var. arvense showed more sensitivity to chlorsulfuron, while the other two biotypes were less sensitive. There was no difference in the germination behaviour of the biotypes, thus all varieties can be present on the field at the same time. The less sensitive biotypes have a thicker cuticle and less stoma on the leaves than the more sensitive one. There is no significant difference between sensitive and resistant biotypes in absorption and translocation of the 14C chlorsulfuron and florasulam. Sensitivity of the ALS-enzyme was significantly reduced in the resistant biotypes, although the enzyme still functions. Since that cereal fields in Eastern Europe are infested with C. arvense biotypes with different susceptibilities to chlorsulfuron, it is important to consider resistance management when selecting herbicides. Selection pressure for ALS resistance can be reduced by including other herbicides with an alternative mode of action; as tank mixes, premixes, or separate applications.

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Trace elements in Jamaican soils

I. The parishes of Clarendon, St. Catherine, Portland, and St. Elizabeth

Journal of Radioanalytical and Nuclear Chemistry
Authors:
H. Robotham
,
G. Lalor
,
A. Mattis
,
R. Rattray
, and
C. Thompson

Abstract  

The results of the analysis of approximately 100 soil samples for Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, As, Sb, Ba, La, Sm, Eu, Dy, Lu, Hf, Th, and U by neutron activation analysis, in three soil horizons from four of the main agricultural parishes of Jamaica are presented. While there is some regional variation in the abundances, there are no statistically significant distributions of abundances across the horizons. The results for a few selected elements are compared with abundances in other countries.

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Abstract  

A Radionuclide Aerosol Sampler/Analyzer (RASA Mark 4) has been developed at PNNL for use in verifying the Comprehensive Nuclear Test Ban Treaty (CTBT). The RASA Mark 4 collects about 20,000 m3 of air per day on a 0.25 m2 filter. This filter is automatically decayed for 24 hours, then advanced to a germanium detector for a 24 hour count. This system has been operated in Richland, WA for a limited period of time in a predeployment testing phase. The germanium-detector gamma-ray spectra have been analyzed by automatic spectral analysis codes to determine Minimum Detectable Concentrations (MDC) for a number of isotopes of interest. These MDC's have been compared to other atmospheric measurements in the field and in the laboratory.

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Abstract  

Radionuclide monitoring, though slower than vibrational methods of explosion detection, provides a basic and certain component of Comprehensive Test Ban treaty (CTBT) verification. Measurement of aerosol radioactive debris, specifically a suite of short-lived fission products, gives high confidence that a nuclear weapon has been detonated in or vented to the atmosphere. The variable nature of wind-borne transport of the debris requires that many monitoring stations cover the globe to insure a high degree of confidence that tests which vent to the atmosphere will be detected within a reasonable time period. To fulfill the CTBT aerosol measurement requirements, a system has been developed at PNNL to automatically collect and measure radioactive aerosol debris, then communicate spectral data to a central data center. This development has proceeded through several design iterations which began with sufficient measurement capability (<30 μBq/m3 140Ba) and resulted in a system with a minimal footprint (1 m×2 m), minimal power requirement (1600W), and support of network infrastructure needs. The Mark IV prototype (Fig. 1) is currently the subject of an Air Force procurement with private industry to partially fulfill US treaty obligations under the CTBT. It is planned that the system will be available for purchase from a manufacturer in late 1997.

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Abstract  

A large area beta scintillation detector has been developed which is currently capable of determining Sr-90/Y-90 contamination in surficial soils. The detector system employs scintillating fiber optic arrays, with active dimensions approximately 15 cm wide by 100 cm long, both ends of which are coupled to multiple photomultiplier tubes (PMTs). Electronic processing includes coincidence requirements to optimize sensitivity and selectivity for the 2.28 MeV (maximum) beta particle from Y-90. Low energy beta particles and gamma rays are discriminated against using double ended and multi-layer coincidence requirements. The detector system is personal-computer-software controlled and data restored in a format compatible with standard database software for ease of final data reduction. Experimental calibration studies have shown a linear response for Sr-90/Y-90 soil concentrations from 12 to over 500 pCi/g and a discrimination factor of 50 to 1 versus Cs-137.

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Abstract  

A novel scintillating-fiber sensor for detecting high-energy beta particles has been designed and built at the Pacific Northwest Laboratory to characterize238U and90Sr in surface soils. High-energy betas generate unique signals as they pass through multiple layers of scintillating fibers that make up the active region of the detector. Lower-energy beta particles, gamma rays, and cosmic-ray-generated particles comprise the majority of the background interferences. The resulting signals produced by these latter phenomena are effectively discriminated against due to the combination of the sensor's multi-layer configuration and its interlayer coincidence/anti-coincidence circuitry.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
T. Bowyer
,
K. Abel
,
C. Hubbard
,
A. McKinnon
,
M. Panisko
,
R. Perkins
,
P. Reeder
,
R. Thompson
, and
R. Warner

Abstract  

A fully automatic radioxenon sampler/analyzer (ARSA) has been developed and demonstrated for the collection and quantitative measurement of the four xenon radionuclides,131mXe(11.9 d),133mXe(2.2 d),133Xe(5.2 d), and135Xe(9.1 hr), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a Comprehensive Test Ban Treaty (CTBT). Activity ratios of these radionuclides permit source attribution. Xenon, continuously and automatically separated from the atmosphere, is automatically analyzed by electron-photon coincidence spectrometry providing a lower limit of detection of about 100 μBq/m3. The demonstrated detection limit is about 100 times better than achievable with reported laboratory-based procedures for the short-time collection intervals of interest.

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