Search Results

You are looking at 1 - 10 of 39 items for

  • Author or Editor: J. Smith x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Robust sample handling and liquid scintillation counting (LSC) procedures have been developed to routinely monitor tritium in the field relative to the 20,000 pCi/L drinking water standard. This procedure allows tritium to be monitored hourly during 24 hour drilling operations at depths in the saturated zone potentially contaminated by sub-surface nuclear weapons testing at the Nevada Test Site. Using retrofitted, shock hardened, vibration damped counters and strict analytical protocols, tritium may be measured rapidly in the field under hostile conditions. Concentration standards and dead tritium backgrounds are prepared weekly in a central laboratory and delivered to remote drilling locations where they are recounted daily as a check on counter efficiency and calibration. Portable LSC counters are located in trailers and powered off a battery pack and line filter fed by mobile generator. The samples are typically groundwaters mixed with drilling fluids returned after circulation through a drill string. Fluids are aerated and de-foamed, filtered, mixed with scintillation cocktail and dark adapted before counting. Real-time monitoring affords drilling and field personnel early warning against intercepting down-gradient plumes of radioactivity. For routine operations, the tritium activity may not exceed a 10,000 pCi/L threshold.

Full access

Abstract  

The determination of bromine in biological material by thermal neutron activation analysis using instrumental [Ge(Li)] and radiochemical separation techniques is described. The radiochemical method is ten times more sensitive (0.4 ng) than the instrumental technique but both may be used for analysis of the majority of human tissue samples. Both techniques are rapid, simple, accurate and may be used for batch analysis.

Full access

Testing the ecological communities of different areas for convergence, in the sense of remarkable similarity in the characteristics of the species present, has a long history in biology. Recently, numerical methods have been developed for comparing community-level convergence to an explicit null model. No valid method has been known for testing the significance of texture convergence when the species are weighted by their abundance. Six combinations of method variants are tested on random datasets. A valid P value (i. e., with P . 0. 05 in no more than 5% of the cases) is obtained so long as for each species the distribution of abundances across sites is retained, and only the assignment of character values is randomised. Further restriction is not necessary for obtaining a valid P value, and can lead to a test with considerably lower power to detect convergence. The power of the test with free matching of character values to species is only moderate with 10 sites, though improved with larger numbers of sites. Previous methods for detecting texture convergence have examined convergence only in the mean value for any character. It is possible that the external environment might be reflected in the community mean of a character, leaving the imprint of convergence on the shape of the distribution, rather than the mean. A method for comparing the shape is described, and it is shown that the null model is valid also for this test statistic.  

Full access

Abstract  

A survey of the mercury content of the diet in the Glasgow area is described. A higher intake of mercury (60 μg/day/person) than that expected is found. However, there does not appear to be any concentration of mercury by man. None of the foodstuffs show any exceptional mercury content. Fish levels are similar to other foods and a preliminary sample of shellfish from the Clyde estuary, a contaminated area, shown no sign of their having concentrated mercury to any significant degree.

Full access

Abstract  

Current techniques for determining low levels of dissolved thorium involve chemical separations, generally by coprecipitation with a carrier cation, purification by ion exchange procedures, electroplating and, finally, alpha counting by alpha spectrometry. Similarly, measurements of low228Ra and224Ra activities requires concentration, by coprecipitation with barium sulfate, followed by gamma counting. An improved method for determining radium and thorium from the232Th decay series has been developed which measures the activity of220Rn as an assay of its parents. Although some ingrowth corrections and minor separation procedures for Th are required, the results to date show that the dynamic counting of220Rn via de-emanation and alpha counting by the alpha-scintillation method is a preferable approach for determining these radium and thorium isotopes accurately and efficiently. The method for lower limit detection depends on the emanation rate, which depends on purge-gas flow rate and sample volume analyzed. Using 50-cc and 1000-cc bubblers, and maximum effective purge gas flow rate, a lower limit of detection of 0.4 and 0.06 pCi/L220Rn can be obtained, respectively.

Full access

Abstract  

Rare-Earth Element (REE) concentrations in briny groundwaters are very low, and range from ppb to ppt levels. REE can be measured at these low levels using prechemistry to concentrate the REE, postchemistry as an REE group separation following neutron activation, and reactivation for chemical yields. The brine solutions appear to be stable with respect to trace elements (such as the REE) over the four years of sample storage. The brine REE patterns are highly fractionated from light REE to heavy REE, including a negative Eu anomaly. The REE patterns appear to be characteristic of each formation and its source region.

Full access

Abstract  

This paper describes the measurement of210Bi by Cerenkov counting in a commercial liquid scintillation counter. The counting efficiency in water is 0.17 counts per second per Becquerel (17%). When the enhancers Triton X-100 (15% v/v) and sodium salicylate (1% m/v) are added to the solution the counting efficiency for210Bi increases from 17% to 75%. The210Po daughter of210Bi causes interference of 0.85 counts per second per Becquerel in the presence of the enhancers but not in water. When210Bi and210Po are present in secular equilibrium the total counting efficiency is 160%. When210Bi and210Po are not in secular equilibrium the210Po can be removed immediately before counting by plating onto silver foil. The use of the enhancers gives a substantial increase in counting efficiency compared to counting in water. Compared with solutions used in liquid scintillation counting the enhancer solution is inexpensive and can be disposed of without environmental hazard.

Full access

Abstract  

A method for measuring radium activity using electrodeposition onto stainless steel from solutions to which platinum ions have been added was developed. This gave high recovery with reduced electroplating times, and yielded deposits giving alpha-spectra of high resolution. Retention of the decay products in the deposit allows inference of some Ra isotopes from measurement of the activities of the high energy Po daughters. Application of the method to determination of226Ra in a marine manganese deposit is described.

Full access