Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: U. Narayanan x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Interception/deposition factors for airborne85Sr,131I,137Cs following atmospheric releases under simulated raining condition have been evaluated in three different type of vegetables, i.e., beans (Phaseolus vulgaries), spinach (Spinacia oleracia) and radish (Raphamus sative). The rainfall rate in the chamber was 2 mm/h (48 mm/d). Activity was injected in the form of liquid aerosols having a size distribution of 2.33 μm (AMAD) with a GSD of 1.98 μm into the experimental chamber containing the vegetable plants having an arrangement to simulate rainfall. Samples were collected soon after the 30-minute rainfall period for the evaluation of interception/deposition factor (IF/DF) of85Sr,131I,137Cs on these plants. The maximum value of the interception/deposition factor was 6.04 m3·kg−1 which was observed for131I deposition to beans plant as a whole. Interception/deposition factor values were about 4 to 7 times higher compared to dry condition for the same of aerosols and inventories. The fraction of root activity to the activity of above soil parts has also been evaluated to determine the transfer of activity to the roots.

Restricted access

Abstract  

Study of plutonium and americium in the mango leaves and the distribution of their concentration in different parts of the mango fruit were performed. The generally observed trend is leaves > cotyledon > shell > fresh. These results suggest that the contamination of mango fruits by Pu and Am will not pose any radiation risk because the edible portion of the mango has the lowest activity.

Restricted access

Abstract  

Geochemical association of plutonium in the coastal environment of Trombay has been studied. A sequential leaching method was employed for chemical partitioning of plutonium in sediments. The results show that 95±15% of plutonium was extracted by different leaching reagents out of which 85±14% was associated with organic matter and hydrous oxide and 9±4% with residual fraction.The presence of significant fraction of Pu bound with organic matter of the sediment is an important factor in determining the extent to which an element becomes available to bottom feeding biota and so enters the aquatic food chain.

Restricted access

Abstract  

The characterized concentrations of 24 impurity elements in New Brunswick Laboratory (NBL) Certified Reference Material (CRM) 124 were reevaluated. A provisional certificate of analysis was issued in September 1983 based upon the “as prepared” values (gravimetric mixing). The provisional certificate does not state uncertainties for the characterized values, or estimate the degree of homogeneity. Since release of the provisional certificate of analysis various laboratories have reported analytical results for CRM 124. Based upon the reported data a re-evaluation of the characterized values with an estimate of their uncertainties was performed in this work. An assessment of the degree of homogeneity was included. The overall difference between the re-evaluated values for the 24 impurity elements and the “as prepared” values from the provisional certificate of analysis is negligible compared to the uncertainties. Therefore, NBL will establish the “as prepared” values as the certified values and use the derived uncertainties from this work for the uncertainties of the certified values. The traceability of the “as prepared” values was established by the gravimetric mixing procedure employed during the preparation of the CRM. NBL further recommends a minimum sample size of 1 g of the CRM material to ensure homogeneity. Samples should be dried by heating up to 110 °C for one hour before use.

Restricted access

Abstract  

The calorimetry exchange (CALEX) program is administered by New Brunswick Laboratory (NBL). The main objective of the program is to provide an independent verification of the internal quality control practices in nuclear material safeguards facilities making plutonium accountability measurements by non-destructive calorimetry/gamma spectrometry techniques. Facilities measure the calorimetric power, and plutonium and 241Am isotope abundances of CALEX program standards using routine accountability procedures. The measurement results as well as two other quantities (effective specific power and plutonium mass) calculated from these results are evaluated for accuracy (or bias) and precision. In this paper, a limited number of measurement results of a CALEX program standard (identified as Calex I) are evaluated with specific goals to identify a suitable method for uncertainty estimation and to identify the major contributors to the uncertainties. In order to achieve the goals, the Calex I measurement results were evaluated using two different methods: the first method confined to uncertainty estimation from random variations of the measurement results alone, and the second method providing a more comprehensive evaluation of uncertainties from both the measurements and the characterized values of the measured standard according to the Guide to the Expression of Uncertainty in Measurement (GUM). The results of this study, and a subsequent study extended to a larger number of results in the CALEX program database, are expected to provide relevant input for developing the International Target Values for plutonium measurements by the calorimetry/gamma spectrometry method.

Restricted access

Abstract  

The International Organization for Standardization (ISO) Guide to the expression of Uncertainty in Measurement (GUM) was developed to meet the demand for a standardized way of evaluating and expressing uncertainties. The Davies and Gray (D&G) titrimetry method is routinely used in nuclear safeguards for uranium accountability measurement and a statement of the uncertainty that can reasonably be attributed to the measured assay value is therefore of importance. A mathematical model for an uncertainty evaluation of D&G measurements in compliance with ISO GUM is presented. This is illustrated by a numerical example and the utilization of the uncertainty budget is explored.

Restricted access

Abstract  

Mobilisation of alpha emitting radionuclides from silicious base sample is one the challenging task for environmental radiochemist. During this study, rapid and complete dissolution of the siliceous base samples were carried out by optimizing temperature, pressure and power of the microwaves. The Pu-239+240 in digested samples was pre-concentrated by scavenging Fe as Fe(OH)3. Pu-239+240 was isolated from the Fe(OH)3 by co-precipitating Pu with Bi(PO4) in HNO3 medium at pH 2. Pu-239+240 was separated from Bi(PO4) and other transuranics by passing through cation and anion exchange resin. Pu-239+240 was counted by alpha spectrometry after electroplating on stainless steel planchet. The detection limits achieved for Pu-239+240 was 60 μBq/g (2.6 × 10−14 g/g). Pu-242 was used as a tracer for the evaluation of recovery of Pu-239+240. Samples prepared after complete destruction of matrix in microwave, showed 10–20% higher concentration of Pu-239+240 compared to conventional acid leached. Consistent recovery in the range of 97–99% for Pu-242 were observed in microwave digested samples whereas inconsistent results were observed in acid leached samples where the recoveries were in the range of 75–86%. Siliceous matrix degradation was tracked by monitoring the surface morphology and composition of the residue left at various stages of digestion using Scanning Electron Microscope (SEM) coupled with Energy dispersive X-ray spectrometer (EDS).

Restricted access