Charged particle ratio in222Rn indoor atmosphere

The majority of radon daughter products are positively charged; however, their charge is masked by atmospheric ions created along the path of the accompanying -particles. The resulting positive-to-negative particle ratio P, which is usually higher than unity can change during the mitigation of radon daughters; such a change gives evidence that the mechanism is controlled by electric forces.     

A simple passive collector for direct measurement of radon flux from soil

A simple technique for measurement of the soil-atmosphere radon flux has been developed by fastening a charcoal canister inside a PVC cylindrical container. This device, which is deployed at the ground surface for approximately 16 hours, captures radon emanating from the soil by adsorption onto the charcoal surface. After recovery of the canister and measurement of the radon daughter activity on a NaI detector, the radon flux may be calculated if the adsorption efficiency of radon onto the charcoal is known. This parameter was determined by exposure of charcoal canisters to²²⁶Ra-spiked barium palmitate filter sources for timed intervals. Since this compound is known to emanate 100% of the²²²Rn generated during radium decay, it forms a useful flux standard. The accuracy of our flux measurements was assessed by comparison to a more established technique, the enclosed-chamber or accumulator method. Concentration measurements were made for the chamber over a less than 2-hour period while the canister flux measurements were based on single overnight deployments. The experiment was repeated 5 times at two different sites and the two techniques generally agreed within a 95% confidence interval.     

On-line scintillation counting on MeltilexTM basis

A detection system is described for monitoring on-line radioactive process solutions by solid scintillation counting. The system consists of a flow cell with perspex windows coated with the plastic scintillator Meltilex^TM. The cell is confined in a chamber welded to a La Calhène container. Thus the detection device is easily attached to, detached from and transported between glove boxes, and the electronic parts and the multiplers can be kept outside the box containment. Using outside coated windows, the detector responds to radiation, using inside coated windows, and particles can be detected. Selective measurements can be carried out by installing a chromatographic column in the detector loop. The detection limits of the cell for Am amount to 4·10^–9 g Am/ml for outside coated windows and 10^–9 g Am/ml for inside coated windows. windows and 10^–9 g Am/ml for inside coated windows.     

A continuous monitor for assessment of 222Rn in the coastal ocean

Radon-222 is a good natural tracer of groundwater flow into the coastalocean. Unfortunately, its usefulness is limited by the time consuming natureof collecting individual samples and traditional analysis schemes. We demonstratehere an automated system which can determine, on a continuousbasis, the radon activity in coastal ocean waters. The system analyses ²²²Rn from a constant stream of water passing through an air-water exchangerthat distributes radon from the running flow of water to a closed air loop.The air stream is feed to a commercial radon-in-air monitor which determinesthe concentration of ²²²Rn by collection and measurement of theemitting daughters, ²¹⁴Po and ²¹⁸Po, via a charged semiconductordetector. Since the distribution of radon at equilibrium between the air andwater phases is governed by a well-known temperature dependence, the radonconcentration in the water is easily calculated.     

A micro electron capture detector for temperature programmed analysis with capillary columns for a wide range of applications

Summary The electron capture detector (ECD) has become a indispensable and widely used tool for the detection of halogenated compounds in gas chromatography. The ECD is successfully used for routine analysis particularly in the field of environmental survey, residue determination in the food and agriculture chemistry and even more so in clinical chemistry. However, its application with high resolution glass capillary columns revealed a substantial drawback of existing ECD's, primarily the relatively large internal detector volume. The micro ECD described, with its very small cell volume (140 mm³), particularly designed for use with high resolution capillary columns, minimizes drastically the loss of separation efficiency since diffusion effects are negligible. The micro ECD permits the use of splitless or split injection techniques, as well as temperature programmed analysis to optimize sample separation. Very stable baseline and low noise conditions lower the detection limits considerably (2 pg Lindane full scale). The micro ECD can be operated either with direct current, pulsed frequency or constant current modes. Examples demonstrating the capabilities of this detector include the detection of halogenated organic volatiles in water at subnanogram levels, the determination of PCB's and pesticide residues in food as well as selected analysis in clinical chemistry, such as bile acids and amino acids in body fluids.     

Measurement of radon in air by α track method enhancement of detection sensitivity using a lamp

A new α track method is proposed for the measurement of radon (²²²Rn) concentration in environmental levels. This involves collecting radon daughters on the surface of pilot lamp and detecting α-particles emitted from the nuclides (²¹⁸Po and²¹⁴Po) by a detector (LR 115). The detection sensitivity of this method is 6 times greater than that of the conventional α track method.     

The influence of the lithology and depth on water recharge of wells in two Moroccan Atlantic coastal regions by using solid state nuclear track detectors and radon as a natural tracer

Uranium and thorium contents as well as radon and thoron -activity concentrations were evaluated inside different underground water samples by using a method based on calculating the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) detection efficiencies for the emitted -particles and measuring the resulting track density rates. The validity of the SSNTD technique utilized was checked by analysing uranium nitrate standard solutions. A relationship between water radon concentration and recharge of wells dug in two Moroccan Atlantic coastal regions, for a given lithology, was found. The influence of the lithology and depth on radon concentration and salinity of well waters studied was investigated.     

Influence of the building material and ventilation rate on the concentration of radon, thoron and their progenies in dwelling rooms using SSNTD and Monte Carlo simulation

A new Monte Carlo computer code was developed for determining the detection efficiencies of the CR-39 and LR-115 II solid state nuclear track detectors (SSNTD) for a-particles emitted by radon (²²²Rn) and thoron (²²⁰Rn) series inside the atmosphere of dwelling rooms. Alpha-activities due to radon, thoron and their decay products, were evaluated for the determination of the detection efficiencies of the SSNTD utilized for the emitted a-particles by measuring the corresponding track densities. The influence of the ventilation rate and building material on the concentration of radon, thoron and their progenies was investigated. Equilibrium factors between radon and its progeny and between thoron and its daughters have been evaluated in the air of the rooms.     

Comparison of four types of gamma- and X-ray detectors for environmental applications in the 10–450 keV energy range

The performance of four types of - and X-ray radiation detectors for environmental applications was evaluated in the 10–450 keV energy range. Two cadmium zinc telluride (CdZnTe) room temperature semiconductor detectors were evaluated along with a cryogenically cooled semiconductor detector and two different types of scintillation detectors. The energy resolution, absolute peak detection efficiency and peak-to-background ratio of each of the detectors were calculated and intercompared. The advantages and disadvantages of environmental applications of each detector, along with their performance results, are summarized.     

Radon measurement by coincidence gamma-ray spectrometry

A method of radon measurement by a multidetector -ray spectrometer,based on coincidence counting of 609 keV photons from two-step cascade transitionsthat follow â – decay of 214 Bi, is proposed. Besides a good accuracy,the method has better sensitivity than some standard methods of radon measurementcurrently in use. Applying this method to the PRIPJAT-2M spectrometer with6 NaI(Tl) detectors, and counting a 1 l sample of well water for 30 minutes,a minimum detectable radon activity of 0.25 Bq/l is experimentally determined.     

Preparation and Pharmacokinetic Evaluation of Iodine-125 Labeled Alphamethyl-L-Tyrosine

A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of ⁶⁰Co and ¹⁵²Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated ²⁵²Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the ²⁵²Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.     

Industrial commercial respirator filter as indoor radon monitor

This paper presents a method for measuring indoor radon concentrations using a commercially available air-purifying respirator filter as a component of the radon monitor. The filter used was Survivair’s NIOSH (National Institute for Occupational Health and Safety)-approved 100800 model. The method is based on the diffusion of radon gas into the activated carbon of the filter and the measurement of the radioactive daughters resulting from the radon decay. The photopeaks of the ²¹⁴Bi daughter gamma rays (0.609 MeV) were analyzed with a Hyper-Pure Germanium (HPGe) detector and a multichannel system. A monotonically increasing and very close to linear response relation between the integrated area under the ²¹⁴Bi photopeak and the radon concentration of the activated carbon was found. A well-defined relation held for radon levels ranging from 15 to 4,700 Bq/m³. This procedure results in highly reproducible and reliable measurements of indoor radon levels. Interesting applications include the investigation of radiological accidents involving radon and the retrospective measuring of indoor radon concentrations by analyzing the filters of the respirators worn by personnel working during the relevant period.     

The efficiency calibration of radioxenon isotopes of inhomogeneous adsorption column for HPGe γ spectrometry

In this paper, a new efficiency calibration scheme is proposed for the inhomogeneous adsorption column, in which the segment efficiencies modeled by the Monte Carlo toolkit Geant4 are weighted according to the fraction distributions of the adsorbed radioxenon based on the equilibrium adsorption theory. In order to verify the scheme, an experiment of efficiency calibration of HPGe detector by employing radon daughters was performed, and as a result the relative errors between the measured value and simulated value was less than ±?2.3%. This method developed in this paper is useful for the development of rapid test device of radioactive gas.     

Microcolumn ion chromatography with conductimetric detection

Summary A miniaturized flow cell for an electrical conductivity detector has been made and applied to the ion chromatography of inorganic anions. It consisted of stainless steel tubes (0.13 mm ID×0.31 mm OD) and PTFE tubes (0.25 mm ID×2 mm OD). The detection limit for chloride at S/N=3 was 36 pg or 0.33 ppm for a 0.11 l injection.     

An automated system for track measurement for the employment of CR-39 as alpha spectrometer in radon and its daughters monitoring

In this work we studied an automated analysis of alpha particle tracks in CR-39, by employing a MITAKA photo-microdensitometer with a C1522 HAMAMATSU Image Analysis System. This system can be used to measure track diameters (with a nominal precision of 0.8 m), superficial track density, and track darkness. This information can be used to determine the alpha particle energies and also their incidence angles (azimuthal and zenithal). The performance of such an automated system, to analyze CR-39 samples which were exposed to alpha particles of known energies, was studied, comparing its response with measurements performed manually by experienced microscopists. The experimental results indicate that the MITAKA/HAMAMATSU system is very reliable for alpha track analysis in CR-39, making possible its use to perform time-consuming measurements in microscopy, as in the case of radon and its daughters surveys.     

A highly sensitive high-performance liquid chromatographic procedure for the determination of isocyanates in air

Summary A sensitive high-performance liquid chromatographic procedure is described to analyse hexamethylene diisocyanate (HDI), 2,4- and 2,6-toluene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI) in air. The isocyanates are trapped on a sorbent coated with 1-(2-methoxyphenyl)piperazine (MPP). The resulting derivatives are separated using a column switching technique using either a diode array UV detector or an electrochemical detector. Working ranges are 1–5000 and 0.05–400 pmol for UV and EC detection, respectively. Virtually no breakthrough occurs if an air volume of up to 1500 l is sampled, and relative detection limits between 0.1 and 1 ng/m³ can be achieved. The procedure can be used to determine HDI and MDI in work place atmospheres and indoor air.Dedicated to Prof Dr. E. Lahmann on the occasion of this 65th birthday     

Passive α-particles spectrometry by polycarbonate SSNTD using new etching conditions

By adding ethylenediamine to the common etchant composition (potassium hydroxide, water, methanol and/or ethanol) in electrochemical etching of lexan polycarbonate detectors, a passive α-particle spectrometry is resulted in the energy range of 0.8–5.2 MeV. This spectrometry is based on the track size distributions, which have a tailed normal shape and FWHM of less than 0.5 MeV. Also the energies of α-particles emitted by a ²²⁶Ra micro-precipitated source and its α-emitter daughters, which were detected by this method, were in accord with that of a surface barrier detector. Consequently, this method can be developed for alpha spectrometry such as radon/thoron and their α emitter daughters’ detection, separation and measurements.     

Gamma radiation and radon levels in Mexico City dwellings

Gamma exposure rate and radon levels were measured in 75 single-family dwellings in Mexico City in order to correlate them with local environment. Radon monitoring was performed both indoors and outdoors using a continuous working level monitor for short-lived radon decay products; the gamma exposure rate was measured using CaSO₄: Dy+PTFE. The results obtained show a log-normal distribution. The mean indoor radon concentration is lower than 45 Bq/m³ and the mean indoor gamma exposure rate was 11.29 R/h.     

Background airborne radioactivity in an equatorial Brazilian town

The aim of this work was to determine the background airbome radioactivity in the town of Natal, Brazil. Indoor radon concentrations were measured inside 24 buildings using solid state nuclear track detectors which were exposed for a period of about 180 days. The average indoor radon level resulted to be 15.4±10.6 Bq·m^–3. Measurements of gross - and -activities were performed at six different sites for airbome particulate samples collected over cellulose nitrate filters. Mean values of 0.15±0.06 mBq·m^–3 and 0.42±0.10 mBq·m^–3 were obtained for the gross -and gross -activity, respectively.     

Uranium and thorium determination in Brazilian coals by epithermal neutron activation analysis

An experimental technique has been developed to determine impurities in coal. Uranium was determined by counting the²³⁹Np 106.1 keV -ray with a LEPS detector and thorium by counting the²³³Pa 311.8 keV -ray with a Ge(Li) detector. Seventeen coal samples were analyzed with an average precision of 3% and a quantitative determination limit of 0.153 g/g for uranium and 0.078 g/g for thorium. The technique allows determinations of up to twenty elements besides U and Th and can be applied in routine analysis.