Direct evidence for neutrino flavor transformation from neutral-current interactions in the Sudbury Neutrino Observatory.

Observations of neutral-current nu interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard 8B shape, the nu(e) component of the 8B solar flux is phis(e) = 1.76(+0.05)(-0.05)(stat)(+0.09)(-0.09)(syst) x 10(6) cm(-2) s(-1) for a kinetic energy threshold of 5 MeV. The non-nu(e) component is phi(mu)(tau) = 3.41(+0.45)(-0.45)(stat)(+0.48)(-0.45)(syst) x 10(6) cm(-2) s(-1), 5.3sigma greater than zero, providing strong evidence for solar nu(e) flavor transformation. The total flux measured with the NC reaction is phi(NC) = 5.09(+0.44)(-0.43)(stat)(+0.46)(-0.43)(syst) x 10(6) cm(-2) s(-1), consistent with solar models.

Measurement of day and night neutrino energy spectra at SNO and constraints on neutrino mixing parameters.

The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted 8B spectrum, the night minus day rate is 14.0%+/-6.3%(+1.5%)(-1.4%) of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the nu(e) asymmetry is found to be 7.0%+/-4.9%(+1.3%)(-1.2%). A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the large mixing angle solution.

Measurement of the rate of nu(e) + d --> p + p + e(-) interactions produced by (8)B solar neutrinos at the Sudbury Neutrino Observatory.

Solar neutrinos from (8)B decay have been detected at the Sudbury Neutrino Observatory via the charged current (CC) reaction on deuterium and the elastic scattering (ES) of electrons. The flux of nu(e)'s is measured by the CC reaction rate to be straight phi(CC)(nu(e)) = 1.75 +/- 0.07(stat)(+0.12)(-0.11)(syst) +/- 0.05(theor) x 10(6) cm(-2) s(-1). Comparison of straight phi(CC)(nu(e)) to the Super-Kamiokande Collaboration's precision value of the flux inferred from the ES reaction yields a 3.3 sigma difference, assuming the systematic uncertainties are normally distributed, providing evidence of an active non- nu(e) component in the solar flux. The total flux of active 8B neutrinos is determined to be 5.44+/-0.99 x 10(6) cm(-2) s(-1).

Theoretical considerations regarding the migration of 222Rn and 220Rn from uranium- and thorium-bearing underground environments.

Theoretical calculations are presented for partially enclosed uranium- and thorium-bearing subterranean environments, such as tunnels and underground uranium mines. The variables of practical interest considered here are the 222Rn and 220Rn concentrations in the wall, and the flux densities of the same radioactive gases in the wall and at the wall/air interface of these underground sites. Calculations have been conducted based on a plane, semi-infinite geometry model (commonly used to predict radiation levels in mines) and a cylindrical (i.e., tunnel) geometry model. The 220Rn flux density, J(220Rn), calculated according to the plane and cylindrical geometries agree with each other within 5% for wall media of porosity equal to or greater than about 2%, even for tunnels of small radii. However, for 222Rn the cylindrical geometry gives values for the 222Rn flux density, J(222Rn), substantially higher (by a factor of 1.4 to approximately 3) than those predicted by the plane semi-infinite geometry. A practical difficulty arises in the experimental verification of the models in underground environments. The results are relevant for predicting radioactivity levels (222Rn, 220Rn, and their progeny) in underground environments such as uranium mines. Health Phys.

Characterization of long-lived radioactive dust in uranium mill operations.

The characteristics of long-lived radioactive dust clouds generated in several mechanical and physiochemical operations in a uranium mill have been investigated. The study consisted of the determination of dust size distribution and of the size distribution of radionuclides associated with particulate matter in the size range less than 0.1 to 26 microns. Experiments were conducted by using two different types of cascade impactors operating at different sampling flow rates. Radionuclide identification was done by using alpha-spectrometry. Long- and short-lived radionuclides were identified in dust samples. The characteristics of the dust clouds depended on the mill operation, such as crushing (vibrating grizzly, jaw crusher, cone crusher); screening; ore transportation; grinding; acid leaching; counter-current decantation; yellow cake precipitation and drying; and yellow cake packaging. In addition, other dust and radioactivity measurements have been carried out.

Practical difficulties in determining 222Rn flux density in underground uranium mines.

Radon-222 flux density, J, has been determined in a number of locations in an underground U mine. Measurements were conducted using the Two-Point Measurement (2PM) method, consisting of measuring the 222Rn concentration at two different points a distance apart within a given section of the mine. Several mine models were used for determining J by the above method. The 2PM method is sensitive to sources and sinks of 222Rn other than mine walls, as well as mining operations and mining activities of a diverse nature, and to local variations in airflow conditions. Because of this, J obtained by the 2PM method represents an "apparent" flux density. Significant differences were found in the flux density calculated according to different mine models. In addition, J measurements using the flux "can" method were also carried out in mine walls and compared with the values obtained by the 2PM method. Wide discrepancies between the two methods were found. The practical and theoretical difficulties in determining J are discussed.

Desorption of 220Rn progeny from large surfaces by alpha- and beta-recoil processes.

Transfer (i.e., desorption or detachment) of 220Rn progeny from a substrate (metal disc, filter material, and activated charcoal) to its surroundings has been investigated. The technique, methodology, and materials used differ from the work of others in a number of significant ways. For instance, 220Rn progeny were deposited on substrates by plate-out techniques, and detached 220Rn progeny were measured using a silicon barrier alpha-particle detector as both the host "receiving" surface and the detector for the detached radionuclides. Transfer of 220Rn progeny from the substrates to the detector was observed by alpha- and beta-recoil processes. The latter were demonstrated by using nonadsorbing 220Rn substrates. Other possible mechanisms of 220Rn progeny transfer are also discussed.

Electrical charge characteristics of long-lived radioactive dust.

Respirable long-lived radioactive dust (LLRD), i.e., dust containing long-lived radionuclides such as 238U, 232Th, 226Ra, 224Ra and 228Th, interacts with unipolar and bipolar atmospheres through diffusion charging, electrical charge neutralization, and electrical self-charging mechanisms. Because of these interactions, and depending on the type of dust as well as its method of production, LLRD is found in electrically charged and neutral states. Electrical charge is important because it influences the deposition of particles in the human respiratory system. Particle size, electrical charge, and radioactive particle size distributions were measured in an area of an underground U mine where U ore crushing and transportation operations were conducted. In addition, concurrent measurements of 222Rn progeny and 220Rn progeny were made. A variety of instrumentation was used, such as particle counters. The electrical charge associated with dust generated in the primary crushing operation was substantially higher (3e- at 1 microns and approximately 500e- at 3 microns) than for the conveyor belt (2e- at 1 microns and approximately 50e- at 8 microns). In both cases the charge distribution was significantly higher than that predicted by Boltzmann's distribution.

Some observations on the electrical characteristics of radioactive (222Rn progeny) and nonradioactive aerosols.

The electrical characteristics of 222Rn, 222Rn progeny atmospheres have been investigated. Experiments were conducted in a 222Rn/220Rn Test Facility (RTTF) of the walk-in type using an electrical elutriator of the split-flow variety, originally designed by Johnston. Experiments were carried out with the "undisturbed" atmosphere, and when this atmosphere was exposed to a source of electrically charged particles produced by a negative ion-generator. Under normal conditions, the average electrical charge of the 222Rn, 222Rn progeny atmosphere was substantially less than one elementary unit. Under the influence of the ion-generator, however, the electrical charge exceeded two elementary units, and the electrical charge distribution was non-symmetrical. It was found that the particle concentration in the RTTF substantially decreased with the operation of the ion-generator.

Reduction of airborne radioactive dust by means of a charged water spray.

An electrostatic precipitator based on charged water spray technology has been used in an underground uranium mine to control long-lived radioactive dust and short-lived aerosol concentration in a mine gallery where dust from a rock breaking/ore transportation operation was discharged. Two main sampling stations were established: one upstream of the dust precipitator and one downstream. In addition, dust samplers were placed at different locations between the dust discharge and the end of the mine gallery. Long-lived radioactive dust was measured using cascade impactors and nylon cyclone dust samplers, and measurement of the radioactivity on the samples was carried out by conventional methods. Radon and thoron progeny were estimated using standard techniques. Experiments were conducted under a variety of airflow conditions. A maximum radioactive dust reduction of about 40% (approximately 20% caused by gravitational settling) at a ventilation rate of 0.61 m3/sec was obtained as a result of the combined action of water scrubbing and electrostatic precipitation by the charged water spray electrostatic precipitator. This represents the optimum efficiency attained within the range of ventilation rates investigated. The dust reduction efficiency of the charged water spray decreased with increasing ventilation rate, i.e., decreasing air residence time, and hence, reduced dust cloud/charged water droplets mixing time.

Relationship of 220Rn and 222Rn progeny levels in Canadian underground U mines.

Radon-222 and 220Rn progeny are found in some Canadian underground U mines. Because both can contribute to lung dose, their experimental determinations are important. The relationship between 222Rn progeny Working Level [WL(Rn)] and 220Rn progeny Working Level [WL(Tn)] has been investigated in U mines. Experimental measurements extended from 1981 to 1986 and consisted of about 700 measurements of each WL(Rn) and WL(Tn). The data were analyzed by standard linear and power-function regression analysis. A power-function relationship between WL(Rn) and WL(Tn) seemed to fit the experimental data best. The relationship obtained permits the calculation of WL(Tn) from experimental values of WL(Rn). The relationship is useful for lung-dose-calculation purposes and in mine-ventilation-engineering calculations.

Radon (thoron) daughter measurements with an automated, programmable, radiation monitor.

A technical evaluation of an automated, programmable, grab-sampler manufactured by Pylon Electronic Development under the commercial name WL-1000C has been conducted. Six different methods are implemented in the instrument for analyzing radiation data. Any one method can be used on command and easily selected by means of a keyboard. Available radiation data that can be retrieved on command include radon (thoron) daughter concentrations and radon (thoron) Working Levels. Measurements were carried out under laboratory-controlled conditions in a large (26 m(3)) radon/thoron test facility, designed for calibration purposes, and at an underground uranium mine. Data obtained with the WL-1000C have been compared with conventional grab-sampling (e.g., Kusnetz, Thomas-Tsivoglou and Markov methods) and with other automated radiation instrumentation previously tested at our laboratories. Tests were done under constant radiation conditions and also under rapidly fluctuating conditions in order to determine the response of the instruments and methods in these two cases of practial interest. The Working Level used in these experiments was in the approximate range of 0.01 to 10 WL. Tests were conducted under a variety of environmental conditions. Good agreement with grab-sampling data was found for radon daughters. Some discrepancies with grab-sampling data were found for radon daughter/thoron daughter mixtures. Disagreement in the latter case is to be expected because of α-energy overlap between RaA and ThC.

Theoretical models for determining 222Rn and 220Rn progeny levels in Canadian underground U mines--a comparison with experimental data.

Use has been made of several theoretical models to predict radiation levels in underground U mines. The models used are the Evans model, the Thomas-Epps mine model, the isolated mine model, the mine tunnel with no air flow and the mine tunnel with air flow (Beckman and Holub). Calculations based on the above models have been extended to include 220Rn gas and its progeny, a common occurrence in some Canadian U mines. Theoretical predictions include 222Rn and 220Rn progenies working levels and concentrations, as well as some ratios of great practical interest. The main differences between the models are pointed out and comparison is made with experimental data gathered during the last 3 yr in several Canadian underground U mines. In general terms, the mine models reported in the literature and presented here are neither satisfactory nor clearly distinguishable for practical application on the basis of the experimental data so far collected. The reason for such lack of agreement lies mainly in the unrealistic assumptions on which the models are based. Compounded is the gross oversimplification of quite complex dynamic situations encountered in actual practice. Deficiencies inherent to the models are noted and suggestions to improve the applicability of mine models to practical situations are indicated.

On the effect of a negative ion-generator and a mixing fan on the plate-out of radon decay products in a radon box.

Studies have been conducted on the effect of a negative ion-generator and a mixing fan on the radon daughter Working Level produced in an environmental radon "box". A dramatic decrease in the Working Level has been observed when either the ion-generator or the mixing fan is operating. The combined effect of the ion-generator and the mixing fan was substantially larger than that from either one of them alone. Experiments have been carried out over a wide range of relative humidity (45-95%) and at a temperature of 20 +/- 3 degrees C. The effects observed were nearly independent of relative humidity in the box. Preliminary experiments seem to indicate that the decrease in the Working Level is somewhat related to the possible build-up of electrostatic charge on the inner walls of the radon box. However, there is some difficulty in accepting charge build-up at high levels of relative humidity. To better understand the phenomena observed, a number of measurements are planned on the inner walls of the box. These include electrostatic charge, electric field, and measurement of alpha- and beta-activity.

Determination of the working level of radon/thoron mixtures by personal α-dosimeters and environmental α-monitors using gross α-counting.

Analytical procedures are presented which permit the determination of the Working Levels of the radon and thoron progenies with personal α-dosimeters and α-particle environmental monitors, operating on time integrating principles, from gross α-counts. Experiments have been carried out in an underground uranium mine and in a radon/thoron environmental chamber, specially designed for calibration purposes, to verify theoretical data. In general, and notwithstanding a number of complicating factors, fair to good agreement has been found between theoretical and experimental data. Experimental values have been found to be lower than theoretical values, an observation which is partly ascribed to plate-out of decay products in the instrument's sampling heads.