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By Robert S. Post

A highly respected coal mining company in West Virginia updated their stacker belt by switching to a new magnetic coupling. The savings they achieved are the subject of this paper. A steep incline and heavy belt loads are powered by a dual drive arrangement. The magnetic couplings were custom designed for complete fluid coupling retrofit and easy installation in the field. Maintenance personnel updated the drives in just a few hours. Over the following several weeks, adjustments were made to the couplings for optimum performance. Cost savings are found in reduced down time, no coupling maintenance, and equipment protection.

Jan 1, 2000

By T. J. DeMull

AMAX's Sleeper Mine uses conventional cyanidation milling and heap leaching techniques to produce gold. Since milling operations commenced in March 1986, average ore processing rates have improved from the design rate of 455 tonnes per day to more than 720 tonnes per day. Heap leaching was added to the process facilities in September 1986 at a design rate of 1,500 tonnes per day, and current heap leaching rates exceed 2,680 tonnes per day. Presented are descriptions of the Sleeper processing facilities with emphasis on the crushing and grinding circuits, a review of the selection of crushing and grinding equipment, and a summary of operating performance during the first 16 months of operations.

Jan 1, 1988

By R. Sharma, S. Svoronos, S. Gupta, N. A. Abdel-Khalek

This paper presents the results of a column flotation study on a fine feed sample of Florida phosphate. A central composite design was used to study the main and interaction effects of parameters affecting column efficiency. The statistical design is also used to determine the optimum conditions. The results indicate that, depending on the experimental conditions, it is possible to produce a high-grade concentrate with a high recovery. A 15ppm concentration of nonionic frother was found sufficient to maximize the recovery at pH of 9.5.

Jan 1, 2002

By D. P. Tao, J. G. Groppo, R. Killmeyer, W. W. Wen, B. K. Parekh

Economical dewatering of ultra-fine (minus 74 m) clean coal slurry produced in column flotation to a 20 percent or lower moisture level will be an important step in successful implementation of the advanced fine coal cleaning processes. The main objective of the present study was to evaluate efficiency and effectiveness of three dewatering techniques, namely, hyperbaric, vacuum and screen bowl centrifuge, in dewatering of ultra-fine (D50 ~ 25 m) clean coal slurry produced by the `Ken-Flote' columns operating at the Powell Mountain Coal Company, St. Charles, Virginia. he hyperbaric filter using 3 bar pressure and 165o cake formation angle, provided a filter cake with 23.6percent moisture with a throughput of 800 Kg/m2-h and air consumption of 868 Nm3/t (460 scfm/t). The vacuum filter with 30 percent submergence provided a filter cake with 27.8 percent moisture with a throughput of 122 Kg/m2-h. The screen bowl centrifuge provided a dewatered product containing 32.9 percent moisture at a feed rate of 450 Kg/hr, however, the solids capture was only65 percent. Addition of 1 Kg/t of a cationic surfactant provided filter cakes with 19.1 percent, 23percent, and 34 percent moisture using hyperbaric, vacuum, and centrifuge, respectively. Similarly, addition of 0.5 Kg/ton of copper chloride lowered filter cake moisture to 20.7 percent and 24.8percent, using hyperbaric and vacuum. With the centrifuge no improvement in filter cake moisture was noted. However, use of 80 Kg/ton of `orimulsion' in the centrifuge provided dewatered product containing 26 percent moisture, and the solids capture increased from 65 to 95 percent. The dewatered product appeared dry and was easily handleable.

Jan 1, 1999

By F. J. Chernosky

In the past, a number of papers have been written on the use of various reagents as coal flotation frothers. For the most part, these papers have attempted to correlate the intrinsic chemical and physical properties of the reagents or reagent groups to the floatability of various fine coals. Because of the type or nature of evaluations made, chemically pure reagents were normally used. Generally, these reagents are unavailable in commercial quantities. Therefore, the results obtained with these reagents were usually limited in usefulness to the plant operator or metallurgist. This paper presents the results of a study in which commercially available forms of various reagents were used as flotation frothers. Flotation procedures which would conform in general to those employed in a large number of commercial coal flotation plants were utilized. The objective of the test was to compare these reagents on yield-selectivity-cost basis, that is, (1) the yields obtained, (2) the ash levels obtained, and (3) the reagent cost relating to these results.

Jan 1, 1962

By W. S. Hannan

History Leaching of sulfide ore was first attempted by the Phelps Dodge Corporation about 1900 at Bisbee, Arizona, when Dr. James Douglas conducted experiments in an attempt to apply the leaching techniques then in use at Rio Tinto, Spain. Although this initital attempt was unsuccessful, research work was continued which culminated in successful leaching operations at Tyrone, New Mexico, in 1917 and at Bisbee beginning in 1920. Leaching has continued intermittently since that date, with material from the Lavender Pit being leached today. The Lavender Pit Leach Dump Stripping for the Lavender Pit was started in 1951, with mining operations on stream in 1954 and continuing to the present. All material removed from the pit has been classified as waste, leach material, milling ore, or direct smelting ore, depending upon grade and degree of oxidation. Lavender Pit leach material has been stockpiled in a single dump, called No. 7 Dump. This dump covers an area of approximately 135 acres and average about 300 feet in height. The dump has been deposited over a period of 20 years by truck haulage and contains several layers, each of which has a permeable boulder layer at the bottom and a compacted layer at the top. Leaching of Lavender Pit material was started in 1956 and has proceeded simultaneously with dump construction. Former leach pond areas and haulage surfaces have been ripped with D-9 tractors before deposition of succeeding layers of ore.

Jan 1, 1972

By S. Boone, J. N. Shirlaw

INTRODUCTION Soft, near normally consolidated clays generally provide ideal conditions for tunneling using Earth Pressure Balance (EPB) shields. It is easy to turn the clay into a low permeability, viscous spoil that can be pressurized to maintain the required face pres-sure. Despite this, there are records of relatively large, and often quite variable, surface settlements over EPB driven tunnels in soft clay. To understand this variation it is necessary to identify the various factors that contribute to settlement. Tunnels in soft clay are ideal for study these effects in the field, as an unsupported void will close almost immediately, due to the low shear strength of the soil. In the short term, deformation in a soft clay will occur at constant volume, so short term surface settlements can be related to movements at tunnel level. In this paper, data will be used from EPB driven tunnels in Singapore marine clay. In all of the cases discussed the lining consisted of precast concreted segmental rings erected in the tail of the shield. The marine clay in Singapore has been studied, among others, by Tanaka et al.(2001). The clay typically has a plasticity index of 40 to 60, and the undrained shear strength (SU ) can be derived from: SU = 0.22 svo' where svo' is the current vertical effective stress. Figure 1 shows a summary of undrained strength/depth plots used for design on two sections of Singapore’s North East Line. The stability of a tunnel in clay can be assessed by comparing the stability number (N) of the tunnel with the stability number at total collapse (NTC). The stability number can be calculated from the equation: N = (?Z + q – Pt)/SU where: ? = the average unit weight of the ground above the springline of the tunnel Z = the depth to the springline of the tunnel from the ground surface q = the surcharge Pt = the support pressure within the tunnel The stability number at total collapse depends on the size, geometry and depth of the tunnel, and typically ranges between 5 and 9. Charts for assessing the number at total collapse are provided in Kimura and Mair (1981), based on the testing of model tunnels in a geotechnical centrifuge. For tunnels in the Singapore marine clay, the stability number of an unsupported tunnel would be over nine if the tunnel ois more than 8m deep. As a result, a support pressure

Jan 1, 2007

By R. J. Sweigard

Many states are considering the need to establish or modify policy relating to the disposal of coal ash. One of the primary concerns is the impact of leachate from the ash disposal sites upon groundwater and nearby bodies of surface water. A detailed site investigation was conducted at a coal ash disposal facility associated with a power generation station. The disposal site is situated alongside a major river. Monitoring wells were installed and soil samples were taken for characterization. Groundwater models were used to simulate migration of leachate from the disposal site toward the river. Such models have the potential to be used to verify regulatory compliance. This paper addresses the validation and adaptability of these models to this case and their usefulness as possible tools to be used in future environmental audits.

Jan 1, 1993

By Jürg Schlumpf

Concrete is one of the decisive construction materials, also for the AlpTransit Gotthard Tunnel. The client has many requirements, and many are the solution possibilities that concrete systems can offer. Cement producers and concrete admixture manufacturers have been challenged to design and test jointly concrete systems for cast and sprayed concrete. The testing operation followed the scenario laid out by the Gotthard AlpTransit Project management?s instructions ?Testing system for concrete mixes.? Various supplier teams have applied for the concrete systems for sections Amsteg/Erstfeld, section Sedrun and/or sections Bodio/Faido and have also followed through with the tests. As was to be expected, the rate of failed mixes matched the level of the requirements. Thanks to this system, it was nevertheless possible to test complete concrete systems for all sections and to get them approved. The joint ventures tendering for the contracts were allowed to include only approved mix designs in their bids. Workability and durability are of paramount importance for cast and sprayed concrete mixes. Durability is influenced by the chosen mix design where binder concept and well-defined water content, i.e., impermeability, are determinant. Aggregates for AlpTransit are to be considered as given. The concrete mix design also determines workability. Because ambient conditions and also requirements with respect to workability are subjected to change, it is necessary that the mix designs include control measures. The choice and number of components for the concrete systems (cement, additives and admixtures) allow adaptation to changing conditions. For AlpTransit such adaptive measures must meet very strict requirements.

Jan 1, 2008

By Arnolfo A. Valdivia

Prior to 1971, there were several clinical trials to evaluate programs for early detection of lung cancer. Among these, the Philadelphia Pulmonary Neoplasm Research Project,(3) the Veterans Administration Study published by Lilienfeld,(7) and the controlled trial of the Kaiser Foundation Health Plan showed an overall five year survival rate of 8% for newly detected cases (the same as the national statistic for unscreened patients). In 1971, the National Cancer Institute initiated three randomized, controlled mortality studies using lung cancer screening of persons at high risk (male smokers over 45 years old). The studies are being conducted at the Johns Hopkins University Hospital, the Mayo Clinic, and the Memorial Sloan-Kettering Cancer Center. The studies have slightly different designs in the combination of sputum cytology and chest x-rays. At the Mayo Clinic the study group is offered screening with sputum cytology and chest x-rays every four months, whereas the control group is advised to have an x-ray and cytology every year. No reminders are sent, and it is believed that only about 20% of the control group is screened. At Johns Hopkins and Memorial, both experimental and control groups are offered annual chest x-rays. The experimental group is additionally offered sputum cytology every four months.(5) At present all of the programs show that screening can detect cancers that are undetectible by other means. However, at this time mortality rates in the control and experimental groups are not significantly different in any of the three studies. OUR PROGRAM Our clinic is located in Grants, New Mexico and we provide most of the pre-employment physical examinations for the mines operating in the Grants area (Kerr McGee Nuclear, Homestake Mining, United Nuclear, Western Nuclear, and Ranchers). In the examinations, we obtain the previous mining history of the worker, a chest x-ray, a sample of sputum for cytological examination, and a blood sample. We also provide routine annual physical examinations of the workers, with special interest in the detection of bronchogenic carcinoma. In the early seventies, we did not have a definite surveillance program. We did not know whether we should have a program like the one started at Memorial or like the one started at the Mayo Clinic. After long consideration, we decided to have a program that does not demand a sputum cytology and chest x-ray every four months, but that allows as many chest x-rays and sputum cytologies as needed to diagnose lung cancer as early as possible. We believe that, if a screening method for cancer is to be optimally effective, it must detect the process at stages early enough for curative therapy. We order a test depending on the age of the miner, the race, the mining history, the smoking history, the radiation exposure levels, and the results of the previous chest x-ray and sputum cytology. With the help of the computer, we have a list of all the miners who should be watched closely because of age, race, mining history, smoking history, radiation exposure, etc. Examination of the miners is performed at our clinic, where all the records are kept. The sputum is collected there but examined in Grand Junction, Colorado, by Dr. Geno Saccomanno. There are two ways to collect sputum. The best way is to collect three consecutive morning samples. For this, we need the cooperation of the miners. They have to follow these instructions and mail the bottle containing the sample to Grand Junction. "Instructions for obtaining a good cough specimen" The enclosed plastic bottle contains a preservative solution, so do not empty out the liquid in it. When you go to bed, place the plastic bottle at your bedside where it will be handy in the morning. When you first get up in the morning (before breakfast) try to cough up some "phlegm" from deep in your chest, and spit it into the liquid in the bottle. Try coughing several times. If you have difficulty coughing, try inhaling deeply the steam from a teakettle (or home-type inhalator). Keep the amount of saliva (ordinary spit) that you put into the bottle along with the cough specimen as small as possible. Do not collect the "phlegm" or mucous that comes from the back of your nose. Put the cap back on the bottle, and shake it vigorously for two minutes. If the amount of material you have coughed up is quite small, then keep the bottle at your bedside for three or four days, and each morning try to add another cough specimen. After obtaining your cough specimen, repack the bottle in the mailing container, and attach the enclosed mailing label. It does not require any postage stamps. Unfortunately, some miners "forget" to mail the sample and end up with an incomplete physical examination. To avoid this some companies, like Homestake, request that we obtain the sample in our clinic by forcing cough and expectorant with a nebulizer machine. This method does not give as good a sputum sample as the previous one, but we do get a sputum sample for every miner. The policies of different companies, in regard to annual physical examinations are different. All

Jan 1, 1981

Every two years, industry leaders and practitioners of tunneling and underground construction gather at the Rapid Excavation and Tunneling Conference (RETC) to learn from their peers about the most recent advances and breakthroughs in this unique fleld. Industry experts from around the world highlight their most recent projects and share real-world experiences. They also share with their colleagues new technologies and methodologies that attendees can take home to their respective projects. The 2013 RETC was held June 23-26 in Washing-ton, D.C., itself home to several major tunneling and underground construction projects. The conference is sponsored by SME. Attendance was 1,384 professionals. The accompanying exhibit hosted 159 companies in 188 booths. A few of the topics covered in the technical sessions dealt with caverns and large spans, contracting practices, tunnel linings, design and planning, geotechnical considerations and instrumentation. The conference was preceded by four short courses, all well attended. They were ?Grouting in Underground Construction,? ?Tunnel Lining Design,? ?Microtunneling Application? and ?Risk, Uncertainty and Hard Decisions.? In addition, a sold-out field trip to D.C. Water?s Blue Plains Tunnel took place following the conference. The Blue Plains Tunnel is part of the agency?s Clean Rivers Project. Also during the meeting, three students each received $5,000 scholarships from the UCA of SME, while another three students each received $2,500 scholarships from RETC (See page 53).

Sep 1, 2013

By M. E. Poad

The Research and development review arrived too late to appear in the May issue. The competitiveness of the US mining industry in a world market depends on many factors. The introduction of new and innovative methods, though, can have a significant, long-term impact. As industry cuts back its own long- term research and development efforts, the federal government continues to provide the major support for mining and minerals research. The US Bureau of Mines works with the mining industry and the academic community to develop innovative concepts for the mining and processing of non-fuel minerals. The Bureau’s research focuses on exploration and mining technology, minerals and materials science, processing technology, health and safety and environmental technology. Mine design A conical caving system, being designed by the Bureau, would allow the development of low-grade ore bodies, early startup at lower initial capital costs and increased safety and versatility in development and production. This method is a form of mass caving that allows the ore to be drawn from a central loading point at the bottom of the cone- shaped caving zone (Fig. 1). A simulation laboratory model and computer analysis show initial promise for predicted performance. For tabular, flat-lying ore deposits, the Bureau is investigating a version of the Finnish slot-and-fill system. For this total extraction method, a pattern of rectangular panels is laid out. One panel is extracted in a series of parallel slots and is replaced by alternating-row pillars of backfill. After one panel is mined, equipment and operations are transferred to another panel. By transforming this rectangular layout to a curvilinear geometry, one continuous spiral can be mined without re positioning equipment. Instead of parallel slots and pillars aligned in a rectangle, the slots and pillars are arranged in a spiral.

Jan 1, 1992

By C. R. Rinschler, G. R. S. Smith

A high-strength, industrial-grade membrane filter- cloth capable of high flow rates and sub-micrometric particle retention has been developed. A filtration system using this filter- combined with special filtration techniques and using tubular-filters makes possible the filtration of many difficult-to-jilter slurries. Small, discrete, slowly-settling particles are formed into filter cakes that when pulsed of the membrane filter cloth do not redisperse but settle rapidly to form a dense filter under- flow. A positive separation of solids from liquids is obtained.

Jan 1, 1991

By R. H. King, D. R. Schricker, R. E. Cameron

Mine managers rely on their experience, section foreman's daily reports and occasional time studies to make important production, maintenance and forecasting decisions. This information is often subjective and imprecise, consumes expensive engineers time, is often biased and is restricted to short time periods. Managers need better information. Furthermore, if a recently purchased machine is being evaluated, a large increase (>10%) in productivity may be obvious, but small increases are usually masked by other variables. In today's highly competitive markets, cumulative small changes are important, especially since managers have already exhausted most available, obvious avenues of improvement. A technique to separate these charges from effects of other variables and to quantify the target effect is necessary. CSM researchers are addressing this need by developing an intelligent decision support system (IDSS). It provides key production and maintenance information to support management decisions by recognizing patterns in mining machine sensor data and representing knowledge about mine management, operations, layout and equipment. A continuous miner section at Western Fuels-Utah Inc.'s Deserado Mine in Rangely, CO is the test facility for the research. Power transducers located in the sections load center provide kilowatt versus time data from continuous section equipment. The IDSS pattern recognition algorithms classify the kilowatt versus time patterns into individual machine operating modes. It produces an output similar to a typical industrial engineering time study but continuously, automatically and without an engineer in the section. It is relatively easy for a time-study engineer to identify the stop and end points of a cycle element and classify it by looking at the machine and glancing at a stop watch. The problem is that monitoring system hardware and software do not have these unique capabilities. Consequently, IDSS algorithms must automatically define the begin and end points of machine tasks and identify the task by recognizing patterns in kilowatt versus time data. However, many mines have file drawers of time-study type data that are not very useful. So, IDSS contains the knowledge representation subsystem (IDSS/KRS) to produce short reports containing only key information. This is difficult because mine environments continually change and information requirements differ for each management level. Consequently, IDSS/KRS must learn and adapt to new conditions in a dynamic mining environment. Western Fuels-Utah owns and operates the Deserado Mine, located about 19 km (12 miles) northeast of Rangely, CO (Upadhyay, 1988; King and Eros, 1988). One longwall and two continuous miner sections produce about 900 kt (1 million st) of coal annually for the Deseret Generation and Transmission Cooperative's 4000 MW power plant located near Bonanza, UT. Three mine monitoring systems control the underground mine, the preparation plant and the unit train load out. Pattern recognition IDSS/PRS produces a listing of begin and end times for each machine operating event as shown is Table 1.

Jan 1, 1991

By P. Tong-jiang

We studied mineralogical characteristics of the vermiculite samples from seven mines in China. We found three types of interstratified structures in the investigated samples: 1:1 regular interstratified structure, segregated interstratified structure, and random interstratified structure. The vermiculite samples from six mines are mainly composed of phlogopite?vermiculite interstratified minerals, and the samples from the other mine are composed of chlorite?vermiculite interstratified mineral. The samples with phlogopite?vermiculite structure have high contents of K2O, TiO2 and Na2O. The samples with chlorite?vermiculite structure have the highest contents of MgO and Al2O3. The cation exchange capacity of the samples is 17.3?99.0 mmol/100g.The exchangeable cations of phlogopite?vermiculite samples from Weili Mine mainly include Na+ and Ca2+, while those of phlogopite?vermiculite samples from Tongguan Mine mainly include Mg2+ and Ca2+. The thermal expansion ratio of the samples is between 9 and 32. The exfoliated vermiculite products from Weili Mine have the best mechanical strength.

Feb 27, 2013

By Erich U. Petersen

Recognition of mineralogical and chemical zoning patterns associated with mineralization is an integral part of mineral exploration. Even though the origin of zoning may not always be known, zoning patterns as expressed by the systematic distribution of ore and gangue minerals, alteration or elemental assays (soil and rock geochemistry) have received much attention and are extremely useful in guiding exploration efforts toward locating economic mineralization. By contrast, the potential of using zoning information recorded in solid-solution minerals to address practical geological-engineering problems has received less attention. Solid-solution minerals can provide critical information for common problems faced in exploration, mine development and valuation. Mineral zoning information from solid-solution minerals can now be easily obtained because advances in electron microprobe instrumentation have made these instruments a most efficient, accurate, economical and practical tool for analysis of large numbers of samples. Now entire mines and districts can be studied in a timely and cost-effective manner as required by modern mineral exploration and mining practice. This article shows how knowledge of the composition of fahlore minerals can be used in addressing important problems in exploration, development and valuation. Situations are described in which drilling intersected "low grade zones" (Case one: Orcopampa, Peru, precious metal system) and where there was a need to determine the "lateral correlation of multiple ore intercepts" (Case two: Sheep Creek, Montana, sediment-hosted sulfide deposit).

Jan 1, 1992

By Jack Parker

Cycles of mine convergence coincide with annual cycles of temperature and humidity in the mine. Laboratory measurements confirm that the presence of moisture reduces rock strength and induces internal rock stress. Findings are used in the design of mine openings.

Jan 1, 1969

By Erling Stranden, Leiv Berteig

INTRODUCTION The measurement of the total activity of radon daughters in the air of mines has become a routine procedure in order to control the radiation exposure in miners due to the inhalation of these radionuclides. Normally the measured concentration is given in terms of total potential L-energy of the short lived radon daughters. The unit most frequently used is 1 WL (working level), which is defined as the potential a-energy of 1.3.105 MeV per 1 of air. The a-dose to the respiratory tract is, however, not proportional to the inhaled potential a-energy. In addition, the degree of equilibrium between the daughter products in air and the fraction of daughter products not attached to aerosol particles (the unattached fraction) must be known. Theoretical calculations of the equilibrium between daughters and the unattached fraction have been presented by different authors (Jacobi, 1972; Porstendörfer et al, 1978). Such calculations must take into account the plateout of daughters on surfaces, the attachment of daughters to aerosols and removal of daughters by the ventilation. The situation in mines will however be very complex and no single model will cover all situations. In most cases the radon and radon daughter concentrations will be described by a combination of different models. Domanski (1979) used the experimental results of Breslin et al. (1969) from uranium mines to relate the equilibrium between the individual daughters to the equilibrium factor, F. Once the equilibrium factor is known, this seems to be a useful approach to assess the individual daughter concentrations. The concentrations of radon and daughter products may vary considerably during the day. Seasonal variations are also frequently found. It is therefore important to have knowledge of the magnitude of these variations and of the factors having the strongest influence upon the concentrations. The unattached fraction of radon daughters in uranium mines was investigated by George and Hinchliffe (1972) and Raghavayya and Jones (1974). Mercer (1975) later modified the results of Raghavayya and Jones. Both these investigations indicated that the aerosol particle concentrations was the main influencing factor upon the unattached fraction. In this paper we will summarize the main results of a study on the radiological characterics of nonuranium mines. We will also discuss the correlations between the unattached fraction of the potential a-energy and the unattached fraction of the individual daughters, and between the equilibrium factor F, and the individual daughter ratios. More detailed discussions of this study will be published elsewhere (Stranden and Berteig, 1981 and Stranden and Berteig 1981 a). MATERIAL AND METHODS During 4 two-weeks periods corresponding to the seasons in the Norwegian mine where the highest radon daughter concentrations occure, the parameters listed in table 1 were studied. TABLE 1 Parameters measured during the study [Parameter Methods Radon Scintillation flask/Continuous ionization chamber Radon daughters Tsivoglou(1953)/Kusnetz(1956) Respirable dust Cyclone Unattached fraction Wire screen (Stranden and Berteig 1981) Atmospheric pressure Continuous baragraph Temperature and Continuous thermohygrograph humidity] At a fixed location, the radon concentration was measured continuously by a ionization chamber (Stranden, 1981), during these two-weeks periods in order to study short-time and seasonal variations. RESULTS Correlation between equilibrium factor and individual daughter ratios. The mean value of the equilibrium factor in all Norwegian mines measured during the last ten years was 0.46 with a minimum of 0.08 and maximum of 0.93 (Stranden and Berteig, 1981). The correlations between the equilibrium factor F, and the individual radon daughter/radon ratios were studied and the results indicated high correlations. In table 2, these correlation formulae are listed together with the correlation coefficients. TABLE 2 Correlation between the equilibrium factor, F, and individual radon daughter ratios [Formula Correlation coefficient RaA/Rn = 1.14 F 0.551 0.76 RaB/Rn = 1.00 F 0.940 0.99 RaC/Rn = 0.77 F 1.120 0.92]

Jan 1, 1981

By E. Piesch, M. Urban, G. M. Hassib

INTRODUCTION In radon dosimetry diffusion chambers with passive [a]-detectors are now in current use to investigate the long-term accumulated indoor exposure of radon and daughters. For the diffusion chamber developed at Karlsruhe the electrochemical etching technique (ECE) was applied to reveal [a]-particles in polycarbonate plastic detectors. Compared to conventional etching, the main advantages of the ECE are the large track diameter, simple track counting in a single field of about 1 cm2, stability of the latent tracks to humidity and temperature and ability for a long-term accumulation up to 1 year. The electrochemical etching system was designed to etch in one run about 101 foils by using a 200 W high voltage generator. The commercial available radon dosimeter system is applied for a country wide program of measuring radon in dwellings. Because of an increasing interest of radon monitoring in mines, environmental monitoring and personnel dosimetry the properties of several track etch detectors have been studied. In the comparative study, Makrofol E, LR 115 and CR 39 were used in the diffusion chamber to investigate the etching techniques, the relative efficiency, the measurable [a]-energy range, and the counting statistic for the measurement of radon concentration. THE KARLSRUHE DIFFUSION CHAMBER The design of the Karlsruhe diffusion chamber is presented in Fig. 1. The upper part of the chamber is closed by a fibreglass filter to separate radon from aerosols, heavy dust particles and radon decay products. Inside the diffusion chamber [a]-particles from radon and daughters are detected by two passive radon detectors, one on the bottom of the chamber and the other in front of the filter. With the fibreglass filter applied the diffusion time is about 1 minute for radon. Therefore, also short-term variations in the radon concentration are recorded by the track detector. Mainly because of the short halflife of thoron (56 s) only about 7 % of the thoron concentration is expected in the diffusion chamber. Radon monitoring provides the estimation of the long-term accumulated mean value of the radon concentration with a lowest detectable concentration of 0.1 pCi/1 after 3 months accumulation by using polycarbonate track etch detectors, an electrochemical etching technique and track counting in a single field of 1 cm2. The diffusion chamber was optimized for the polycarbonate track detector with respect to chamber geometry and detector position [1]. Table 1 presents data for 3 different diffusion chamber designs. The radon sensitivity of the diffusion chamber depends on the [a]-energy discrimination and the angular response of the [a]-track detector. The difference between foil No 2 and foil No 1 can be explained by an additional plate-out effect of radon daughters on foil No 3. The high sensitivity of foil No 3 compared to that of foil No 2 is caused by an increase of the effective volume and the effective area for [a]-particle from radon and from plated-out decay products, respectively. Additional experiments have been performed in order to investigate the electrostatic properties of the plastic material and the properties of the diffusion filter [1]. The properties of bare a-detectors were compared with those inside the diffusion chamber. In contrast to laboratory results, dust particles deposited on the detector surface or in the environment of the detector obviously affect the reproducibility of the bare detector significantly. After 4 months exposure in dwellings the scatter of 10 dosimeters exposed in the same room exceeds a factor of 3 compared to 15 % for the diffusion chamber. COMPARATIVE STUDY OF TRACK ETCH DETECTORS Detector types and evaluation technique In the comparative study the properties of the following plastic track etch detectors have been applied: - LR 115 from Kodak Pathé, France, is a red dyed cellulose nitrate layer of 13 µm thickness on a 100 µm thick polyester support. The holes appears as bright spots in a dark red background. In an optical microscope counting of through etched [a]-tracks which must penetrate the detector layer - CR 39 from Pershore, England, is an ally1 diglycol carbonate plastic of about 300 m thickness. The normal etched [a]-tracks are counted by an optical microscope and the ECE [a]-tracks by a microfiche reader.

Jan 1, 1981

By Bernard Amadei, Michael J. Robison

The purpose of this paper is to present the results of 102 mu1tiaxial tests conducted on cubical specimens of Indiana limestone using the mu1tiaxial apparatus available at the University of Colorado at Boulder. These tests include (1) uni-axia1 compression and tension, (2) bi-axial and tri-axial compression, (3) biaxial compression- tension and (4) tri-axial compression-compression- tension. The applicabi1ity of existing failure criteria to predict the strength of the tested materia1 is discussed.

Jan 1, 1986