REVIEW OF E-PERM * PASSIVE INTEGRATING ELECTRET IONIZATION CHAMBERS FOR MEASURING RADON IN AIR, THORON IN AIR. RADON IN WATER AND RADON FLUX FROM SURFACES AND MILL TAILINGS

E-PERM @ @-PERM * is a trade name for the Electret Ion Chambers manufactured by Rad Ele

MEASUREMENT OF LOW LEVELS OF DISSOLVED RADON AND RADIUM IN WATER P,Kotrappa

Standard method of measuring dissolved radon in water consists of sealing a known volume of water sample in a jar, measuring airborne radon concentration using an E-PERM radon monitor, and calculating the radon concentration in water. The method is also usable for measuring dissolved radium in water. Anew method described in this paper improves the sensitivity by two orders of magnitude. This method consists of immersing an E-PERM radon monitor encased in a water barrier ( thin plastic or tyvek) which permits exchange of radon between water and the detector air volume, and measuring radon gas concentration over the desired time interval. Radon in water is then calculated using appropriate partition constants and other parameters. Results of such measurements agreed well with other standard methods. The method is usable for measuring extremely low levels such as 0.25 to 1.0 pCi/L of dissolved radon. For measuring radium in water, water is filled in a 4 liter glass jar and sparged to remove any radon already present in water. An EPERM radon monitor encased in a suitable water barrier is immersed in water and the jar sealed. Using appropriate theoretical equation relating the average radon concentration as measured by E-PERM radon monitor and the exposure time, the radium concentration in water can be calculated. Levels as low as 1 to 5 pCi/L is measurable by this method in about 10 days. Ability to measure such low level extends this method to several basic research areas in oceanography and geophysical research

CHARACTERIZATION AND USE OF AN ACCUMULATING TYPE OF RADON TEST CHAMBER

There are two general types of radon test chambers. One type can be described as a “flow-through ” radon chamber while the second type can be described as an “accumulation ” type of radon chamber. The Bowser-Morner, Inc. radon test chamber is an example of a “flow-through ” type. These are generally used for “performance testing” by certified radon professionals. By comparison, an “accumulation ” chamber is typically much smaller (ranging in size up to approximately 125 liters), and are relatively inexpensive to fabricate and operate. The radium source and radon detectors are introduced into an “accumulation ” chamber through a sealable port, after which the port is sealed. When a NIST Radon Emanation Standard is used as a radium source, it is possible to calculate the expected radon concentration after a specified accumulation period. This paper describes a typical “accumulation ” chamber, provides the equations needed to calculate the radon concentration at any specified accumulation time, and highlights some practical and unique applications of such test chambers

SMALL VOLUME (53ML) EIC WITH ON/OFF MECHANISM

The small volume “L ” Chamber (58 ml) Electret Ion Chamber (EIC) that was previously manufactured by Rad Elec Inc. did not incorporate a mechanism that allowed the chamber to be turned on and off. To rectify this problem, a re-designed small volume chamber, designated an “L-OO ” Chamber, is currently being produced by Rad Elec. This newly designed L-OO Chamber (53 ml) incorporates a slide mechanism with an aperture that can be positioned over the electret in the “ope n ” position while a solid section of the slide mechanism covers the electret in the “closed ” position. The new L-OO Chamber does not respond to ionizing radiation that may occur during transit or storage. These new devices, designated as a LST-OO when loaded with a ST Electret or a LLT-OO when loaded with a LT Electret, have been approved by the NEHA-NRPP and have been assigned the following device codes: LST-OO is 8230-25 and LLT-OO is 8234-25. The L-OO Chambers, which are significantly less expensive than “S ” Chambers, have been designed for radon measurements lasting from approximately 30 days to 365 days, depending upon the type of electret being used

THE USE OF BARRIER BAGS WITH RADON DETECTORS

Radon detectors are widely used for research and for monitoring indoor and outdoor radon. During some applications, detectors need to be enclosed in barrier bags which are completely transparent to radon. In other applications, radon detectors need to be enclosed in barrier bags that are opaque to radon. In certain applications, barrier bags may provide resistance to human manipulation. Tyvek ® bags appear to meet most requirements for being transparent to radon, while providing some protection from water in harsh environments and from human manipulation. Aluminized Mylar ® bags and Mylar ® bags with or without activated carbon (AC) bags appear to meet the requirement of being opaque to radon. The current work includes examining the performances of these barrier bags at both low and high radon concentrations and over extended periods of time

MEASUREMENT OF ""Rn (THORON) USING ELECTRET ION CHAMBERS

Recently there has been an increased interest in the measurement of airborne ""Rn (thoron). Such measurements are particularly targeted in areas rich in thorium, and in facilities processing thorium compounds and associated radioactive wastes. Standard electret ion chambers @-PERMSR) * designed for making indoor and outdoor "^Rn (radon) measurement have very little response to "¡R (thoron). However, such units when modified by increasing the area of the filtered inlets respond to "¡R (thoron). Such units, termed as thoron E-PERMS were calibrated and tested in Canadian National Thoron Testing Facility located at Elliot Lake. The paper describes the procedures for making ""Tn measurements in air using these modified E-PERMS

NIST TRACEABLE RADON CALIBRATION SYSTEM FOR CALIBRATING TRUE INTEGRATING RADON MONITORS-

The NIST (National Institute of Standards and Technology) has recently made available 222Rn emanation standards for test and evaluation. The NIST certified parameters include the ^~a strength and the emanation coefficient. When such a source is loaded into a radon leak tight enclosure of a known volume, 222~n accumulates over time and it is possible to calculate precisely the time integrated average radon concentration after any given accumulation time. For example, if 25 Bq(676pCi) NIST source is loaded into a jar with an air volume of 3.72 liter, the time integrated average radon concentration is 973 Bq m'3 (26.3 pCi after an accumulation time of exactly two days. If the radon detector placed in the jar is non-radon absorbing and a true integrator, the radon detector must yield the theoretically predicted results. The paper describes a study involving 30 randomly chosen E-PERM % and 15 NIST sources in 15 different calibration jars. The study indicated that E-PERM % give results within about 5 % of the predicted results. The study also shows how a NIST source can be used in practice. Theavailability of N1ST sources in the future with precisely known radon emanation characteristics is considered to be a major advancement in radon metrology.The methodology is within the reach of any quality conscious radon measurement laboratory. KEY WORDS: electret, ion chamber, radon, radon emanation standard

Passive E-perm Radon Flux Monitors for Measuring Undisturbed Radon Flux from the Ground

The measurement of radon flux (radon emanated from a unit surface area per unit time, expressed in pCi m-2sec"1) from the ground or other surfaces without interfering with the physical nature of the soil or the surface is of interest for several practical applications: (1) to determine the radon emanating potential of the ground at a building site, (2) to meet the EPA compliance limits of radon flux at uranium mill tailings piles or phosphogypsum stacks, and (3) to determine the radon flux from the building materials and other surfaces. The passive radon flux monitor consists of 1000 ml volume vented electret ion chamber (EIC) with a 180 cm2 electrically conducting Tyvek widow. The principle of passive flux measurements, the calibration. the applications, and sensitivities are discussed

A NEW ELECTROSTATIC RADON PROGENY COLLECTION METHOD

A new method for collecting radon progeny was investigated that reduces particle concentration including radon progeny in indoor air without air movement. The LECA (for bge Electrostatically Charged-) system uses a high voltage source to charge the collector surfaces (e.g., furniture pieces were used) once they have been electrically isolated from ground by teflon film. When a piece was touched by the high voltage lead its entire surface immediately become charged to about 60 % of the line voltage regardless of its material makeup. By limiting the current to 250 ua no sparking or shock sensation was experienced when touching the charged wire or collector surfaces. Progeny collection efficiencies were measured for collector areas from 8.6 to 5 1.8 m2 and voltages from 2.5 to 9 KV in an 82 m3 test-room. The optimum LECA configuration tested reduced all particulate in the test-room including both the attached and unattached progeny by about 92%. BACKGROUND Lung cancer, the priiciple radon health effect, is not caused by the radon gas itself but by its progeny, especially by the smaller unattached progeny particles that can penetrate into the deep respiratory tract. Several researchers have investigated methods of reducing progeny in indoor air but most methods tried have been unsuccessful because of their inability to remove enough of those more hazardous unattached progeny

PASSIVE RADON PROGENY DOSIMETERS: FEASIBILITY STUDIES

Radon progeny measurements can improve dose estimates based on radon gas measurements alone. The airborne activity-size distribution ratio affects the available dose rate per unit radon. Measurements of surface deposited alpha activity and radon concentration can be used in a semi-empirical model to estimate the equilibrium ratio, the free fraction and airborne dose rate. Since residential atmospheres are dynamic, several measurement approaches, including electret ion chamber and track registration techniques, are being studied to develop passive, integrating detectors. Preliminary tests show good correlation between surface deposited activity or energy, airborne progeny concentrations and dose rate. Tests are underway to assess the performance in other home environments