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Calibration Requirements for Radon Laboratories and Measurement Providers offering Analytical Services
Activated Charcoal Adsorption (AC) - Each configuration of AC device (including specific canister types and charcoal amounts), gamma detector, etc., should be calibrated at least annually in a qualified radon chamber. This chamber may be an in-house facility if there is an intercomparison program of some sort with other radon chambers. The typical intercomparisons are with DOE’s EML lab in NY, U.S. EPA’s labs in AL or NV, and Bowser Morner in OH. There may be others that I have not mentioned here.
The radon chamber exposures should be done at different radon concentrations and with various environmental conditions such as humidity, temperature and exposure duration. This should be done periodically and specifically before a new batch of charcoal is put into use. The data obtained should be compared to the data originally used to produce the calibration factors (curves) and changes to the curves should be done accordingly.
Alpha Track Detection (AT) – ATs require exposure in radon chambers at least annually. The calibration is done for each batch of plastic or the average of very similar batches from the same manufacturer. Radon exposures should be done at various radon levels (usually low, medium and high), with a minimum of 10 exposures at each level. The calibration exposures are used to obtain or verify the conversion factor between net track per unit area and radon concentration.
Charcoal Liquid Scintillation (LS) - Each type of vial (including canister type and filter type), should be calibrated at least annually in a qualified radon chamber. This chamber may be an in-house facility if there is an intercomparison program of some sort with other radon chambers. The typical intercomparisons are with DOE’s EML lab in NY, U.S. EPA’s labs in AL or NV, and Bowser Morner in OH. There may be others that I have not mentioned here.
The radon chamber exposures should be done at different radon concentrations and with various environmental conditions such as humidity, temperature and exposure duration. This should be done periodically and specifically before a new batch of charcoal is put into use. The data obtained should be compared to the data originally used to produce the calibration factors (curves) and changes to the curves should be done accordingly.
Electret Ion Chambers (ES and EL) – The manufacturer of the E-Perm variety of the electret devices calibrates each batch of electrets prior to releasing the devices to users. Their documentation shows only slight variations in the response of short-term varieties and long-term varieties. With this in mind, users of the E-Perm devices need to have their electret (voltage) readers calibrated annually along with the re-certification of the reference electrets to the recently calibrated reader. The manufacturer, Rad Elec, Inc., provides both of these services back to back during the "calibration" process.
Within the last couple of years, another style of electret device has appeared in the marketplace. The manufacturer is RTCA. It is believed that this electret device requires calibration as described in EPA’s "device protocols", (EPA 402-R-92-004), which includes actual radon chamber exposures. This procedure requires exposure of at least 10 devices to three different radon concentrations, low medium and high. A gamma exposure rate measurement is also required while in the chamber.
Continuous Radon Monitors (CRM) – CRM devices require annual calibration in known radon environments. The manufacturer of the instrument performs most calibrations, but this is not always the case. Some calibration facilities have the permission of the manufacturers to change the device’s internal settings to correct for bias discovered during the calibration process. (Note that an inherent element of the process is a thorough determination of the background count rate using clean, aged air or nitrogen). At the conclusion of the calibration a certificate should be issued and a sticker should be attached to the monitor to display the calibration date, facility, and expiration.
Some CRMs sample through scintillation cells. (Some Scintrex/EDA and Pylon Electronics equipment does this.) When these devices are calibrated, each scintillation cell requires independent calibration as well.
Continuous Working Level Monitors (CW) – CW devices require annual exposure to known amounts of radon decay products in a radon chamber. The manufacturers calibrate most CW devices. Similar to the CRMs, certificates and stickers should be issued upon successful calibration.
This document was prepared as a Guide for use by the National Environmental Health Association (NEHA) National Radon Proficiency Program (NRPP). The content was gathered from the U.S. EPA’s Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA 402-R-92-004), July 1992, and interpretations provided by Mr. Samuel W. Poppell, Jr., former Program Manager for the U.S. EPA Radon Proficiency Program (RPP). Prepared by Shawn Price, Air Chek, Inc., former Quality Assurance Coordinator for the EPA RPP. Specific appeal to this document should be made in writing to the NEHA NRPP, PO Box 2109, Fletcher, NC 28732, fax (828) 890-4161 or email angel@neha-nrpp.org.
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