About the radioactivity counts:

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System and data collection: The radiation measurements purposefully emphasize radon activity while not excluding other ambient radioactivity sources. Measurements were made with an Aware Electronics RM-70 “pancake” geiger counter. The RM-70 is connected to a Dell Latitude XPi laptop running Aware's Aw-Radw and Aw-Graph software. (see picture of setup). For most plots, each data point represents a 2 hour mean to keep the 2-sigma counting uncertainty less than 5%, unless the plot's title or description states otherwise.

The pancake detector is in a vertical orientation (i.e. the center axis of the compressed cylinder is parallel to the floor). The vertical orientation reduces the non-alpha background slightly and avoids excessive dust accumulation on the detector face.

Location and Sources: Prior to mid-December 2006, the detector sat on the wooden floor of a living room, which is on the first floor above a crawl space in a wooden-framed house. Mid-December 2006 to early August 2008, the detector was placed on a side table, 2 feet above the former position. The side table location seems to be less drafty than the floor location. In early August 2008, the detector was moved to the dining room, also on the first floor. At first the detector was supported by a storage box of dinnerware under some furniture in the dining room, but the dinnerware seems to have been adding about 4 cpm to the results. On Sept 14 2008, the supporting box was removed and the detector was placed directly on the wooden dining room floor.

Plastic sheeting covers the ground of the crawl space but is not sealed. The crawl space has two passive ventilation vents. This is a small home with a cathedral ceiling. The indoor temperature usually is kept in the high 60s to mid 70s during the summer and in the 40s-60s in some lower, non-plumbed areas in the winter (where the detector is kept). These seemingly trivial construction and temperature details should have some impact on daily radon variations that might have some relation to air movements in the home. The detector position is about 1.5 feet (prior to mid-December 2006 and after mid-September 2008) or 3.5 feet (mid-December 2006 to mid-SEptember 2008) away from a concrete block foundation. The position prior to mid-December 2006 on the floor was purposefully placed near a floor seam to emphasize detection of radon infiltration from below, but may have been more drafty than the later location. Prior to Aug 7 2004 the floor was carpet over wood, after which the carpet was removed.

On Jan 12 2005 the windows were upgraded, reducing drafts. In October 2006, a higher efficiency two-stage furnace went into use for the first time along with a programmed thermostat, both of which may impact the ventilation flow velocity and ventilation frequency. In late Novemember 2006, wood siding was replaced with wood sheathing and fiber/concrete siding. This was not expected to change background levels, unless it tightened up the home's air leakage.

The location of the home is about 25 miles NW from Washington, D.C. in western Montgomery County, Maryland. The geological formation on which the house sits is the New Oxford Formation, a triassic red-bed.

Tests of local wells report the following: Rn-222 (Radon) up to ~2700 pCi/L; "Beta/photon emitters" up to 10 mrem/year; "Alpha emitters" up to 14 pCi/L; "Combined radium" up to ~5 pCi/L; Uranium up to 13 pCi/L. These values do not exceed Federally regulated levels.

Correlation of activity concerning wind direction with regard to a nearby Cobalt-60 plant, coal-fired power plant or incinerator, all in or near Dickerson, MD has not been noticed.

Large peaks not part of daily pattern: A few of the anomalously large peaks appear to coincide with excessive rains in a statistically significant way, although other excessive rains have not corresponded with elevated activity measurements.

Baseline activity and trends: The baseline activity is about 13-19 cpm (cpm = counts per minute), usually about 13.5 cpm in the warmest months. The baseline variation is believed to have some dependence on the barometric situation and season. The degree to which the baseline may have a dependence (or not) on the heating system has not been evaluated.

Barometric pressure variations will change the amount of cosmic ray counts. As the barometric pressure decreases, the total mass of air through which cosmic radiation will pass decreases, corresponding to higher count rates. Count rate appears to be slightly higher in the fall and winter. It should be noted that air temperature may cause air density to vary, and that surface conditions do not account for the total air column.

Examples of baseline variations are shown in the Oct 6-23 2004 (underlying a diurnal pattern), October 2006 and December 2006 plots.

Daily (diurnal) peak pattern: Daily variation of radioactivity levels is often observed at the detector location in this home, adding typically 1-2 cpm to the baseline prior to Fall 2006, and typically 5-10 cpm more than baseline since then. The daily variation is not always present.

It is known that radon can show a diurnal pattern. Daily variation of radioactivity has been attributed to many things in various studies by others. In many of these studies, daily patterns have been attributed to outdoor daily heating and nightly cooling that affect convective air movement in a building. The convective movement can affect pressure differentials between the lowest floor and radon-bearing ground beneath the building, thereby affecting radon influx into and distribution through the building. Radon variation patterns have also been reported by some researchers to have some degree of correlation with indoor ventilation patterns, such as door and window opening and heating and cooling system use.

Our diurnal peaks seem to have increased in intensity quite significantly since the Fall 2006 when 3 changes occurred: the siding and furnace upgrades and movement of the detector to what subjectively feels like a less drafty location. The degree to which the two detector locations makes a difference, thereby increasing or decreasing the apparent contribution of the siding or furnace change, cannot be clearly ascertained without a second simultaneously operating detector.

The time of occurrence for each diurnal peak measured in this home, when present, may have some seasonal dependence but has not been fully analyzed. The timing of each peak maximum does not seem to be correlated with nearby window and door use. Any possible correlation with furnace, AC, kitchen exhaust, bathroom exhaust, outdoor barometric pressure, outdoor temperature and wind has not been analyzed. Correlation with ground freezing as reported by some researchers has not been observed. If any such correlations exist, they are not distinct.

Seasonal patterns: In general, the average radon concentration indoors in January (as the coldest month) has been reported to be about twice that of July [Miles and Algar, J. Radiol. Prot. 8(1988)103]. In this home, diurnal peak heights relative to warmer or colder months has not been fully analyzed. The baseline varies from about 13 to 15 cpm in summer and about 13 to 19 cpm in winter. (cpm = counts per minute.)

Other comments:

The crawlspace under the house, in one short (4 day) test in winter, appeared to be about 1 to 3 cpm higher compared to the normal measurement position within the living room.

The difference between the measurement location and a common usage area just two feet higher, the living room chairs, was checked as follows. On December 10, 2006 5:50 PM, the count rate at the usual location on the floor near a seam was about 17 cpm +/- 1 cpm, which is consistent with a seasonally elevated winter count rate. The counter was then placed on the arm of a chair just a few feet away until 7:30 PM, while maintaining the vertical detector orientation. The detector was then returned to its original location. The count rate on the arm of the chair went UP to about 21.5 cpm, whereas the floor position, which seems to receive drafts from a nearby door, was lower.

Dust traveling from the east coast of Asia can take about 2 weeks to reach the east coast of the U.S.A., e.g., see the NASA news story on the Pacific Dust Express, or the L.A. Times story (April 26, 2002 by Gary Polakovic) on the Asian Dust Express.

Comments or questions about this web site and radiological data may be e-mailed to zeissler{at}aol{dot}com.