Environmental levels of penetrating ionizing radiation were measured in the lower Arkansas and White River valleys of Arkansas. Measurements of environmental gamma and cosmic rays were made using a portable high pressure ionization chamber. The surveyed area encompassed a large coal-fired industrial plant. Observed exposure rates ranged from 5.9 microRoentgens per hour (μR/h) to 13.4 μR/h. The average exposure rate for the region was 8.8 μR/h. This value corresponds to 77 millirem (mrem) or 0.77 milliSieverts (mSv) per year. In comparison, a prior state-wide survey reported an average dose equivalent rate of 78.2 mrem (0.782 mSv) per year in Arkansas

Epperson, C. E.

Meiners, S.

Swindle, D.

English

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 40 Article 11 1986 Penetrating Ionizing Radiation Levels Observed in the Lower Arkansas and White River Valleys of Arkansas C. E. Epperson University of Arkansas for Medical Sciences S. Meiners University of Arkansas for Medical Sciences D. Swindle University of Arkansas for Medical Sciences Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Environmental Monitoring Commons Recommended Citation Epperson, C. E.; Meiners, S.; and Swindle, D. (1986) "Penetrating Ionizing Radiation Levels Observed in the Lower Arkansas and White River Valleys of Arkansas," Journal of the Arkansas Academy of Science: Vol. 40 , Article 11. Available at: https://scholarworks.uark.edu/jaas/vol40/iss1/11 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. PENETRATING IONIZING RADIATIONLEVELSOBSERVED INTHE LOWER ARKANSAS ANDWHITE RIVER VALLEYSOF ARKANSASC. EPPERSON, S. MEINERS, and D. SWINDLEUniversity of Arkansas for Medical SciencesLittle Rock, AR 72205ABSTRACTEnvironmental levels ofpenetrating ionizing radiation weremeasured in the lower Arkansas and WhiteRiver valleys of Arkansas. Measurements of environmental gamma and cosmic rays were made usinga portable high pressure ionization chamber. The surveyed area encompassed a large coal- fired industrialplant. Observed exposure rates ranged from 5.9 microRoentgens per hour (jtR/h) to 13.4 /*R/h.The averageexposure rate for the region was 8.8 j*R/h.This value corresponds to77 millirem (mrem) or 0.77 milliSieverts(mSv) per year. In comparison, a prior state-wide survey reported an average dose equivalent rate of78.2 mrem (0.782 mSv) per year in Arkansas.INTRODUCTION exposure rates. Itwas suggested that this area be more extensivelysurveyed in the future.Man has always been exposed to radiation since the environment inwhich we evolved is radioactive. This environmental radio-activity iscomposed of natural radioactivity (terrestrial and cosmic) as well asman's contribution from nuclear fallout and industrial practices.Until less than a century ago however, natural radiation was man's onlysource of exposure. The exposure to man has increased over the past40 years because of widespread fallout from nuclear weapons tests, in-creased use of nuclear energy, and a greater use ofradioisotopes. Never-theless, natural background still remains the greatest contributor to theradiation exposure of the United States population today (Spires, 1956;Salon, Lowder, Shambon and Blatz, 1960; Oakley, 1973; and Harley,1975).The purpose of the study was twofold. The major objective was tomore clearly define the magnitude and profile of environmentalpenetrating background radiation in the Arkansas and White Rivervalleys south of the U.S. Interestate Highway 40. Was this area reallymore radioative than the rest of the state of Arkansas? Additionally,a detailed survey of the area would for future reference generate anexposure baseline for the entire area.MATERIALSANDMETHODSThe area surveyed was bounded on the north by Interstate 40 fromNorth LittleRock to Brinkley; on the east by Highway 49-S and 1-Sfrom Brinkley to McGehee; on the south by a line from McGehee toMonticello to Fordyce; and on the west byHighway 167 from Fordyceto North Little Rock.There have been few systematic studies ofenvironmental penetratingradiation exposure. Most such efforts in the United States have beendevoted to aerial surveys oflimited areas around large nuclear installa-tions. A variety of instruments and methods have been applied tomeasuring environmental exposure rates (Lowder, Beck and Condon,1967; Lowder and Condon, 1965) which are typically at levels ofmicroRoentgens per hour (/tR/h). The recent advent ofportable, ruggedand highly sensitive large volume, high pressure ionization chambershas vastly simplified the process of environmental surveys.The area encompasses the counties of Arkansas, Jefferson, Lincoln,most of Cleveland, Southern Prairie and Lonoke, northern Drew andDesha, and eastern Grant. A large coal-fired electric power plant islocated in the Northwest quadrant of this area. Measurements were alsomade over the plant's coal pile and flyash waste dump. Total coveragerepresents approximately 5600 sq. miles.Ion chambers measure ionizing radiation exposure. The Roentgenis the unit ofExposure to X-and gamma rays. Itis a direct physicalmeasure ofthe ionization produced per unitmass ofair. For regulatoryand administrative purposes, a Dose Equivalent unit is used. The DoseEquivalent combines absorbed energy per unit mass withestimates ofbiological detriment to produce a single normalized value. The SI unitof Dose Equivalent is the Sievert (Sv) which replaces the old unit, therem (ICRU, 1980). For X-and gamma rays, one Roentgen is essential-ly equal to .01 Sievert (or 1 rem).Exposure measurements were made with a Reuter-Stokes ModelRSS-111 Environmental Radiation Monitor, a portable high-pressureionization chamber (PIC) especially designed for environmental surveys.The spherical detector, containing ultra-pure argon gas at 25 atmosphereof pressure, responds to X-and gamma rays only. Accuracy is ±5%at 10 /tR/h. Exposure readings are displayed byan instantaneous digitalreader (infiR/h), by an integral strip chart recorder and by a mechanicalsealer (inaccumulated /tR.)Portable pressurized ion chamber surveys have recently been reportedfor some areas in the United States and in Europe (Stranden, 1977;Powers and Watson, 1978; and McAuley and Colgan, 1980). A Georgiasurvey reports 3.5 to 40 /tR/h. Surveys inNorway (6.2-9.1 /tR/h) andIreland (10.2-14.3 /tR/h) have been reported.The PIC was initiallycalibrated with Ra 226 by the manufacturer.During the study, instrument reproducibility was checked daily usinga calibrated disc source of Co-60 affixed to a reference point on thePIC housing. The Co-60 disc was of sufficiently lowactivity as to pro-duce an instrument response twice that ofnormal background. The valueof the standard was determined to be 81.18 /tR//tCi Co-60 witha per-missable error of ±5% as this was the manufacturers stated accuracyfor the RSS-1 11.Calibration checks using the Co-60 source were per-formed both before and after each day of fielduse. Variance of dailycheck source readings never varied more than +3°7o ofcalibration value.The measured average exposure rate in the United States fromnatural-ly occurring gamma-ray emitters is about 8.2 /tR/h at one meter abovethe soil. Natural radiation contributes a dose equivalent of70 to 200mrem (0.70 to2.0 mSv) per year to the United States population (Oakley,1973, and Harley, 1975).Two different modes of data collection were used. Stationary in-tegrated readings at selected sites and instantaneous readings whiledriving from site to site were made.Rolniak (Rolniak, 1982) conducted a population weighed study in1980-1981 with a pressurized ion chamber to establish the naturalpenetrating radiation background component in all Arkansas cities witha population greater than 5,000. He found readings in the Arkansasand White River Valleys, south of Interstate Highway 40 to be higherthan the rest of the state. There was noapparent reason for these higherThe PIC was mounted ina low density foam rubber housing whiletravelling from site to site. The detector, about one meter above groundlevel, was located in the rear ofthe vehicle which was used throughoutProceedings Arkansas Academy off Science, Vol. XXXX,198630Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 11Published by Arkansas Academy of Science, 1986C. Epperson, S. Meiners, and D. Swindlethe survey. Instantaneous readings were made every eight kilometers(5miles) while travelling from one location to the next. Aninstantaneousreading was also made at every county line, citylimit, train track, andmajor road intersection. The vehicle acted as a shield for the radiationfromoutside. Values measured inside the vehicle had to be multiplied| by a factor of 1.21 to obtain the proper value for unshielded externalI radiation exposure.The survey area was divided into a 16.1 by 16.1 kilometer (10 x 10mile)grid for stationary open-air measurements. Atleast one stationarymeasurement was made withineach of the grids. Readings were madeas close as feasible to the grid center. Sites were also chosen tobe neara location which would be easily found on a state orcounty road map,such as major road intersections. Measurement locations were from75 to 100 meters (246-328 feet) off the highway, usually utilizing dirt-I access roads. In all cases, the chosen area was level, withgood soilpermeability, and where no overwash would occur. The detector wastripod-mounted well away from the car at one meter above ground level.One meter was chosen as the sampling height since this is the acceptedgonadal dose level to man and because gamma fluxand exposure arenearly identical at one meter above the ground. Ten minutemeasurements were made at each site. The instantaneous value wasrecorded once every 30 seconds. The mean of these 20 values was usedto develop an environmental penetrating radiation contour map (FigureTable 1. Averaged stationary exposure rates observed in the surveyedarea. Units are jtR/h.Fairendale 7.0 Sherrill 8.4Monticello 6.2 Gethsemane 9.3Backgate 5.9 Hwy 165 E/England 9.4Redfield 8.0 England 8.8Noble Lake 10.4 Scott 8.6Gould 8.2 Hwy 161 N/Enqland 9.9Garrett Bridge 8.7 Hwy 31 North of Pettis 9.2Hazen 8.9 Hwy 381 North of Culler 8.7Wattensaw Wildlife Area 8.8 Humphrey 8.7Hwy 33 & 86 8.0 Bayou Meto 8.4Preston Ferry 9.2 St. Charles 9.7Hwy 146 E/Preston Ferry 9.4 Hwy 146 E/Holly Grove 9.0Almyra 8.7 Hwy 1 N/Crossroads 9.5Hwy 152 S/Dewitt 8.9 Hwy 65, 167 13.4Hwy 276 & 11 8.3 Dixon Road (S/L. Rock) 11.0Hwy 343 (end of road) 8.9 Hwy 46 North of Sheridan 11.3Hwy 86 South of Carlisle 8.2 Hardin 8.4Hwy 343 & 165 7.5 Pine Bergen 7.1Crockets Bluff 8.3 Nebo 9.1Hwy 153 W/Crockets Bluff 8.4 Ticnor 9.4Hwy. 153 & I 8.0 Ethyl 9.7Hwy 33 & 130 8.4 Clarendon 8.9Hwy 165 West of Dewitt 8.4 Hwy 190 South of Hardin 7.6Rydel 10.0 Hwy 54 E/Grapevine 8.0Hwy 88 South of Altimer 9.1 Toltec 9.8Hwy 15 & 79 9.2 Hwy 161 South of Scott 9.8RESULTSStationary outdoor exposure rate measurements obtained at theselected locations within the study area are shown in Table 1. Thesevalues are expressed as /xR/h and include all background contributions.The values range from 5.9 to 13.4 /*R/hwith a mean of8.8 /xR/h anda standard deviation of ±1.2 /*R/h.The value of 8.8 /tR/h comparesfavorably withRolniak's (1982) average value, 9.3 /*R/h for the stateofArkansas. Forty-eight of the 52 values fall within two standard devia-tions of the mean. Two values were greater than plus two standard devia-tions from the mean and two were less. The two high deviations arebelieved due to outcrops ofignious rocks from Granite Mountain. Thetwo low deviations were made inregions ofsand and sandy-loam soilswhich are high in silica.A few highly localized areas inArkansas exhibit significantly highexposure rates. Two prime examples are Granite Mountain near LittleRock with14-16 /iR/h and the thermal springs in HotSprings NationalPark with 50-80 /*R/h. Even portions of Interstate 40 East and Westof Little Rock show readings as high as 14:8 /tR/h.Measurements made in the middle of the power plant's coal fieldregistered exposure rates of6pR/h. Readings in the plant's flyash dumpswere 12 /*R/h. Flyash was expected to be higher than coal, since itrepresents a coal "ash" residue consisting mainly of silica and concen-trated metals.Figure 1.Background penetrating radiation contour map of study area.Units are /*R/h.Abackground penetrating radiation contour map of the study areais depicted in Figure 1. This map was computer-generated using thedata obtained by this study. The contours are approximations since theywere generated by mathematical extrapolations from observed datapoints.DISCUSSIONPotassium-40, cosmic radiation, and a half dozen members of theuranium/thorium-series radioactive chain produce almost all the natural-occurring gamma rays. Igneous rock (granite), clays and dark shales(organically enriched) are usually enriched inK-40 and members of theuranium and thorium chains. Sand and sandstones are typically verylow in radionuclidic species. Rolniak (1982) found this to be true ofmost all sandy soils, sandstones and clays in Arkansas. This was alsoborn out in our survey.Rolniak's observations in east central Arkansas were based largelyon highway measurements. The elevated readings were due to roadbedmaterials, such as granite and clay foundations and igneous chat usedin road surfacing materials. Readings as high as 14 /xR/h have beenobserved on the roadbed, whereas the surrounding countryside hasusually read no more than 6 to 8 /*R/h.A roadbed effect was noted in this study. Subsequently, highwayreadings were excluded from the data. Only those readings taken off-Proceedings Arkansas Academy off Science, Vol. XXXX,1986 31 31Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 11https://scholarworks.uark.edu/jaas/vol40/iss1/11Proceedings Arkansas Academy of Science, Vol.XXXX,198632Penetrating IonizingRadiation Levels Observed in the Lower Arkansas and White River Valleys off Arkansasroad and outside the vehicle were used to generate usable data in thefinal results.The flyash from the western coal burned by the power plant measuressomewhat higher than the average for the itirearea surveyed. However,the plant's electrostatic precipitators remove more than 99.9% of flyashfrom stack discharge. Virtually all flyash is scrubbed, recovered fromstack gases, and stored on plant property. The flyash from the powerplant is believed to make no contribution to the area-wide radiationbackground.The range of exposure rates found in East Central Arkansas speakfor themselves. Radiation levels in this area are essentially the sameas the rest of the state of Arkansas.ACKNOWLEDGEMENTSWe wish to thank Dr.Robert Walls for his invaluableassistance indata treatment and presentation and GaryRowlett for his technical assistance on this project. Thisstudy was supported, inpart, by a grant from ArkansasPower and Light Company.LITERATURE CITEDHARLEY, J. H. 1975. Natural Background Radiation in the UnitedStates. National Council on Radiation Protection andMeasurements, Report No. 45.ICRU. 1980. Radiation Quantities and Units. International Commissionon Radiation Units and Measurements, Report No. 33:11-14.LOWDER, W. M., H. L. BECK, and W. J. CONDON. 1964.Spectrometric determination ofdose rates from natural and falloutgamma-radiation in the United States. Nature 202:745-749.LOWDER, W. M., and W. J. CONDON. 1965. Measurement of theexposure ofhuman populations toenvironmental radiation. Nature206:658-662.McAULEY,I.R., and P. A.COLGAN. 1980. Gamma raybackgroundradiation measurement in Ireland. Health Phy. 39:821-826.OAKLEY,D. T. 1973. Natural Radiation Exposure in the United States.Environmental Protection Agency 3:12.ROLNIAK, R. M. 1982. Population exposure to environmentalpenetrating radiation in Arkansas. Unpubl. M.S. Thesis. CollegeofPharmacy, University ofArkasnas for Medical Sciences, LittleRock.SOLON, L. R., W. M.LOWDER, A. SHAMBON, and H.BLATZ.1960. Investigations of natural environmental radiation. Science3:903-906.SPIRES, F. W. 1956. Radioactivity in man and his environmentBrit. J. Radiology 8:409-417.STRANDEN, E. 1977. Population doses from environmental gammaradiation inNbrway. Health Phy. 33:319-333.32Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 11Published by Arkansas Academy of Science, 1986

Penetrating Ionizing Radiation Levels Observed in the Lower Arkansas and White River Valleys of Arkansas

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 40 Article 111986Penetrating Ionizing Radiation Levels Observed inthe Lower Arkansas and White River Valleys ofArkansasC. E. EppersonUniversity of Arkansas for Medical SciencesS. MeinersUniversity of Arkansas for Medical SciencesD. SwindleUniversity of Arkansas for Medical SciencesFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Environmental Monitoring CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationEpperson, C. E.; Meiners, S.; and Swindle, D. (1986) "Penetrating Ionizing Radiation Levels Observed in the Lower Arkansas andWhite River Valleys of Arkansas," Journal of the Arkansas Academy of Science: Vol. 40 , Article 11.Available at: http://scholarworks.uark.edu/jaas/vol40/iss1/11PENETRATING IONIZING RADIATIONLEVELSOBSERVED INTHE LOWER ARKANSAS ANDWHITE RIVER VALLEYSOF ARKANSASC. EPPERSON, S. MEINERS, and D. SWINDLEUniversity of Arkansas for Medical SciencesLittle Rock, AR 72205ABSTRACTEnvironmental levels ofpenetrating ionizing radiation weremeasured in the lower Arkansas and WhiteRiver valleys of Arkansas. Measurements of environmental gamma and cosmic rays were made usinga portable high pressure ionization chamber. The surveyed area encompassed a large coal- fired industrialplant. Observed exposure rates ranged from 5.9 microRoentgens per hour (jtR/h) to 13.4 /*R/h.The averageexposure rate for the region was 8.8 j*R/h.This value corresponds to77 millirem (mrem) or 0.77 milliSieverts(mSv) per year. In comparison, a prior state-wide survey reported an average dose equivalent rate of78.2 mrem (0.782 mSv) per year in Arkansas.INTRODUCTION exposure rates. Itwas suggested that this area be more extensivelysurveyed in the future.Man has always been exposed to radiation since the environment inwhich we evolved is radioactive. This environmental radio-activity iscomposed of natural radioactivity (terrestrial and cosmic) as well asman's contribution from nuclear fallout and industrial practices.Until less than a century ago however, natural radiation was man's onlysource of exposure. The exposure to man has increased over the past40 years because of widespread fallout from nuclear weapons tests, in-creased use of nuclear energy, and a greater use ofradioisotopes. Never-theless, natural background still remains the greatest contributor to theradiation exposure of the United States population today (Spires, 1956;Salon, Lowder, Shambon and Blatz, 1960; Oakley, 1973; and Harley,1975).The purpose of the study was twofold. The major objective was tomore clearly define the magnitude and profile of environmentalpenetrating background radiation in the Arkansas and White Rivervalleys south of the U.S. Interestate Highway 40. Was this area reallymore radioative than the rest of the state of Arkansas? Additionally,a detailed survey of the area would for future reference generate anexposure baseline for the entire area.MATERIALSANDMETHODSThe area surveyed was bounded on the north by Interstate 40 fromNorth LittleRock to Brinkley; on the east by Highway 49-S and 1-Sfrom Brinkley to McGehee; on the south by a line from McGehee toMonticello to Fordyce; and on the west byHighway 167 from Fordyceto North Little Rock.There have been few systematic studies ofenvironmental penetratingradiation exposure. Most such efforts in the United States have beendevoted to aerial surveys oflimited areas around large nuclear installa-tions. A variety of instruments and methods have been applied tomeasuring environmental exposure rates (Lowder, Beck and Condon,1967; Lowder and Condon, 1965) which are typically at levels ofmicroRoentgens per hour (/tR/h). The recent advent ofportable, ruggedand highly sensitive large volume, high pressure ionization chambershas vastly simplified the process of environmental surveys.The area encompasses the counties of Arkansas, Jefferson, Lincoln,most of Cleveland, Southern Prairie and Lonoke, northern Drew andDesha, and eastern Grant. A large coal-fired electric power plant islocated in the Northwest quadrant of this area. Measurements were alsomade over the plant's coal pile and flyash waste dump. Total coveragerepresents approximately 5600 sq. miles.Ion chambers measure ionizing radiation exposure. The Roentgenis the unit ofExposure to X-and gamma rays. Itis a direct physicalmeasure ofthe ionization produced per unitmass ofair. For regulatoryand administrative purposes, a Dose Equivalent unit is used. The DoseEquivalent combines absorbed energy per unit mass withestimates ofbiological detriment to produce a single normalized value. The SI unitof Dose Equivalent is the Sievert (Sv) which replaces the old unit, therem (ICRU, 1980). For X-and gamma rays, one Roentgen is essential-ly equal to .01 Sievert (or 1 rem).Exposure measurements were made with a Reuter-Stokes ModelRSS-111 Environmental Radiation Monitor, a portable high-pressureionization chamber (PIC) especially designed for environmental surveys.The spherical detector, containing ultra-pure argon gas at 25 atmosphereof pressure, responds to X-and gamma rays only. Accuracy is ±5%at 10 /tR/h. Exposure readings are displayed byan instantaneous digitalreader (infiR/h), by an integral strip chart recorder and by a mechanicalsealer (inaccumulated /tR.)Portable pressurized ion chamber surveys have recently been reportedfor some areas in the United States and in Europe (Stranden, 1977;Powers and Watson, 1978; and McAuley and Colgan, 1980). A Georgiasurvey reports 3.5 to 40 /tR/h. Surveys inNorway (6.2-9.1 /tR/h) andIreland (10.2 - 14.3 /tR/h) have been reported.The PIC was initiallycalibrated with Ra 226 by the manufacturer.During the study, instrument reproducibility was checked daily usinga calibrated disc source of Co-60 affixed to a reference point on thePIC housing. The Co-60 disc was of sufficiently lowactivity as to pro-duce an instrument response twice that ofnormal background. The valueof the standard was determined to be 81.18 /tR//tCi Co-60 witha per-missable error of ±5% as this was the manufacturers stated accuracyfor the RSS-1 11.Calibration checks using the Co-60 source were per-formed both before and after each day of fielduse. Variance of dailycheck source readings never varied more than +3°7o ofcalibration value.The measured average exposure rate in the United States fromnatural-ly occurring gamma-ray emitters is about 8.2 /tR/h at one meter abovethe soil. Natural radiation contributes a dose equivalent of70 to 200mrem (0.70 to2.0 mSv) per year to the United States population (Oakley,1973, and Harley, 1975).Two different modes of data collection were used. Stationary in-tegrated readings at selected sites and instantaneous readings whiledriving from site to site were made.Rolniak (Rolniak, 1982) conducted a population weighed study in1980-1981 with a pressurized ion chamber to establish the naturalpenetrating radiation background component in all Arkansas cities witha population greater than 5,000. He found readings in the Arkansasand White River Valleys, south of Interstate Highway 40 to be higherthan the rest of the state. There was noapparent reason for these higherThe PIC was mounted ina low density foam rubber housing whiletravelling from site to site. The detector, about one meter above groundlevel, was located in the rear ofthe vehicle which was used throughoutProceedings Arkansas Academy off Science, Vol. XXXX,198630Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 11Published by Arkansas Academy of Science, 1986C. Epperson, S. Meiners, and D. Swindlethe survey. Instantaneous readings were made every eight kilometers(5miles) while travelling from one location to the next. Aninstantaneousreading was also made at every county line, citylimit, train track, andmajor road intersection. The vehicle acted as a shield for the radiationfromoutside. Values measured inside the vehicle had to be multiplied| by a factor of 1.21 to obtain the proper value for unshielded externalI radiation exposure.The survey area was divided into a 16.1 by 16.1 kilometer (10 x 10mile)grid for stationary open-air measurements. Atleast one stationarymeasurement was made withineach of the grids. Readings were madeas close as feasible to the grid center. Sites were also chosen tobe neara location which would be easily found on a state orcounty road map,such as major road intersections. Measurement locations were from75 to 100 meters (246-328 feet) off the highway, usually utilizing dirt-I access roads. In all cases, the chosen area was level, withgood soilpermeability, and where no overwash would occur. The detector wastripod-mounted well away from the car at one meter above ground level.One meter was chosen as the sampling height since this is the acceptedgonadal dose level to man and because gamma fluxand exposure arenearly identical at one meter above the ground. Ten minutemeasurements were made at each site. The instantaneous value wasrecorded once every 30 seconds. The mean of these 20 values was usedto develop an environmental penetrating radiation contour map (FigureTable 1. Averaged stationary exposure rates observed in the surveyedarea. Units are jtR/h.Fairendale 7.0 Sherrill 8.4Monticello 6.2 Gethsemane 9.3Backgate 5.9 Hwy 165 E/England 9.4Redfield 8.0 England 8.8Noble Lake 10.4 Scott 8.6Gould 8.2 Hwy 161 N/Enqland 9.9Garrett Bridge 8.7 Hwy 31 North of Pettis 9.2Hazen 8.9 Hwy 381 North of Culler 8.7Wattensaw Wildlife Area 8.8 Humphrey 8.7Hwy 33 & 86 8.0 Bayou Meto 8.4Preston Ferry 9.2 St. Charles 9.7Hwy 146 E/Preston Ferry 9.4 Hwy 146 E/Holly Grove 9.0Almyra 8.7 Hwy 1 N/Crossroads 9.5Hwy 152 S/Dewitt 8.9 Hwy 65, 167 13.4Hwy 276 & 11 8.3 Dixon Road (S/L. Rock) 11.0Hwy 343 (end of road) 8.9 Hwy 46 North of Sheridan 11.3Hwy 86 South of Carlisle 8.2 Hardin 8.4Hwy 343 & 165 7.5 Pine Bergen 7.1Crockets Bluff 8.3 Nebo 9.1Hwy 153 W/Crockets Bluff 8.4 Ticnor 9.4Hwy. 153 & I 8.0 Ethyl 9.7Hwy 33 & 130 8.4 Clarendon 8.9Hwy 165 West of Dewitt 8.4 Hwy 190 South of Hardin 7.6Rydel 10.0 Hwy 54 E/Grapevine 8.0Hwy 88 South of Altimer 9.1 Toltec 9.8Hwy 15 & 79 9.2 Hwy 161 South of Scott 9.8RESULTSStationary outdoor exposure rate measurements obtained at theselected locations within the study area are shown in Table 1. Thesevalues are expressed as /xR/h and include all background contributions.The values range from 5.9 to 13.4 /*R/hwith a mean of8.8 /xR/h anda standard deviation of ±1.2 /*R/h.The value of 8.8 /tR/h comparesfavorably withRolniak's (1982) average value, 9.3 /*R/h for the stateofArkansas. Forty-eight of the 52 values fall within two standard devia-tions of the mean. Two values were greater than plus two standard devia-tions from the mean and two were less. The two high deviations arebelieved due to outcrops ofignious rocks from Granite Mountain. Thetwo low deviations were made inregions ofsand and sandy-loam soilswhich are high in silica.A few highly localized areas inArkansas exhibit significantly highexposure rates. Two prime examples are Granite Mountain near LittleRock with14-16 /iR/h and the thermal springs in HotSprings NationalPark with 50-80 /*R/h. Even portions of Interstate 40 East and Westof Little Rock show readings as high as 14:8 /tR/h.Measurements made in the middle of the power plant's coal fieldregistered exposure rates of6pR/h. Readings in the plant's flyash dumpswere 12 /*R/h. Flyash was expected to be higher than coal, since itrepresents a coal "ash" residue consisting mainly of silica and concen-trated metals.Figure 1.Background penetrating radiation contour map of study area.Units are /*R/h.Abackground penetrating radiation contour map of the study areais depicted in Figure 1. This map was computer-generated using thedata obtained by this study. The contours are approximations since theywere generated by mathematical extrapolations from observed datapoints.DISCUSSIONPotassium-40, cosmic radiation, and a half dozen members of theuranium/thorium-series radioactive chain produce almost all the natural-occurring gamma rays. Igneous rock (granite), clays and dark shales(organically enriched) are usually enriched inK-40 and members of theuranium and thorium chains. Sand and sandstones are typically verylow in radionuclidic species. Rolniak (1982) found this to be true ofmost all sandy soils, sandstones and clays in Arkansas. This was alsoborn out in our survey.Rolniak's observations in east central Arkansas were based largelyon highway measurements. The elevated readings were due to roadbedmaterials, such as granite and clay foundations and igneous chat usedin road surfacing materials. Readings as high as 14 /xR/h have beenobserved on the roadbed, whereas the surrounding countryside hasusually read no more than 6 to 8 /*R/h.A roadbed effect was noted in this study. Subsequently, highwayreadings were excluded from the data. Only those readings taken off-Proceedings Arkansas Academy off Science, Vol. XXXX,1986 31 31Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 11http://scholarworks.uark.edu/jaas/vol40/iss1/11Proceedings Arkansas Academy of Science, Vol.XXXX,198632Penetrating IonizingRadiation Levels Observed in the Lower Arkansas and White River Valleys off Arkansasroad and outside the vehicle were used to generate usable data in thefinal results.The flyash from the western coal burned by the power plant measuressomewhat higher than the average for the itirearea surveyed. However,the plant's electrostatic precipitators remove more than 99.9% of flyashfrom stack discharge. Virtually all flyash is scrubbed, recovered fromstack gases, and stored on plant property. The flyash from the powerplant is believed to make no contribution to the area-wide radiationbackground.The range of exposure rates found in East Central Arkansas speakfor themselves. Radiation levels in this area are essentially the sameas the rest of the state of Arkansas.ACKNOWLEDGEMENTSWe wish to thank Dr.Robert Walls for his invaluableassistance indata treatment and presentation and GaryRowlett for his technical assistance on this project. Thisstudy was supported, inpart, by a grant from ArkansasPower and Light Company.LITERATURE CITEDHARLEY, J. H. 1975. Natural Background Radiation in the UnitedStates. National Council on Radiation Protection andMeasurements, Report No. 45.ICRU. 1980. Radiation Quantities and Units. International Commissionon Radiation Units and Measurements, Report No. 33:11-14.LOWDER, W. M., H. L. BECK, and W. J. CONDON. 1964.Spectrometric determination ofdose rates from natural and falloutgamma-radiation in the United States. Nature 202:745-749.LOWDER, W. M., and W. J. CONDON. 1965. Measurement of theexposure ofhuman populations toenvironmental radiation. Nature206:658-662.McAULEY,I.R., and P. A.COLGAN. 1980. Gamma raybackgroundradiation measurement in Ireland. Health Phy. 39:821-826.OAKLEY,D. T. 1973. Natural Radiation Exposure in the United States.Environmental Protection Agency 3:12.ROLNIAK, R. M. 1982. Population exposure to environmentalpenetrating radiation in Arkansas. Unpubl. M.S. Thesis. CollegeofPharmacy, University ofArkasnas for Medical Sciences, LittleRock.SOLON, L. R., W. M.LOWDER, A. SHAMBON, and H.BLATZ.1960. Investigations of natural environmental radiation. Science3:903-906.SPIRES, F. W. 1956. Radioactivity in man and his environmentBrit. J. Radiology 8:409-417.STRANDEN, E. 1977. Population doses from environmental gammaradiation inNbrway. Health Phy. 33:319-333.32Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 11Published by Arkansas Academy of Science, 1986

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Penetrating Ionizing Radiation Levels Observed in the Lower Arkansas and White River Valleys of Arkansas

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