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  • International Journal of Radiation Research, April 2016 Volume 14, No 2

    Variation of radon progeny concentration over a continental location

    INTRODUCTION

    Close to theEarthssurface,overcontinentalregions, the ionizing radiation ismainly due to

    the radioactive materials from Earths surfaceand galactic cosmic rays of extraterrestrialorigin that leads to the ionizationof air (1). The

    rocks and soil in the solid earth containradioactive elements such as uranium, radium,thorium,etc.andtheirconcentrationsvaryfrom

    regiontoregion.Withintheplanetaryboundarylayer, radiation from radioactive gases such asradonexhaledfromtheEarthssurfaceandtheir

    progeny predominantly ionize theatmosphere(2-4).Radon is a long lived gas product of the

    natural radioactive decay of radium that is the

    decay product of primordial radioactive nucleiuranium, which occurs naturally in the earth'scrust. Theprincipaldecaymodesandhalf-lives

    of222Rnanditsshort-livedprogenyinorderare222Rn-,3.82days;218Po-,3.05m;214Pb-,26.8m;214Bi-,19.7mand214Po-,200ms,ofmajor

    concern.Theradiationssuchas,andwereemitted during the decay of radon and itsprogeny cause ionization in the atmosphere.

    Radon decay products tend to collect on theaerosol particles in the atmosphere and wheninhaled, the dose for the respiratory tract andthe lungs is predominantly caused by the

    deposition of radon progeny attached toaerosols.The-particlesemittedbythedecayof

    K. Charan Kumar1, T. Rajendra Prasad2, T. Narayana Rao2, M. Venkataratnam2, K. Nagaraja1*

    1AtmosphericandSpaceScienceResearch(ASSR)Lab,DepartmentofPhysics,BangaloreUniversity,Bangalore

    560056,India2NationalAtmosphericResearchLaboratory,Gadanki,517112,India

    ABSTRACT

    Background: The variaon of the radon progeny concentraon in outdoor

    environment and meteorological parameters at fine resoluon were studied

    for one year at a connental locaon, Naonal Atmospheric Research

    Laboratory, Gadanki, India. Materials and Methods: The concentraons were

    measured using Alpha Progeny Meter by collecng air samples at a height of

    1 m above the Earths surface at a known flow rate. Results: Radon progeny

    concentraon shows temporal variaons on diurnal and monthly scales, and

    is due to mixing in the atmosphere. Peak in the early morning hours and low

    values during a*ernoon compared to nigh+me are due to differenal heat

    contrast between earths surface and its atmosphere. However, the acvity

    during February shows maximum compared to June/July months. The diurnal

    variaon of radon progeny shows posive correlaon with the relave

    humidity and negave correlaon with ambient temperature. The monthly

    mean acvity of radon progeny for the year 2012 was found to be 4.76 0.73

    mWL. Conclusion: The mean concentraon of radon progeny in the study

    region is relavely high compared to the other locaons in India and may be

    due to the rocky terrains and trapping of air-masses near the observaon site

    due to its topography. Keywords: Radon progeny, NARL, alpha progeny meter, work ing level.

    *Correspondingauthor:

    Dr.KamsaliNagaraja,

    Fax:+918023219295

    E-mail:

    kamsalinagaraj@bub.ernet.in

    Revised: March 2015 Accepted: May 2015

    Int. J. Radiat. Res., April 2016; 14(2): 105-111

    Original article

    DOI: 10.18869/acadpub.ijrr.14.2.105

  • deposited radon daughters interact with the

    sensitive lung tissues, and of prolongedexposuremayleadtomalignanttransformation,whichmayresultsinlungcancer(5-9).

    Radon (222Rn) atoms from the terrestrialradio nuclide 238U are transported through thesubsoil pore spaces and, while an amount of

    themwilldecay,therestwillbereleasedintotheatmosphere. The amount of radon depends onthe amount of 238U in the ground and is

    in8luencedby the type, porosity, dampness andtemperatureofthesoilcover.Radonhasalonghalf-life of 3.823 days. However, its decayproductsaretypicallyshort-lived,sotheyfollow

    the distribution of radon. The only long-livedproduct is 210Pb with a half-life of 22.3 years.Radonanditsshort-liveddaughters218Po,214Pb,214Bi and 214Po are also valuable as naturaltracers in the troposphere, in particular at theboundary layer near to the ground. In the

    present study, the importance is given only tothealphaemittingradonprogeniesi.e.218Poand214Po. Due to the inhalation of progenies and

    high ionization power of -particles emittedduring decay, the existence of progenies maydamagethelungcellstoagreaterextent(10).

    Even though, the extensive study onatmospheric aerosols has been conducted atNational Atmospheric Research Laboratory,

    Gadanki,which isaruralsiteand freefromtheanthropogenic activities. The measurement ofradon and aerosol attached radon progeny

    concentrations were not reported till date.Hence, in 2012, a campaign was conducted tostudy the activity concentrations of aerosolattachedradonprogeniesand itsbehaviorwith

    associated meteorological parameters. Thispaperpresentsthepreliminaryresultsobtainedin 2012, with an intention to extend our

    understanding of the activity of aerosolsattached radon progeny concentrations in thetypicaltropicalregioninrelationtotheweather

    parametersandtheircorrelation.

    MATERIALSANDMETHODS

    Methodologyandstudyarea

    The alpha emitting radon progenyconcentrations that were attached to aerosols

    were measured using Alpha Progeny Meter

    developed by SaphymoGmbH (formerly knownas Genitron Instruments, Germany) (8igure 1).Air is drawn through a glass micro-8iber 8ilter

    paper of pore size 0.5 mwith a constant 8lowrate of 2 liters per minute and alpha countedusing CANBERRA made CAM300AM

    semiconductor detector unit with a samplingfrequency of 10minutes. The air 8low rate andsampling period were maintained constant

    throughout the campaign. At the end of thesampling period, the accumulated alpha countsarefedtotheacquisitionsystem (11). Thealphaactivity of radon progenies were

    expressed inWorking Level (WL), where 1WLcorresponds to potential alpha energy of allshort-livedradondaughters inequilibriumwith

    radonconcentrationof3700Bqm3(12). Continuous observationswere carried out at

    the National Atmospheric Research Laboratory

    (NARL), Gadanki (13.5 0N, 79.2 0E), a ruraltropicalwarmlocationinpeninsularIndia,about2kmaway frommain residential areaswithno

    majorindustrialactivities.Thelocativemapandtopography of NARL is shown in8igure 2, respectively. Gadanki region

    experiences both summer (Southwest) andwinter (Northeast) monsoons. Overall winddirection was southerly and southeasterly

    during April, westerly from May to Septemberand northeasterly during October andNovember(13).

    106

    Charan Kumar et al. / Variation of radon progeny concentration

    Figure 1. Typical alpha progeny meter (Saphymo GmbH).

    Int. J. Radiat. Res., Vol. 14 No. 2, April 2016

  • RESULTSANDDISCUSSION

    The observed diurnal variation of radon

    progenyconcentrationataheightof1mabove

    earths surface is shown in 8igure 3. The

    concentration is observed for some of the

    typical days covering all the seasons and the

    concentration shows peak during the early

    morninghours(0409hrsof IST)andminima

    duringafternoonhours(14-18hrsofIST).The

    higheractivityofradondaughtersinairduring

    morningatthegroundlevelmaybeattributed

    to the formation of temperature inversion,

    which traps the atmospheric constituents

    including radon progenies within planetary

    boundarylayerandminimumconcentrationin

    the afternoon hours is mainly because of

    increasedverticalmixingandrisingofaerosols

    to the higher altitudes due to raise in

    Charan Kumar et al. / Variation of radon progeny concentration

    Figure 3. Diurnal variaon of radon progeny concentraon in different seasons. Dark line is running average of 6-points for

    every hour.

    Figure 2. Locaon of NARL, Gadanki, India.

    107 Int. J. Radiat. Res., Vol. 14 No. 2, April 2016

  • temperature of the atmosphere. The rapid

    8luctuations in the concentrations were due to

    local variations inwind speedanddirection (14,

    15). It varies frommonth tomonthor season to

    seasondependingontheweatherconditionand

    the exhalation rateof radon.The concentration

    willberelativelyhighduringstableatmosphere

    in nighttime compared to the unstable

    atmosphereduringdaytimedue to theonsetof

    convectionbecauseofsolaractivity.Thesimilar

    reasons were attributed to the days of winter

    compared to the summer seasons. However,

    during rainy season several parameters will

    in8luence including the washout of radon

    progenyduetoprecipitationandminimizesthe

    buildupofradonneartotheearthssurface(16).

    The 8igure 4 shows the variation of hourly

    averagedradonprogenyconcentrationswiththe

    ambient temperature for a typical day in the

    month of February. The trend observed is as

    usual and has the same reasoning explained

    before for its peak in the morning hours and

    minimum during noon hours. In addition, the

    variation of temperature and relative humidity

    are also plotted in the same graph to see their

    dependencesoneachotherandits in8luenceon

    progeny concentration. The concentration of

    radonprogenyrangesfrom1to24mWLandis

    showssigni8icantdiurnalvariationsoftheorder

    24 for10-minutes samplingwhereas forhourly

    averages it varies from 5 to 17 mWL with a

    magnitude of 4-fold variation. The average for

    longer period minimizes the 8luctuations but

    mai