Alpha indirect conversion radioisotope power source

AppliedRadiationandIsotopes66(2008)173–177

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Alphaindirectconversionradioisotopepowersource

MaximSychovÃ,AlexandrKavetsky,GalinaYakubova,GabrielWalter,ShahidYousaf,

QianLin,DorisChan,HeatherSocarras,KennethBower

TRACEPhotonicsInc.,1680WestPolk,Charleston,IL61920,USA

Received1October2006;receivedinrevisedform5August2007;accepted3September2007

Abstract

Advantagesofradioisotope-poweredelectricgeneratorsincludelongservicelife,widetemperaturerangeoperationandhigh-energydensity.Wereportdevelopmentofalong-lifegeneratorbasedonindirectconversionofalphadecayenergy.Prototypingused300mCiPu-238alphaemitterandAlGaAsphotovoltaiccellsdesignedforlowlightintensityconditions.Thealphaemitter,phosphorscreens,andvoltaicarrayswereassembledintoapowersourcewiththefollowingcharacteristics:Isc¼14mA;Uoc¼2.3V;poweroutputÀingthisprototypewehavepoweredaneight-digitelectroniccalculatorandwristwatch.r2007ElsevierLtd.Allrightsreserved.

Keywords:Microbatteries;Plutonium;Phosphor;Indirectconversion;Powergeneration

1.Introduction

Anewgenerationofultralowpowerdevicesneedsminiaturelong-lastingelectricsources.Oneoptionistheutilizationofradioisotope-poweredmicrogeneratorsasshownbyOlsen(1992)andSimsetal.(1995).Advantagesofradioisotope-poweredenergysourcesarelongservicelife(over10yearsdependingonisotope),lowweight,smallsize,wideoperatingtemperaturerangeandhighreliability(Boweretal.,2002;Sychovetal.,2002).

Amongthemanyradioisotopedecayenergyconversiontechniques,weheredescribealphaindirectconversion.Thekineticenergyofalphaparticlesisconvertedtolightinaphosphorscreen.Thematchedphotonwavelengthsarethenguidedtothephotovoltaic.Thephosphorscreenisopticallycoupledtothephotovoltaicdevice,asshowninFig.1.

Indirectconversionusinganalphasourcehasseveraladvantagestobothdirectconversionofalphasandutilizationofbetaemitters:

speci cpower(powerperunitsurface)comparedtobetaparticles.Therefore,lessphotovoltaicsurfaceareaisneeded,makingthedevicesmallerandcheaper.

Forthesamereason,alpharadioluminescence(RL)isbrightercomparedtobeta-excitationandphotovoltaicconversionismoreef cientatbrighterlightlevels.

Comparedtodirectconversionofalphas,initialoverallef ciencyislower,butthestabilityismuchhighersincephosphorsaremorestablethanvoltaics.Overthelongterm,theindirectpoweroutputsurpassesthatofdirectalphavoltaics.

InthispaperwedescribefabricationandtestingofpowersourcesusingPu-238.2.Phosphorscreenfabrication

Phosphorwasdepositedonglasssubstratesusingthefollowingprocedure:glassslides2.5Â2.5cm2werewashedwithalkalinesolutionandthenwithasolutionofpotassiumdichromateinsulfuricacid.Phosphorpowderwasmixedwitha5%solutionofphosphoricacidinacetoneandthatmixturewaspouredintoavialinwhichwasplacedtheweighedglassslides.Afterseveralhoursofsedimentation,theslidesweretakenoutofthevial,bakedat2501Candweighedagain.Thedifferencebetween

Thehighenergyofalphaparticlesprovideshigher

Correspondingauthor.Tel.:+12173486703;fax:+12173486394/

6713.

E-mailaddress:msychov@(M.Sychov).

0969-8043/$-seefrontmatterr2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.apradiso.2007.09.004