Alpha indirect conversion radioisotope power source(4)

Table1

PropertiesofphosphorstestedunderalphaexcitationPhosphorChemicalcompositionKfor26,300kGy(%perkGy)B-3g(Zn,Cd)S:Ag,Cl3.80EÀ03Mih-Y

(Zn,Mg)F2:Mn7.36EÀ04RST-612RGd2O3:Eu1.93EÀ03K-78RY2O3:Eu

2.65EÀ03K-78B-W

Y2O2S:Tb,Dy

2.68EÀ

03

takenfromMikhalchenko(1988)K¼

I0ÀI

ID

Â100%,(3)

0whereI0isinitialRLintensity,IistheRLintensityatcertainabsorbeddoseDinkGy.TocalculateabsorbeddoseinGy(J/kg),weusedD¼

Pat

H

,(4)

wherePaistheenergy uxfromthealphasourceinW/cm2,ttheisexposuretimeinseconds,andHisthesurfacedensityofphosphorlayerabsorbingallalphaenergy,kg/cm2.

ResultsofradiationstabilitytestsarepresentedinFig.6.SomeofthecurvesinFig.6a,showperiodicincreasesinRLintensity.Thiswasobservedwhenstabilityexperimentswereinterruptedforaweekend.Therefore,thesephos-phorsshowself-repairofradiationdamageatroomtemperature.ThecurvesofFig.6bshowchangeintheradiationstabilitycoef cient,K,withincreaseddose.Initialdegradation(highKvalues)leveloutforoxideandoxysul dephosphors.Forthesul de-typephosphor,Kstabilizesatahighervalueofabsorbeddoses.The uoride-typephosphorshowinitialimprovementofRL(negativevaluesofK),andthenKlevelsatthelowestvalueamongtestedphosphors.Valuesoftheradiationstabilitycoef cientfor26.3MGydosearepresentedinthelastcolumnofTable1.

Electricgeneratorsbasedonplutoniumemitters,phos-phorscreensandvoltaicarraysweresuccessfullyfabricatedandtested.Optimizedgeneratorsproducedshortcircuitcurrentof14mA,opencircuitvoltageof2.3Vandmaximumpoweroutputof21mWat0.11%overallef ciency.Thisbatterypoweredelectroniccalculatorsandanelectronicwatchclearlyshowingtheabilityofradio-isotope-basedpowersourcestoproduceenoughenergyformoderncircuits.StabilitytestsallowedustoidentifythemoststablephosphorunderthePu-238exposure:(Zn,Mg)F2:Mnlostonly19%ofinitialRLintensityafterthe26.3Â107J/kgabsorbeddosewhichcorrespondsto411hofcontinuousirradiationwithhigh-activityPu-238.Acknowledgments

Authorsgratefullyacknowledgeprojectsupportpro-videdbyDARPAandUSArmy,PicatinnyArsenal,underContractW15QKN-04C-1123.LowlightarraysprovidedbyProf.V.M.Andreevweregreatlyappreciated.References

Andreev,V.M.,Kavetsky,A.G.,Kalinovsky,V.S.,Khvostikov,V.P.,Ustinov,V.A.,Khvostikova,O.A.,Shvarts,M.Z.,2001.BetavoltaiccellsandarraysbasedonAlGaAs/GaAsheterostructures.In:Proceedingsofthe17thEPVSEC,Munich,p.VA1/38.