大約在同一時期，喬治·薩涅克，一位年輕的物理學家在進行有關於X射線的研究，他經常到我們實驗室同皮埃爾進行討論，他認為X射線同它附帶產生的射線及放射性物質產生的射線之間，可能會有相似之處。他提議對此進行研究，於是他們兩人便一起對那些附帶射線攜帶著的電荷進行了研究。
除去我們的合作者之外，我們很少在實驗室裡接待別人。因為皮埃爾在物理學的多個領域內已經頗有名氣了，所以不時地會有一些物理學家或者化學家來對我們的實驗進行參觀，或是向皮埃爾求教。他們一來，就會到黑板前進行討論。這種討論至今仍舊令人回味無窮，因為它們能夠激發起人們對於科學的興趣，催人奮進，同時又能激發人們的想像力，有助於人們進行積極的思考，而這並不會將實驗室真正寧靜、肅穆的氣氛擾亂。
我們與貝蒙一起對鐳的發現進行宣佈的，因為他和我們合作進行過實驗。——原作
者注
２我想通過引述波爾森寫給皮埃爾的一封感謝信來進行證明，因為自年起皮埃爾便開始將放射性物質提供給他了。
尊敬的先生和同事：
我於冰島北部收到了你在月日寫來的信，對此，我表示非常感謝。
我們先前對固定導電體某一點的電壓進行計量時是憑借其周圍的空氣來進行確定的，現在我們已經將這種方法放棄，而改為應用你的放射性粉末的方法……
請接受我發自內心的謝意，尊敬的先生和同事，再次感謝你給予我研究工作的巨大支持。
亞當·泣爾森
年月日
於雅克雷伊
——原作者注
ChapterVDicoveryofRadium
IhavealreadysaidthatinPierreCuriewasoccupiedwithaninvestigationonthegrowthofcrystals.Imyselfhadfinished,bythebeginningofvacation,astudyofthemagnetizationoftemperedsteelswhichhadresultedinourgettingasmallsubventionfromtheSocietyfortheEncouragementofNationalIndustry.OurdaughterIrenewasborninSeptember,andassoonasIwaswellagain,Iresumedmyworkinthelaboratorywiththeintentionofpreparingadoctor'sthesis.
OurattentionwascaughtbyacuriousphenomenondiscoveredinbyHenriBecquerel.ThediscoveryoftheX-raybyRoentgenhadexcitedtheimagination,andmanyphysiciansweretryingtodiscoverifsimilarrayswerenotemittedbyfluorescentbodiesundertheactionoflight.WiththisquestioninmindHenriBecquerelwasstudyinguraniumsalts,and,assometimesoccurs,cameupona,phenomenondifferentfromthathewaslookingfor:thespontaneousemissionbyuraniumsaltsofraysofapeculiarcharacter.Thiswasthediscoveryofradioactivity.
TheparticularphenomenondiscoveredbyBecquerelwasasfollows:uraniumcompoundplaceduponaphotographicplatecoveredwithblackpaperproducesonthatplateanimpressionanalogoustothatwhichlightwouldmake.Theimpressionisduetouraniumraysthattraversethepaper.Thesesamerayscan,likeX-rays,dischargeanelectroscope,bymakingtheairwhichsurroundsitaconductor.
HenriBecquerelassuredhimselfthatthesepropertiesdonotdependonapreliminaryisolation,andthattheypersistwhentheuraniumcompoundiskeptindarknessduringseveralmonths.Thenextstepwastoaskwhencecamethisenergy,ofminutequantity,itistrue,butconstantlygivenoffbyuraniumcompoundsundertheformofradiations.
Thestudyofthisphenomenonseemedtousveryattractiveandallthemoresobecausethequestionwasentirelynewandnothingyethadbeenwrittenuponit.Idecidedtoundertakeaninvestigationofit.
Itwasnecessarytofindaplaceinwhichtoconducttheexperiments.MyhusbandobtainedfromthedirectoroftheSchooltheauthorizationtouseaglassed-instudyonthegroundfloorwhichwasthenbeingusedasastoreroomandmachineshop.
InordertogobeyondtheresultsreachedbyBecquerel,itwasnecessarytoemployaprecisequantitativemethod.Thephenomenonthatbestlentitselftomeasurementwastheconductibilityproducedintheairbyuraniumrays.Thisphenomenon,whichiscalledionization,isproducedalsobyX-raysandinvestigationofitinconnectionwiththemhadmadeknownitsprincipalcharacteristics.
Formeasuringtheveryfeeblecurrentsthatonecanmakepassthroughairionizedbyuraniumrays,IhadatmydispositionanexcellentmethoddevelopedandappliedbyPierreandJacquesCurie.Thismethodconsistsincounterbalancingonasensitiveelectrometerthequantityofelectricitycarriedbythecurrentwiththatwhichapiezo-electricquartzcanfurnish.TheinstallationthereforerequiredaCurieelectrometer,apiezo-electricquartz,andachamberofionization,whichlastwasformedbyaplatecondenserwhosehigherplatewasjoinedtotheelectrometer,whilethelowerplate,chargedwithaknownpotential,wascoveredwithathinlayerofthesubstancetobeexamined.Needlesstosay,theplaceforsuchanelectrometricinstallationwashardlythecrowdedanddamplittleroominwhichIhadtosetitup.
Myexperimentsprovedthattheradiationofuraniumcompoundscanbemeasuredwithprecisionunderdeterminedconditions,andthatthisradiationisanatomicpropertyoftheelementofuranium.Itsintensityisproportionaltothequantityofuraniumcontainedinthecompound,anddependsneitheronconditionsofchemicalcombination,noronexternalcircumstances,suchaslightortemperature.
Iundertooknexttodiscoveriftherewereotherelementspossessingthesameproperty,andwiththisaimIexaminedalltheelementsthenknown,eitherintheirpurestateorincompounds.Ifoundthatamongthesebodies,thoriumcompoundsaretheonlyoneswhichemitrayssimilartothoseofuranium.Theradiationofthoriumhasanintensityofthesameorderasthatofuranium,andis,asinthecaseofuranium,anatomicpropertyoftheelement.
Itwasnecessaryatthispointtofindanewtermtodefinethisnewpropertyofmattermanifestedbytheelementsofuraniumandthorium.Iproposedthewordradioactivitywhichhassincebecomegenerallyadopted;theradioactiveelementshavebeencalledradioelements.