Ib qho tsis ruaj khov (piv txwv li, xov tooj cua) lub pob hluav taws xob tuaj yeem ua kom ruaj khov tom qab tom qab emitting particles thiab lub zog. Cov txheej txheem no hu ua lwj (Radioactive decay). Cov xaim no lossis lub zog (tom kawg tawm los ntawm hluav taws xob xaim hluav taws xob) yog suav sau ua hluav taws xob. Cov hluav taws xob tawm ntawm cov hluav taws xob tsis ruaj khov tuaj yeem ua cov alpha (helium nucleus) hais me me, beta (hluav taws xob lossis positrons) hais, gamma rays lossis neutrons.
Thaum lub sij hawm lwj xaj ntawm lub radionuclide, tus naj npawb ntawm nuclei ntawm maj mam tsawg dua. Lub sijhawm yuav tsum tau txiav tawm mus rau tsuas yog ib nrab ntawm thawj qhov loj hu ua ib nrab-lub neej ntawm lub nuclide. Txhua qhov radionuclide muaj qhov tshwj xeeb ib nrab-lub neej, thaj tsam li ntawm ob peb microseconds mus txog ntau lab xyoo.
Ib qho kev tshwm sim nyob rau hauv uas ib qho atomic nucleus ua lub nucleus tshiab vim qhov emission ntawm qee yam particle. Lub nucleus yog qhov system quantum. Lub pas nqus hluav taws xob tawg yog qhov tshwm sim hloov los ntawm lub keeb. Nws yog txheej txheem kev hloov pauv hauv quantum thiab nws ua raws li kev cai ntawm quantum txheeb cais. Rau ib qho radionuclide, lub sijhawm tseem ceeb ntawm nws qhov kev lwj yog qhov tsis paub meej, tab sis raws li qhov tseeb, txoj cai ntawm kev lwj yog qhov tseeb heev. Yog hais tias muaj pes tsawg tus nuclear txiav tawm hauv dt lub sijhawm sib txawv yog dN, nws yuav tsum muaj kev sib npaug ntawm cov lej ntawm cov atomic nu N tam sim ntawd lub sijhawm ntawd, thiab pom tseeb kuj muaj sib npaug rau lub sijhawm sib kis dt.
Muaj peb hom kev lwj: alpha lwj, beta lwj thiab gamma lwj.
Nuclear fission
Nuclear fission yog hais txog kev faib tawm ntawm ib qho nucleus mus rau ntau lub nuclei. Nuclear fission feem ntau yog tshwm sim los ntawm neutrons bombarding lub nucleus nrog qhov loj dua. Tom qab lub pob hluav taws xob tawg, ob feem ntawm qhov sib npaug loj yog tsim thiab lub zog raug tso tawm, qee zaum ua rau muaj cov saw hlau tshwm sim. Zog=qhov loj ╳ ceev ntawm lub teeb sib tshooj