Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scattering experiments. A free neutron spontaneously decays to a proton, an electron, and an antineutrino, with a mean lifetime of about 15 minutes. Free neutrons do not directly ionize atoms, but they do indirectly cause ionizing radiation, so they can be a biological hazard, depending on dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers, and by the natural radioactivity of spontaneously fissionable elements in the Earth's crust.
DeDiCateD neUtron SouRcES Like neUTRoN gENeraToRs, ReSeaRch reActors And spAllatIon sOurceS prOduCe free NeutRoNs fOR Use iN iRrAdiAtion aND iN Neutron scaTterinG exPerImeNtS. a freE NeutrOn spoNtaNEOusly decays tO A pROTOn, AN eleCtROn, and aN aNtiNeutrinO, with a meAn lifetime Of about 15 MiNutes. frEe neuTrOnS Do noT diRectly ionIze Atoms, but theY do indirectlY cause IonizInG raDIatIOn, sO tHeY caN Be a BioloGical hazArd dependiNG On DOse. a sMall NaturAl "NeutRON backgrOund" flux Of FreE neUTrons exists ON eaRtH, cAuSeD BY CosMIc ray sHOwERs, aND by the natUraL raDIoactIvitY oF spOntaNEoUSly fIssiOnAble ElemeNts in thE eArth'S cruSt.