Nuclear cov tshuaj tiv thaiv (NR) - txheej txheem uas lub nucleus ntawm lub atom hloov pauv los ntawm kev sib tsoo lossis sib txuas nrog lub nucleus ntawm lwm lub atom. Yog li, nws yuav tsum ua rau kev hloov pauv tsawg kawg ib qho nuclide mus rau lwm qhov. Qee lub sij hawm, yog tias lub nucleus cuam tshuam nrog lwm lub nucleus lossis cov khoom uas tsis hloov pauv qhov xwm txheej ntawm nuclide, cov txheej txheem raug xa mus rau kev tawg ntawm nuclear. Tej zaum qhov tseem ceeb tshaj plaws yog kev sib xyaw ua ke ntawm cov teeb pom kev zoo, uas cuam tshuam rau lub zog tsim cov hnub qub thiab lub hnub. Cov tshuaj tiv thaiv ntuj kuj tshwm sim hauv kev sib cuam tshuam ntawm cosmic rays nrog teeb meem.
Natural nuclear reactor
Qhov tseem ceeb tshaj plaws ntawm tib neeg cov tshuaj tiv thaiv yog cov tshuaj tiv thaiv fission uas tshwm sim hauv cov reactors nuclear. Cov no yog cov cuab yeej siv rau kev pib thiab tswj cov kab sib txuas nuclear. Tab sis tsis tsuas yog cov khoom siv dag zog xwb. Lub ntiaj teb thawj zaug nuclear reactor tau pom nyob rau xyoo 1972 ntawm Oklo hauv Gabon los ntawm Fab Kis tus kws kho mob Francis Perrin.
Cov xwm txheej raws li lub zog ntawm lub zog ntawm cov tshuaj tiv thaiv nuclear tuaj yeem tsim tau raug kwv yees xyoo 1956 los ntawm Paul Kazuo Kuroda. Tsuas paub qhov chaw hauvntiaj teb no muaj 16 qhov chaw nyob rau hauv uas nws tus kheej-sustaining tshwm sim ntawm no hom tshwm sim. Qhov no ntseeg tau tias muaj nyob ib ncig ntawm 1.7 billion xyoo dhau los thiab txuas ntxiv mus rau ntau pua txhiab xyoo, raws li pov thawj los ntawm xenon isotopes (cov khoom siv roj fission) thiab qhov sib txawv ntawm U-235 / U-238 (natural uranium enrichment).
Nuclear fission
Cov phiaj xwm kev sib khi lub zog qhia tias nuclides nrog qhov loj dua 130 teev sawv ntxov. yuav tsum spontaneously cais los ntawm ib leeg los tsim sib dua thiab ruaj khov nuclides. Kev sim, cov kws tshawb fawb tau pom tias qhov tshwm sim ntawm qhov tshwm sim ntawm cov ntsiab lus ntawm cov tshuaj tiv thaiv nuclear tshwm sim tsuas yog rau cov nuclides hnyav tshaj plaws nrog cov lej ntawm 230 lossis ntau dua. Txawm hais tias qhov no ua tiav, nws qeeb heev. Ib nrab-lub neej rau spontaneous fission ntawm 238 U, piv txwv li, yog 10-16 xyoo, los yog txog ob lab lub sij hawm ntev dua lub hnub nyoog ntawm peb ntiaj chaw! Fission cov tshuaj tiv thaiv tuaj yeem raug ntxias los ntawm irradiating cov qauv ntawm cov nuclides hnyav nrog qeeb thermal neutrons. Piv txwv li, thaum 235 U absorbs lub thermal neutron, nws tawg mus rau hauv ob qhov ntawm qhov tsis sib xws thiab tso tawm qhov nruab nrab ntawm 2.5 neutrons.
Kev nqus ntawm 238 U neutron induces vibrations nyob rau hauv lub nucleus, uas deform nws mus txog rau thaum nws tawg mus rau hauv fragments, ib yam li ib tee dej yuav tawg mus rau hauv me me droplets. Ntau tshaj 370 tus ntxhais nuclides nrog atomic masses ntawm 72 thiab 161 a.m.u. yog tsim thaum lub sij hawm fission los ntawm ib tug thermal neutron 235U, nrog rau ob yam khoom,qhia hauv qab no.
Isotopes ntawm cov tshuaj tiv thaiv nuclear, xws li uranium, raug cuam tshuam los ntawm kev tawg. Tab sis tib lub ntuj isotope 235 U muaj nyob rau hauv abundance ntawm tsuas yog 0.72%. Lub induced fission ntawm no isotope tso tawm qhov nruab nrab ntawm 200 MeV ib atom, los yog 80 lab kilojoules ib gram ntawm 235 U. Qhov attraction ntawm nuclear fission raws li ib tug lub zog qhov chaw yuav to taub los ntawm kev sib piv cov nqi nrog rau 50 kJ / g tso tawm thaum ntuj tsim. gas hlawv.
Thawj nuclear reactor
thawj lub tshuab hluav taws xob hluav taws xob tsim hluav taws xob tau tsim los ntawm Enrico Fermi thiab cov neeg ua haujlwm koom nrog hauv University of Chicago football chaw ntau pob thiab muab tso rau hauv kev ua haujlwm thaum Lub Kaum Ob Hlis 2, 1942. Lub reactor no, uas ua tau ntau kilowatts ntawm lub hwj chim, muaj ib pawg ntawm 385 tons ntawm graphite blocks stacked nyob rau hauv cov khaubncaws sab nraud povtseg ntawm ib tug cubic lattice ntawm 40 tons ntawm uranium thiab uranium oxide. Kev ua txhaum ntawm 238 U lossis 235 U hauv lub reactor no tsim cov neutrons tsawg heev. Tab sis muaj uranium txaus, yog li ib qho ntawm cov neutrons induced fission ntawm 235 U nucleus, yog li tso qhov nruab nrab ntawm 2.5 neutrons, uas catalyzed lub fission ntawm ntxiv 235 U nuclei nyob rau hauv ib tug saw cov tshuaj tiv thaiv (nuclear tshua).
Tus nqi ntawm cov khoom fissile xav tau los txhawb nqa cov tshuaj tiv thaiv kab mob hu ua qhov loj heev. Cov xub ntsuab qhia txog kev sib cais ntawm cov uranium nucleus nyob rau hauv ob fission fragments emitting tshiab neutrons. Qee qhov ntawm cov neutrons tuaj yeem ua rau muaj kev cuam tshuam tshiab (cov xub dub). Ib txhia ntawmneutrons tej zaum yuav poob rau hauv lwm yam txheej txheem (xub xub). Cov xub liab qhia qeeb neutrons uas tuaj txog tom qab los ntawm cov hluav taws xob fission fragments thiab tuaj yeem ua rau muaj kev cuam tshuam tshiab.
Tsim kev tawm tsam nuclear
Cia peb saib cov khoom tseem ceeb ntawm atoms, suav nrog tus lej atomic thiab atomic mass. Tus naj npawb atomic yog tus naj npawb ntawm protons hauv lub nucleus ntawm ib lub atom, thiab isotopes muaj tib tus lej atomic tab sis txawv ntawm cov neutrons. Yog hais tias thawj nuclei yog denoted a thiab b, thiab cov khoom nuclei yog denoted c thiab d, ces cov tshuaj tiv thaiv tuaj yeem sawv cev los ntawm qhov sib npaug koj tuaj yeem pom hauv qab no.
Qhov kev tawm tsam nuclear tshem tawm rau cov teeb pom kev tsis zoo siv tag nrho? Hauv ntau qhov xwm txheej, daim ntawv cog lus yog siv los piav txog cov txheej txheem no: a (b, c) d yog sib npaug rau a + b tsim c + d. Lub teeb hais feem ntau yog luv luv: feem ntau p stands rau proton, n rau neutron, d rau deuteron, α rau alpha los yog helium-4, β rau beta los yog electron, γ rau gamma photon, thiab lwm yam.
Hom kev tawm tsam nuclear
Txawm tias tus lej ntawm qhov ua tau zoo li no loj, lawv tuaj yeem txheeb los ntawm hom. Feem ntau ntawm cov tshuaj tiv thaiv no yog nrog los ntawm gamma hluav taws xob. Nov yog qee qhov piv txwv:
- Elastic tawg. tshwm sim thaum tsis muaj zog pauv ntawm lub hom phiaj nucleus thiab cov khoom tuaj.
- Inelastic scattering. tshwm sim thaum lub zog hloov mus. Qhov sib txawv ntawm lub zog kinetic tau khaws cia hauv cov nuclide zoo siab.
- Capture cov lus teb. ob leeg them thiabnruab nrab hais tuaj yeem ntes tau los ntawm nuclei. Qhov no yog nrog los ntawm emission ntawm ɣ-rays. Cov khoom ntawm cov tshuaj tiv thaiv nuclear hauv cov tshuaj tiv thaiv neutron yog hu ua radioactive nuclides (induced radioactivity).
- Kev sib kis. Kev nqus ntawm ib qho particle, nrog rau emission ntawm ib los yog ntau tshaj, yog hu ua kev hloov tshuaj tiv thaiv.
- Fission reactions. Nuclear fission yog ib qho tshuaj tiv thaiv uas cov nucleus ntawm ib lub atom tau muab faib ua me me (sib zog nuclei). Cov txheej txheem fission feem ntau tsim cov neutrons dawb thiab photons (nyob rau hauv daim ntawv ntawm gamma rays) thiab tso tawm ntau lub zog.
- Fusion cov tshuaj tiv thaiv. tshwm sim thaum ob los yog ntau tshaj atomic nuclei sib tsoo ntawm qhov kub ceev heev thiab ua ke los ua ib hom tshiab ntawm atomic nucleus. Deuterium-tritium fusion nuclear particles muaj kev txaus siab tshwj xeeb vim lawv lub peev xwm los muab lub zog rau yav tom ntej.
- Splitting reactions. Muaj tshwm sim thaum lub nucleus raug ntaus los ntawm ib qho particle uas muaj lub zog txaus thiab lub zog los tsoo qee qhov me me los yog tawg mus rau ntau qhov tawg.
- Rearrangement reactions. Qhov no yog qhov nqus ntawm ib qho particle, nrog rau emission ntawm ib lossis ntau qhov hais:
- 197Au (p, d) 196mAu
- 4He (a, p) 7Li
- 27Al (a, n) 30P
- 54Fe (a, d) 58Co
- 54Fe (a, 2 n) 56Ni
- 54Fe (32S, 28Si) 58Ni
Cov kev hloov pauv sib txawv hloov pauv tus lej ntawm cov neutrons thiab tus naj npawb ntawm protons.
Nuclear lwj
Nuclear cov tshuaj tiv thaiv tshwm sim thaum lub atom tsis ruaj khov poob lub zog los ntawmhluav taws xob. Nws yog txheej txheem random nyob rau theem ntawm ib qho atoms, txij li raws li quantum txoj kev xav nws tsis tuaj yeem kwv yees thaum tus neeg atom yuav lwj.
Muaj ntau hom xov tooj cua decay:
- Alpha radioactivity. Alpha hais yog tsim los ntawm ob protons thiab ob neutrons ua ke nrog ib tug particle zoo ib yam li helium nucleus. Vim nws loj heev thiab nws cov nqi, nws muaj zog ionizes cov khoom thiab muaj ib tug luv luv ntau yam.
- Beta radioactivity. Nws yog high-zog, high-speed positrons, los yog electrons, emissions los ntawm tej yam hom ntawm radioactive nuclei, xws li potassium-40. Beta hais muaj qhov nkag mus ntau dua li alpha hais, tab sis tseem tsawg dua gamma rays. Ejected beta particles yog ib daim ntawv ntawm ionizing hluav taws xob, tseem hu ua nuclear saw cov tshuaj tiv thaiv beta rays. Kev tsim cov beta hais yog hu ua beta decay.
- Gamma radioactivity. Gamma rays yog hluav taws xob hluav taws xob hluav taws xob ntau zaus thiab yog li ntawd muaj zog photons. Lawv raug tsim thaum nuclei lwj thaum lawv mus los ntawm lub xeev siab zog mus rau lub xeev qis hu ua gamma lwj. Feem ntau cov tshuaj tiv thaiv nuclear yog nrog los ntawm gamma tawg.
- Neutron emission. Neutron emission yog ib hom xov tooj cua decay ntawm nuclei uas muaj ntau tshaj neutrons (tshwj xeeb tshaj yog cov khoom fission), uas cov neutron tsuas yog ejected ntawm lub nucleus. Hom nohluav taws xob ua lub luag haujlwm tseem ceeb hauv kev tswj cov hluav taws xob hluav taws xob vim tias cov neutrons tau ncua sijhawm.
Zoo
Q-tus nqi ntawm lub zog ntawm cov tshuaj tiv thaiv nuclear yog tus nqi ntawm lub zog tso tawm lossis nqus thaum lub sijhawm cov tshuaj tiv thaiv. Nws yog hu ua lub zog tshuav, lossis Q-tus nqi ntawm cov tshuaj tiv thaiv. Lub zog no tau qhia tias qhov sib txawv ntawm lub zog kinetic ntawm cov khoom thiab tus nqi ntawm cov reactant.
Kev pom dav dav ntawm cov tshuaj tiv thaiv: x + X ⟶ Y + y + Q ……(i) x + X ⟶ Y + y + Q ……(i), qhov twg x thiab X yog reactants, thiab y thiab Y yog cov khoom siv tshuaj tiv thaiv, uas tuaj yeem txiav txim siab lub zog ntawm cov tshuaj tiv thaiv nuclear, Q yog lub zog sib npaug.
Q-tus nqi NR yog hais txog lub zog tso tawm lossis nqus hauv cov tshuaj tiv thaiv. Nws tseem hu ua NR lub zog tshuav, uas tuaj yeem ua tau zoo lossis tsis zoo nyob ntawm qhov xwm txheej.
Yog tias Q-tus nqi zoo, cov tshuaj tiv thaiv yuav yog exothermic, kuj hu ua exoergic. Nws tso lub zog. Yog tias Q-tus nqi tsis zoo, cov tshuaj tiv thaiv yog endoergic, lossis endothermic. Cov tshuaj tiv thaiv no yog ua los ntawm kev nqus lub zog.
Nyob rau hauv nuclear physics, xws li cov tshuaj tiv thaiv yog txhais los ntawm Q-tus nqi, raws li qhov sib txawv ntawm qhov sib npaug ntawm cov pawg ntawm thawj zaug reactants thiab cov khoom kawg. Nws yog ntsuas nyob rau hauv lub zog units MeV. Xav txog cov tshuaj tiv thaiv ib txwm nyob rau hauv uas projectile a thiab lub hom phiaj A tawm los rau ob yam khoom B thiab b.
Qhov no tuaj yeem qhia tau zoo li no: a + A → B + B, lossis txawm tias nyob rau hauv ib qho kev sib cog lus ntau dua - A (a, b) B. Hom lub zog hauv cov tshuaj tiv thaiv nuclear thiab lub ntsiab lus ntawm cov tshuaj tiv thaiv notxiav txim los ntawm tus qauv:
Q=[m a + m A - (m b + m B)] c 2, uas coincides nrog lub zog kinetic ntau dhau ntawm cov khoom kawg:
Q=T kawg - T pib
Rau cov tshuaj tiv thaiv uas muaj qhov nce hauv lub zog kinetic ntawm cov khoom, Q yog qhov zoo. Q cov tshuaj tiv thaiv zoo yog hu ua exothermic (lossis exogenous).
Muaj qhov tso tawm ntawm lub zog, txij li lub zog kinetic ntawm lub xeev kawg yog ntau dua hauv lub xeev thawj. Rau cov tshuaj tiv thaiv uas txo qis hauv lub zog kinetic ntawm cov khoom raug pom, Q yog qhov tsis zoo.
Ib nrab neej
Lub neej ib nrab ntawm cov khoom siv hluav taws xob yog cov yam ntxwv tas mus li. Nws ntsuas lub sij hawm yuav tsum tau rau ib tug npaum li cas ntawm cov teeb meem yuav tsum tau txo los ntawm ib nrab mus rau lwj thiab yog li ntawd tawg.
Archaeologists thiab geologists siv ib nrab-lub neej rau hnub tim ntawm cov khoom organic hauv cov txheej txheem hu ua carbon dating. Thaum lub sij hawm beta lwj, carbon 14 hloov mus rau nitrogen 14. Thaum lub sij hawm tuag, cov kab mob nres tsim carbon 14. Vim hais tias ib nrab-lub neej yog tas li, qhov ratio ntawm carbon 14 mus rau nitrogen 14 muab ib tug ntsuas ntawm lub hnub nyoog ntawm tus qauv.
Hauv kev kho mob, lub zog ntawm cov tshuaj tiv thaiv nuclear yog cov xov tooj cua ntawm Cob alt 60, uas tau siv rau kev kho hluav taws xob kom txo qis cov qog uas yuav tom qab tshem tawm kev phais, lossis tua cov qog nqaij hlav hauv kev ua haujlwm tsis tau.qog nqaij hlav. Thaum nws lwj mus rau hauv cov nickel ruaj khov, nws tawm ob lub zog siab heev - gamma rays. Niaj hnub no nws tau hloov los ntawm electron beam radiotherapy systems.
Isotope ib nrab-lub neej los ntawm qee cov qauv:
- oxygen 16 - infinite;
- uranium 238 - 4,460,000,000 xyoo;
- uranium 235 - 713,000,000 xyoo;
- carbon 14 - 5,730 xyoo;
- cob alt 60 - 5, 27 xyoo;
- silver 94 - 0.42 seconds.
Radiocarbon dating
Ntawm tus nqi ruaj khov, cov pa roj carbon monoxide tsis ruaj khov 14 maj mam ua rau cov pa roj carbon 12. Qhov piv ntawm cov pa roj carbon isotopes qhia txog hnub nyoog ntawm qee cov neeg nyob hauv ntiaj teb.
Radiocarbon dating yog ib txoj hauv kev uas muab lub hom phiaj kwv yees lub hnub nyoog ntawm cov khoom siv carbon. Hnub nyoog tuaj yeem kwv yees los ntawm kev ntsuas cov pa roj carbon 14 tam sim no hauv cov qauv thiab muab piv rau cov qauv siv thoob ntiaj teb.
Qhov cuam tshuam ntawm radiocarbon sib tham nyob rau hauv lub ntiaj teb niaj hnub no tau ua rau nws yog ib qho tseem ceeb tshaj plaws nrhiav pom ntawm lub xyoo pua 20th. Nroj tsuag thiab tsiaj assimilate carbon 14 los ntawm carbon dioxide thoob plaws hauv lawv lub neej. Thaum lawv tuag, lawv nres pauv cov pa nrog lub biosphere, thiab lawv cov pa roj carbon 14 cov ntsiab lus pib poob qis ntawm tus nqi txiav txim los ntawm txoj cai ntawm cov hluav taws xob tawg.
Radiocarbon dating yog qhov tseem ceeb rau kev ntsuas qhov seem ntawm cov xov tooj cua. Paub txog pes tsawg carbon 14 tshuav nyob rau hauv cov qauv, koj tuaj yeem paublub hnub nyoog ntawm lub cev thaum nws tuag. Nws yuav tsum raug sau tseg tias cov txiaj ntsig ntawm radiocarbon dating qhia thaum lub cev muaj sia nyob.
Cov txheej txheem yooj yim rau kev ntsuas hluav taws xob
Muaj peb txoj hauv kev tseem ceeb siv los ntsuas cov pa roj carbon 14 hauv ib qho kev muab piv txwv suav nrog, cov khoom siv hluav taws xob ua kua hluav taws xob thiab cov accelerator mass spectrometry.
Kev suav roj av ntau yog cov txheej txheem xov tooj cua sib tham uas siv rau hauv tus account beta hais tawm los ntawm cov qauv muab. Beta hais yog cov khoom lwj ntawm cov khoom siv hluav taws xob. Hauv cov qauv no, cov qauv carbon yog thawj zaug hloov mus rau cov pa roj carbon dioxide ua ntej ntsuas hauv cov pa ntsuas ntsuas.
Scintillation kua suav yog lwm txoj kev ntawm radiocarbon dating uas tau nrov nyob rau xyoo 1960. Nyob rau hauv txoj kev no, tus qauv yog ua kua thiab ib tug scintillator ntxiv. Qhov scintillator no tsim lub teeb ntawm lub teeb thaum nws cuam tshuam nrog beta particle. Cov qauv raj tau dhau los ntawm ob lub photomultipliers thiab thaum ob lub cuab yeej sau npe lub teeb nyem, suav tau.
Cov txiaj ntsig ntawm Nuclear Science
Txoj cai ntawm kev tawm tsam nuclear yog siv ntau yam ntawm cov ceg ntawm kev tshawb fawb thiab thev naus laus zis, xws li tshuaj, lub zog, geology, chaw thiab kev tiv thaiv ib puag ncig. Nuclear tshuaj thiab hluav taws xob yog cov kev kho mob uas koom nrog kev siv hluav taws xob lossis hluav taws xob rau kev kuaj mob, kho, thiab kev tiv thaiv.kab mob. Thaum radiology tau siv rau yuav luag ib puas xyoo, lo lus "nuclear tshuaj" pib siv li 50 xyoo dhau los.
Nuclear fais fab tau siv rau ntau xyoo lawm thiab yog ib qho kev xaiv lub zog loj tshaj plaws rau cov teb chaws nrhiav kev ruaj ntseg hluav taws xob thiab kev siv hluav taws xob qis qis.
Archaeologists siv ntau txoj hauv kev nuclear los txiav txim lub hnub nyoog ntawm cov khoom. Cov khoom qub xws li Shroud of Turin, Dead Sea Scrolls thiab Crown of Charlemagne tuaj yeem sau hnub tim thiab lees paub siv cov tswv yim nuclear.
Nuclear cov tswv yim yog siv hauv cov zej zog ua liaj ua teb los tua kab mob. Cov khoom siv hluav taws xob tau siv dav hauv kev lag luam mining. Piv txwv li, lawv tau siv rau hauv kev sim tsis muaj kev puas tsuaj ntawm cov blockages hauv cov kav dej thiab cov welds, hauv kev ntsuas qhov ntom ntawm cov khoom xuas nrig ntaus.
Nuclear science ua lub luag haujlwm tseem ceeb hauv kev pab peb nkag siab keeb kwm ntawm peb ib puag ncig.
