Fission ntawm uranium nuclei. Saw cov tshuaj tiv thaiv. Hauj lwm ntawm tus txheej txheem

Faib cov tub ntxhais - ib tug hnyav atom splitting mus rau hauv ob tawg tsam ntawm kwv yees li sib npaug zos luj, ua raws li los ntawm liberation ntawm ib tug loj npaum li cas ntawm lub zog.

Tus foundations ntawm nuclear fission pib ntawm ib tug tshiab era - "atomic muaj hnub nyoog". Lub peev xwm ntawm nws tau siv thiab qhov nqi koj tshuav ntawm kev pheej hmoo tau txais txiaj ntsim los ntawm nws cov kev siv, tsis tsuas muab sawv mus rau ib tug ntau ntawm cov sociological, kev nom kev tswv, nyiaj txiag thiab kev achievements, tab sis kuj yog ib tug teeb meem loj. Txawm los ntawm ib tug txhob txwm scientific point of view, cov nuclear fission cov txheej txheem tsim ib tug loj tus naj npawb ntawm learn thiab teeb meem, thiab ib tug ua kom tiav theoretical piav rau nws yog ib tug tshaj plaws ntawm lub neej yav tom ntej.

Sib koom - pab

losis tswvyim dabtsi zog (ib nucleon) txawv nyob rau hauv txawv nuclei. Nyhav muaj ib sab losis tswvyim dabtsi zog tshaj hais tias nyob rau hauv nruab nrab ntawm lub periodic rooj.

Qhov no txhais tau tias hnyav nuclei nyob rau hauv uas lub atomic tooj siab tshaj 100, advantageously muab faib ua ob me tawg tsam, li no tso zog uas yog hloov dua siab tshiab rau hauv kinetic zog ntawm cov tawg tsam. Qhov no yog hu ua splitting atomic nucleus.

Nyob rau hauv raws li cov stability nkhaus, uas qhia tau hais tias lub dependence ntawm tus xov tooj ntawm protons los ntawm ruaj khov nuclides rau neutron cev ntas nucleus xav tau ib tug loj tus naj npawb ntawm neutrons (piv nrog rau cov xov tooj ntawm protons) tshaj lighter. Qhov no qhia tias nyob rau hauv tas li ntawd mus rau lub splitting txheej txheem yuav tsum tawm txim liab ib co "spare" neutrons. Nyob rau hauv tas li ntawd, lawv yuav tau siv sij hawm tshaj ib co ntawm lub zog tso. Txoj kev tshawb no fission ntawm uranium atoms tsom tias qhov no generates ib tug neutron 3-4: U → ^{238 145 90} La + Br + 3n.

Lub atomic tooj (thiab cov atomic loj) ntawm lub fragment yog tsis sib npaug zos rau ib nrab lub atomic loj ntawm tus niam txiv. Qhov txawv ntawm cov masses ntawm atoms tsim raws li ib tug tshwm sim ntawm cleavage yog feem ntau hais txog 50. Txawm li cas los, yog vim li cas rau qhov no yog tsis tau nkaus ntshiab.

Lub losis tswvyim dabtsi energies ntawm ²³⁸ U, ¹⁴⁵ La Br thiab ⁹⁰ yog 1803, 1198 thiab 763 MeV feem. Qhov no txhais tau tias lub zog yog tso tawm uranium fission sib npaug zos 1198 + 158 = 763-1803 MeV los ntawm cov tshuaj tiv thaiv.

txawj fission

txawj splitting dab yog paub nyob rau hauv cov xwm, tab sis lawv yeej muaj tsawg. Qhov nruab nrab lub neej ntawm txoj kev no yog hais txog 10 ^17, thiab, piv txwv li, lub nruab nrab lub neej ntawm alpha-lwj ntawm lub radionuclide yog hais txog 10 ^11.

Yog vim li cas rau qhov no yog hais tias nyob rau hauv thiaj li yuav cais mus rau hauv ob qhov chaw, cov tub ntxhais yuav tsum xub yauv deformation (stretch) nyob rau hauv ib tug ellipsoidal daim ntawv, thiab ces, ua ntej yuav kawg cleavage rau hauv ob tawg tsam tsim ib tug "caj dab" nyob rau hauv nruab nrab.

tej zaum teeb meem

Nyob rau hauv lub deformed lub xeev nyob rau cov tub ntxhais ntawm ob rog. Ib tug ntawm lawv - lub muaj zog nto zog (nto nro kua mob piav nws kheej kheej zoo), thiab lwm yam - lub Coulomb repulsion ntawm lub fission tawg tsam. Ua ke lawv tsim lub peev xwm teeb meem.

Raws li nyob rau hauv cov ntaub ntawv ntawm alpha lwj tshwm sim txawj fission ntawm uranium atomic nuclei, cov tawg tsam yuav tsum kov yeej no barrier los ntawm txoj kev quantum tunneling. Cov teeb meem yog hais txog 6 MeV, raws li nyob rau hauv cov ntaub ntawv ntawm alpha-lwj, tab sis qhov tshwm sim ntawm tunneling ntawm α-hais yog considerably ntau dua qhov ntau cev ntas khoom splitting atom.

yuam degradation

Ntau npaum li cas yuav yog ntxias fission ntawm uranium nuclei. Nyob rau hauv cov ntaub ntawv no, tus niam txiv nucleus yog irradiated nrog neutrons. Yog hais tias ib tug niam txiv nws absorbs, ces lawv ua txhua yam los tso rau losis tswvyim dabtsi zog nyob rau hauv daim ntawv ntawm vibrational zog uas yuav muaj nqi tshaj 6 MeV yuav tsum tau los mus kov yeej lub peev xwm teeb meem.

Qhov twg ntxiv neutron zog yog tsis txaus los mus kov yeej lub peev xwm teeb meem, qhov teeb meem neutron yuav tsum muaj ib tug yam tsawg kawg nkaus kinetic zog nyob rau hauv thiaj li yuav tau ntxias cov splitting hauv lub atom. Nyob rau hauv cov ntaub ntawv ntawm ²³⁸ U ntxiv neutron losis tswvyim dabtsi zog yog uas ploj lawm txog 1 MeV. Qhov no txhais tau tias lub fission ntawm uranium nuclei ntxias tsuas neutrons nrog ib tug tig tau lub zog loj dua 1 MeV. Nyob rau lwm cov tes, ²³⁵ U isotope muaj ib unpaired neutron. Thaum ib tug nucleus absorbs ntxiv, nws cov ntaub ntawv nrog nws ib tug ob peb thiab ib qho ntxiv losis tswvyim dabtsi zog yog ib tug tshwm sim ntawm no pairing. Qhov no yog txaus rau tso tus nqi ntawm lub zog yuav tsum tau los mus kov yeej lub peev xwm barrier ntawm lub nucleus thiab lub division ntawm isotopes tshwm sim nyob rau hauv ib tug kev sib tsoo nrog tej neutron.

beta lwj

Txawm tias muaj tseeb hais tias cov fission cov tshuaj tiv thaiv yog tawm txim liab los ntawm peb los yog plaub neutrons, tawg tsam tseem muaj ntau neutrons tshaj lawv ruaj khov isobars. Qhov no txhais tau tias lub cleavage tawg tsam yog feem ntau tsis ruaj tsis khov nrog rau kev hwm mus beta lwj.

Piv txwv li, thaum muaj ib tug faib ntawm lub nucleus ntawm uranium ²³⁸ U, ruaj khov isobars nrog A = 145 ¹⁴⁵ yog neodymium Nd, uas txhais tau tias cov fragment lanthanum La ¹⁴⁵ tsob rau hauv peb ua sawv, txhua lub sij hawm los ntawm radiating electron thiab ib tug neutrino kom txog thaum ib tug ruaj khov nuclide yog tsim. Ruaj isobars nrog A = 90 ⁹⁰ yog zirconium Zr, yog li cleavage fragment bromo Br ⁹⁰ tawg rau hauv tsib theem saw β-lwj.

Cov saw β-lwj emit ntxiv zog uas yog nqa deb yuav luag tag nrho cov ntawm cov electron thiab ib tug neutrino.

Nuclear tshua: fission ntawm uranium

Direct nuclide los ntawm neutron tawg nrog loj heev tooj ntawm lawv los xyuas kom meej qhov stability ntawm lub nucleus yog tsis zoo li. Ntawm no yog lub point yog tias yog tsis muaj Coulomb repulsion, thiab thiaj li cov nto zog nyhav khaws cov neutron vim rau niam txiv. Cuaj kaum, nws zaum kuj tshwm sim. Piv txwv li, fission fragment Br ⁹⁰ nyob rau hauv thawj beta-lwj ua ib tug Krypton-90, uas tej zaum yuav nyob rau hauv ib tug pog lub xeev uas muaj txaus lub zog los mus kov yeej tus nto lub zog. Nyob rau hauv rooj plaub no tus neutron tawg tej zaum yuav tshwm sim ncaj qha mus rau tsim ib tug Krypton-89. Qhov no isobars yog tseem tsis ruaj tsis khov nrog rau kev hwm mus beta-lwj twb tsis tau mus rau hauv lub ruaj khov yttrium-89, yog li ntawd lub Krypton-89 yog muab faib ua peb theem.

Uranium fission: Saw tshuaj tiv thaiv

Neutrons tawm txim liab nyob rau hauv lub cleavage tiv thaiv yuav yuav absorbed los ntawm lwm tus niam txiv-nucleus, uas ces undergoes self-ntxias fission. Nyob rau hauv cov ntaub ntawv ntawm uranium-238 peb neutrons, uas tshwm sim tawm nrog energies tsawg tshaj li 1 MeV (lub zog tso rau hauv lub fission ntawm uranium tub ntxhais - 158 MeV - feem ntau hloov dua siab tshiab rau hauv kinetic zog cleavage tawg tsam), li ntawd, lawv yuav tsis ua rau ib tug ntxiv division ntawm no nuclide. Txawm li cas los, Yog hais tias ib tug tseem ceeb concentration ntawm cov tsis tshua muaj isotope U ²³⁵ cov dawb neutrons yuav yuav los ntawm lub nuclei ntawm ²³⁵ U, nws muaj peev xwm ua tau ua cleavage, txij thaum nyob rau cov ntaub ntawv no yog tsis muaj lub zog pib hauv qab no uas cov division yog tsis ntxias.

Qhov no yog lub ntsiab cai saw tshuaj tiv thaiv.

Hom ntawm Nuclear tshua

Cia k - tus naj npawb ntawm neutrons ua nyob rau hauv ib tug qauv ntawm cov fissile khoom nyob rau hauv kauj ruam n ntawm lub saw, muab faib los ntawm tus xov tooj ntawm neutrons ua nyob rau hauv theem n - 1. Qhov no muaj pes tsawg tus yuav nyob ntawm seb tus xov tooj ntawm neutrons ua nyob rau hauv kauj ruam n - 1, yog absorbed los ntawm cov tub ntxhais, uas yuav undergo vim raug yuam fission.

• Yog hais tias k <1, cov saw tshuaj tiv thaiv yog tsuas tawm ntawm chav thiab tus txheej txheem yuav tsis heev sai sai. Qhov no yog dab tsi tshwm sim nyob rau hauv lub natural uranium ore, nyob rau hauv uas lub concentration ^{ntawm 235} U yog li ntawd me me hais tias tus yuav haum ntawm ib tug neutron no isotope yog tsis tshua muaj negligible.

• Yog hais tias k> 1, cov saw hlau tshuaj tiv thaiv yuav mus ntxiv loj hlob raws li ntev raws li tag nrho cov fissile khoom yuav tsis tau siv (lub atomic foob pob). Qhov no yog tiav los ntawm pom tej yam ntuj tso ore kom tau ib tug txaus siab concentration ntawm uranium-235. Rau kheej kheej qauv nqi k tsub kom nrog qhov tshwm sim ntawm neutron haum, uas yog nyob rau ntawm voos kheej-kheej ntawm tus kheej. Yog li ntawd U hnyav yuav tsum ntau tshaj ib tug tej yam tseem ceeb heev loj rau fission ntawm uranium (chain reaction) yuav tshwm sim.

• Yog hais tias k = 1, ces muaj yog ib tug tshuaj cov tshuaj tiv thaiv. Nws yog siv nyob rau hauv nuclear reactors. Cov txheej txheem yog tshuaj muab faib rau cov uranium pas nuv ntses ntawm cadmium los yog boron, uas nqus feem ntau ntawm cov neutrons (cov ntsiab muaj peev xwm ntawm capturing neutrons). Faib uranium cores nws yog txiav tshuaj los ntawm tsiv lub pas nrig yog li ntawd lub k nqi tseem sib npaug zos rau ib tug.