Cov Lus Nug Piv Txwv Sib Tham Txog Beta (β) Decay
Kev puas tsuaj ntawm cov khoom siv hluav taws xob yog cov txheej txheem uas lub nucleus atomic tsis ruaj khov tso tawm cov khoom me me kom ua tiav lub xeev ruaj khov dua. Hauv tsab xov xwm no, peb yuav tsom mus rau kev puas tsuaj ntawm beta (β), ib hom kev puas tsuaj ntawm cov khoom siv hluav taws xob. Peb lub hom phiaj tseem ceeb yog kom nkag siab txog kev puas tsuaj ntawm beta los ntawm cov piv txwv thiab lawv cov kev daws teeb meem. Cia peb pib los ntawm kev kawm txog cov hauv paus ntawm kev puas tsuaj ntawm beta ua ntej nkag mus rau hauv cov piv txwv.
Cov Ntsiab Lus Tseem Ceeb ntawm Beta Decay
Kev lwj ntawm beta cuam tshuam txog kev hloov pauv ntawm qee lub nuclei atomic los ntawm kev tso tawm cov beta particles. Muaj ob hom kev lwj ntawm beta:
1. Beta-minus (β-) lwj: Hauv qhov lwj no, ib lub neutron hauv lub nucleus hloov mus ua ib lub proton, ib lub electron (hu ua beta particle), thiab ib lub electron antineutrino. Cov qauv tshuaj tiv thaiv yog:
\[
n \rightarrow p + e^- + \bar{\nu}_e
\]
Ntawm no, \(n \) yog neutron, \(p \) yog proton, \(e^- \) yog (beta) electron, thiab \(\bar{\nu}_e \) yog electron antineutrino.
2. Beta-plus (β+) lwj: Qhov no tshwm sim thaum ib qho proton hauv lub nucleus hloov mus ua ib qho neutron, ib qho positron (antielectron), thiab ib qho electron neutrino. Cov qauv yog:
\[
p \rightarrow n + e^+ + \nu_e
\]
Qhov twg \( e^+ \) yog positron thiab \( \nu_e \) yog electron neutrino.
Piv txwv 1: Beta-minus Decay
Lo lus nug:
Ib lub nucleus carbon-14 (\( ^{14}_{6}\text{C} \)) raug kev puas tsuaj beta-minus. Txheeb xyuas cov khoom ntawm qhov kev puas tsuaj no thiab sau cov qauv nuclear.
Kev Sib Tham:
Ua ntej, peb txheeb xyuas tias carbon-14 (\( ^{14}_{6}\text{C} \)) muaj tus lej atomic ntawm 6 thiab tus lej mass ntawm 14. Hauv beta-minus decay, ib qho ntawm cov neutrons hauv lub nucleus hloov mus ua proton. Qhov no txhais tau tias tus lej atomic ntawm lub nucleus nce ntxiv los ntawm ib chav, thaum tus lej mass tseem zoo li qub.
Nov yog qhov beta-minus decay equation rau carbon-14:
\[
^{14}_{6}\text{C} \rightarrow ^{14}_{7}\text{N} + e^- + \bar{\nu}_e
\]
Qhov twg:
– Cov khoom ntawm qhov lwj yog nitrogen-14 (\( ^{14}_{7}\text{N} \)).
- Cov electrons (\( e^- \)) yog cov beta particles uas raug tso tawm.
– \( \bar{\nu}_e \) yog ib qho electron antineutrino uas kuj raug tso tawm.
Piv txwv 2: Beta-plus Decay
Lo lus nug:
Lub fluorine-18 nucleus (\( ^{18}_{9}\text{F} \)) dhau los ua beta-plus lwj. Txheeb xyuas cov khoom ntawm qhov lwj no thiab sau cov qauv nuclear.
Kev Sib Tham:
Fluorine-18 (\( ^{18}_{9}\text{F} \)) muaj tus lej atomic ntawm 9 thiab tus lej mass ntawm 18. Hauv beta-plus decay, ib qho proton hauv lub nucleus hloov mus ua neutron uas txo tus lej atomic los ntawm ib qho, tab sis tus lej mass tseem zoo li qub.
Nov yog qhov beta-plus decay equation rau fluorine-18:
\[
^{18}_{9}\text{F} \rightarrow ^{18}_{8}\text{O} + e^+ + \nu_e
\]
Qhov twg:
- Cov khoom ntawm qhov lwj yog oxygen-18 (\( ^{18}_{8}\text{O} \)).
- Positron (\( e^+ \)) yog ib qho beta particle uas raug tso tawm.
- \( \nu_e \) yog ib qho electron neutrino uas kuj raug tso tawm.
Piv txwv lus nug 3: Lub zog lwj
Lo lus nug:
Xam lub zog uas tso tawm thaum lub sijhawm beta-minus decay yog tias lub isotope strontium-90 (\( ^{90}_{38}\text{Sr} \)) decays rau yttrium-90 (\( ^{90}_{39}\text{Y} \)). Lub cev hnyav ntawm strontium-90 yog 89,907738 u, thiab lub cev hnyav ntawm yttrium-90 yog 89,907152 u. Lub cev hnyav ntawm ib lub electron yog 0,000548 u.
Kev Sib Tham:
Lub zog uas tso tawm thaum lub sijhawm beta-minus decay tuaj yeem suav los ntawm qhov sib txawv ntawm cov khoom thiab cov reactants, tom qab ntawd hloov mus ua lub zog siv Einstein tus qauv \(E=mc^2\).
Qhov kev hloov pauv ntawm qhov hnyav (\( \Delta m \)) yog qhov sib txawv ntawm qhov hnyav pib thiab qhov hnyav kawg, suav nrog qhov hnyav ntawm cov electron uas tawm los:
\[
\Delta m = (\text{mass} ^{90}_{38}\text{Sr}) – (\text{mass} ^{90}_{39}\text{Y} + \text{electron mass})
\]
Kev hloov tus nqi:
\[
\Delta m = 89,907738 \, \text{u} – (89,907152 \, \text{u} + 0,000548 \, \text{u})
\]
\[
\Delta m = 0,000038 \, \text{u}
\]
Hloov cov kev hloov pauv ntawm qhov hnyav mus rau lub zog (1 u = 931.5 MeV/c²):
\[
E = \Delta m \times 931.5 \text{MeV/c}^2
\]
\[
E = 0,000038 \, \text{u} \times 931.5 \, \text{MeV}
\]
\[
E \approx 0,03537 \, \text{MeV}
\]
Lub zog tso tawm thaum lub sijhawm lwj yog li 0,03537 MeV.
Xaus
Kev lwj ntawm beta yog ib qho xwm txheej txaus nyiam uas pab peb nkag siab txog kev hloov pauv me me uas tuaj yeem tshwm sim hauv cov nuclei atomic. Los ntawm kev kawm txog beta-minus thiab beta-plus lwj, peb tuaj yeem txheeb xyuas seb cov ntsiab lus hloov pauv mus rau lwm cov ntsiab lus li cas thiab xam lub zog tso tawm thaum lub sijhawm ua haujlwm. Los ntawm qhov teeb meem piv txwv no, peb tau txais kev nkag siab tob dua txog cov dynamics uas cuam tshuam nrog kev lwj ntawm radioactive thiab qhov tseem ceeb ntawm cov tswv yim tseem ceeb hauv nuclear physics.
