RADIOACTIVITY Radioactive Decay
T HE A TOM
T YPES OF R ADIOACTIVE D ECAY T YPES OF R ADIOACTIVE D ECAY 1. Alpha Decay: The transmutation of and atom with an emission of an alpha particle 2. Beta Decay: The transmutation of and atom with an emission of a beta particle 3. Gamma Decay: The nucleus of an atom settles to a lower energy state and releases electromagnetic energy (photon)
A LPHA D ECAY An alpha particle ( ) is a helium nucleus, a cluster of two protons and two neutrons
B ETA D ECAY In beta decay ( ) a neutron decays into a proton, an electron and an antineutrino The beta particle is an electron Neutrinos are particles 10 millionths the mass on an electron with no charge.
G AMMA D ECAY In gamma decay ( ) a nucleus settles to a lower energy state and release a photon The gamma particle is a photon
R EACTION E XAMPLES 1. Find the daughter nucleus for the beta decay of thorium Predict the daughter nucleus that results from alpha decay of radium-226.
NUCLEAR PROCESSES Fission & Fusion
F ISSION VS. F USION
In nuclear fusion, two nuclei combine to form a more massive nucleus. Fusion means the merging together of different elements to make a new element. In nuclear fission, a massive nucleus splits into two lighter nuclei. Fission means breaking something up into parts.
L AW OF C ONSERVATION OF M ASS -E NERGY Mass can be transformed into energy and energy can be transformed into mass. This explains the mass defect: when nucleons are bound together, their energy is reduced, so their mass is also reduced. The binding energy of a nucleus is the mass-energy equivalent of its mass defect.
N UCLEAR R EACTIONS
N UCLEAR F ISSION Fission is the reaction in which a massive nucleus splits into two or more lighter nuclei. 1. Spontaneous Fission: Spontaneous fission occurs when an unstable isotope splits into two or more smaller nuclei without any external interaction. It is only seen in nuclei with atomic mass numbers above 230 (elements near thorium). Induced Fission: a nucleus absorbs a neutron, forming a highly unstable isotope that breaks up almost instantly into two lighter nuclei
N UCLEAR F ISSION Thorium-230 decays to polonium-218 by three alpha decays. Write the equations for the reactions. Use a periodic table.
N UCLEAR F ISSION
N UCLEAR F USION The dominant fusion reaction in stars the size of our Sun or smaller is the proton-proton chain.
N UCLEAR F USION Another form of fusion is neutron absorption.