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Types of Nuclear Decay Topic 7.2 The ABC’s of Radioactivity Nuclear Decay Review Describe the nuclear decay process. Name the 2 key items involved What is the relationship between the rate of decay and the number nuclei in the sample? Describe the term half-life Why is the nuclear activity is more meaningful than the number of particles in the nuclei? During the decay process… the nucleus is ‘broken up’ into smaller pieces How does this happen? Where does the initial energy come from? How would the masses compare before and after a decay? Are there certain types of particles that come out of a decay or is it random? Binding energy This is the work required to completely separate the nucleons of the nucleus. Note: Binding Energy is NOT the energy contained by the nucleus that holds the nucleons together. Binding energy This is the work required to completely separate the nucleons of the nucleus. What happens if the nucleus is unstable? Binding energy per nucleon This is the work required to completely separate the nucleons of the nucleus divided by the number of nucleons. It is a measure of how stable the nucleus is. This is an important graph for this topic The Binding Energy curve Types of Nuclear Decay They are defined by the 3 main types of particles that can be ejected from an unstable nuclei. Types of Nuclear Decay What is the main reason that make unstable isotopes ‘decay’? Alpha particles α Alpha particles 2 protons and 2 neutrons joined together The same as the nucleus of a helium atom Stopped by paper or a few cm of air Highly ionising Deflected by electric and strong magnetic fields 4 2 2+ He Alpha Decay Alpha Decay Atomic mass goes down by 4 235 231 4 92 90 2 U 2+ He + Th Atomic number goes down by 2 Ionization by alpha particles Ionization by alpha particles Beta particles β Beta particles Fast moving electrons Effectively massless Stopped by about 3 mm of aluminium Weakly ionising Deflected by electric and magnetic fields 0 e -1 Beta Decay Beta Decay In the nucleus a neutron changes into an electron (the beta particle which is ejected) and a proton (which stays in the nucleus) During beta decay the mass number stays the same but the proton number goes up by 1. Remember the electron comes from the nucleus! 231 Th 90 231 0 91 -1 Pa + e Beta Decay – Mono energetic? Unlike alpha particles, beta particles can be emitted with different energies How do we conserve the energy with each reaction? 231 Th 90 antimatter antineutrino Pa + e + עe 231 91 0 -1 0 0 Antiparticles Produced naturally symmetry in the universe! Particle + Antiparticle = ENERGY (photons) How did matter dominate in our universe? antimatter 231 Th 90 positron neutrino Pa + e + עe 231 91 0 +1 0 0 Gamma rays Gamma rays High frequency electromagnetic radiation Stopped by several cm of lead Very weakly ionising NOT affected by electric or magnetic fields Gamma rays Associated with daughter nucleus of alpha decay 235 231 92 90 U Th + α Types of Nuclear Decay Particles in a Magnetic Field If the magnetic field is coming out of the page, name the three types of radiation that’s present in this diagram Particles in a Magnetic Field Use the right hand rule for alpha particle! α Particles in a Magnetic Field Use the left hand rule for beta particle! β α Particles in a Magnetic Field Gamma rays have no charge! β ϒ α Cloud Chamber Utilizes ionization properties of alpha & beta particles Vapour condenses around small particles of ‘dust’ cloud Similar to vapour trails left by airplanes PhET Simulations Alpha Decay Beta Decay