3 main types of particle

Topic 7.2

The ABCs of RadioactivityTypes of Nuclear DecayNuclear Decay ReviewDescribe the nuclear decay process. Name the 2 key items involvedWhat is the relationship between the rate of decay and the number nuclei in the sample?Describe the term half-lifeWhy is the nuclear activity is more meaningful than the number of particles in the nuclei?nuclear decay is a random process and that the probability of decay is related to the amount of energy that will be released when it happens.Understand that the number of decays per second in a sample of material is directly proportional to the number of nuclei.Understand how half life gives a measure of the rate of decay of a sample.Understand why the activity is also exponential and that the activity is more useful to us than the number of particles.

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3During the decay processthe nucleus is broken up into smaller piecesHow 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?classical ideas of potential energy do not explain where the energy is transferred to when a nucleus is split up.Accept that increased mass would give an answer if mass and energy were equivalent E=mc2.Introduce the electron Volt as a unit of energy.Have a feeling for the scale of difference between energy associated with chemical and nuclear reactions.Understand that binding energy is not in the nucleus but has been released.Introduce the Unified mass unit.Understand how to calculate binding energy from tables of mass and plot the BE/nucl curve.Deduce from knowledge of mechanics that physical systems will tend to a state of lowest energy.

4Binding energyThis 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.

5Binding energyThis is the work required to completely separate the nucleons of the nucleus.

What happens if the nucleus is unstable?

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Binding energy per nucleonThis 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 topic7The Binding Energy curve

8Types of Nuclear Decay

They are defined by the 3 main types of particles that can be ejected from an unstable nuclei.

9AimsUnderstand that if a nucleus can change into one with higher BE then it will as this will release energy.Distinguish between , and radiationIdentify and particle as a Helium nucleus.Write the nuclear equation for decay and calculate the amount of energy released.Apply the conservation of momentum and energy to predict that radiation is mono-energetic.Understand why particles are so ionising and see how this property enables them to be easily detected by ionisation and cloud chambers but means they have short range.

Types of Nuclear Decay

What is the main reason that make unstable isotopes decay?

10It is important to remember that all atoms (and its nucleus) and all physical systems will tend to a state of lowest energy.Alpha particles

11Alpha particles2 protons and 2 neutrons joined togetherThe same as the nucleus of a helium atomStopped by paper or a few cm of airHighly ionisingDeflected by electric and strong magnetic fieldsHe242+12

Alpha DecayAlpha DecayU92235Th90231+Atomic number goes down by 2Atomic mass goes down by 4He242+14Ionization by alpha particles

Ionization by alpha particles

Beta particles

17Beta particlesFast moving electronsEffectively masslessStopped by about 3 mm of aluminiumWeakly ionisingDeflected by electric and magnetic fields

e-1018Beta Decay

Beta DecayIn 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!

+e -10Th90231Pa9123120Beta Decay Mono energetic?Unlike alpha particles, beta particles can be emitted with different energiesHow do we conserve the energy with each reaction?-10e + eTh90231Pa91231+00antineutrinoantimatter21AntiparticlesProduced naturally symmetry in the universe!Particle + Antiparticle = ENERGY (photons)How did matter dominate in our universe?

+10e + eTh90231Pa91231+00neutrinoantimatterpositron22Gamma rays

23Gamma raysHigh frequency electromagnetic radiationStopped by several cm of leadVery weakly ionisingNOT affected by electric or magnetic fields

24Gamma raysAssociated with daughter nucleus of alpha decayU92235Th90231+

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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 thats present in this diagramParticles in a Magnetic FieldUse the right hand rule for alpha particle!

Particles in a Magnetic FieldUse the left hand rule for beta particle!Particles in a Magnetic Field

Gamma rays have no charge!Cloud ChamberUtilizes ionization properties of alpha & beta particles Vapour condenses around small particles of dust cloudSimilar to vapour trails left by airplanes

The radiation produces dense straight tracks showing intense ionisation.Notice that all the tracks are similar in length.

The highenergy ray tracks are thinner and less intense.The tracks vary in length and most of the tracks are much longer than the particle tracks.

The rays do not produce continuous tracks.

32PhET SimulationsAlpha Decay

Beta Decay