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Beta Decay
Beta Decay
The loan kit also contains some particle zoo items! You can use these soft toys to demonstrate some elements of particle physics. The items provided are:
A reversible proton-neutron
An electron
A positron
An electron-neutrino
An electron-antineutrino
These five particles are involved in the beta-decay process - find more about them further down the page! There are also the virtual W-bosons that mediate the reaction, (but they are not included for simplicity).
Beta decay was first hypothesised in 1930 by Wolfgang Pauli. Beta decay is the conversion of a neutron into a proton, or vice versa, through the weak nuclear force. The word "beta" refers to the electron, or positron, emitted. The W- boson is a virtual particle, (they don't exist as free particles) and its stage of the decay process happens in a billionth of a billionth of a billionth of a second.
Beta-plus Decay
Beta-plus Decay
Starting with a proton, if you turn it inside out, it turns into a neutron. In this radioactive process, an electron-neutrino and a positron are emitted by the way of an intermediate (virtual) W+ boson.
The half-life of a proton is estimated to be 1032 years. The decay equation is shown below:
p → n + β+ + νe
Since a proton consists of 2 up quarks and 1 down quark (uud), and a neutron consists of 2 down quarks and 1 up quark (udd), β+ decay is the conversion of an up quark to a down quark.
This quark equation is shown below:
u → d + β+ + νe
Beta-minus Decay
Beta-minus Decay
Starting with a neutron, if you turn it inside out, it turns into a proton. In this radioactive process, an electron-antineutrino and an electron are emitted by the way of an intermediate (virtual) W- boson.
The half-life of a neutron is around 10.3 minutes. The decay equation is shown below:
n → p + β- + ̅νe
Since a neutron consists of 2 down quarks and 1 up quark (udd), and a proton consists of 2 up quarks and 1 down quark (uud), β- decay is the conversion of one of a down quark to an up quark.
This quark equation is shown below:
d → u + β- + ̅νe
In the video below, Abby-Rhian Powell and Kayleigh Gates from the University of Glasgow explore more about quarks, the role of the strong force, and how current experiments are discovering new particles with different quark combinations.
Particles
Particles
You can some information about the particles included in the particle zoo set below! You can also find out more information about the standard model, as well as key discoveries of the subatomic universe.
Proton
Proton
Hadron / Baryon: uud
A proton is a hadron, meaning it is made up of quarks. It is also classed as a baryon, meaning it is made up of three quarks.
Protons are made of two up quarks, (each with a charge of +2/3) and one down quark, (with a charge of -1/3). So, it overall has a charge of +1.
As quarks are fermions, so are protons. Protons, and neutrons, are not standard model particles.
Neutron
Neutron
Hadron / Baryon: udd
Like a proton, neutrons are also classed as hadrons and baryons.
Neutrons are made of one up quark, (with a charge of +2/3) and two down quarks, (each with a charge of -1/3). So, it overall has a neutral charge.
Neutrons decay into protons via beta minus decay, releasing an electron and an electron-antineutrino.
Electron
Electron
Lepton
Electrons are one of the key fundamental particles in our universe.
They are fermions, meaning they obey the Pauli-Exclusion principle, (no two fermions can occupy the same space simultaneously).
They are also described as leptons - they are (usually) light particles that can exist independently, (don't need to bind to each other).
Positron
Positron
Lepton & Antiparticle
The positron is a particle of antimatter. It is the antiparticle of the electron - it is an electron with a positive charge, but is identical to the electron in every other way. The positron was the first particle of antimatter to be discovered, (in 1932).
Positrons are used in positron emission tomography, (PET) a medical imaging technique used to scan bodily organs for cancer and other disease.
Electron-neutrino
Electron-neutrino
Lepton / Neutrino
The electron-neutrino is a neutral particle of practically zero mass, and so is very difficult to detect. It is called the "electron-neutrino" as it is in the same generation as the electron.
Weighing in at less than 3 eV, it travels close to the speed of light and rarely interacts with anything. This explains why there are trillions of them travelling through your body right now.
Electron-antineutrino
Electron-antineutrino
Lepton & Antiparticle
The electron-antineutrino is the antiparticle to the electron-neutrino. In beta minus decay, the weak force converts a neutron into a proton whilst emitting an electron and an electron-antineutrino.
They are also used to monitor nuclear reactors in the enforcement of non-proliferation.
Teaching Material
Teaching Material
Post-16 Masterclass
Post-16 Masterclass
Module 6: Particle Physics meets Nuclear Physics
In the Post-16 Masterclass, we introduce the standard model of particle physics, looking at quarks, leptons, and the gauge bosons.
Class Worksheets
Class Worksheets
When using the particle zoo with your classes, you may wish to use the worksheets below to consolidate their knowledge about the standard model. There are three documents: a Post-16 student worksheet, answers to this worksheet, and an accompanying teacher document:
Isaac Physics Questions
Isaac Physics Questions
You can find some Isaac Physics questions you can set to your students related to particle physics below. Please feel free to look at our page for help setting up an account on Isaac Physics!
Post-16 Level
Further Information
Further Information
Feynman Diagrams
Feynman Diagrams
Feynman diagrams are a graphical representation of the (mathematical) mechanism of particle interactions. For example, we can draw the Feynman diagrams for beta decay. In the Feynman diagrams below, time is represented going vertically upwards, (i.e. the arrows from matter travel up, but the arrows from anti-matter, e.g. positrons, travel down).
The quark equation for β+ decay is shown below:
u → d + β+ + νe
We can also see the Feynman Diagram for beta-plus decay (below). An up quark is converted to a down quark by releasing a positron and a neutrino.
The quark equation for β- decay is shown below:
d → u + β- + ̅νe
We can also see the Feynman Diagram for beta-minus decay (below). A down quark is converted to an up quark by releasing an electron and an anti-neutrino.
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