Chapter 11 Particle Physics Flashcards
1
Q
Rutherford Scattering
A
- Evidence for the structure of the atom was discovered by Ernest Rutherford in the beginning of the 20th century from the study of α-particle scattering
- The experimental setup consists of alpha particles fired at thin gold foil and a detector on the other side to detect how many particles deflected at different angles
2
Q
α-particle scattering experiment set up
A
3
Q
α-particles are what?
A
the nucleus of a helium atom and are positively charged
4
Q
From this experiment, Rutherford results were: (alpha scattering)
A
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The majority of α-particles went straight through (A)
- This suggested the atom is mainly empty space
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Some α-particles deflected through small angles of < 10o
- This suggested there is a positive nucleus at the centre (since two positive charges would repel)
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Only a small number of α-particles deflected straight back at angles of > 90o (C)
- This suggested the nucleus is extremely small and this is where the mass and charge of the atom is concentrated
- It was therefore concluded that atoms consist of small dense positively charged nuclei, surrounded by negatively charged electrons
5
Q
Atomic Structure
A
- The atoms of all elements are made up of three types of particles: protons, neutrons and electrons.
- A stable atom is neutral (it has no charge)
- Since protons and electrons have the same charge, but opposite signs, a stable atom has an equal number of both for the overall charge to remain neutral
6
Q
Antimatter
A
- All matter particles have antimatter counterparts
- Antimatter particles are identical to their matter counterpart but with the opposite charge
7
Q
Atomic Mass Unit (u)
A
- The unified atomic mass unit (u) is roughly equal to the mass of one proton or neutron:
- 1 u = 1.66 × 10−27 kg
- It is sometimes abbreviated to a.m.u
8
Q
The term nuclide
A
is used to refer to a nucleus with a specific combination of protons and neutrons
9
Q
The term nucleon
A
is the used to mean a particle in the nucleus – i.e. a proton or neutron
10
Q
Isotopes
A
- An isotope is an atom (of the same element) that has an equal number of protons but different number of neutrons
- Remember, the neutron number of an atom is found by subtracting the proton number from the nucleon number
- Since nucleon number includes the number of neutrons, an isotope of an element will also have a different nucleon/mass number
- Since isotopes have an imbalance of neutrons and protons, they are unstable. This means they constantly decay and emit radiation to achieve a more stable form
11
Q
AZX Notation
A
- The top number A represents the nucleon number or the mass number
- Nucleon number (A) = total number of protons and neutrons in the nucleus
- The lower number Z represents the proton or atomic number
- Proton number (Z) = total number of protons in the nucleus
12
Q
Conservation of Nucleon Number & Charge
A
- Nuclear processes such as fission and fusion are represented using nuclear equations (similar to chemical reactions in chemistry)
- The number of protons and neutrons in atom is known as its constituents
13
Q
what does this equation represent?
A
- The above equation represents a fission reaction in which a Uranium nucleus is hit with a neutron and splits into two smaller nuclei – a Strontium nucleus and Xenon nucleus, releasing two neutrons in the process
- In nuclear equations, the nucleon number and charge are always conserved
- This means that the sum of the nucleons and charge on the left hand side must equal the sum of the number of nucleons and charge on the right hand side
- In the above equation, the sum of the nucleon (top) numbers on both sides are equal
235 + 1 = 236 = 90 + 144 + 2 × 1
- The same is true for the proton (bottom) numbers
92 + 0 = 92 = 38 + 54 + 2 × 0
- By balancing equations in this way, you can determine the nucleon, proton number or the number of missing elements
14
Q
Balancing the number of nucleons shows that 3 neutrons must be released in the reaction
A
15
Q
Alpha, Beta & Gamma Particles
A
- Some elements have nuclei that are unstable
- This tends to be when the number of nucleons does not balance
- In order to become more stable, they emit particles and/or electromagnetic radiation
- These nuclei are said to be radioactive
16
Q
Alpha (α) particles
A
- are high energy particles made up of 2 protons and 2 neutrons (the same as a helium nucleus)
- They are usually emitted from nuclei that are too large
17
Q
Beta (β−) particles
A
- are high energy electrons emitted from the nucleus
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Beta (β+) particles are high energy positrons (antimatter of electrons) also emitted from the nucleus
- β− particles are emitted by nuclei that have too many neutrons
- β+ particles are emitted by nuclei that have too many protons
18
Q
Gamma (γ) rays
A
- are high energy electromagnetic waves
- They are emitted by nuclei that need to lose some energy
19
Q
When radiation passes close to atoms, it can knock out electrons, ionising the atom
A
20
Q
The properties of the different types of radiation are summarised
A
- u is the atomic mass unit (see “Atomic Mass Unit (u)”)
- e is the charge of the electron: 1.60 × 10-19 C
- c is the speed of light: 3 × 108 m s-1
21
Q
Neutrino Emission
A
- An electron neutrino is a type of subatomic particle with no charge and negligible mass which is also emitted from the nucleus
- The anti-neutrino is the antiparticle of a neutrino
- Electron anti-neutrinos are produced during β– decay
- Electron neutrinos are produced during β+ decay
22
Q
Alpha particles have discrete energy levels whilst beta particles have a continuous range of energies
A
23
Q
When the number of β particles is plotted against kinetic energy, the graph shows
A
- a curve
- This demonstrates that beta particles (electrons or positrons) have a continuous range of energies
- This is because the energy released in beta decay is shared between the beta particles (electrons or positrons) and neutrinos (or anti-neutrinos)
- This was one of the first clues of the neutrino’s existence
- The principle of conservation of momentum and energy applies in both alpha and beta emission
24
Q
Alpha Decay
A
- Alpha decay is common in large, unstable nuclei with too many protons
- The decay involves a nucleus emitting an alpha particle and decaying into a different nucleus
- An alpha particle consists of 2 protons and 2 neutrons (the nucleus of a Helium atom)
- When an unstable nucleus (the parent nucleus) emits radiation, the constitution of its nucleus changes
- As a result, the isotope will change into a different element (the daughter nucleus)
25
***Alpha decay equation***
* When an alpha particle is emitted from a nucleus:
* The nucleus loses 2 protons: **proton number decreases by 2**
* The nucleus loses 4 nucleons: **nucleon number decreases by 4**
26
***Alpha decay produces a daughter nucleus and an alpha particle (helium nucleus)***
27
β– decay
* A β– particle is a high energy electron emitted from the nucleus
* β– decay is when a **neutron turns into a proton emitting an electron and an anti-electron neutrino**
* When a β– is emitted from a nucleus:
* The number of protons increases by 1: **proton number increases by 1**
* The total number of nucleons stays the same: **nucleon number remains the same**
28
***Equation for beta minus emission***
29
β+ decay
* ***A β+ particle is a high energy positron emitted from the nucleus***
* ***β+ decay is when a proton turns into a neutron emitting a positron (anti-electron) and an electron neutrino***
* ***A β+ particle is a high energy positron emitted from the nucleus***
* ***β+ decay is when a proton turns into a neutron emitting a positron (anti-electron) and an electron neutrino***
30
***Equation for beta plus emission***
* When a β+ is emitted from a nucleus:
* The number of protons decreases by 1: **proton number decreases by 1**
* The total number of nucleons stays the same: **nucleon number remains the same**
31
**Fundamental Particles: Quarks**
* Quarks are **fundamental particles** that make up other subatomic particles such as **protons and neutrons**
* Protons and neutrons are in a category of particles called **hadrons**
* Hadrons are defined as any particle made up of quarks
* **Fundamental** means that quarks are not made up of any other particles. Another example is electrons
* Quarks have never been observed on their own, they’re either in pairs or groups of three
* There are six flavours (types) of quarks that exist
32
***The six flavours of quarks***
33
**Properties of Quarks**
* The charge of a hadron is determined by the sum of the charges of its quarks
* Each flavour of quark has a certain relative charge:
34
***Each flavour of anti-quark has a charge of either -⅔e or +⅓e. The quark composition of anti-protons and anti-neutrons changes to anti-quarks***
35
**Fundamental Particles: Leptons**
* **Leptons** are a group of **fundamental** (elementary) particles
* This means they are not made up of any other particles (no quarks)
* There are six leptons altogether:
* The muon and tau particle are very similar to the electron but with slightly larger mass
* Electrons, muon and tau particles **all** have a charge of -1e and a mass of 0.0005u
* There are three **flavours** (types) of neutrinos **(electron, muon, tau)**
* Neutrinos are the most abundant leptons in the universe
* They have **no charge** and **negligible** mass (almost 0)
* Leptons interact with the weak interaction, electromagnetic and gravitational forces
* However, they do **not** interact with the strong force
* Although quarks are fundamental particles too, they are not classed as leptons
* Leptons do **not** interact with the strong force, whilst quarks do
36
**Quark Composition: Protons & Neutrons**
* Protons and neutrons are **not** fundamental particles. They are each made up of three quarks
* **Protons** are made up of **two up quarks and a down quark**
* **Neutrons** are made up of **two down quarks and an up quark**
37
**Baryons & Mesons**
* **Hadrons** are the group of subatomic particles that are made up of quarks
* These may be either a:
* **Baryon (3 quarks)**
* **Meson (quark and anti-quark pair)**
38
Anti-hadrons can be either
* **Anti-baryons (3 anti-quarks)**
* **Anti-meson (quark and anti-quark pair)**
39
Note that all baryons or mesons have
* integer (whole number) charges eg. +1e, -2e etc.
* This means quarks in a baryon are either all quarks or all anti-quarks. Combination of quarks and anti-quarks don’t exist in a baryon
* The anti-particle of a meson is still a quark-antiquark pair. The difference being the quark becomes the anti-quark and vice versa
40
**Quark Composition: β– & β+ decay**
* Beta decay happens via the **weak interaction**
* This is one of the four fundamental forces and it’s responsible for radioactive decays
41
Quark Composition: β– decay
* Recall that **β– decay is when a neutron turns into a proton emitting an electron and anti-electron neutrino**
* More specifically, a neutron turns into a proton because a **down quark turning into an up quark**
42
Quark Composition: β+ decay
* Recall that **β+ decay is when a proton turns into a neutron emitting an positron and an electron neutrino**
* More specifically, a proton turns into a neutron because an **up quark turns into a down quark**
