Nuclear/Particle Physics Flashcards

Question

Roughly, how much larger is an atom in comparison to its nucleus?

Answer 1

* The diameter of an atom is 10^-10m * The diameter of a nucleus is 10^-15m * This means that the atom is around 100,000 times larger than the nucleus

Answer 2

Dalton imagined that all matter was made of tiny solid particles called atoms. His model proposed: * Atoms are the smallest constituents of matter and cannot be broken down any further * Atoms of a given element are **identical** to each other and atoms of different elements are **different** from one another * When chemical reactions occur, the atoms rearrange to make different substances

Answer 3

Thomson discovered the electron, which lead him to propose the 'plum pudding' model of the atom. In this model: * The atoms consists of positive and negative charge in equal amounts so that it is neutral overall * They were modelled as spheres of positive charge with uniformly distributed charge and density * The negatively charged electrons were thought to be stuck to the sphere like currants in a plum pudding

Answer 4

Rutherford's model came as a result of an experiment conducted by Hans Geiger and Ernest Masden to test the plum pudding model (where they fired alpha particles at very thin gold foil, but whilst these particles **should** have passed straight through, many of them were backscattered). Rutherford suggested: * Atoms have a central, positively charged nucleus containing the majority of the mass * Electrons orbit the nucleus, like planets around a star

Answer 5

Bohr simply improved on Rutherford's model by using mathematical ideas to show that electrons occupy **shells** or **energy levels** around the nucleus, which are at particular distances from the nucleus

Answer 6

Schrödinger expanded on Bohr's model further by using equations to calculate the liklihood of finding an electron in a certain position. This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is greatest and vice versa. * The atom was thought to only have a positively charged nucleus surrounded by negatively charged electrons. James Chadwick then discovered the neutron in 1932, which completes the model of the atom we know today.

Answer 7

The process of releasing **conduction electrons** from the surface of a metal when the metal gets heated (which causes the conduction electrons to gain energy to leave the surface)

Answer 8

* The photoelectric effect refers to the energy that the electrons of a metal absorb via incident **photons** a.k.a. **light energy** * Thermionic emission refers to the energy that the electrons of a metal absorb via **thermal energy**

Answer 9

The electrons may be accelerated by **electric** or **magnetic fields** (e.g. electrons may be emitted from the (negative) cathode, and accelerated to the (positive) anode)

Answer 10

v = √((2eV)/m) Where: * v = velocity of the particle (ms^-1) * e = particle charge (C) * V = potential difference (V) * m = mass (kg)

Answer 11

To accelerate charged particles to high speeds so their collisions can be used to investigate the structure of atoms and subatomic particles

Answer 12

* Ionisation (charged particles ionise atoms in a medium) * Deflection (particles can be deflected by applied electric fields inside the detector, which causes scattering of the particles)

Answer 13

Electrons within a metal that are free to move throughout the material (responsible for conducting electricity and heat).

Answer 14

The conduction electrons will gain energy

Answer 15

Rutherford/Bohr's model

Answer 16

A type of particle accelerator that accelerates ions (charged particles) to very high speeds in **straight lines**

Answer 17

* They use **electric fields** within and between metallic tubes which act as oppositely charged **electrodes** * They accelerate ions through **progressively longer** tubes * The tubes are connected to an **alternating power supply** (AC) to ensure the ions are always accelerating from one tube to the next (the ions are **attracted** to the **midpoint** of the tube, at which point the AC supply will **switch**, and the charge of the tube will repel the particle and push it towards the exit and the next tube will attract the particle. This repeats in a **straight line** until the end of the accelerator) * The frequency of the alternating current supply is **fixed** (meaning the charge of each tube switches at a constant rate)

Answer 18

The ions are **speeding up**. Lengthening the tubes allows ensurance that the ions spend the same amount of **time** under acceleration in each tube.

Answer 19

The higher-energy ions produced are used in collider experiments (to enable the investigation of the internal structure of atoms and subatomic particles)

Answer 20

A type of particle accelerator that accelerates from a central entry point around a **spiral** path.

Answer 21

* They have two hollow semicircular electrodes called '**dees**' * A uniform **magnetic field** applied **perpendicularly** to the electrodes * An **AC power supply** applied across each dee, which creates an **electric field** in the **gap** between them

Answer 22

* A source of charged particles is placed at the **centre of the cyclotron** and they are fired into one of the dees * The magnetic field in the electrode makes them follow a **circular path**, since it is perpendicular to their motion until they eventually leave the electrode * The potential difference applied between the electrode **accelerates** the ions across the **gap** to the next dee (since there is an **electric field** in the gap) * In the next dee, the ions continue moving in a circular path within the magnetic field * The potential difference is then **reversed** so the ions **again** accelerate across the **gap** * This process is repeated as the particles spiral outwards and eventually have a speed large enough to exit the cyclotron

Answer 23

* The **uniform magnetic field** inside the dees bends the particles' path into a circle * While the **electric field** in the gap **accelerates** them each time they cross **between** the dees, causing the **radius** to get **larger**

Answer 24

* Electric fields (in the gap between the dees) * Magnetic fields (inside the dees)

Answer 25

The particle transfers energy to the medium, usually by ionising atoms within it

Answer 26

The removal of one or more electrons from an atom, leaving it with a charge

Answer 27

* High-energy charged ions transfer some of their energy to surrounding atoms (as it passes through a **medium**, such as a **gas** in a **Geiger-Muller tube**) * This is usually through the process of **ionisation**, where the charged particle knocks electrons off atoms in the medium, creating ions and free electrons * The ions and electrons produced are then **accelerated** by applied **electric fields** (from the electrodes) * When these charged particles move, they create a tiny pulse of **electric current** * This electric pulse travels through the circuit to the **electronic counter** * The electronic counter counter counts each pulse (each pulse means one particle was detected passing through the medium)

Answer 28

To measure what comes from the collision of accelerated charged particles, which can be used to study what happens to these tiny particles (e.g. new particles are created, or particles bounce off of each other)

Answer 29

* When a charged particle is accelerated into a GM tube, and it travels through the tube, it passes close to atoms in the gas * The electric field of the particle is strong enough to rip electrons out of those gas atoms as they speed past (ionisation): Atom --> Positive ion + electron * This matters because the ions and electrons move to the electrodes, forming a pulse of electric current that the tube counts as a detected particle

Answer 30

* Geiger-Muller (GM) tubes * Spark chambers * Gas chambers * Cloud chambers

Answer 31

Because the magnetic force F is always perpendicular to its velocity v (where F is always directed towards the centre of orbit)

Answer 32

The magnetic force

Answer 33

F = Bqv Where: * F = centripetal force (N) * B = magnetic field strength (T) * q = charge of particle (C) * v = linear velocity (ms^-1)

Answer 34

* Starting equation: F = Bqv * Recall another equation for centripetal force: F = mv²/r * Substitute for centripetal force: mv²/r = Bqv * Rearrange for the radius: r = mv/Bq * Since mv = momentum: r = p/Bq * Therefore: r = p/Bq Where: * r = radius of orbit (m) * p = momentum of charged partice (kgms^-1) * B = magnetic field strength (T) * q = charge of particle (C)

Answer 35

* r ∝ p (particles with a larger momentum (either larger mass or speed) move in larger circles) * r ∝ 1/q (particles with greater charge move in smaller circles) * r ∝ 1/B (particles moving in a strong magnetic field move in smaller circles)

Answer 36

They can't distinguish different types of particle

Answer 37

* They can show the paths of charged particles * This means that physicists are able to interpret the characteristics of the particle

Answer 38

The particles momentum

Answer 39

The particle has a smaller momentum r ∝ p

Answer 40

The particle has a larger momentum r ∝ p

Answer 41

Velocity is decreasing (because its momentum is decreasing: r ∝ p)

Answer 42

Kinetic energy is decreasing (as velocity is decreasing due its momentum is decreasing: r ∝ p) due to **ionising** other particles in its path

Answer 43

particle-antiparticle creation

Answer 44

The charge of the particle (which can be determined using Fleming's Left Hand Rule)

Answer 45

* Their **paths** are in **opposite directions** because they are **oppositely charged** * Therefore the **magnetic force** on them is **oppositely directed** * They have the same radius because they have the same mass (and therefore the same momentum)

Answer 46

* Charge * Energy * Momentum

Answer 47

* When electrons are accelerated to very high energies, they can collide with nucleon targets * The scattering pattern is used to analyse the size and structure of nucleons * To resolve detail, like the nucleon diameter, the de Broglie wavelength of the electron must be comparable to the size of the nucleon * Note that electrons do not experience the **strong nuclear force** (therefore, they are able to get extremely close to the nucleons without interacting, which allows them to build up a better idea about the size of the nucleus than alpha particles which are comprised of protons and neutrons)

Answer 48

The de Broglie wavelength equation: λ = h/mv ≈ nucleon diameter Where: * λ = de Broglie wavelength (m) * h = Planck's constant (6.63 x 10^-34) (J s) * m = mass (kg) * v = velocity (ms^-1)

Answer 49

* The de Broglie wavelength becomes even **smaller** * This is because λ ∝ 1/v * Therefore, the faster the electrons, the smaller their de Broglie wavelength

Answer 50

* Since the de Broglie wavelength gets smaller for faster electrons, the electron wavelength can become small enough to be used to distinguish tiny features about the **internal** structure of a nucleon * Such an electron beam would be able to detect individual **quarks** inside the nucleon

Answer 51

When a particle meets its equivalent anti-particle, they both are destroyed and their mass is converted into energy in the form of two gamma ray photons (e.g. when an electron and positron collide, their mass is converted into energy in the form of two photons emitted in opposite directions)

Answer 52

When a photon interacts with a nucleus or atom and the energy of the photon is used to create a particle-antiparticle pair (e.g. When a photon with enough energy interacts with a nucleus, it can produce an electron-positron pair)

Answer 53

A nearby neutron, proton or nucleus (A body of mass that can absorb some momentum)

Answer 54

* A photon has momentum in one direction * If it just suddenly "turned into" two particles, there is no way to arrange the particle and antiparticles movements so that both energy and momentum add up to the original photon * This is why we need a third object, like a nucleus or a neutron, to absorb some of the momentum so that both energy and momentum can be conserved

Answer 55

* The photon must have energy at least equal to the total rest mass energy of the particle-antiparticle pair it creates: E_γ ≥ 2mc² * If the photon's energy is less than this, pair production cannot occur.

Answer 56

The minimum energy required to create both particles at rest Calculated by 2∆E = 2∆mc² Where: * ∆E = the rest mass energy of one particle * ∆m = the rest mass of one particle * c = the speed of light

Answer 57

The mass of a particle measured when it is at rest (not moving)

Answer 58

The energy equivalent of the particle's rest mass, given by E = mc²

Answer 59

∆E = ∆mc² Where: * ∆E = rest mass energy of the particle (J) * ∆m = rest mass of the particle (kg) * c = speed of light (ms^-1)

Answer 60

Energy can be converted into mass and vice versa

Answer 61

* The energy of a gamma photon * It is the most common type of photon that causes pair production

Answer 62

E_photon = hf **OR** E_photon = hc/λ **OR** E_photon = ∆mc²

Answer 63

1 MeV = 1 x 10^{6^{eV = 1.6 x 10^-13 J}}

Answer 64

1 GeV = 1 x 10^{9^{eV = 1.6 x 10^-10 J}}

Answer 65

∆m = ∆E/c²

Answer 66

By division of c² (due to the equation: ∆m = ∆E/c²), possible units of mass in terms of mass and energy are: * MeV/c² **OR** * GeV/c²

Answer 67

* 1 MeV/c² = 1.78 x 10^-30 kg * 1 GeV/c² = 1.78 x 10^-27 kg This works because energy and mass are related by E = mc²

Answer 68

1. Use Einstein's equation : E = mc² 2. Rearrange for mass: m = E/c² 3. Recall known values: (1 GeV = 1.6 x 10^-10 J), (c = 3 x 10⁸ ms^-1), (c² = 9 x 10¹⁶ ms^-2) 4. Substitute and calculate: m = (1.6 x 10^-10)/(c² = 9 x 10¹⁶) = 1.78 x 10^-27 kg

Answer 69

When particles have such high velocities and energies, **relativistic effects** begin to become more important

Answer 70

* Physical phenomena that occur when objects move at speeds **close to the speed of light** * These effects cause measurements of **time**, **length**, and **mass** to **differ** from those measured at **rest**, as described by **Einstein’s theory of relativity**

Answer 71

Time dilation

Answer 72

Length is measured to be **shorter** compared to when the object is at rest (Length contraction)

Answer 73

Time **slows down** (Time dilation)

Answer 74

Length contraction

Answer 75

With his theory of special relativity: * Time, length and mass can change depending on an object's speed relative to an observer * This is especially true at speeds close to the **speed of light**

Answer 76

Due to time dilation, their lifetimes appear longer in the lab, allowing them to travel further before decaying

Answer 77

Because they travel at relativistic speeds, time dilation increases their lifetimes so they can reach the surface before decaying

Answer 78

When particles move at speed greater than 90% of the speed of light

Answer 79

Particles like muons would decay too quickly and wouldn't be detected at ground level

Answer 80

**Quarks** and / or **leptons**

Answer 81

By charge and mass

Answer 82

They make up all ordinary matter

Answer 83

A composite subatomic particle made up of quarks which interacts with the strong nuclear force

Answer 84

**Baryons** and **mesons**

Answer 85

A type of hadron that consists of 3 quarks

Answer 86

A type of hadron that consists of a quark-antiquark pair

Answer 87

* Protons * Neutrons

Answer 88

* Pions * Kaons

Answer 89

The strong nuclear force

Answer 90

Either **in pairs** or **in groups of three**

Answer 91

They all have integer (whole number) charges (e.g. +1e, -2e etc.)

Answer 92

A group of **fundamental** (elementary) particles meaning they are not made up of any other particles (no quarks)

Answer 93

Through **weak**, **electromagnetic** or **gravitational** interactions

Answer 94

* The electron (e^-) * The electron neutrino (v_e) * The muon (μ^-) * The muon neutrino (v_μ)

Answer 95

The muon is 200x more **massive** than the electron m_e = 0.0005u m_μ = 0.11u Note: massive means more mass, not size

Answer 96

Exactly one twelfth the mass of a carbon-12 atom

Answer 97

1 u = 1.66 x 10^-27 kg

Answer 98

-1e Where: * e = elementary charge (1.60 x 10^-19 C)

Answer 99

-1e Where: * e = elementary charge (1.60 x 10^-19 C)

Answer 100

* The most abundant leptons in the universe * No charge * Negligible mass (almost 0)

Answer 101

* They are **uncharged** * They have zero **mass**

Answer 102

Because they mediate one of the fundamental forces (electromagnetism) (e.g. the electrostatic repulsion between two electrons is understood in terms of exchanging photons)

Answer 103

* Up quark (u) * Down quark (d) * Charm quark (c) * Strange quark (s) * Top quark (t) * Bottom quark (b)

Answer 104

Q_{up = +2/3 e}

Answer 105

Q_down = -1/3 e

Answer 106

Q_charm = +2/3 e

Answer 107

Q_strange = -1/3 e

Answer 108

Q_{top = +2/3 e}

Answer 109

Q_bottom = -1/3 e

Answer 110

The antiparticle of a quark which has the same properties but an opposite charge

Answer 111

Q_anti-up = -2/3 e

Answer 112

Q_anti-down = +1/3 e

Answer 113

Q_anti-charm = -2/3 e

Answer 114

Q_anti-strange = +1/3 e

Answer 115

Q_anti-top = -2/3 e

Answer 116

Q_anti-bottom = +1/3 e

Answer 117

A positron (Q = +1e)

Answer 118

An anti-proton (Q = -1e)

Answer 119

An anti-neutron (Q = 0)

Answer 120

An anti-neutrino (Q = 0)

Answer 121

Neutral particles (such as a neutron, neutrino or photon) is its own antiparticle since charge doesn't change

Answer 122

These values remain the same for both

Answer 123

m_p = 1.67 x 10^-27kg

Answer 124

m_anti-proton = 1.67 x 10^-27kg

Answer 125

m_n = 1.67 x 10^-27kg

Answer 126

m_anti-neutron = 1.67 x 10^-27kg

Answer 127

m_e = 9.11 x 10^-31

Answer 128

m_positron = 9.11 x 10^-31

Answer 129

m_neutrino = 0

Answer 130

m_{anti-neutrino} = 0

Answer 131

E_p = 938.26 MeV

Answer 132

E_anti-proton = 938.26 MeV

Answer 133

E_n = 939.55 MeV

Answer 134

E_anti-neutron = 939.55 MeV

Answer 135

E_e = 0.51 MeV

Answer 136

E_positron = 0.51 MeV

Answer 137

E_neutrino = 0

Answer 138

E_{anti-neutrino} = 0

Answer 139

Numbers that describe properties of particles (such as charge, baryon number, and lepton number) and must be conserved in particle interactions

Answer 140

* Charge, Q * Baryon number, B * Lepton number, L

Answer 141

The interaction **isn't possible** and therefore is **not allowed** by the laws of physics

Answer 142

The number of baryons in a particle (which shows whether the particle is a baryon, anti-baryon, or neither)

Answer 143

B = 0 (because it is **not** a baryon)

Answer 144

The baryon number must be conserved in an interaction, and therefore combining quarks and anti-quarks would lead to a baryon number that is not an integer (whole number)

Answer 145

The number of leptons in an interaction (which shows whether the particle is a lepton, anti-lepton or neither)

Answer 146

L = 0 (because it is not a lepton)

Answer 147

1. β^- decay is when a **down quark** **changes into an up quark** (this changes a neutron into a proton) 2. Charge of the left hand side of the equation (the quark composition of a neutron is udd) 3. Adding up the quark charges: +2/3 - 1/3 - 1/3 = 0 (the left hand side has a charge of 0) 4. Charge on the right hand side of the equation (the quark composition of a proton is uud) 5. Adding up the quark charges: +2/3 + 2/3 - 1/3 = +1 6. The electrons charge is -1, the anti-neutrinos charge is 0, the right hand side has a charge of +1 - 1 + 0 = 0 7. Since the charges are equal on both sides, it is conserved in the beta decay equation.

Answer 148

uud (two up quarks, one down quark)

Answer 149

udd (one up quark, two down quarks)

Nuclear/Particle Physics Flashcards

(190 cards)