3.2 Particles and radiation Flashcards by Oliver Stickley

What is a nucleon?

A proton or neutron

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What is the nucleon number?

The number of protons and neutrons in an atom (atomic mass)

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What is a nuclide?

A particular nucleus

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What is an isotope?

An atom with the same number of protons but a different number of neutrons

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What is the process in which isotopes can be used to find the approximate age of an object containing organic material?

Carbon dating

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What is the role of the strong nuclear force?

To keep the nucleus stable

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What particles can feel the strong nuclear force?

Hadrons

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What is the range of the strong nuclear force?

0.5 - 3 fm (x10^-15 m)
Repels hadrons <0.5 fm
Attraction up to 3 fm

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What is the specific charge of a particle?

The charge-mass ratio

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Why are some nuclei unstable?

They have too many protons, neutrons or both

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What is the word equation for β- decay?

Neutron -> proton + electron + anti-electron neutrino

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What is the symbol equation for β- decay?

n -> p + e- + (bar) Ve

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What is the quark equation for β- decay?

udd -> uud
d -> u

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What is the word equation for β+ decay?

Proton -> neutron + positron + electron neutrino

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What is the symbol equation for β+ decay?

p -> n + e+ + Ve

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What is the quark equation for β+ decay?

uud -> udd
u -> d

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What is the only difference between between a particle and its corresponding anti-particle?

They are oppositely charged (baryon and lepton number also different) (mass and rest energy is the same)

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What is the anti-particle of an electron?

Positron

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What is annihilation?

When a particle and its corresponding anti-particle collide, resulting in their masses being converted into energy
This energy, along with the kinetic energy of the two particles, is released in the form of 2 identical gamma photons moving in opposite directions in order to conserve momentum

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What is pair production?

Where a photon is converted into an equal amount of matter and antimatter

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When can pair production occur?

When a photon has an energy greater than the total rest energy of both particles, as any excess energy is converted into kinetic energy of the particles

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What are the 4 fundamental forces?

Gravity, electromagnetic, strong nuclear force and weak nuclear force

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What is the exchange particle in a weak interaction?

W boson (W+ or W-)

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What is the range of the weak nuclear force?

10^-18 m

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What does the weak nuclear force act on?

All particles

What is the exchange particle in an electromagnetic interaction?

Virtual photon (Y)

What is the range of an electromagnetic interaction?

Infinite

What does an electromagnetic interaction act on?

Charged particles

What is the range of gravity?

Infinite

What does gravity act on?

Particles with mass

What are the two classes of hadrons?

Baryons (protons, neutrons) (and antibaryons (antiprotons and antineutrons) and mesons (pions, kaons)

What is the baryon number of a baryon?

What is the charge of the up (u) quark?

+2/3 e

What is the charge of the down (d) quark?

-1/3 e

What is the charge of the strange (s) quark?

-1/3 e

What is the baryon number of the up (u) quark?

1/3

What is the baryon number of the down (d) quark?

1/3

What is the baryon number of the strange (s) quark?

1/3

What is the strangeness of the strange (s) quark?

-1

What is the quark composition of a baryon?

3 quarks

What is the quark composition of a meson?

A quark and an antiquark (baryon number of 0)

What is the quark composition of an anti-baryon?

3 anti quarks

Is the baryon number always conserved in particle interactions?

Yes

Is the lepton number always conserved in particle interactions?

Yes

What is the only stable baryon?

Proton

What is the exchange particle of the strong nuclear force?

Pion

What is the particle that can decay into pions?

Kaons

What particle decays into an electron?

Muon

How are strange particles produced?

Through the strong interaction and decay through the weak interaction (eg kaons)

In what type of interaction is strangeness always conserved?

Strong interactions

What values are conserved in all interactions?

Energy, momentum, charge, baryon number, electron lepton number, muon lepton number

What is the quark composition of K+?

Up, anti-strange

What is the quark composition of K-?

Anti-up, strange

What is the quark composition of K0?

Down, anti-strange

What is the quark composition of anti-K0?

Anti-down, strange

What is the quark composition of π+?

Up, anti-down

What is the quark composition of π-?

Anti-up, down

What is the quark composition of π0?

Up/down/strange, anti-up/anti-down/anti-strange

What are the consequences of electron capture?

The proton-rich nucleus of a neutral atom absorbs an electron from an inner shell, changing a proton to a neutron and emitting an electron neutrino

What is the photoelectric effect?

Photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it

What is the threshold frequency?

The frequency for a type of metal that allows for the photoelectric effect to happen, where the energy of a photon is equal to the work function

What is the photon model of light?

- EM waves travel in discrete packets called photons, which have an energy directly proportional to frequency - Each electron can absorb a single photon, therefore a photoelectron is only emitted if the frequency is above the threshold frequency - If the intensity of the light is increased, and the frequency is above the threshold, more photoelectrons are emitted per second

Why can’t threshold frequency be explained by wave theory?

Wave theory suggests that any frequency of light should be able to cause photoelectric emission as the energy absorbed by each electron will gradually increase with each incoming wave

What is the work function of a metal?

The minimum energy required for electrons to be emitted from the surface of a metal

What is the stopping potential?

- The potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy - Measuring it allows you to find the maximum kinetic energy of the released photoelectrons

What is ionisation?

Where electrons gain enough energy in an atom to be lost from it

What is excitation?

- When an electron doesn’t gain sufficient energy to be lost from the atom, so it is temporarily promoted to an energy level further from the nucleus - It will then fall back to its original energy level and release the energy in the form of a photon of EM energy

Describe the fluorescent tube.

- Mercury vapour inside low pressure tube - Mercury atoms are ionised (releasing more free electrons) and excited by colliding with free electrons - Mercury atoms de-excite to release ultraviolet photons - Fluorescent coating on inside of tube absorbs UV photons, exciting electrons in the coating, which de-excite to emit photons in the visible light spectrum

What is an electron volt?

The energy gained by one electron when passing though a potential difference of 1 volt

How do you convert from J to eV?

Divide by e (1.6x10^-19)

How do you convert from eV to J?

Multiply by e (1.6x10^-19)

What does each line in a line spectrum represent?

A different wavelength of light emitted

Why is a line spectrum not continuous?

It only contains discrete values of wavelength

What is the evidence for electrons in atoms only being able to transition between discrete energy levels?

Line spectra only show discrete values of wavelength, that the only photon energies emitted will correspond to

What are examples of light acting as a wave?

Diffraction and interference

What is an example of light acting as a particle?

The photoelectric effect

How and why does the amount of diffraction change when the momentum of the particle is changed?

When momentum increases, wavelength decreases, and therefore the amount of diffraction decreases, so the concentric rings of the interference pattern become closer (λ=h/mv)

What is the de Broglie hypothesis?

All particles have a wave-like nature and a particle nature, λ=h/mv

What must happen in order for experimental evidence to be validated?

Peer review

How does electron diffraction provide experimental evidence for the de Broglie hypothesis?

It showed that electrons (particles) can undergo diffraction, which can only be experienced by waves