Particles and radiation Flashcards
Describe the structure of an atom
-there is a massive, +ve charge located in the centre of the atom (nucleus) containing protons and neutrons
-there are e- which orbit the nucleus in fixed energy levels
What are the charges of protons, neutrons and electrons?
p- 1.60 x 10^-19 C
n- 0
e- -1.60 x 10^-19 C
What are the relative charges of protons, neutrons and electrons?
p- +1e
n- 0
e- -1e
What are the masses of protons, neutrons and electrons?
p- 1.67 x 10^-27 kg
n- 1.67 x 10^-27 kg
e- 9.11 x 10^-31 kg
What are the relative masses of protons, neutrons and electrons?
p- 1
n- 1
e- 1/2000
What is a nuclide?
a very specific nucleus, there is a specified number of protons and neutrons
What is a nucleon?
a particle from the nucleus such as a proton or neutron
What is an isotope?
nuclei with the same number of protons but different number of neutrons
What is an ion and how are they formed?
-a charged particle
-formed when there is an imbalance of electrons and protons in an atom
What is specific charge? What is its units?
the ratio of charge to mass
units- Ckg^-1
How do you work out specific charge?
specific charge (Ckg^-1) = charge of particle (C) / mass (kg)
Calculate the specific charge of a proton
charge= 1.60 x 10^-19 C
mass= 1.67 x 10^-27 kg
Divide charge by mass to get 9.58 x 10^7 Ckg^-1
List the 4 fundamental forces of particle interactions
E-M force
Gravitational force
Strong nuclear force
Weak interaction
Describe the E-M force
acts on charged particles
Describe the gravitational force
-very weak
-acts on mass
-always attractive
Describe the strong nuclear force (3)
-very strong
-short range
-acts on nucleons to bind the nucleus
Describe weak interaction (4)
-short range
-decay of particles
-does not need to conserve strangeness
-allows one quark to change into another (changes quark flavour)
What is the strong nuclear force?
a fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons
Draw a diagram showing the strong nuclear force on nucleons and label it
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/02/4.-Strong-Nuclear-Force_-Graph.png
Describe how the strong nuclear force changes as the distance between two nucleons is changed.
-for nucleon separation less than 0.5fm, the strong nuclear force is repulsive
-between 0.5fm and 3fm, the force is attractive
-beyond 3fm nucleon separation, the force is 0
Why can’t the strong nuclear force stabilise all particles?
as some unstable nuclei have too many of protons, neutrons (or both) therefore this force isn’t enough to keep them stable
What other decay could be used if the strong nuclear force doesn’t work?
alpha decay
beta minus decay
Describe alpha decay and provide a general formula for it
occurs in large nuclei, with too many of both protons and neutrons
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/08/6.2.7-GCSE-Alpha-Equation.png
What is an alpha particle?
a particle which contains two protons and neutrons, the same as a helium nucleus
Describe beta minus decay and provide a general formula for it
-occurs in nuclei which are neutron-rich
-a neutron is changed into a proton
-releases an electron and electron antineutrino
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
What are the laws of nature? (3)
-total energy is conserved
-charge is conserved
-momentum is conserved
How was the existence of the neutrino hypothesised?
the energy of particles after beta decay was lower than before, so the neutrino was introduced to account for the excess energy
Describe beta plus decay and produce a general formula for it
-occurs in nuclei which are ‘proton’ rich
-a proton is changed to a neutron
-releases a positron (anti-electron) and electron neutrino
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/08/6.2.7-GCSE-Beta-Plus-Equation.png
State two properties of the electron neutrino
-zero charge
-very low mass
What is an antiparticle?
For every type of particle there is an antiparticle which has the same rest energy and mass but all its other properties are opposite the particles such as charge
What is the antiparticle for an electron?
positron
How does E-M radiation travel? What does it do?
-travels through photons
-transfers energy
How can we work out the energy of a photon? What are the possible equations?
e= hc/λ
energy of a photon (J) = plancks constant (Js) x wave speed (ms^-1) / wavelength (m)
OR
e= hf
energy of a photon (J) = plancks constant (Js) x frequency (Hz)
What is plancks constant?
6.63 x 10^-34 Js
How can we work out power from a stream of photons?
power (W) =no. photons per sec (s^-1) x energy of a photon (J)
How can we work out rest energy?
e= mc^2
energy (J) = mass (kg) x speed of light in a vaccum^2
How is rest energy often represented?
in electron volts (eV)
How can we convert electron volts to joules?
1eV= 1.60 x 10^-19 J
What is annihilation?
when a particle and their corresponding antiparticle meet which then causes their masses to convert into energy in the form of two photons which move in opposite directions to conserve momentum
Draw a diagram showing annihilation
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What is an application of annihilation?
in PET scanners:
-done by introducing a positron-emitting radioisotope into the patient
-as positrons are released they annihilate with electrons already in the patients system,
-emits gamma photons which can easily be detected
What is pair production?
-where a photon interacts with matter and creates a particle-antiparticle pair
-any excess energy is converted into kinetic energy of the particles
Why must pair production occur near a nucleus?
to conserve momentum and energy
Why must a photon have a frequency above the min. value for pair production to occur? How can we work out the min. energy for this?
the photon energy will be greater than the sum of the energies of the particles, therefore allowing pair production to occur
2 x rest energy of particles
What are exchange particles?
particles carry energy and momentum between the particles experiencing the fundamental forces
What are the exchange particles for the fundamental forces?
E-M–> virtual photon
strong nuclear force–> pions/gluon
weak interaction–> W boson
What particles are affected by the fundamental forces?
E-M–> charged particles
strong nuclear force–> hadrons
weak interaction–> all particles
What ranges to the fundamental forces cover?
E-M–> infinite range
strong nuclear force–> short range
weak interaction–> short range
What processes is the weak interaction responsible for?
-beta decay
-electron capture
-electron-proton collision
Draw the particle interaction diagrams for beta decay, electron capture and electron-proton collision
beta minus decay:
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/Beta-Minus-Decay.png
beta plus decay:
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/Beta-Plus-Decay.png
electron capture:
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/2.3.3-Electron-Capture-and-Collision.png
electron-proton collision:
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/2.3.3-Electron-Capture-and-Collision.png
What are fundamental particles?
particles that cannot be broken down any further e.g. e-
What is a hadron?
a subatomic particle which can take part in the strong interaction (strong nuclear force)
What is the only stable hadron? What does this mean?
the proton
-all other particles will decay into a proton eventually to become stable
What are the two classes of hadrons? What is their quark content?
-baryons (3 q’s)
-mesons (q and anti-q)
What are the most common baryons?
protons and neutrons (and their antiparticles)
What are the most common mesons?
pions and kaons
What particle does a kaon decay into?
a pion
What are leptons?
group of fundamental particles
What are the most common leptons?
-electron, e–
-electron neutrino, ve
-muon, μ–
-muon neutrino, vμ
(including their antiparticles)
What are muons? What do they decay into?
known as a “heavy electron”, and muons decay into electrons
What are strange particles?
a property of particles, which shows that strange particles must be created in pairs, as strangeness must be conserved in strong interactions
How are strange particles produced and decayed?
produced through the strong interaction and decay through the weak interaction
Which properties must be conserved in particle interactions apart from the three laws of nature? (3)
-electron and muon lepton number
-baryon number
-strangeness (only for strong interaction)
What are the three types of quarks?
up
down
strange
(and their antiquarks- oppositely charged)
What is the quark content of a proton and its antiparticle?
proton- uud
antiproton- (antiquark for all quarks)
What is the quark content of a neutron and its antiparticle?
neutron- udd
antineutron- (antiquark for all quarks)
What is the quark content for a pion? (+/-/0)
π⁰ –> up, anti up OR down, anti down
π+ –> up, anti down
π- –> anti up, down
What is the acronym to check if the particle properties are being conserved?
SQUIBBLE
s- strangeness
q- charge
b- baryon number
l- electron lepton number
l- muon lepton number
e- energy
When does strangeness not need to be conserved?
if the decay is undergoing weak interaction
How do we describe a decay when the properties are/are not conserved
decay is viable
decay is not viable
What can the weak interaction do to particles? Give some examples
-changes quark type
beta minus- neutron (udd) changes into proton (uud) therefore d changes into a u
beta plus- proton changes into a neutron therefore u changes into a d
What is an electron volt? (eV)
the energy gained by an electron travelling through a potential difference of one volt
How can we convert eV into joules?
1 eV = 1.6 × 10^-19 J
What is the photoelectric effect?
when electrons are emitted from the surface of a metal after light/photons above a certain frequency is shone on it
What do we mean by threshold frequency?
the minimum frequency of the photon for electron emission to take place.
What process can be used to show particle-like behaviour of waves/light?
The photoelectric effect
What happens if you shine E-M radiation (photons) on metal above the threshold frequency?
it will instantly emit electrons (called photoelectrons)
How does the photoelectric effect work?
free electrons in the metals near to the surface absorb the energy from E-M radiation (photons) which increases their kinetic energy. if there is enough energy they can escape the surface
What does the photon model of light suggest?
-each electron can absorb a single photon (1:1) so photoelectrons only emitted if Frequency > Threshold frequency
-if intensity increases, the more photoelectrons are released per second (as long as F > Tf)
What is the work function of a metal? Show its symbol and units
the minimum energy required for electrons to be emitted from the surface of a metal
Φ, J
What is stopping potential?
the potential difference required to stop photoelectron emission from occurring with the max kinetic energy
How do we work out stopping potential from an I-V graph?
https://phys.libretexts.org/@api/deki/files/15628/CNX_UPhysics_39_02_photoexp1.jpg?revision=1
Show the equation used for Ekmax and the stopping potential. Include units
Ek(max)= eVs
where:
Vs= stopping potential (V)
e= charge of an electron (coulombs)
Ek(max)= maximum kinetic energy of emitted photons(J)
Write the photoelectric equation. Include units
hf = Φ + Ekmax
where:
hf= energy of a photon (h= plancks const., f=frequency of photon) (J)
Φ= work function (J)
Ekmax= maximum kinetic energy of emitted photoelectrons(J)
How can the photoelectric equation be presented as a graph?
Ekmax= hf - Φ
where:
h= gradient
f= x (x-axis)
Φ= c
Ekmax= y (y-axis)
Why do photoelectrons have a range of kinetic energy’s from 0≤ Ek ≤Ekmax? Refer to photons
-electrons that absorb photons at the surface can escape with the max kinetic energy
-if photons penetrate deeper into the metal, then the electrons may collide and transfer energy to the ionic lattice before escaping with a lower kinetic energy than the maximum
What do we mean by the ground state of an atom?
the lowest energy level available
How can electrons move between energy levels?
need energy:
collisions with other atoms or electrons
absorbing/emitting a photon
a physical source, such as heat
What is excitation?
when electrons are excited they move up energy levels when energy is absorbed (usually by absorbing a photon)
What is de-excitation?
when electrons are de-excited, the move down energy levels and energy is released in the form of a photon
What happens after excitation?
the electron will de-excite back down to its ground state/original energy level
What is ionisation?
when electron gains enough energy to be removed from the atom entirely
How can we work out the change in energy when electrons are excited/de-excited?
ΔE= E2-E1
(energies can also be worked out using e= hf)
Provide a real-life use of excitation. Explain how it works (7)
used in a fluorescent tube to create light
-apply high p.d. to electrodes at each end of a low pressure gas tube.
-electrons in the gas accelerate
-collisions between electrons and gas atoms occur.
-collisions cause some electrons to excite energy levels or ionize some atoms.
-excited electrons de-excite and release UV photons.
-UV photons are absorbed by atoms in the tube coating.
-electrons become excited and later de-excite in a cascade, emitting visible light.
What are the different types of line spectra?
-emission spectra
-absorption spectra
Describe how an excited gas produces a discrete emission spectrum
-electrons are excited above their ground level by collisions
-electrons later de-excite between discrete energy levels therefore releasing energy in the form of photons but with different frequencies
-these frequencies are observed in emission spectrum
Describe how a spectrum of light passing through a cool gas can result in a discrete absorption spectrum
-in a cool gas, only photons of a specific frequency are absorbed making electrons excite up energy levels
-these create gaps in the spectrum at certain frequencies where absorption occurs
Why are photon emission and absorption spectras further evidence of particle-like behaviour of light?
there is a 1:1 interaction of photons (light) and electrons
How can electrons be shown having wave properties?
electrons are able to diffract
What was De Broglie’s hypothesis about wave-particle duality?
-matter particles have a dual wave-particle nature
-these can be described as ‘matter wave’
What is De Broglie’s equation?
λ= h/mv
where:
λ= matter wavelength (m)
h= plancks constant (Js)
mv= mass (kg) x particle velocity (ms^-1)—> momentum (kgms^-1)
How and why is the diffraction affected when momentum is changed from De Broglie’s equation?
λ= h/mv
if mv increases, lower wavelength
if mv decreases, high wavelength
-the longer the wavelength, the more the light spreads out hence a larger radius is produced
-the shorter the wavelength, the smaller the radius produced
How did De Brogile provide evidence for the ‘matter waves’?
-electrons from filament are accelerated from an electric field in a vacuum
-electrons are then directed at crystalline graphite (which acts as a diffraction grating)
-the electrons then produced interference patterns from superposition showing wave-like behaviour
