18: Looking Inside the Atom Flashcards
Rutherford experiment disproved which model for the atom?
describe the model
The Thompson model or plum pudding model
atoms were a plum pudding with electrons embedded throughout a positive sphere
how do you investigate the structure of an atom
with scattering experiments
particles are accelerated to a high energy and directed at a target
there are detectors surrounding the target track to identify particles created and those scattered in coliision
Describe Rutherford’s experiment
A stream of alpha particles from a radioactive source was fired at a very thin gold foil.
The angles at which the particles were scattered were recorded
some passed straight through (so most atom is empty space)
but a few of the alpha particles bounced right back from the foil being scattered at angles greater than 90 degrees
What could Rutherford conclude after his experiment?
The atom is mainly empty space.
the core must be massive on an atomic scale to deflect alpha particles through large angles, but its much smaller than an atom as very few particles deflected through more than 90 degrees
alpha particles deflected due to electric repulsion between positively charged alpha particles and positive core in gold atoms.
The centre of the atom must have a large, positive charge. Rutherford named this the nucleus.
The nucleus must be tiny, but massive (mass).
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what happens to the deflection angle if the alpha particles are slowed down
how is scattering affected if the nuclei has less electric charge
relationship between scatter angle and inverse square law
what happens to the deflection angle if the alpha particles have more energy
if alpha particles are slowed down more would be deflected at greater angles since the nucleus would be able to turn them back more easily
nuclei of smaller electric charge scatter alpha particles less strongly
the pattern of number of alpha particles scattered at different angles fits the pattern expected from the inverse square law for electric repulsion
angle decreases and fraction deflecting through an angle decreases because the nucleus cannot deflect as easily because the deflecting force acts for less time
What did Rutherford discover about charge at the centre of the atom? How did he know?
Some of the alpha particles were deflected through large angles, so the centre of the atom must have a large positive charge to repel them.
What value do you need when you are estimating the distance of closest approach of an alpha particle that has been fired at a gold nucleus?
The alpha particles initial kinetic energy
kinetic energy of alpha particle at its closest approach
0 kinetic energy
what is electrical potential energy equal to at a large distance from the nucleus
at a large distance from the nucleus, alpha particle electrical potential energy is equal to its initial kinetic energy
equation for initial kinetic energy
charge on alpha particle
charge on gold particle
alpha: 2e = 2 *(1.6*10-19)
gold: 79e = 79 * (1.6*10-19)
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What value do you need to find the charge of the nucleus?
The atom‘s proton number, Z
What is the charge on an alpha particle?
+2e
What holds the nucleus together? What stops the nucleus flying apart due to the overall positive charge?
The strong interaction force
What are hadrons?
Particles feel the strong interaction e.g. protons and neutrons
What are hadrons made of?
Fundamental particles called quarks. Must be more than one quark
Name four different hadrons
Protons, neutrons, sigmas, mesons
Which particle is the only stable hadron?
The proton
What will all hadrons, except for protons, do?
Decay into other particles
What does the neutron decay into?
It is an unstable particle that decays into a proton
A neutron decaying into a proton is an example of what kind of decay? what is this caused by?
It is an example of beta minus decay which is caused by the weak interaction
What is the half life of a free neutron?
Half life of 15 minutes
What is a free neutron?
A neutron that isn’t held in the nucleus
Describe leptons
They are fundamental particles that don’t feel that strong interaction. They interact with other particles via the week interaction and gravity (and the electromagnetic force if they’re charged)
What are the two types of lepton we need to know about and what are the symbols?
Electrons and neutrinos
e and ν (nu)
Describe neutrinos
They have zero, or almost 0, mass and zero electric charge – so they don’t do much. Neutrinos only take part in week interactions. They can pass right through Earth without anything happening to it
What is lepton number?
The number of leptons
What is conserved in a particle reaction?
Lepton number and baryon number
Energy, charge and momentum
Classifying particles: if there is only one fundamental particle what can it be?
A fermion or a boson
Classifying particles: if the are more than one fundamental particle what is the particle?
Composite
Classifying particles: what two types of fermion can you have?
Leptons and quarks
Classifying particles: What is a composite particle composed of quarks called?
Hadron
Classifying particles: what two types of hadrons are there? What is the difference between the two?
If there are two quarks it is a meson
If there are three quarks it is a baryon
What are the six different quarks?
Up and down
Charm and strange
Top and bottom
What are the six types of leptons?
Electron neutrino, muon neutrino, tau neutrino
Electron, muon, tau
What are the four types of bosons?
Week force, strong force, photon, gluon
What is a positron?
Positrons have identical mass to electrons but they carry a positive charge
An anti-electron
Does every particle have an anti-particle? Describe the mass and charge of the antiparticle?
Yes (but not bosons). Same mass, but with opposite charge
What has a baryon number of +1?
Matter baryons
What has a baryon number of -1?
Anti-matter baryons
What has a baryon number of zero?
Anything that isn’t a baryon
What has a lepton number of +1?
Matter leptons
What has a lepton number of -1?
Antimatter leptons
What has a lepton number of zero?
Anything that isn’t a Lepton
What is the relative charge of a proton, neutron, electron, neutrino?
Proton +1
Neutron 0
Electron -1
Neutrino 0
What is the relative charge of the antiproton, antineutron, positron, antineutrino?
Antiproton -1
Anti-neutron 0
Positron +1
Antineutrino 0
What can you assume about neutrinos in particle collisions?
That they have zero mass and zero charge
From energy you can create matter and what?
Antimatter
What happens when energy is converted into mass?
You get equal amounts of matter and antimatter
What is pair production?
When you fire two protons at each other at high-speed and you’ll end up with a lot of energy at the point of impact. This energy might be converted into more particles.
If an extra proton is formed then there will always be in antiproton to go with it. It’s called pair production
What is each particle antiparticle pair produced from?
A single photon
When/where does pair production happen?
If one gamma ray photon has enough energy to produce that much mass. It also tends to happen in a nucleus, which helps conserve momentum
What is the most common pair to be produced in a proton collision? Why?
Electron positron pairs because they have a relatively low rest mass