IB Physics Topic 7

Quarks

-distinct group of subatomic particles
-up,top,charm
-down,bottom,strange

Leptons

-distinct group of subatomic particles
-electron,muon,tau
-electron neutrino, muon neutrino, tau neutrino

Protons and neutrons are made up of...

Quarks
(Which qualify as baryons)

Baryons

Particles containing three quarks or three antiquarks

Mesons

Particles containing exactly a quark and an antiquark

Hadrons

Any particle made from quarks and/or antiquarks

Electromagnetic force:

-mediated by photons, y
-does not act upon neutrinos

Strong nuclear force

-mediated by gluons, g
-acts upon only quarks

Weak nuclear force

-mediated by W+ bosons, W- bosons, Z0 bosons
-acts upon all matter particles

Gravitational force

-particle physics can't explain it
-acts upon all matter particles (everything with mass)

Matter particles

------>------ (move forwards in time)

Antimatter particles

------

Exchange particles

~~~~~~~~~~~~~

Vertex

-intersection of two arrows and one wiggly line
-one arrow must point in and the other must point out of the vertex

Bound electrons

Are attached to a nucleus by electric attraction
-bound by an electric force

Electronvolt

-a unit of energy
-the energy an electron gain when moved across 1 V of potential difference

How are energy levels described?

As discrete or quantized
-the electron's energy levels are not continuous

What does absorb a photon mean?

Go up a level

An electron the reaches the highest energy level (0eV) is...

Free and the atom in ionized

An electron is bound to the atom as long as its energy...

Is negative

What does release a photon mean?

Go down a level

Ground state

The first/lowest energy level (n=1)

Excited states

Higher energy levels (n > 1)

If a bound electron is struck by a photon whose energy doesn't match any of the energy changes between the electron's discrete energy levels, then...

The photon won't be absorbed by the electron

An electron jumping between discrete energy levels produces...

Discrete emission and absorption spectra

Explain why only certain colors are emitted from a hydrogen atom when its bound electron is repeatedly excited.

-certain photons' frequencies don't fit the discrete energy levels of a hydrogen atom

Nucleus of an atom

Contains neutrons (N) and protons (Z)

Because neutrons and protons are both in the nucleus, they are called...

Nucleons (A)

Element

Nucleus with a particular number of protons

Nuclide

A nucleus with a particular number of protons and neutrons

Isotopes

A particular element which all have the same number of protons but different numbers of neutrons

State two differences between the electrostatic/Coulomb/electric force and the strong force.

-Coulomb is long range, nuclear is short range
-coulomb can be repulsive but strong is attractive
-electric force acts on charged particle but nuclear forces act on nucleons

How do the forces acting between two extremely close protons compare with the forces acting between two distant protons?

-when they're close together strong force dominates
-when they're far away electric force dominates

Explain why larger nuclei need more neutrons than protons in order to b e stable.

-the strong nuclear force is short range and attractive whereas the electric force is long range and repulsive
-in smaller nuclei, the protons are so close the electric repulsion between protons is overcome by the attractive nuclear force
-in larger nuclei, the electric repulsion is not overcome by the strong nuclear force because protons are spread over larger distances
-so, in larger nuclei, a greater proportion of neutrons is needed for stability

Unified atomic mass (amu)

One-twelfth the mass of a carbon-12 atom

Mass and energy are equivalent; therefore...

All energy has an associated mass and all mass has an associated energy
-revealed through the equation E=mc^2

When nucleons join together to form a nucleus...

The individual nucleons lose some of their mass, which is converted into a gamma ray photon

A nucleus which is bound always has _________ energy and _______ mass than the free nucleons collectively (when unbound)

Less

Mass defect/deficit

The mass lost when a nucleus forms

The mass lost and its equivalent energy is release as a...

Photon

Binding energy

-The total energy released when a nucleus is formed from its nucleons
-the total energy required to completely separate the nucleons
-the energy equivalent of the mass defect

How is stability measured?

Using the binding energy per nucleon

Steps for calculating binding energy

1) calculate the mass parts (*remember to multiply the mass by the number of particles)
2) calculate the difference between the mass parts and the amu
3) multiply this value by the correct conversion factor to find the BE

The higher the binding energy per nucleon...

The more stable the nucleus

Radioactive decay

When some nuclei are unstable so they spontaneously emit an alpha particle, beta particle, or gamma ray photon

What does "spontaneous" mean?

The decay occurs without any influence from the external environment and without any input of energy

Alpha particle

4^ He 2
-has no electrons

Alpha decay

A heaver nucleus emit an alpha particle
-atomic number and mass number are conserved
-mass and energy are not conserved

Parent nucleus

The nucleus before the decay

Daughter nucleus

The bigger nucleus after the decay

Negative beta particle

An electron with no mass and a proton number of -1

Positive beta particle

Anti-electron/positron with no mass and a proton number of +1

Negative Beta Decay

-emit an electron and an antineutrino
-within the nucleus one of the neutrons transmutes into a proton

Positive Beta Decay

-emit a positron and a neutrino
-within the nucleus, one of the protons transmutes into a neutron

In gamma decay...

The parent nucleus does not transmute or change identity as it does in beta and alpha decay

Gamma Decay

-the parent nucleus simply loses some energy and mass which is emitted as a gamma ray photon (high energy)
-sometimes occurs with alpha or beta decay

In all radioactive decays...

Mass-energy and momentum are conserved

Half-life

The time it takes for half of a sample of a radioactive substance to decay

Range/Penetration and Ionizing Ability of alpha, beta, and gamma radiation:

a: stopped by a piece of paper(1), strongest ionising ability because highly charge and big mass
B: stopped by tin foil(2), medium ionising ability because they have less charge and smaller mass
y: stopped by several cm of lead(3), weakest ionising -> can only cause 1 ionisation

Explain why a particle that is highly ionising has a short range

-because it come into contact with more particles it begins to ionise sooner and at a shorter range
-the more interactive/ionising the emission, the quicker it loses its energy and stops

Natural transmutation

Alpha, beta, gamma decay
-spontaneous

Artificial transmutation

Requires energy/bombardment by other particles

Fusion

-what occurs in stars (like the Sun)
-it is extremely difficult to produce in a laboratory setting
-energy is released
-produces a bigger nucleus from smaller nuclei
*usually has H in the reactants

Fission

-what occurs in nuclear reactors/power plants
-the two main fission products must be roughly equal-sized
-one or more free neutron must be produced
-energy must be released

Conclusion of Geiger-Marsden-Rutherford Experiment

-nucleus is dense and positively charged
-most of the atom is empty space

Analysis of electron scattering, showed that protons contained...

3 scattering centers (evidence for Quarks)

Are neutrinos affected by electromagnetic fields?

No because they don't have charge

When a matter particle and its exact antimatter counterpart collide they....

Annihilate producing 2 gamma ray photons

Exchange particles/bosons

Transmit forces across empty space

Four fundamental forces

-electromagnetic force
-strong nuclear force
-weak nuclear force
-gravitational force

Electromagnetic force carrier

-photons, y
-acts upon all but neutrinos

Strong Nuclear Force

-gluons, g
-acts upon only quarks

Weak Nuclear Force

-W+, W-, Z0
-acts upon all matter particles

Gravitational Force

-can't be explained by particle physics
-acts upon everything with mass

Standard model

The theory that uses quarks, leptons, and exchange particles to explain the four fundamental interactions and all types of particles

Higgs Field

Gives mass to all exchange particles (except g and y, which are massless)

Pair production

When a photon interacts with a nucleus to spontaneously convert into a matter particle-antimatter particle pair

A strange quark can only decay by what force?

Weak force

Neutron

Udd

Proton

Uud

Confinement

-states that quarks are confined and cannot exist by themselves
-this is because when 2 quarks in a meson, for example, are being separated, as the separation distance increases so does the energy in the gluon field. Once enough energy is built up, it reaches the threshold for pair production where the stored energy converts into a new antiquark-quark pair. Therefore, a quark can never be separated and exist by itself due to the conditions which confine it.

List the four fundamental forces in order of decreasing strength:

-strong nuclear forces
-electromagnetic force
-weak nuclear force
-gravitational force