deep inside the atom

Question 1

What does the Standard Model state about matter

Answer 1

all matter is composed of small elementary particles that exist on their own or in groups to form other subatomic particles, and transmit force (quantum theory states that force acting between objects is caused by force-particles travelling between them.)

Question 2

What are the three types of elementary particles?

Answer 2

• Quarks (matter particles)
• Leptons (matter particles)
• Bosons (force-mediating particles)

Question 3

What are hadrons and what types are there?

Answer 3

Hadrons are particles that consist of quark combinations and are affected by strong force (gluons) because they contain quarks.

The two types are

• Baryons are hadrons which consist of three quark particles. For example, protons and neutrons are baryons.
• Meson are hadrons which consist of two quark particles (one quark and one anti-quark). For example, pions.

Question 4

Which quarks belong in each generation?

Answer 4

Generation I: up and down quarks
Generation II: charm and strange quarks
Generation III: top and bottom quarks

Question 5

What charges do up and down quarks have?

Answer 5

Up: +2/3, Down: -1/3

Question 6

What quarks are protons and neutrons made up of?

Answer 6

a proton with +1 charge is made of two up and one down quark (uud) while a neutron is made of two down and one up quarks (udd).

Question 7

Which leptions belong in each generation?

Answer 7

Generation I: electron and electron neutrino.
Generation II: muon and muon neutrino.
Generation III: tau and tau neutrino.

Question 8

What are the four fundamental forces that the fundamental particles are held together by, mediated by bosons?

Answer 8

• Strong nuclear force which holds protons and neutrons together in the nucleus is mediated by Gluons (g).
• Weak nuclear force which interacts with particles during transmutation through beta decay is mediated by W+, W- and Zo gauge bosons.
• Electromagnetic force which exists between particles is mediated by photons (γ).
• Higgs bosons are a group of force-mediating fundamental particles that are scalar in nature. This means they have no direction, no charge, no spin but have mass.

Question 9

What are the advantages of the standard model of matter?

Answer 9

• explains the composition of sub-atomic particles and the interaction between them.
• explains how the fundamental forces are mediated through the understanding of bosons.
• provides a common understanding of force and matter.
• predicted the existence and nature of sub-atomic particles such as the muon and the Higgs boson.
• consistent with several fields of quantum physics

Question 10

What are the disadvantages of the standard model of matter?

Answer 10

• cannot explain why the mass of sub-atomic particles is greater than the sum of its constituents. For example, the mass of a proton is greater than 3 quarks combined.
• does not explain the disproportion between matter and anti-matter.

Question 11

What is the evidence that suggests that nucleons (protons and neutrons) are not fundamental particles?

Answer 11

Experiments in the early 1970s using particle accelerators showed that neutrons and protons are composed of smaller particles. Therefore, it was shown that nucleons are not fundamental particles because they are divisible like an atom.

Question 12

Outline the discovery of the muon

Answer 12

Anderson and Neddermeyer applied an external magnetic field to the cloud chamber which contained cosmic radiation. Upon interacting with molecules inside the chamber, sub-atomic particles were produced from cosmic rays. This released a particle whose deflection trail was similar to that of an electron (beta-particle). The unknown particles were deflected to the same direction as electrons, but their curvature was less sharp than that of an electron. This indicates that muons have a much greater mass than an electron.

Question 13

What is a pion?

Answer 13

Pions are examples of mesons (particles consisting of two quarks). They can be charged or neutral.

Question 14

What is a muon?

Answer 14

Muons are leptons because they do not interact with strong nuclear force.

Question 15

What is a neutrino?

Answer 15

A particle that is small and neutral in charge with an undetermined mass.

Question 16

Outline the function of a particle accelerator

Answer 16

To better understand matter, physicists examine the components of the atoms. Using particle accelerators, they separate the atom into its components by inputting large amounts of energy. This enables charged particles to be accelerated to very high velocities using electric fields and/or magnetic fields.

Question 17

What are the three main types of particle accelerators?

Answer 17

• Linear
• Cyclotron
• Synchrotron

Question 18

What is a linear accelerator and how does it work?

Answer 18

It is a long track down which a particle is propelled. Particles pass through a series of tubes where alternating electrical potentials help accelerate the particle.

Question 19

What is a cyclotron and how does it work?

Answer 19

It is a high frequency AC current is used to produce a magnetic field that causes the electron/particle to accelerate in a spiral. The charged particle is accelerated between the two semicircular regions by an electric field.

Question 20

What is a synchrotron and how does it work?

Answer 20

It is the most modern and powerful form of particle accelerators. Synchrotrons are adapted from cyclotrons but instead consist of a close circular loop path.
Synchrotrons accelerate particles using magnetic fields which increase in strength as a particle’s kinetic energy increases. Hence, the magnetic field synchronises with the particle.

Question 21

How are synchrotrons different from cyclotrons?

Answer 21

• Synchrotrons are more effective than cyclotrons because the constantly adapting magnetic fields account for a particle’s relativistic mass (also momentum). Therefore, this set-up allows particles to reach speeds just under the speed of light.
• Magnetic fields in a synchrotron change with time such that the circular path of a particle remains constant during its acceleration. This is another distinction from cyclotrons where a particle’s path change in radius (hence the need for a disk-like structure).
• Unlike cyclotrons, synchrotrons cannot accelerate stationary particles due to their sole reliance on magnetic fields. As such, linear accelerators are typically used to produce pre-accelerated particles.

Question 22

What is the role of particle accelerators and what is the advantage of a head-on collision?

Answer 22

Particle accelerators create new particles by colliding pre-existing particles head-on. The advantage of a head-on collision is that the initial total momentum is zero (or negligible) as the momentum of the particles cancel each other out. Thus, final momentum is also zero (or negligible) allowing the energy of the particles to go into a nuclear reaction.