Particle

Question 1

Why do particles curve in opposite directions, during pair production?

Answer 1

In order to conserve momentum

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Question 2

Summarise the discovery of the positron.he

Answer 2

• Path of alpha + beta particles using a cloud chamber ( Transparent container with air saturated with vapour + made cold.) -same conditions as in the high atmosphere)
• Ionising particles leave a visible trail of liquid droplets as they pass through the air - like a jet plane passes a clear sky.
• Carl Anderson 1932, used cloud chamber + camera to photo cosmic rays, see if particles could pass lead chamber.
• With magnetic field applied, charged particles bend in field.
  1) Positive particle deflected by magnetic field opposite directive to a (-) travelling in same direction
  2) Slower it went = more it bends

Question 3

What are gamma ray characteristics?

Answer 3

• Massless
• no charge
• infinite range

Question 4

Role of exchange particles?

Answer 4

-transfer energy, momentum + force

Question 5

Quark?

Answer 5

-Energy required to pull 2 quarks apart is massive (Quark + antiquark are created)

Question 6

How can isotopic data be used?

Answer 6

-To calculate approximate age of organic matter. -EG: % of carbon (radioactive carbon -14 present in object

Question 7

When can alpha decay occur?

Answer 7

• Unstable nucleus

- cant occur if proton no. Is too small

Question 8

When does Beta minus decay occur?

Answer 8

• Isotopes or neutron rich nucleus

Question 9

Explain why there must be a strong nuclear force?

Answer 9

Electrostatic repulsion > (much greater) than gravitational attraction. Without another force, SNF, the nucleus would fly apart.

Question 10

Why does a a nucleus undergo nuclear decay?

Answer 10

• AS forces in a nucleus only have a range of a few fm, so struggle to hold large nuclei together. Making nuclei unstable

Question 11

Explain how neutrino was hypothesised as a result of beta decay?

Answer 11

• Using a cloud chamber to observe tracks left by alpha particles. Using Geiger counter or spark counter to measure the amount of ionising radiation at different distance from an alpha source.

Question 12

Particle of dds?

Answer 12

Particle has a charge = to -1

Question 13

Strangeness is always conserved in strong interactions: What does this tell you about the creation of strange particles.

Answer 13

Strange particles are always created in pairs.

Question 14

For pair production, why must there be a minimum energy

Answer 14

Because energy wont be conserved.
The photon must be near the nucleus because linear momentum also has to be conserved.
Both must be satisfied