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Physics Unit 2 > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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0
Q

Decay is a random event. What is meant by a “random event”?

A

It happens without being provoked and we can not predict when it will happen

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1
Q

Why are some elements radioactive?

A

Because they have an unstable nucleus that only becomes stable by emitting radiation (decaying)

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2
Q

What are the five sources of background radiation?

A

Air (radon), medicine, ground, food and drink and cosmic background radiation. These make a Geiger counter click even when it is not near a radioactive source

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3
Q

Where does background radiation from air come from?

A

When uranium found in certain socks decays to form radon gas

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4
Q

What did Ernest Rutherford’s experiment consist of?

A
  • Apparatus in a vacuum chamber to prevent air molecules absorbing alpha particles
  • Detector consisting of a microscope focused in a small glass plate. Each time the alpha particle hit the plate a spot of light was observed
  • Alpha source in a lead box with a narrow hole focused on thin metal foil
  • Detector moved to different positions and the number of spots if light counted
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5
Q

What did Geiger and Marsden measure and what did they discover?

A

a) The number of alpha particles deflected per second through different angles

b) • Most of the alpha particles passed straight through the metal foil
• The number if alpha particles deflected per minute decreased as the angle of deflection decreased
• 1 in 10,000 alpha particles were deflected more than 90 degrees
• Rutherford deduced that all atoms must have a nucleus at the centre that is positively charged that repels all alpha particles and is much smaller than the atom because most particles pass through it
• It explained what happened what a nucleus emitted radiation and predicted the existence of the neutron

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6
Q

What was the plum pudding model?

A

Positively charged matter in the atom evenly spread with electrons buried inside

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7
Q

What are isotopes?

A

Atoms of the same element with different number of neutrons but the same number of protons and electrons

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8
Q

How does an unstable nucleus become stable?

A

By emitting an alpha or beta particle or by emitting gamma radiation

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9
Q

An alpha particle consists of 2 protons and 2 neutrons with a relative charge of 2+. What are they equivalent to?

A

A helium nucleus

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10
Q

What type of nucleus is a beta particle emitted from?

A

A nucleus which has too many neutrons compared to protons

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11
Q

The relative mass of a beta particle is 0 and the charge is -1

A

40 K —-> 40 Ca + 0 B

19 20 -1

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12
Q

When is gamma radiation emitted?

A

After an alpha or beta particle is emitted

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13
Q

Gamma radiation is uncharged and has no mass so it does not change the number of protons or the number of neutrons in a nucleus

A

Yes.

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14
Q

What type of material is each type of radiation absorbed by and what is their range in air?

A

Alpha - Thin sheet of paper - 5cm

Beta - Aluminium sheet (5mm) and lead sheet (2-3mm) - 1m

Gamma - Thick lead sheet (several cm) and concrete (more than 1m) - Unlimited

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15
Q

Read about how to use a Geiger counter to measure radiation

A

Yes.

16
Q

Beta radiation is easily deflected in the same away as its electrons so it contains mostly negatively charged particles.

A

Alpha radiation is defected in the other direction so consists of positively charged particles.

17
Q

Why do beta particles deflect more easily in a magnetic field at right angles to the plane of paper and an electric field between a positive and negative metal plate than alpha particles?

A

Because although alpha particles have twice the charge that beta particles do, beta particles are 8000x lighter in terms of mass

18
Q

Why is gamma radiation not deflection in a magnetic or electric field?

A

It is electromagnetic radiation so it is uncharged

19
Q

What is ionisation?

A

When radioactive substances knock electrons out of atoms and they become charged

20
Q

Why is ionisation so dangerous?

A

It can damage or kill a cell. When the cell generates more cells, the defect can be passed down

21
Q

Why is alpha radiation more dangerous in the body?

A

Because it has a greater ionising power than beta or gamma radiation

22
Q

What does “activity” mean?

A

The activity of a radioactive isotope is the number of atoms that decay per second

23
Q

As the nucleus of each unstable atom (the parent atom) decays, the number of parent atoms decreases so the activity of the sample decreases.

A

The average time taken for the count rate (and therefore the number of parent atoms) to half is always the same and is called half life

24
Q

What is half life?

A

The half life of a radioactive isotope is the average time it takes for the number of radioactive nuclei in the sample (and therefore the mass of the parent atoms) to halve, therefore meaning the count rate will drop to half of its initial value

25
Q

What is automatic thickness monitoring?

A

It is used when making a metal foil. The radioactive source emits beta radiation and the amount of radiation passing through the foil depends on the thickness of it. I the thickness increases too much, the detector reading drops and a signal is sent to the rollers to increase the pressure on the metal sheet to make it thinner again

26
Q

How do radioactive tracers work?

A

These are given to a patient and used to trace the flow of a substance through a system. To see if a patient’s kidney is blocked, the patient drinks some water containing a small amount of radioactive iodine and a detector is placed on each kidney connected to a chart recorder. The substance flows in and out of a normal kidney so the reading will go up then down. The radioactive substance won’t flow out of a blocked kidney so the reading stays high.

27
Q

Why is radioactive iodine used as a tracer to test if a patient has a blocked kidney?

A

It has a half life of eight days - long enough for the test to be done but it will decay almost completely in a few weeks.

It emits gamma radiation which can be detected easily outside of the body.

It decays into a stable product.

28
Q

What is carbon dating used for?

A

To find the age of ancient wood and other organic material

29
Q

How does carbon dating work?

A

Living wood contains a small proportion of radioactive carbon with a half-life of 5600 years. When a tree dies it no longer absorbs any radioactive carbon. We measure the count rate of the dead wood compared to that of living wood e.g. if the count rate from living wood was twice as much, the sample must be 5600 years old

30
Q

What is uranium dating used for?

A

To find the age of igneous rocks

31
Q

How does uranium dating work?

A

Each uranium atom decays into an atom of lead. We work out the age by measuring the number of atoms of uranium and lead e.g. if the ratio is 1:1, the sample must be 4500 million years old

32
Q

What happens in nuclear fission?

A

The nucleus of an atom of a fissionable substance splits into smaller fragment nuclei which can cause other fissionable nuclei to split to produce a chain reaction of fission events. Energy is released as a result of nuclear fission.

33
Q

What does a nucleus release when it undergoes fission?

A

Two or three neutrons at high speeds and energy in the form of radiation and kinetic energy of the fission neutrons and fragment nuclei

34
Q

In a nuclear fission reactor, one fission neutron from each fission event will go on to produce further fission to ensure energy is released at a steady rate in the reactor.

A

Yes.

35
Q

What fuel does a nuclear fission reactor need?

A

Most use enriched uranium which consists of non-fissionable uranium isotope U-238 and 2-3% fissionable isotope U-235. The 238s do not undergo fission but change into other heavy nuclei including plutonium-239, which can be used in other reactors

36
Q

READ TO END. I AM WAY TO TIRED RIGHT NOW. BUT YOU’RE GONNA DO GREAT!!! :) xxx

A

Yeah!!

Physics Unit 2 (4 decks)

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