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Physics > P7 > Flashcards

P7 Flashcards

1
Q

What are control rods in a reactor?

A

The control rods absorb neutrons (which are travelling between fuel rods)
within the reactor [1]. If the reaction rate gets too high, the control rods
are lowered down further into the reactor [1]. This reduces the number of
fission neutrons which go on to cause further fission reactions (and so
reduces the reaction rate and the power output of the reactor) [1].

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2
Q

What are control rods made of?

A

Boron

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3
Q

The motion of which of the following particles is responsible for nuclear (fission) chain reactions?

A

Neutrons

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4
Q

What is nuclear fusion?

A

Process of forcing the nuclei of two atoms close enough so that they form a larger single nucleus

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5
Q

How does nuclear fusion happens?

A

By making two light nuclei collide at very high speed

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6
Q

Explain how nuclear fusion in the Sun leads to creating of energy

A

The combined mass of the reactants (hydrogen-1 and hydrogen-2) is greater than the mass of the product (helium-3) [1].
The mass which appears to have been ‘lost’ (the mass defect) is actually
converted into energy (by E = m c2
) [1].

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7
Q

Energy is released in both fission and fusion reactions. How is the mass of the products and of the reactants?

A

the mass of the products is less than the mass of the reactants’.

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8
Q

What are the issues related to making fusion a useful source of energy?

A
  1. The plasma of light nuclei has to be heated at very high temperature and pressure before the nuclei will fuse. This is because the two nuclei will repel because of their positive charges. They need to approach each other at high speed
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9
Q

How is the plasma heated in a fusion reactor?

A

By passing a very big electric current through it
The plasma is contained by a magnetic field so that it does not touch the reactors wall. If it did it would get cold and fusion would stop

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10
Q

What are the potential benefits of fusion reactors vs fissions reactors?

A

Fuel for fusion reactors is easily available as heavy hydrogen and is naturally present in sea water.
Reaction product is helium, which is harmless
The energy released could be used to produce electricity

Fission uses uranium which is only found in some part of the world
Nuclear waste

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11
Q

What is Nuclear fission?

A

Splitting of the nucleus into two smaller nuclei and the release of two or three neutrons and energy

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12
Q

When does induced fission occur?

A

When a neutron is absorbed by a uranioum 235 nucleus and the nucleus splits

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13
Q

When does spontaneous fission occur?

A

Without a neutron being absorbed

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14
Q

What does a reactor core contain?

A

Fuel rods, control rods and water at high pressure

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15
Q

What is water in a reactor?

A

A moderator because it slows down the fission of neutrons

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16
Q

What are fuel rods in a reactor?

A
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17
Q

What are alpha particles made up of?

A

2 protons and 2 neutrons

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18
Q

What are the relative mass and charge of an alpha particle?

A

Mr is 4 and Relative charge is 2

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19
Q

What happens when an unstable nucleus emits an alpha particle?

A

Its atomic number decreases by 2 and its mass decreases by 4

20
Q

What is a Beta particle?

A

An electron created and emitted by a nucleus that has too many neutrons compared to its protons. A neutron changes into a proton and a Beta particle (an electron) is released

21
Q

What are the relative Mass and charge of a Beta particle?

A

Mass is effectively zero and charge is -1

22
Q

What happens when an unstable nucleus emits Beta particles?

A

Atomic number increases by 1 and mass number is unchanged (because a neutron changes into a proton). Also, The charge of the nucleus is unchanged and the mass of the nucleus is unchaged

23
Q

What are gamma emissions?

A

A gamma ray is electromagnetic radiation from the nucleus of an atom. It is uncharged and has no mass

24
Q

When are neutrons emitted?

A

Neutrons are emitted by some radioactive substances as a result of alpha particles colliding with unstable nuclei in the substance. This causes the unstable nuclei to become even more unstable and emit a neutron.

25
Q

Why do emitted neutrons pass more easily through substances than alpha and beta particles?

A

because they are uncharged

26
Q

What happens in Alpha decay?

A

Change in nucleus: nucleus looses 2 protons and 2 neutrons
Particle emitted: 2 protons and 2 neutrons emitted as an alpha particle

27
Q

What happens in Beta decay?

A

Change in the nucleus: A neutron in the nucleus is changed into a proton
Particle emitted: an electron is created in the nucleus and instantly emitted

28
Q

What are alpha particles stopped by?

A

Absorber material: thin sheet of paper
Range in air: about 5cm

29
Q

What are beta particles stopped by?

A

Aluminium sheet (about 5mm thick); Lead sheet (2-3mm thick)
Range in air: about 1m

30
Q

What are gamma particles stopped by?

A

Thick lead sheet (several cm thick). Concrete (more than 1 m thick)
In air: unlimited it spreads out without being absorbed

31
Q

What is meant by Ionisation?

A

It is the process by which the radiation from a radioactive substance can knock electrons out of atoms. The atoms become charged because they loose electrons.

32
Q

Does an object become radioactive when it is exposed to ionising radiations?

A

No, it is said to be irradiated but it does not become radioactive

33
Q

What is radioactive contamination?

A

the presence of radioactive atoms in other materials

34
Q

Why are alpha radiations more dangerous to the body than beta or gamma?

A

because alpha ionising power is much stronger

35
Q

Can ionisation cause damage to cells?

A

yes, it can damage or kill cells

36
Q

What does the seriousness of contamination and radiation depends on?

A

They can cause different harm depending on the radiation type.

37
Q

What are the most dangerous radiations OUTSIDE the BODY?

A

Beta and gamma are the most dangerous. This is becasue they can penetrate the body and reach delicate organs. Alpha cannot penetrate the skin and can be easily blocked by a small air gap. High levels of irradiation are dangerous but especially from beta and gamma

38
Q

What are the most dangerous radiations INSIDE the BODY?

A

Aplha because they do all the damage in a very localised area. So contamination rather than irradiation is more concerning when working with alpha.

39
Q

Why are beta radiation less dangerous than alpha inside the body?

A

because they are absorbed over a larger area and some pass out of the body alltogether

40
Q

Why are gamma radiation the least dangerous?

A

The mostly pass straight through the body and have the lowest ionising power.

41
Q

What does radiation do to cells?

A

Lower doses damage the cell without killing it. However they can cause mutations where cells divide uncontrollably (cancer).
High doses kill the cell

42
Q

How are radiations used in medicine? Radioactive Tracers

A

Radioactive tracers: They are used to trace the flow of a substance in the body. The tracer contains a radioactive isotope that emits gamma radiations as this can be detected outside the system. Exaple: radioactive iodine is used to see if a patient has blocked kidneys. Process:
1. Before the test patient drinks a bit of the radioactive substance
2. detector placed against each kidney
3. detector linked to a chart recorder
4. The radioactive material goes in and out a normal kidney so the reading goes up and then down
5. in case of blocked kidney the reading goes up and stays up because the radioactive substance stays in the kidney.

43
Q

Why is radioactive iodine used in radioactive tracers?

A
  1. Short half life: long enough for test to take place but decays almost completely after a few wees
  2. it emits gamma radiation so it can be detected outside the body
  3. it decays into a stable product
44
Q

How are radiations used in medicine? Gamma Cameras

A

Gamma cameras are used to take images of internal organs.
1. Patient injected with solution containing gamma emitting radioactive isotope
2. solution is absorbed by the organ
3. the camera detects the gamma radiation
4. The gamma rays passes through the holes in the thick lead grid in front of the detector
5. the detector signals are used to form an image

45
Q

Radiation to treat cancer

A

Gamma rays are directed carefully and in right dosage to kill cancer cells. Gamma is used because it can penetrate deeper into the body.

46
Q

Radiation to treat cancer

A

Gamma rays are directed carefully and in right dosage to kill cancer cells. Gamma is used because it can penetrate deeper into the body. Isotope of cobalt is used.

Physics (9 decks)

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