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AQA A level Physics > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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1
Q

What was the Plum Pudding model of the atom

A
  • Put forward in 1903

- Uniform sphere of positive charge and negatively charged electrons imbedded

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2
Q

What was the Rutherford experiment and explain how it was conducted

A
  • The experiment aimed to investigate the scattering of alpha particles by a thin foil of gold
  • An Alpha source was placed in a long thin lead lead container to produce a well-directed beam of alpha particles
  • Over a period of months the number of alpha particles were counted
  • The vast majority of alpha particles were deflected through very small angles, but some were deflected through angles of around 150 degrees or more
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3
Q

Why was gold chosen in the Rutherford experiment

A
  • It can be hammered into very thin sheets
  • Need for it to be only a few atoms thick
  • Prevent multiple deflections
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4
Q

What were the conclusions from the Rutherford experiment

A
  • The atom has a very small positively charged nucleus
  • The positive charge on the nucleus is responsible for the repulsive force causing the alpha particle to change direction
  • The fact such few particles undergo large deflections suggests that the nucleus is much smaller in diameter than the atom
  • Nucleus contains nearly all the mass of the atom
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5
Q

Explain the nature of alpha particles

A
  • Alpha particles are the nuclei of helium atoms
  • made up of two protons and two neutrons
  • strongly ionising
  • travel a few cm in air
  • Can be stopped by a thick piece of paper
  • deflected slightly in strong electric/magnetic fields
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6
Q

Explain the nature of Beta particles

A
  • Fast moving electrons (travel just less than speed of light)
  • much less ionising than Alpha particles
  • travel several metres in air
  • absorbed by aluminium
  • deflected through large angles in electric/magnetic fields
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7
Q

Explain the nature of Gamma rays

A
  • Electromagnetic photons
  • neutral emissions
  • not deflected in electric/magnetic fields as they are not charged
  • very weakly ionising
  • very penetrating
  • intensity reduced by a few cm of lead
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8
Q

Explain what is meant by the term background radiation

A

The naturally occurring radiation emitted from rocks in the earth such as uranium, thorium, radon and potassium

  • cosmic rays
  • plants
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9
Q

Explain the inverse square law for gamma radiation

A

Gamma radiation behaves like any other electromagnetic radiation, in that it spreads out symmetrically in all directions from its source. The intensity of a light source obeys an inverse square law.

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10
Q

Why is ionising radiation dangerous for the body

A

it can change the chemistry in our bodies through producing ions. The functions of enzymes can be altered, cells can be damaged and mutations can occur to our DNA, which can lead to cancer.

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11
Q

Which radiation source is the most damaging to the body

A

Alpha particles is the most damaging yo our bodies because many ions are produced in a small volume.

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12
Q

What precautions can be taken to minimise the effects of radiation on the body

A
  • Sourced kept in lead-lined box and locked away in metal cupboards
  • Sources only used for short period of time
  • Sources kept away from the body and handled with long tongs
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13
Q

What is the decay constant

A

The decay constant lamda is the probability of a nucleus decaying per unit time

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14
Q

Why does the decay constant equation have minus sign

A

number of radioactive nuclei in a sample decrease with time

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15
Q

What is the Activity of a radioactive source

A

The number of disintegration per second

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16
Q

Define Half Life

A

One half-life is the time taken for half of a sample of radioactive nuclei to decay

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17
Q

Explain why the neutron number of elements increases at a faster rate than the proton number

A

As the nucleus grows, the number of neutrons required to maintain stability of the electrostatic forces between the protons increases at a faster rate than the protons

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18
Q

What happens to a nucleus when it decays

A

emits radiations which change the nucleus

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19
Q

Explain Alpha emission

A

In alpha decay, the atomic number goes down by 4, while the proton number goes down by 2. This is because an alpha particle is made of of two protons and two neutrons.

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20
Q

Explain Beta emission

A

In B- decay a neutron will be converted into a proton as the elements has too few to be stable. While in B+ a Proton will be converted into a neutron. This pushes the elements towards the line of stability.

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21
Q

Explain how Iodine destroys cells in the thyroid gland

A

B- particle are highly ionising. Ionisation damages the cells by creating acids which can denature DNA

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22
Q

Radiation from Iodine can be detected outside the body. Explain how this is possible

A

Most of the Beta- particles will be stopped by the body

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23
Q

What is a metastable state

A

When an atom or nucleus is in a metastable state, it exists for an extended time in a state other than the systems state of least energy

metastable nuclei lose their energy by radioactive decay, usually by gamma radiation

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24
Q

Explain binding energy and how it links into the mass defect theory

A
  • Binding energy is the energy that corresponds to the mass defect
  • The mass of the protons and neutrons is not equal to the mass of the atom
  • The difference between the two is called the mass defect
  • When this difference is converted into energy this energy is called the binding energy that holds the atom together
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25
Q

Explain how nuclear fusion occurs.

A
  • Light nuclei can join together by nuclear fusion, form a new element and release energy
  • Nuclear fusion occurs naturally in stars
  • It occurs as very high temperatures give nuclei enough kinetic energy to overcome the electrostatic repulsion between the protons in the nucleus. The high density inside the star’s core forces nuclei so close together that the strong force becomes involved
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26
Q

How can a charged gold leaf be used to illustrate the strong ionising power of Alpha radiation

A
  • An alpha source is held above above a positively charged electroscope
  • Alpha particles produce positive and negative ions
  • positive charged ions are repelled by the positively charged electroscope
  • negative ions are attracted to the electroscope and it is discharge

-

27
Q

How can you work out the number of atoms in an element

A

Avrogrados Constant / atomic mass

28
Q

Equation for power

A

Power = A x energy of each particle (x1.6x10^-19)

29
Q

How would you calculate the number of atoms in 40g of Lanthanum 139

A

Avrogrados constant x mass/ (atomic mass)

so.. (6x10^23) x (40/139)

30
Q

Explain how nuclear fission can be used to generate power

A

Fission reactions are established in the nuclear fuel using neutrons travelling slowly enough to be captured when they are fired at U-235 nuclei.

This U-235 nucleus captures a neutron, becomes very unstable, and splits into two or more smaller pieces, and releases energy in the form of heat

Each fission reaction produces 2,3 or 4 neutrons which may be absorbed by other U-235 nuclei if the neutrons are made to travel slowly enough

Called a chain reaction

31
Q

Why do neutrons need to be travelling slowly and how is this achieved in a nuclear reactor

A

Neutrons produced move so fast they are unlikely to be absorbed in uranium nuclei, so they must be slowed down.

The moderator slows neutrons down so they pass through materials like graphite or water

Fast neutrons repeatedly collide with nuclei in the moderator, exiting the nuclei to higher energy levels

The fast neutrons lose energy during these collisions and slow down through elastic collisions

These are called thermal neutrons

Graphite and heavy water are sustainable materials as they do not absorb neutrons

32
Q

What is the purpose of the control rods in a nuclear reactor

A
  • Control rods control the rate of reactions in the reactor

- Materials such as born steel and cadmium absorb neutrons without undergoing fission

33
Q

What is the purpose of the coolant in a nuclear reactor

A

Coolants are fluids that absorb heat from the reactor to drive the turbines that generate the electricity and prevent the reactor from overheating. Most of the UK’s nuclear reactors use carbon dioxide as a cooler.

34
Q

What is the critical mass

A

Chain reactions are only sustainable with a minimum amount of fuel, called the critical mass

35
Q

Describe how you would perform an experiment that demonstrates that gamma radiation obeys inverse square law

A 
use of GM tube + counter/rate-meter (1)
measurement of count rate (1)
at range of distances + suitable ruler or tape measure (1)
specifies suitable range (1)
determines background & corrects (1)
safety precaution given (1)
graph of count rate or corrected count rate against 1/d
2
(1)
36
Q

Explain why gamma radiation obeys an inverse square law but alpha and beta radiation do not

A 
gamma not absorbed (1)
spreads uniformly from a point
source/spherically symmetrically (1)
area over which it spreads is proportional
to radius squared (1)
37
Q

What is A in the nuclear radius equation

A

Nucleon number

38
Q

What is the equation for binding energy per nucleon

A

total binding energy/ number of nucleons

39
Q

What are the three different types of nuclear waste

A
  • Low-level waste - accounts for 90% of waste such as clothing worn by workers etc. but only accounts for 1% of radioactivity.
  • Intermediate waste - chemical sludges and resins produced during the power station decomissioning accounts for 7% of the volume of nuclear waste, and 4% of the radioactivity
  • High-level waste - fuel rods - makes up 95% of the radioactivity. - rods kept under water which acts as a coolant and a shield from the radiation - then process of vitrification required which mixes high level waste with molten gas then solidifies it in molten containers.
40
Q

Explain the risks and benefits of nuclear power stations

A

Nuclear power stations generate electricity using fission reactions, no smoke or greenhouse gasses are emitted

Death rate in coal mining and oil and gas extraction is high, legislation is not constant across the world.

Quantity of waste produced during nuclear power generation is small in comparison to the amounts from other methods of generating electricity

Nuclear is very reliable

Uranium miners take huge risks

Radioactive waste is very dangerous

New nuclear reactors are extremely expensive to build

41
Q

What is the binding energy

A

Energy needed to separate the nucleus into its constituent nucleons

42
Q

What is meant by a thermal neutron

A

A slow moving neutron that can be absorbed by uranium 235

43
Q

What is u for a proton

A

1.00728

44
Q

What is u for a neutron

A

1.00867

45
Q

What are some problems faced dealing with nuclear waste

A

In liquid form the (high level) waste may leak hence the need to vitrify
(and barrel in steel)
The waste will be radioactive for hundreds/thousands of years so storage
needs to be stable in a container hence the need to vitrify (and barrel in
stainless steel)
The waste will be radioactive for hundreds/thousands of years so long
term storage needs to be in geologically stable areas (deep
underground).
Transporting waste presents a potential danger to the public so waste is
transported enclosed in impact/crash resistant/extra thick and strong
casings Or processed onsite or nearby.

46
Q

Give the order of the decay chain

A

Th - Ra - Ac - Rn - Po - Pb - Bi - Ti

47
Q

What is positron emission

A

Beta + decay - Occurs when unstable neutron-poor nuclei require more neutrons to gain stability.

proton converted into a neutron plus a positron and neutrino

48
Q

How does K-capture decay occur

A

P+e- =n + ve

49
Q

How can technetium -99m be used as a Gamma source in medical diagnosis

A

It has a very short half life of 6 hours and produces a relatively high activity but for a short amount of time.

50
Q

In the binding energy v nucleon number graph, what elements are in the region of greatest stability

A

Fe and Cu as they have the greatest binding energies, Fe being the most stable of the two

51
Q

On the binding energy v nucleon number graph - which elements will undergo nuclear fusion and which elements will undergo nuclear fission?

A
  • Nuclei with low mass numbers may undergo nuclear fusion, where light nuclei are joined together under certain conditions so that the final product may have a greater binding energy per nucleon.
  • Nuclei with high mass numbers may undergo nuclear fission, where the nucleus split to give two daughter nuclei with the release of neutrons. The daughter nuclei will possess a greater binding energy per nucleon.
52
Q

What factors affect the choice of materials in a nuclear reactor

A

coolants - must have a high specific heat capacity

moderator - low cross section for neutrons, they don’t absorb - they take kinetic energy

Control rods - must easily absorb neutrons

53
Q

What range does thermal neutrons have energy in

A

infrared range

54
Q

What interaction occurs between alpha particles

A

electrostatic repulsion

55
Q

What is the difference between B- and B+ decay

A

B- always a Neutron first

B+ always a proton first

56
Q

What must half life always be calculated in

A

Half life is always measured in seconds

57
Q

What is meant by the random nature of decay

A

Which atom decays at what time is chance

58
Q

what is meant by electron capture

A
  • When an electron in the k shell is captured by a proton in the nucleus converting it into a neutron
59
Q

Why would an isotope of Uranium 235 decay by alpha emission faster than an isotope of Plutonium 239

A

because there is an inverse relationship between half–life and alpha particle energy

60
Q

Give the conclusions made on nuclear density and the average separation of particles in an atom

A
  • both nuclear density and separation is constant
61
Q

What is the nucleon and proton number of uranium

A

232 - 92

62
Q

What is meant by induced fission

A

a neutron strikes the nucleus and it splits into two fragments

63
Q

What is the relationship between KE and PE

A

loss in k.e. = gain in p.e.

AQA A level Physics (17 decks)

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