P7 Radioactivity

Question 1

What is the difference between radiation from a radioactive substance uranium and radiation from a lamp?

Answer 1

radiation from U consists = particles, radiation from lamp =
electromagnetic waves,
radiation from U is ionising, radiation from lamp is non-ionising

Question 2

How are some substances radioactive?

Answer 2

atoms have unstable nuclei,
these nuclei become stable by emitting radiation

Question 3

What are the three types of radiation?

Answer 3

Alpha particle

Alpha
particle
- is a helium nucleus, two protons and two neutrons. It has a large mass, compared to other ionising radiations, and a strong positive charge. It has the greatest ionisation power.

Beta particle

Beta
particle
- is a fast moving electron. It has a very small mass and a negative charge.

Gamma ray
Gamma ray
- is a high-energy electromagnetic wave.
Gamma rays
are caused by changes within the nucleus. They are part of the
electromagnetic spectrum
and so travel at the speed of light. They have no mass and no charge.

Question 4

What is the electromagnetic spectrum?

Answer 4

The different types of electromagnetic radiation, arranged in order of frequency or wavelength.

Question 5

What is ionisation?

Answer 5

Process by which electrons can be added or removed from an atom to create an ion.

Question 6

Radioactive decay is a ______ event?

Answer 6

Random

Question 7

Write conclusions scientists made about the atom as a result of the discovery of electrons?

Answer 7

atoms not indivisible,
atoms contain negatively charged electrons

Question 8

What are the two differences between the plum pudding model and the nuclear model?

Answer 8

nuclear: all positive charge concentrated in nucleus much
smaller than atom, plum pudding: positive charge spread out
throughout atom,
 nuclear: most mass concentrated in nucleus, plum pudding:
mass spread out throughout atom
 nuclear: most atom empty space, plum pudding: no empty
space

Question 9

Explain why the alpha particle scattering experiment led to the acceptance of the nuclear model and the rejection of the plum pudding?

Answer 9

nuclear model explains why some alpha particles scattered through
large angles,
in plum pudding model such large-angle scattering should not be
observed

Question 10

Compare the penetrating power of the 3 types of radiation?

Answer 10

The energy of the three radiations is absorbed by the material through which the radiation passes. The amount of energy which is absorbed depends on the type of radiation and the type of the absorbing material.

The range of the alpha radiation in an absorbing material is less than that of beta or
gamma
. The alpha radiation transfers more energy to an absorber than beta or gamma radiation. Alpha radiation is absorbed by the thickness of the skin or by a few centimetres of air.
Beta radiation is more penetrating than alpha radiation. It can pass through the skin, but it is absorbed by a few centimetres of body tissue or a few millimetres of aluminium.
Gamma radiation is the most penetrating of the three radiations. It can easily penetrate body tissue. It requires several centimetres of lead or about 1 metre of concrete to absorb it.

Question 11

What are the changes during alpha decay?

Answer 11

nucleus loses 2 protons and neutrons and are emitted as an alpha particle

Question 12

What are the changes in beta decay?

Answer 12

A neutron in the nucleus turns into a proton.
An electron is created in the nucleus and instantly emitted.

Question 13

Why is ionising radiation dangerous?

Answer 13

can knock electrons from atoms,
this ionisation damages cell (or kills cell or affects genes in cell which
can be passed on if
cell generates more cells)

Question 14

What is the half life of a radioactive isotope?

Answer 14

average time for no. nuclei in sample of isotope to halve

Question 15

How to use a geiger counter to find the range of the radiation from the source of alpha radiation?

Answer 15

(place Geiger tube in a holder so it can be moved horizontally,) move
tube so end close to source and Geiger counter detects radiation from
source,
move tube gradually away from source until count rate decreases
significantly,

Question 16

What is a Becquerel?

Answer 16

In the International System of units (SI), the becquerel (Bq) is the unit of radioactivity. One Bq is 1 Decay per second (dps).

Question 17

How does a geiger muller tube work?

Answer 17

Ionising radiation enters a tube full of low-pressure gases.
It ionises the atoms in the gas, knocking electrons out of the atoms.
The gas can now conduct electricity and completes an electric circuit. Current flows between electrodes.
The current produces a clicking noise.
The count-rate is the number of decays recorded each second.

Question 18

The Geiger counter count rate decreases as the ______?

Answer 18

Activity decreases

Question 19

What is the count rate?

Answer 19

Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube.

Question 20

Example question? The half-life of cobalt-60 is 5 years. If there are 100 g of cobalt-60 in a sample, how much will be left after 15 years?

Answer 20

15 years is three half-lives so the fraction remaining will be
1/2 ^3 x 100= 12.5g

As a ratio of what was present originally compared to what was left, this would be 100:12.5 or 1:0.125

Question 21

Other ways of detecting radiation:

Answer 21

When exposed to ionising radiation, photographic film will turn from being transparent to dark and non-transparent. This effect is used by people who work with radiation in detectors called film badges.

Radiation badge closed and open, showing the layer of photographic film sealed in thin plastic.
A
photographic film
is placed inside the film badge holder. The film is already in a paper covering.

The open window allows all types of radiation through, therefore showing exposure to Beta and Gamma radiations.

Windows are plastic of different thicknesses allowing the person examining the film to tell what kinds of Beta radiation they have been exposed to. Windows 4,5 and 6 are of different metals (including lead and tin) allowing the detection of gamma rays and other ionising radiations.

The final exposure of the film will show how much and what kind of radiation the worker has been exposed to.

Film badges worn by medical personnel dealing with radiation are checked regularly.

Cloud chamber
A
cloud chamber
is a small container full of saturated water vapour (like a cloud).

Inside the chamber, ionising radiations like Alpha and Beta will be indicated by tracks in the vapour.

Large Alpha particles have short broad tracks while Beta particles have longer thinner tracks.

Question 22

What is the formula for Absorbed Dose

Answer 22

D=E/m

Absorbed dose (D) is the energy (E) absorbed per unit mass (m) of the absorbing material. The absorbed dose can be calculated by using the following relationship;

If energy is in joules (
) and mass is in kilograms (
) then the unit of absorbed dose is the gray (
) where one gray is one joule per kilogram.

It is important to use the correct mass of tissue. If the energy is concentrated on a small mass of tissue, the absorbed dose is greater.

Question 23

What is Equivalent Dose?

Answer 23

The equivalent dose is a measure of the biological effect of radiation due to several factors. The factors to take into account are as follows:

The type of radiation
The absorbed dose
The body organs or tissue that have been exposed

Question 24

What is the formula for equivalent dose?

Answer 24

Equivalent Dose (H)
is measured in Sieverts (Sv)

Absorbed Dose (D) is measured in Grays (Gy)

Question 25

What are the different radiation weighting factors (Wr) with different radiation types?

Answer 25

alpha particles-20
Beta particles-1
Gamma-1
Slow neutrons-3

Question 26

What is the formula for equivalent dose?

Answer 26

E=DxWr
E=equivalent dose
D=Absorbed dose
Wr=Radiation weighting factor

Question 27

What are natural sources of radiation?

Answer 27

cosmic rays - radiation that reaches the Earth from space
radon gas - this radioactive gas is given off by tiny amounts of uranium that occurs in rocks and soil
rocks and building materials - rock, stone and building materials like concrete, bricks and ceramics all emit radiation
food and drink - plants absorb radioactive materials from the soil and these pass up the food chain
water
air

Question 28

What are Artificial sources of radiation?

Answer 28

medical and dental X-rays
radiation used in medical diagnosis and treatment (eg radiotherapy to treat cancers)
rdioactive fallout from nuclear weapons testing
radioactive waste from nuclear power stations
industrial and consumer use of radiation (eg smoke detectors, UV sterilisation equipment, indutrial measurement equipment)

Question 29

What are some safety precautions against radiation?

Answer 29

The best defence against ionising radiation is distance. The greater the distance, the less chance there is of being exposed to radiation.
Radioactive sources should be kept away from the body and never brought close to the eyes.
The time of exposure to ionising radiation should be limited.
Sources should be shielded from the body and handled using tongs.
Sources should be stored in lead lined containers to ensure no exposure to the environment whilst in storage.
Basic safety precautions such as wearing goggles and washing hands after using a radioactive source should be taken.
The radiation that a person receives can be monitored using film badges.
All areas containing ionising radiation sources will the show the hazard symbol.

Question 30

What is the biological effect of ionising radiation?

Answer 30

Exposing cells to the energy transferred by the radiation will have the following effects on cells:

Cells can be altered by ionising radiation and change their function.
Cell can be destroyed by ionising radiations.
This can lead to the creation of cancer cells.

Question 31

How can radiation be used in medecine?

Answer 31

Destroying cancer cells
Gamma rays can be directed through the body to target tumours that cannot be treated with conventional surgery.

The positioning and the intensity of the gamma ray sources are carefully calculated to ensure that the cancer cells receive enough radiation to kill them whilst the surrounding tissue remains in a healthy condition.

Radioactive tracers
Ionising radiation can also be used to trace blood flow around the body. If a liquid containing a gamma source with a short half-life is injected into your blood, it will travel around your body. Where there is a blockage the activity of the radiation will be highest due to collection of blood. Using a gamma camera - special gamma ray detector - these areas can be located.

Question 32

How a tumour is destroyed using a radioactive implant?

Answer 32

small ‘seeds’ of radioactive isotope placed in tumour,
radiation from isotope destroys cancer cells,
use isotope with half-lives not long enough to damage normal cells
surrounding tumour,
half-life not too short or unstable nuclei decay before radiation destroys
tumour

Question 33

Explain why a radioactive isotope used in a kidney scan should not have a half life too short or too long?

Answer 33

too short: radioactive isotope decays too much before scan completed,
too long: patient exposed to ionising radiation unnecessarily

Question 34

When a tracer is used, why is it better to use an radioactive isotope that decays into a stable isotope?

Answer 34

stable isotope in body (or elsewhere) not dangerous
whereas unstable isotope harmful
as it emits ionising radiation harmful to body

Question 35

What is nuclear fission?

Answer 35

Nuclear fission is the process by which energy is released when a large atom is hit by a neutron, becomes unstable and splits into two or more smaller pieces plus two or three neutrons and energy (usually gamma radiation).When this happens, some of the mass of the atom is ‘lost’ – it has been converted directly into energy. This energy is in the form of heat which can be harnessed and used to generate electricity in a nuclear power station.

Question 36

How is the chain reaction controlled in a reactor?

Answer 36

In a nuclear reactor, the chain reaction is controlled by using Boron control rods. These absorb neutrons and can limit the number of neutrons hitting atoms and so will limit the energy produced.

Question 37

Key vocabulary relating to Nuclear reactors:

Answer 37

The fuel rods: source of enriched Uranium fuel that undergoes fission reactions.
The moderator: the fuel rods are encased in the moderator (graphite is sometimes used) and help the fission reaction to proceed efficiently.
The control rods: normally made of Boron, these help control the fission reaction.
The coolant: This is a liquid or gas that transfers energy from reactor to the heat exchanger. Also used to cool the reactor.
The containment vessel: This is a thick concrete shield that absorbs neutrons and ionising radiation. In practice this can be 5.5m thick.

Question 38

Advantages and Disadvantages of Nuclear Fuel:

Answer 38

Advantages of nuclear fuels
Unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulphur dioxide.
In terms of energy produced: 1kg of nuclear fuel = 2,900,000 kg of coal
Since comparatively small volumes of fuel are used, this can be easily transported by road or rail.
Waste product produced in small volumes.
Disadvantages of nuclear fuels
Like fossil fuels, nuclear fuels are non-renewable energy resources.
If there is an accident, large amounts of radioactive material could be released into the environment. Modern reactor designs are extremely safe and this very rarely happens.
Nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely. Storing nuclear waste is another hotly debated issue.

Question 39

What happens when a neutron collides with both
a) uranium-238 nucleus
b)uranium-235 nucleus

Answer 39

a)nucleus absorbs neutron without undergoing fission,
forms unstable nucleus which decays
b)nucleus splits into two fragments,
releases energy and several neutrons

Question 40

What is induced fission?

Answer 40

Induced fission refers to the process where the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy, when a heavy nucleus absorbs a neutron.

Question 41

Why is the core of the reactor made of thick steel and thick concrete?

Answer 41

thick steel withstands very high temperature and pressure in core,
thick concrete walls absorb ionising radiation
that escapes through steel walls

Question 42

What is nuclear fusion

Answer 42

Forcing the nucleus of 2 small atoms to create a larger atoms

Question 43

How could you replicate nuclear fusion?

Answer 43

making 2 light nuclei collide at high speed

Question 44

Where does fusion happen naturally?

Answer 44

The sun where hydrogen fuse in to deuterium and deuterium fuse with other deuterium into helium and that produces energy.

Question 45

Why does the plasma of a light nuclei need to be very hot in a fusion reactor?

Answer 45

so enough kinetic energy to overcome force of repulsion between nuclei so they
fuse

Question 46

Advantages and Disadvantages of a fusion reactor against a fission reactor?

Answer 46

advantages
any two from:
 nuclear fusion fuel easily available
 fusion products non-radioactive (or less radioactive than) fission
products
 fusion stops if plasma out of control,
disadvantages
any two from:
 very large current needed to heat plasma to start fusion
 plasma difficult to control,
 at present, fission reactors produce far more power than fusion
reactors

Question 47

Why does nuclear waste need to be stored?

Answer 47

hazardous and ∴ a danger to people and animals if it escapes.It contains radioactive isotopes with long half-lives

Question 48

Why is alpha radiation more dangerous inside the body than outside?

Answer 48

absorbed by surrounding tissues
and could damage or kill cells in body or cause cancer
outside less dangerous as α radiation has no penetrating power

Question 49

How to make a existing house safe from radon?

Answer 49

install pipes under house and pump radon gas out of ground before it
seeps into house,
top of outlet pipe from pump needs to be high up outside house