Radioactivity

Question 1

What is used to detect radioactivity?

Answer 1

Photographic film or Geiger counter

Question 2

What is activity and what is it measured in?

Answer 2

Activity is equal to the number of decays per second.
Measured in Becquerels (Bq)
1 becquerel= 1 decay per second

Question 3

What is background radiation

Answer 3

Low level ionization that is produced all the time
Most of this naturally but some of it is due to man-made sources

Question 4

What are 3 natural sources of radiation

Answer 4

Cosmic rays- radiation from space
Rocks and soil- some rocks are radioactive and give off radioactive radon gas
Living things- plants absorb radioactive materials and pass it down the food chain

Question 5

What are artificial sources of radiation and eg

Answer 5

Human activity adds to background radiation through artificial sources of radiation
This includes medical X-rays, radioactive fallout from nuclear weapon testing and radioactive waste from nuclear power stations

Question 6

What is half life

Answer 6

Average time taken for half of the original activity or nuclei to decay

Question 7

What is irradiation and contamination

Answer 7

irradiation- exposure to radioactive source outside the body
Contamination- when radioactive sources enter the body or gets on skin or clothes

Question 8

What are the advantages and disadvantages of irradiation

Answer 8

Advantages
Sterilisation can be done without high temperatures.
It can be used to kill bacteria on things that would melt
Disadvantages
It may not kill all bacteria on an object.
It can be very harmful - standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutation

Question 9

What are the advantages and disadvantages of contamination

Answer 9

Advantages
Can be used as medical tracers
Use of isotopes with short half life means limited exposure
Imaging procedures can replace invasive surgical procedures
Disadvantages
Radioactive isotopes may not always go where they are wanted
Small amounts of isotope may still be left behind
Exposure to radioactive material can damage healthy cells

Question 10

What is Nuclear Fission

Answer 10

Splitting of an atomic nucleus and the forming of smaller nuclei and neutrons

Question 11

Which element goes through fission

Answer 11

Uranium-235

Question 12

What are the products of fission

Answer 12

2 daughter nuclei (with kinetic energy), neutrons, gamma radiation

Question 13

What is a chain reaction

Answer 13

Process in which neutrons released in fission collide with other nuclei and this leads to further reaction

Question 14

What are the daughter products of the fission of uranium-235

Answer 14

Barium-144, krypton-89

Question 15

What does a nuclear reactor do?

Answer 15

It is used to produce a substantial and controllable energy from nuclear fission
Thermal energy produced is used to convert water to high pressure stream
This stream is used to drive turbines which rotate generators to produce energy

Question 16

Name 5 parts of the nuclear fission reactor and its functions

Answer 16

Nuclear fuel rods- uranium isotope that will split when triggered by a slow moving neutron. The fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods
Moderator (graphite core or water) - slow neutron down so that they more likely to be absorbed by U-235 nuclei in fuel rod
Control rods (made of barium or cadmium) - absorb neutrons so that for every 2 or 3 neutrons that are released from fission reaction, only 1 can produce further fusion. Can be used to stop or speed up reaction
Coolant- heated up by energy releases from fission reactions and is used through heat exchangers to boil water to drive turbines in the power station
Concrete shield (containment building) - ensure no radiation is able to penetrate through and escape the reactor

Question 17

What is Nuclear fusion, what restricts it and what helps it

Answer 17

Combining of 2 small, light atomic nuclei to form a larger and heavier nucleus
Both nuclei are positively charged and will repel each other by electrostatic repulsion
The nuclei have to get very close to collide and if they are moving very fast they can overcome the electrostatic repulsion. The hotter the molecule is, faster it will move and more likely to collide

Question 18

Where is Nuclear fusion used?

Answer 18

Stars

Question 19

What happens in a typical fusion reaction

Answer 19

Hydrogen-1 combines with Hydrogen-2 to form Hydrogen-3

Question 20

What is mass deflect

Answer 20

The mass of one helium nucleus is less than the mass of the hydrogen nuclei added together.
The missing mass, sometimes called mass defect, is converted to energy, which radiates away
In all nuclear reactions, a small amount of the mass changes to energy.
The total mass of a nucleus is less than the total mass of the nucleons that make up the nucleus.
The mass defect, is the binding energy that is released.
The mass defect and binding energy are equivalent using E = mc2

Question 21

What is binding energy?

Answer 21

Energy required to break a nucleus into its constituent protons and neutrons

Question 22

Why is Nuclear fusion hard to achieve on earth

Answer 22

Nuclei are positive and will repel
Difficult to get extreme pressure
Extremely high temperatures are needed