Radioactivity

Question 1

What are isotopes

Answer 1

Atoms with the same number of protons but different number of neutrons

Question 2

What is radioactive decay

Answer 2

In a radioactive atom, the nucleus is unstable and so emits particles or waves (radiation) to form a more stable atom

Question 3

Can we predict or influence radioactive decay

Answer 3

No radioactive decay is random- we cannot predict or influence when it will happen

Question 4

What does it mean if a substance is classed as radioactive

Answer 4

They are unstable and continuously emit radiation

Question 5

What did jj thompson discover in 1897

Answer 5

He discovered tiny particles with a negative charge, he had discovered the electron which is a sub atomic particle

Question 6

What did the plum pudding model look like

Answer 6

It is a positively charged sphere with negative electrons distributed throughout it

Question 7

Who was the first to discover the atom and who rejected this idea

Answer 7

Democritus - first to describe an atom (440 bc ) Vs Aristotle - rejected the atom

Question 8

Describe geiger and marsdens gold foil experiment and what conclusions were made

Answer 8

A thin gold sheet was placed in front of the opening of a lead box containing an alpha source. This apparatus and an alpha detector were placed in a dark vacuum chamber.

Most of the alpha particles went straight through the gold foil without any deflection - atoms are mostly empty space
Some alpha particles were slightly deflected by the gold foil - a repulsive electrostatic force is caused by a small nucleus which has the same charge as the alpha particles
A few alpha particles bounced back from the gold foil - most of the mass of the atom is in the nucleus which is more massive than the aloha particle

Question 9

What is an alpha particle

Answer 9

-nucleus of helium atom (2 protons and 2 neutrons)
-most ionising type of radiation
-charge : +2
-speed : less than 10% of the speed of light

Question 10

What is a beta particle

Answer 10

-consists of one electron
-less ionising than alpha particles
-charge: -1
-speed: up to 50% speed of light

Question 11

What are gamma rays

Answer 11

-high frequency electromagnetic wave
-least ionising type of radiation
-no charge
-fastest speed: speed of light

Question 12

Describe alpha radiation

Answer 12

An atom decays into a new atom and emits an alpha particles (2 protons and 2 neutrons- the nucleus of a helium atom )

Question 13

Describe beta radiation

Answer 13

An atom decays into a new atom by changing a neutron into a proton which stays in the nucleus and electron. The fast moving, high energy electron is called a beta particle and it is emitted

Question 14

Describe gamma radiation

Answer 14

After alpha or beta decay surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed

Question 15

What is ionisation

Answer 15

Atoms are ionised when electrons are removed, turning them into an ion which is more likely to take part in chemical reactions

Question 16

How many protons and neutrons are released in alpha decay

Answer 16

The atom looses 2 protons and 2 neutrons. This causes the mass number to decrease by 4 and the atomic number decrease by 2

Question 17

How does mass and atomic number change due to beta decay

Answer 17

Mass number stays the same atomic number increases by 1

Question 18

What is activity

Answer 18

The number of atoms that decay per second OR the rate at which radioactive nuclides decay

Question 19

What happens to reactivity over time

Answer 19

• as time goes on, fewer and fewer radioactive atoms remain
  -this means that the number of atoms decaying in a given time decreases
• so the amount of radiation detected (or count rate) also decreases

Question 20

What is half life

Answer 20

The half life of a radioactive isotope is the average time it takes for half the nuclei in a sample to decay

Question 21

What is alpha radiation stopped by and what is its range in air

Answer 21

Stopped by : skin or paper range in air : 5cm

Question 22

What is beta radiation stopped by and what is its range in air

Answer 22

Stopped by : thin sheet of aluminium range in air : 1m

Question 23

What is gamma radiation stopped by and what is its range in air

Answer 23

Stopped by : thick lead or thick concrete range in air : unlimited

Question 24

Compare the penetration power of alpha beta and gamma radiation

Answer 24

Alpha has the least penetration power
Beta has medium penetration power
Gamma has the most penetration power

Question 25

What is nuclear radiation used for in medicine

Answer 25

The exploration of internal organs Control or destruction of unwanted tissue

Question 26

What is the most common tracer used and why

Answer 26

Technetium -99 because it Only emits gamma rays - it can be detected outside the body by a gamma camera, doesnt cause much ionisation Short half life

Question 27

Describe how cancer can be treated using radiotherapy

Answer 27

Gamma rays are sent through the body at various different angles. This happens inside a large circular machine. On its own each beam has too little energy to harm the body or the cancer. However the beams are aimed so they cross at the point where the cancer need to be killed

Question 28

Sterilizing

Answer 28

Gamma rays can be used to kill bacteria mould and insect in foods, even after the food has been packaged. They are also used sterilise hospital equipment

Question 29

Describe how smoke detectors use radiation

Answer 29

Smoke detectors contain a weak source of alpha radiation. The alpha particles ionize the air, which leads to the creation of an electrical current. It smoke is present it interacts with the ions produced by the alpha particles. This means that current is flowing through the air which causes the alarm to sound

Question 30

How is radiation used safely in medicine

Answer 30

-when radiation is used in medicine patients are given as small a dose as possible and split into a number of treatments - this radiation is targeted at the area of the body being imaged or treated other areas are protected using a lead shield - tracers should contain isotopes that have half lives that are as short as possible, so that the patient is not exposed to radiation in the body for longer than possible

Question 31

What should you do when dealing with radiation

Answer 31

- limit time of exposure -avoid direct contact by using tongs -always wear protective clothing -keep the source in shielded labelled, lead lined storage

Question 32

Explain why gamma emission does not change the atomic number of an element

Answer 32

Gamma radiation is an electromagnetic wave not a particle so it doesn’t affect the number of protons or neutrons in the nucleus since the proton number stays the same the atomic number does not change

Question 33

Describe how irradiated food is different to radioactive food

Answer 33

Irradiated food is treated with radiation to kill germs but it does not absorb the radiation or become radioactive Radioactive food - contains unstable radioactive isotopes that emit harmful radiation

Question 34

What is contamination and irradiation

Answer 34

Contamination is when you take a radioactive material inside your body or if it is put on your skin Irradiation is when there is radioactive material outside your body that can reach you as waves

Question 35

What is nuclear fission

Answer 35

When a large and unstable nucleus absorbs a neutron and splits into two smaller and lighter nuclei releasing a large amount of energy and 2-3 neutrons

Question 36

Examples of isotopes that undergo fission

Answer 36

Uranium -235 and plutonium -239

Question 37

What are the 2 major isotopes of uranium

Answer 37

Uranium- 238 more common ; does not undergo nuclear fission Uranium- 235 less common ; does under go nuclear fission

Question 38

What has to happen before the uranium 235 can be used as fuel

Answer 38

It needs to be enriched until it has 3% of fissionable uranium

Question 39

What are the stages in a nuclear power station

Answer 39

Stage 1- in the reactor, nuclear fission in the uranium fuel rods releases heat, which is used to boil water Stage 2- the boiling water produces high pressure steam. The force of moving steam turns the turbine Stage 3- the turbine turns the generator and electricity is produced Stage 4 - the low pressure steam is condensed back into water in the cooling towers. The water is reused

Question 40

What is a chain reaction

Answer 40

Nuclear fission produces daughter nuclei and neutrons. If these neutrons go on to split other nuclei, this sets up a chain reaction. These released neutrons can cause fission to occur in other nuclei, producinh even more neutrons, which can continue the chain reaction, as each fission occurs more and more neutrons are produced . The rate of fission increases rapidly resulting in a massive release of heat and energy

Question 41

What are the fuel rods

Answer 41

They contain enriched uranium which has an increased percentage of uranium -235 compared to the uranium ore from which it is extracted. This fuel is for the reactor

Question 42

What are the control rods

Answer 42

They are made of cadmium or boron, which can absorb neutrons without undergoing fission. Can be lifted in and out of the reactor to control the number of neutrons so that fission happens at a steady rate

Question 43

What is the coolant

Answer 43

Water flows around the core, transferring heat away from the fuel, to be used to produce steam. The water is usually pressurised to prevent it boiling inside the reactor

Question 44

What is the moderator

Answer 44

Reactors use graphite or the coolant water to slow down fission neutrons. Slow moving neutrons are more readily absorbed by uranium - 235 nuclei so moderation is needed to keep the reaction going.

Question 45

What is nuclear fusion

Answer 45

The process of joining 2 smaller nuclei to form a larger one. The process involves bringing two hydrogen atoms close enough to make them fuse to form helium. This process happens in stars and at very high temperatures and pressures . These conditions are necessary to overcome the electrostatic repulsive forces between all the protons in the nuclei and force them together