P7 - Radioactivity✔️

Question 1

What is a radioactive substance?

Answer 1

Atoms of a radioactive substance each have a nucleus that is unstable - which can become stable or less unstable by emitting alpha,beta or gamma radiation

Question 2

What does it mean if a substance is decaying?

Answer 2

An unstable nuecleus is described as decaying when it emits radiation - no one can tell when an unstable nucleus will decay as it happens without anything being done to the nucelus

Question 3

Why did Geiger and marsdens experiment with alpha particles take place in a vacuum chamber?

Answer 3

To prevent air molecule absorbing the alpha particles

Question 4

How did Geiger and marsden experiment with alpha particles?

Answer 4

They set up the apparatus in a vacuum chamber with a detector (consisting of a microscope focused on a Small glass plane) and each time an alpha particle hit the plate, a spot of light was observed - the detector was moved to different positions and the number of spots of light observed were recorded

Question 5

What were the results from Geiger an marsdens experiment? what did Rutherford conclude?

Answer 5

most of the alpha particles passed straight through the metal foil - he concluded that there is a positivley charged nucleus at the centre of every atom much smaller then the atom because most alpha particles passed straight through the atom without reflection- and most of the atoms mass was located at the centre, rest was empty space

Question 6

How did Niel Bohr adapt the nuclear model?

Answer 6

Adapted the model by suggesting that electrons orbit the nucelus at specific distances - called energy levels

Question 7

What did the work of James Chadwick result in?

Answer 7

Provided the evidence to show the existence of neutrons within the nucleus

Question 8

What was the plum puding model?

Answer 8

Earlier model of the nucleus with positively charged matter spread about (as in a pudding) and electron burried inside (like plum in the pudding) - rutherfords discovery meant that the plum puding model was no longer accepted

Question 9

What are isotopes?

Answer 9

Are atoms of the same element with different number of neutrons

Question 10

Features of an alpha particle?

Answer 10

Made up of two protons plus two neutrons - relative mass is 4 and its relative charge is +2 and is identical to a helium nucleus

Question 11

What happens when a unstable nucleus emits an alpha particle?

Answer 11

-is atomic number goes down by 2 and its mass goes down by 4

-the mass and the charge of the nucelus are both reduced

Question 12

What is a beta particle and how is a beta particle created and emitted?

Answer 12

An electron emitted by a nucelus that has too many neutrons compared with its protons - a neutron in the nucleus changes into a proton and a beta particle (ie and electron) is instanly emitted

Question 13

Features of a beta particle?

Answer 13

-relative mass of a beta particle is effectivley zero

-relative charge is -1

Question 14

What happens to an unstable nucleus when a beta particle is emitted?

Answer 14

-atomic number goes up by 1 and its mass is unchanged(neutron changes into proton)

-the charge of the nucleus is increased, mass of nucelus is unchanged

Question 15

What is gamma radiation?

Answer 15

An electromagnetic radiation from the nucelus of an atom - it is uncharged and has no mass and is able to penetrate far into materials and travel far in air - weakly ionising

Question 16

Symbol for alpha radiation?

Answer 16

α

Question 17

Symbol for beta radiation?

Answer 17

β

Question 18

What material is needed to absorb gamma radiation?

Answer 18

Thick sheets of lead or meters of concrete

Question 19

What material is needed to absorb beta radiation?

Answer 19

sheet of aluminium around 5mm

Question 20

What material is needed to absorb alpha radiation?

Answer 20

Sheet of paper

Question 21

How can you tell when a radioactive substance will decay?

Answer 21

You can’t - radioactive decay is entirley random, so you can’t predict exactly which nucleus in a sample will decay next

Question 22

Define half-life?

Answer 22

The time it takes for the amount of radiation emitted by a source to halve - can be used to make predictions about radioactive sources - its activity is measured in becquerels, Bq

Question 23

What would it mean if a source had a short half-life?

Answer 23

Means the activity falls quickly becuase the nuclei are very unstable and rapidly decay - these sources are dangrous due to the high amount of radiation they emit

Question 24

What would it mean if a source had a long half-life?

Answer 24

Means the activity falls slowly becuase most of the nuclei don’t decay for a long time - can be dangrous because nearby areas are exposed to radiation for millions of years

Question 25

Define background radiation?

Answer 25

Is the low-level radiation that’s around us all the time - result of naturally occurring isotopes which are all around us

Question 26

Give an example of background radiation caused by the enviorment?

Answer 26

Radiation from space, which is known as cosmic rays mostly from the sun - however the earths atmosphere protects us from most the radiation

Question 27

Give an example of background radiation caused by human activity?

Answer 27

Radiation due to fallout from nuclear explosions or nuclear waste

Question 28

What is background radiation measured in?

Answer 28

Measured in sileverts (Sv) - 1 Sv is equal to 1000 millisieverts (mSv)

Question 29

What does irradiation mean?how can it be limited?

Answer 29

Exposure to radiation is called irradiation - can be reduced by keeping sources in lead-lines boxes, standing behind barriers and using remote controlled arms

Question 30

How can we be contaminated by radiation?how can it be prevented?

Answer 30

Contaminating atoms might get into yout system, and then decay releasing radiation which could cause you harm - gloves and tongs should be used when handling sources

Question 31

Which radioactive sources are most dangrous outside the body?

Answer 31

Beta and gamma sources are the most dangerous - because they can penetrate the body and get to delicate organs

Question 32

Why is alpha radiation outside the body not that dangerous?

Answer 32

Alpha can not penetrate the skin and is easily blocked by a small air gap

Question 33

Why is alpha radiation dangerous inside the body?

Answer 33

Alpha sources are very dangerous because they do all their damage in a very localised area so it is more contamination rather then irradiation

Question 34

Why are beta and gamma sources not that dangerous inside the body?

Answer 34

Beta radiation is absorbed over a larger area and some passes out the body - gamma radiation mostly pass out the body and has lower ionising power so it is not as dangerous

Question 35

Give three risks of using radiation?

Answer 35

• can enter living cells and ionise atoms and molecules - can lead to tissue damage
• lower doses can cause mutations in the cells, which is cancer
• higher doses kills cells completely - radiation sickness

Question 36

Explain how gamma sources are usually used in medical traces?

Answer 36

• radioactive isotopes can be injected into people - their progress around the body can be followed using an external detector
• iodine-123 - used to check if the thyroid gland is taking in iodine

Question 37

Why is gamma a suitable type of radiation for medical uses?

Answer 37

Gamma radiation passes out of the body without causing much ionisation - will have a short half-life so the radioactivity inside the patient quickly disapears

Question 38

How can gamma rays be used to kill cancer - explain the process?

Answer 38

Higher enough dosage, able to kill cancer cells but not too damaging to living cells is directed carefully at the site of the cancer - there is quite a bit of damage to living cells which can leave the patient feeling very ill

Question 39

How can beta radiation be used to kill cancer cells?

Answer 39

Radiation-emitting implants (usually beat-emitters) can be put next to or inside tumours

Question 40

Issues and benefits with using radiation for medical purposes?

Answer 40

• traces can cause cancer - but can diagnose life-threatening conditions
• prolonged exposure to radiotherapy poses future risks - many choose it to still get rid of the cancer completely

Question 41

Define nuclear fission?

Answer 41

Type of nuclear reaction that is used to release energy from large, unstable atoms by splitting them into smaller atoms

Question 42

What happens during nuclear fission?

Answer 42

When the atom splits it forms two new lighter elements that are roughly the same size - and have same energy in their kinetic energy store - two or three neutrons are also released when an atom splits

Question 43

How can a chain reaction occur from nuclear fission?

Answer 43

When two or three neutrons are released from the atom spliting they can be absorbed by another nucleus (if they are moving slow enough) - can cause more fission to occur

Question 44

Explain how gamma rays are released from nuclear fission?

Answer 44

The energy not transferred to the kinetic energy stores of the products is carried away by gamma rays

Question 45

Explain how nuclear fission can be used to generate electrcity?

Answer 45

Energy carried away by gamma rays, and in the kinetic energy stores of the remaining free neutrons can be used to heat water, making steam to turn turbines and generators

Question 46

How is the amount of energy released by nuclear fission controlled?

Answer 46

changing how quickly the chain reaction can occur - by using control rods which are lowered and raised inside a nuclear reactor, to absorb neutrons - which slows down the chain reation and controls the amount of energy released

Question 47

How do nuclear weapons work?

Answer 47

Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion

Question 48

Define nuclear fusion?

Answer 48

Collision of two light nuclei at high speed which fuse to create a larger, heavier nucleus - does not have as much mass as the two seperate light nuclei because some energy is released as radiation

Question 49

Why is it hard to utilise nuclear fusion to produce energy?

Answer 49

The temperature and pressure needed for fusion are so high that fusion reactors and hard and expensive to build