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Understand Nuclear Decay

Worksheet Overview

QUESTION 1 of 10

Before we start, you’ll want access to a periodic table for this activity. You’ll also want to have looked at our activities on atomic structure in chemistry as well as the ones on isotopes.

 

2011, an earthquake hit Japan registering as a 9 on the Richter scale – the largest earthquake in Japans history and the 4th biggest in the world. This created a tsunami 6 meters high and killed over 15,000 people. One of the places hit by the earthquake was a town called Fukushima where they had a nuclear reactor. Unfortunately – the damage caused by the tsunami stopped the reactors form working correctly and three of the reactors suffered meltdowns spewing radioactive material into the environment. People were evacuated from their homes and a 5km exclusion zone was set up to protect people from the damage of the radiation. But what is radiation and how is it caused? This is what we will be looking at in this activity.

 

We are constantly exposed to radiation all the time. It is made by the rocks we build our houses from; it comes from space and it is even in our fruit! We call it background radiation – and there is nothing that we can do to avoid it.

 

So, if there is so much radiation around us all the time, then why are we not all being killed? Well, that is because the level of radiation that we are exposed to is quite low. We measure radiation using a device called a Giger Muller tube (GM tube), and it measures ionisation events inside the tube. The more ionisation events, the more radiation there is. The GM tube will give us a ‘count-rate’ telling us how many ionisation events there are.

 

The count-rate is not the same as the activity of a sample, however! Because science is never simple… The activity of a sample is defined by a unit called a Becquerel (Bq), where one Bq is one nucleus undergoing a nuclear decay every second – a decay is when a particle shoots out some radiation. Are you feeling overwhelmed by all the new words yet? We have made a handy list of words and their meaning for you at the bottom of this explanation to help you out!

 

When the nuclear commission was helping the clean-up from Fukushima, they took a range of readings looking for all of the different types of radiation. They needed to do this because different types of radiation each cause more or less damage depending on where they are. Let’s look at the different types of radiation in detail:

 

Alpha (α):

Alpha radiation causes the most ionisation, but only travels a very short distance before it stops (about 15cm). it can be stopped by the skin and so it is safe outside of your body – but if you inhale it or drink it, then it can be deadly. A Russian spy, Litvinenko, was killed by a VERY small amount of alpha radiation being put in their tea.

 

Alpha radiation is made of 2 Protons and 2 Neutrons – it is a helium nucleus. This gives it a charge of +2, meaning that it will rip electrons off things it comes near causing damage to them – but it can only do this twice.

 

 

Beta (β):

This is moderately ionising and can travel up to about 1 meter. It is not really safe inside or outside your body, so it’s best to stay away from it full stop – but unlike alpha, it is less likely to kill you unless you have a high dosage of it.

It is made of a fast-moving electron usually spat out from the inside of a nucleus. It causes damage by hitting other electrons and removing them from their atoms.

 

Gamma (γ):

This is a strange one because it is a wave, not really a particle (although it is carried by photons). It is the least ionising of all of the three that we have looked at so far because it needs to hit stuff at just the right speed to cause damage. So as a result, it normally just passes through everything. Safe on the inside and the outside, unless there is a lot of it.

 

 

Neutrons (N):

These are the ones that you need to be afraid of and the ones that they were most concerned where being realised from Fukushima. They are made of a Neutron (who would have guessed, right?) and they are so dangerous because if they collide with a nucleus then they will make the nucleus itself radioactive, causing it to release alpha, beta and gamma radiation. This can then, in turn, lead to more neutrons being released. The long and short of it is that you don’t want to be anywhere near these things unless they are bound to your nuclei!

 

 

Alpha, beta, gamma and neutron radiation come from the nucleus of a radioactive atom. Alpha can be stopped by a thin piece of paper; beta penetrates the paper but can be stopped by a 3mm thick piece of aluminium and gamma can penetrate a 3m thick lead block and concrete. The diagram shows this in more detail:

 

 

As you can see, the α doesn't go through the paper, the &beta will go through the paper, but not the aluminium and the γ will go through everything but is only reduced by the lead.

 

Alright? You got it? Good! Here is that handy list of keywords that we were talking about earlier.

 

Keyword Meaning
Ionisation When an atom gains or loses an electron
Event When a decay or ionisation happens
Decay When a nucleus emits a particle of radiation
Count rate How many ionisation events happen in a set amount of time.
Activity Have many decays a radioactive element is doing per second.
Becquerel The unit of activity.
GM tube A device used to measure ionisation - gives results in count rate.

 

Select the correct symbols for the different types of radiation. 

N

γ

α


β

Ω

What is the definition of a nuclear decay?  (1 mark)

A particle of uranium emits an alpha particle. What is an alpha particel made of?

Chose the correct shielding for beta radiation from the choices below.

Paper

Skin

Plastic

Aluminium

Thin Lead

Thick Lead

Which of the following can travel the furthest in air? Choose one answer. 

α

β

γ

N

An atom of uranium has 92 protons and decays into an atom of thorium by alpha decay. How many protons does thorium have? Chose one correct answer.

88

89

90

91

92

A source of radiation is Thorium 90. It is an α emitter and needs to be stored for safe transportation. Chose the safest way to store the Thorium during transportation for the list below. Select one answer.  

Paper bag

Plastic box

Plastic box with an aluminium lining

Lead box

What is the unit of activity? 

Describe the difference between the required shielding and penetrating depths in air for &alpha, &beta and &gamma. (4 marks)

Describe the difference between activity and count rate. (2 marks)

  • Question 1

Select the correct symbols for the different types of radiation. 

CORRECT ANSWER
N
γ
α
β
EDDIE SAYS
Exams tend to refer to them as alpha, beta, gamma and neutrons OR α, β, γ and N. You need to be familiar with both of these ways of writing and this will only come from practice. Get out some old exam papers or take a look at our exam papers and practice the nuclear decay questions!
  • Question 2

What is the definition of a nuclear decay?  (1 mark)

CORRECT ANSWER
EDDIE SAYS
A decay happens when the nucleus cannot stay in the state that it is in. It's like it's moved in with some housemates and they are really messy, they thought it would be fun, but they just want it to be clean now. So they move out - that's what the radiation does, it moves out of the nucleus. With alpha, beta and neutrons, this changes the nucleus forever and it is much cleaner afterwards. That is a stretched metaphor!
  • Question 3

A particle of uranium emits an alpha particle. What is an alpha particel made of?

CORRECT ANSWER
2 protons and 2 neutrons
2 neutrons and 2 protons
EDDIE SAYS
This is the most highly charged of all of the radiation, which is why it can cause so much damage but only travels a really short distance. Having 2 protons and 2 neutrons, it is one of the most highly charged objects for its mass in the universe. Impressive right? Little unassuming alpha, kicking everyone else into the ground!
  • Question 4

Chose the correct shielding for beta radiation from the choices below.

CORRECT ANSWER
Aluminium
EDDIE SAYS
You only need some thin aluminium to stop beta radiation, this is because it will lose all of its energy is it collides with a nucleus or another electron. In aluminium, there are a lot of nuclei and other electrons just flying around. This means that it is more likely to have a collision event.
  • Question 5

Which of the following can travel the furthest in air? Choose one answer. 

CORRECT ANSWER
γ
EDDIE SAYS
Gamma can travel through 100 light years of lead if it gets lucky - it can get spat out by the sun and then travels straight through the earth. Impressive, right? This has the added effect of letting it travel through the air forever. At least, we think it is forever.
  • Question 6

An atom of uranium has 92 protons and decays into an atom of thorium by alpha decay. How many protons does thorium have? Chose one correct answer.

CORRECT ANSWER
90
EDDIE SAYS
An alpha particle is made of 2 protons and 2 neutrons. These particles are not created from thin air, they have to come from somewhere - that place is the nucleus of the atom they came from. In this case, Uranium had 92 protons, but would have lost 2 during the decay (as well as 2 neutrons) - so now it would only have 90 protons (92 - 2 = 90).
  • Question 7

A source of radiation is Thorium 90. It is an α emitter and needs to be stored for safe transportation. Chose the safest way to store the Thorium during transportation for the list below. Select one answer.  

CORRECT ANSWER
Plastic box with an aluminium lining
EDDIE SAYS
When it comes to safety, you always overestimate the safety needs you have rather than underestimating them. A paper bag could rip and spill the contents - this would not be very safe if people breathed it in. A plastic container would be much safer, but might also be prone to breaking or melting if it got hot. The p[lastic container with the metal inside is much safer as the metal provides an extra security level. The lead box is heavy, and lead is also soft, so things could damage it and it could damage the Thorium. Not a good idea in general.
  • Question 8

What is the unit of activity? 

CORRECT ANSWER
Bq
Becquerel
EDDIE SAYS
Did you remember it? We would have accepted Bq or Becquerel, but only if you got the capitalisation correct! It is really important that when we have units named after scientists like this (or the Newton (N)) that we remember to capitalise them. This is because lower case units could mean something else.
  • Question 9

Describe the difference between the required shielding and penetrating depths in air for &alpha, &beta and &gamma. (4 marks)

CORRECT ANSWER
EDDIE SAYS
You need to know your penetration depths! It's really important if you ever find yourself in a Fallout 4 style nuclear apocalypse and you need to create a safe way of shielding yourself from the harmful radioactive fallout from nuclear weapons. Paper, aluminium, lead - it's like the new hip and cool version of rock paper scissors! All the cool kids are doing it!
  • Question 10

Describe the difference between activity and count rate. (2 marks)

CORRECT ANSWER
EDDIE SAYS
There are a lot of different measurements of radiation because there are a lot of different ways that radiation can be created. The two most common are count rate (this tells us the average amount of radiation that is in the environment) and activity (which is specific to that one sample of radiation). The reason I bring this up is because you should now take a look at our activity on Half-Life where we will be using these terms non-stop! Luck you (again)...
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