Physics
Neutrinos: Hunting
ghosts
This lesson is about neutrinos.
In this lesson you will investigate the following:
• Beta decay and the discovery of neutrinos
• Neutrinos from the Sun
• Neutrinos from space
Find out how the ‘ghosts of matter’ may tell us the secrets of matter.
This is a print version of an interactive online lesson.
To sign up for the real thing or for curriculum details
about the lesson go to www.cosmosforschools.com
Neutrinos: Introduction
This lesson is all about neutrinos – tiny ghostly particles much smaller than an atom. Billions of them have flewn through
your body since you started reading this introduction.
Most neutrinos come from space, travelling at the speed of light, and scientists are trying to find out more about them. To do so
they have built an expensive neutrino detector deep in the ice near the South Pole.
But before you read the article and look at the pictures, you will need to understand a few simple terms used there.
The article talks about “subatomic particles”, which, as you might be able to guess, are the tiny particles that go together to make
atoms.
It also talks about “fusion”, this is the atomic reaction that happens when two atoms are joined, or fused, together. When they are,
they release a lot of energy. The Sun and the stars give out light and heat energy because they are made up of billions of hydrogen
atoms joining together to make helium. This is one way that neutrinos are formed, too.
Another way neutrinos are created is when a large star explodes at the end of its life and becomes what we call a “supernova”.
Now, go ahead and read the original Cosmos Magazine ​story to find out how the IceCube Neutrino Observatory is studying these
elusive little particles.
Read the full Cosmos Magazine article h
​ ere
The neutrinos that we receive here on Earth come from the Sun and the deep reaches of space. Image credit: NASA
Question 1
Interpret: The opening section of the Cosmos Magazine ​article is titled "Freezing a ghost". Why do you think the writer chose this
catchy title?
Question 2
Interpret: To help you understand the article, after reading each section try to think of another phrase for its heading.
Cosmos heading
Freezing a ghost
Under the ice
Captured
Where in the Cosmos?
Alternative heading
Neutrinos: Gather
Left to right: Lise Meitner, Wolfgang Pauli, Enrico Fermi & Wang Ganchang. Image credits: Getty Images & Wikipedia.
Many people have contributed to our current understanding of neutrinos. Here is a little history of this tiny particle:
1911
Lise Meitner and Otto Hahn study beta decay and find evidence that the initial energy before decay is not accounted for by
all of the decay products that they can detect.
1930
Wolfgang Pauli suggests that the missing energy is carried by a very small neutral particle.
1931
Enrico Fermi, an American born and brought up in Italy, names the particle "neutrino", Italian for "little neutral one".
1942
Wang Ganchang proposes a method for detecting the neutrino.
1956
Clyde Cowan and Frederick Raines detect the neutrino, receiving the Nobel Prize in 1995.
Question 1
Imagine: The word "babyccino" describes a little capuccino. The word "neutrino" has its origins in Italian. Think up an English word
to describe "a little neutral one".
There may be students in your class from a non-English speaking background. You may wish to also ask them what word in their
language could mean "a little neutral one".
Symbols are used to represent elements. For example, C is the symbol for carbon and N is the symbol for nitrogen.
The total number of particles in the nucleus, as well as the number of protons in the nucleus, can also be easily represented. For
example, a carbon atom with 14 particles in the nucleus, 6 of which are protons, can be written as 6C14. Of course this means that
there are 14 - 6 = 8 neutrons in the nucleus.
Similarly there are symbols for the parts of atoms, including the neutrino.
Particle
Symbol
electron
0
-1e
proton
p
neutron
n
neutrino
ν
The symbol for the neutrino is ν, the Greek letter nu, which is the first syllable of neutrino. It is like the letter v but both lines are
curved the same way.
A typical beta decay is 6C14 → 7N14 + -1e0 + ν
Putting this into words it would read:
A carbon nucleus decays into a nitrogen nucleus plus an electron and a neutrino.
You will notice that the top numbers balance, i.e. 14 = 14 + 0, which means the total number of particles does not change. Also the
bottom numbers balance 6 = 7 + -1, which means the total amount of charge does not change. These are called conservation rules.
Question 2
​ alculate: Write the following decay in words: 19K40 → 20Ca40 + -1e0 + ν
C
Question 3
Calculate: Find the unknown numbers, x and y, in each of the following:
Equation
210
82Pb
234
yTh
x
→ xBi210 + -1e0 + ν
→
x
91Pa
+
0
-1e
+ν
y
N/A
Neutrinos are not only produced in beta decay but in nuclear
events in the Sun, by supernovae and when matter falls into a
black hole. In fact, billions of neutrinos are passing through
your body every second, mainly from the Sun.
This animated video looks at a neutrino called Nino that comes
from the Sun and his travels from the Sun to the Earth, through
the Earth and beyond. It is a six-minute cartoon with English
subtitles, while the characters speak in Italian.
Loading
Nino Neutrino. Video credit: AGI / YouTube
Question 4
Recount: Describe Nino's journey mentioning the different characters he meets on the way.
Question 5
Describe: ​What happens to the protons and photons that Nino meets?
Question 6
Calculate: The ​Cosmos Magazine article mentioned that 28 high energy neutrinos have been detected by the IceCube Neutrino
Observatory. This was in the first two years of operation. Calculate the average time from detecting one neutrino to detecting the
next.
Question 7
Recall: ​In "Under the ice" the article refers to neutrinos hitting subatomic particles in hydrogen and oxygen nuclei. What subatomic
particles exist in these nuclei?
Question 8
Calculate: The section "Captured" mentions the light detectors. How many light detectors are there? If all the money (see opening
section) had been spent on light detectors, how much would each have cost? ​
Neutrinos: Process
Artist's impression of some of the IceCube Neutrino Observatory neutrino detectors.
The section "Captured" also describes the detection of a very energetic neutrino. Its energy was measured at 1040.7 TeV. What is
this unit of energy, eV, and what does the prefix, "T", stand for?
You will have seen distances measured in kilometres, written as 50 km, the "k" means multiply by 1000 or 103, to give 50,000
metres. Similarly you may have heard about megahertz and gigabytes. "kilo", "mega" and "giga" are all multipliers. T stands for
"Tera" and is another multiplier.
Question 1
Infer: Complete the table below.
Name
Thousand
Prefix
Kilo
Symbol
Power
Number
k
103
1,000
1,000,000
1,000,000,000
Million
Mega
M
106
Billion (US)
Giga
G
109
1012
Trillion
Tera
T
Quadrillion
Peta
P
Googol
N/A
N/A
1,000,000,000,000,000
10100
Too long for this box!
Question 2
I​ nfer: The neutrino's energy is 1040.7 TeV, which is 1040.7 x 1015 eV in power form. Write this value in number form with lots of
zeroes.
"eV" stands for electron volt. It is a unit of energy like Joules or kilowatt-hours, except that it is a very small value that is used when
talking about electrons and protons.
Where are these neutrinos coming from?
After a neutrino impact, the amount of light that each detector receives can be used to work out the point in space from which the
neutrino came. The oval image in the article (see Figure 3 below) is a map of the sky showing the part of the sky where each of the
28 detected neutrinos came from. But it looks very complicated. So, let us start with something familiar.
Figure 1: The familiar map of the Earth.
The flat map of the Earth is this peculiar shape because the Earth is a round ball but it is impossible to put the complete surface of a
round ball on a sheet of paper, so this shape is a way of showing the curved surface of a sphere on a flat surface.
The sky above us is also a bit like a round ball, so a similar map can be used. In the map of the sky in the ​Cosmos ​Magazine article
(Figure 3, below), the line through the middle from left to right is the sky above the earth's equator. The top is the sky above the
North pole and the bottom is the sky above the South pole.
Figure 2 below is another map of the sky, this one showing the different constellations.
Figure 2: A map of the night sky, also known as the atlas of the Universe. Image credit: Richard Powell
Figure 3: A map showing where in the Universe the neutrinos detected by IceCube came from. Image credit: IceCube
collaboration
Question 3
Compare: In the map showing where the neutrinos came from (Figure 3) there is one area where many neutrinos seem to come
from, that is, numbers 25, 24, 2, 14, etc. Look at the map of the constellations (Figure 2) and work out from which constellations
these neutrinos came from.​
Careful! Figure 2 has the centre of our galaxy (marked 0°) at the centre of the map, where as Figure 3 has it on the far right. When
comparing the two maps make sure to keep this in mind.
Question 4
​ ompare: Where do numbers 3 and 6 appear to come from?
C
Question 5
​ ompare: Which neutrinos seem to come from Orion?
C
Question 6
Speculate: The centre of our galaxy, the Milky Way, is located at 0° on Figures 2 and 3. The map showing where the neutrinos came
from (Figure 3) is blank at 0°. So far, no neutrinos have been observed coming from the centre of our galaxy, which is thought to
have a large black hole.
Suggest some reasons why this might be the case.
Neutrinos: Apply
Popcorn, neutrinos and Nobel prizes
Image credit: iStock
This activity is divided into two parts: a short experiment and some additional Cosmos questions. You may complete the tasks in
whichever order suits you best.
Part 1: Experiment - The missing energy of popping corn
Aim
To learn about beta decay, neutrinos and the IceCube Project by measuring the mass of popcorn before and after popping.
Materials
Popping corn: Some popping corn can be purchased already bagged for the microwave oven. It is also available in larger
quantities and you will need to bag it yourself.
Measuring cup, if needed.
Paper bag, if needed.
Microwave oven.
Top loading balance accurate to at least 0.01 g. Note: the balance is very sensitive and should be used with care.
Method
1. Do you have pre-bagged popping corn? If so, go to step 3.
2. Put ¼ cup of popping corn in a paper bag and fold over the top, tight enough to keep the popping corn in, but not so tight that
the popping corn may tear the bag or prevent all the corn from popping.
3. Put the bag of popping corn on the balance and record the mass.
4. Put the bag in the microwave oven and put the oven on for just over two minutes, or as per the instructions on the bag if you
are using pre-bagged corn. When the sounds of the popping corn are about five seconds apart, the oven can be turned off.
5. Remove the bag from the oven and record its mass again on the balance. Note: the bag may be hot, so take care removing it
from the oven and you may need a petri dish to support the bag before putting it on the balance.
Question 1
Did you find a difference in the mass? If so, calculate its value.
Question 2
Express this difference as a percentage of the initial mass.
Question 3
What factors or variables might affect the outcome of this experiment?
Question 4
How could you re-design this experiment to be more accurate?
The change in the popcorn could be explained either as a physical change or a chemical change. A physical change explanation
would be that water, as a liquid, was converted to steam and expanded inside the kernel, causing it to burst. A chemical change
explanation would be, as for a rising cake, a chemical substance such as sodium bicarbonate breaks down releasing carbon dioxide
which causes the kernel to burst.
Question 5
How would you test these two explanations?
Question 6
If this experiment is an analogy for beta decay, such as 6C14 → 7N14 + -1e0 + ν
what does an unpopped corn kernel represent?
what does a popped corn kernel represent?
what represents the neutrino?
Part 2: Additional Cosmos questions
Question 7
Interpret: ​The section "Under the ice": what do you think is the purpose of the round objects in the image?
Note: This is the same image as the one at the top of "Process".
Question 8
Interpret: What do you think the black lines are for?​
Question 9
Speculate: It has been suggested that the discovery of neutrinos from space may be awarded a future Nobel Prize. However the
rules for the prize limit the number of people who can share the prize to three.
Who should get the prize ? The people who thought up the idea of the IceCube, the people who designed and built it or the people
who used it to discover the neutrinos?
Decide who should get the prize and give your reasons.
Neutrinos: Career
Geoffrey Taylor is a physicist from Melbourne who hunts down neutrinos in the search for clues to the origins of our
universe.
What is our universe made of? And how did it begin? These are
questions that physicist Geoffrey Taylor hopes to answer.
Growing up in Western Australia, Geoffrey’s high school maths
teacher told him to study physics at university.
Geoffrey’s teacher must have had an eye for talent - Geoffrey
now works with the world-renowned Large Hadron Collider at
the CERN laboratory in Switzerland. As its name suggests, the
Large Hadron Collider is a massive machine that accelerates
particles to incredible speeds before it smashes them together.
Geoffrey’s job is to sift through the “debris” of the collision to
search for elusive subatomic particles like neutrinos and quarks.
The discovery of these particles could answer many questions
about our universe.
It is both inspiring and challenging to try to understand the
origins of the universe with experiments here on Earth, Geoffrey
says. And there’s no better place to do it than CERN. More than
3,000 physicists from 38 countries work alongside Geoffrey on
the Large Hadron Collider, and he loves being surrounded by
intelligent, enthusiastic scientists. He fondly recalls CERN’s
cafeteria, which he describes as an amazing hub where
everyone from Nobel Prize winners to young PhD students can
meet and discuss many topics.
Image credit: University of Melbourne.
While his job takes him as far as Japan and Switzerland, Geoffrey
calls Melbourne home. He enjoys participating in racing
triathlons and meeting friends over dinner or coffee.
Question 1
Imagine: You are sitting at a table in CERN's cafeteria for lunch. Sitting at the same table are Nobel prize winners and young
aspiring PhD students. What would you wish to talk to them about? Why?
Cosmos Lessons team
Education Editor: Bill Condie
Art director: Robyn Adderly
Profile author: Yi-Di Ng
​Lesson authors: Dan O'Keeffe and Daniel Pikler