Transcript radioactivity: types of radiation

RADIOACTIVITY: TYPES OF RADIATION
By the end of this presentation you should be
able to……
 List the three types of nuclear radiation
 Describe the nature of each type.
 Complete equations that illustrate the
different types of emission.
There are three types of radiation.
1. What is Alpha radiation? (a)
• A clump of two protons and two neutrons,
• A helium nucleus
4He
•
2
•
•
Is positively charged
It is the largest of all the three types of
radiation.
226Ra
88
This is an unstable
atom of radium. It
has 88 protons and
(226 -88) 138
neutrons.
When it “throws out” a particle of
radiation, it is said to have “decayed”.
4He
Since222
the
nucleus
this atom is now
Rn
+ of
86 from the original,
2
different
86 protons
and 136 neutrons, this means a
new element
has been
formed,
radon.
The alpha particle that
is thrown out has alot
of energy and can
damage human cells.
2.
•
•
•
What is Beta radiation? (b)
A fast moving (high energy) electron.
It is negatively charged.
When a neutron in the nucleus
disintegrates, it forms an electron (which is
emitted as a beta particle) and a proton
which remains in the nucleus.
Caesium-55 decays by beta emission
and changes into barium-56.
This is what
happens inside
the nucleus.
137Cs
55
137Ba
56
+
0e
-1
3. What is Gamma radiation? (g)
• High frequency electromagnetic radiation
• No charge
Barium-137 is unstable and decays by gamma emission. The
gamma ray takes some of the energy of the nucleus away with
it so the remaining barium atom is more stable. The mass does
not change.
Gamma ray
This type of radiation is usually emitted along with alpha or
beta particles. It is the most penetrating of all three. For this
reason it can be the most dangerous if the source of radiation
is outside of the body.
UNDERSTANDING RADIOACTIVITY EQUATIONS
Almost every year, equations representing radioactive
decay will appear within examination questions! You must
try to remember the composition of particles of radiation,
along with how they are represented in equations.
PARTICLE
Alpha
Beta
MASS NUMBER
4
0
PROTON NUMBER
2
-1
SYMBOL
4He
;
4a
0e
;
0b
2
-1
2
-1
Remember that gamma radiation (g) may occur at the
same time as the others and since it is an electromagnetic
wave, will not affect the mass of the element.
Look carefully at how the mass numbers (at the
top) add up to the same number before and after
226Ra
88
222Rn
86
+
4He
2
....a radiation
The proton numbers (at the bottom) should also
add up to the same number before and after decay
137Cs
55
137Ba
56
+
0e
....b radiation
-1
Examination questions may provide you with
equations with some numbers missing and ask you
to complete it, or to recognise the type of
radioactivity being emitted.