This presentation talks about the basics of radioactivity and how it can be applied in our day to day lives. It also lists properties of radiation and some important radioisotopes. Ideal for revision or studying IGCSE physics.

1. Radioactivity
Applications

2. In this presentation:
 All about types of radiations :α,β,γ and their properties.
 Brief description of half-life
 Biological effects of radioisotopes.
 Uses related to penetrating power
 Uses related to cell damage
 Uses related to detectability
 Uses related to radioactive decay
 Some significant radioisotopes

3. α,β,γ : Their properties
Name Structure Charge Penetrating
power
Ionising
power
Obstruction Mass Speed
Alpha Helium
nucleus(2p,2n)
+2 Up to 5 cm
in air.
Strongly
ionising
Thin sheet of
paper
Mass of
p*4
~3 X 107
Beta Electron(0n,-
1p)
-1 Easily travels
through air
and paper
Highly
ionising
Few mm of
metal foil
(Mass of
p)/1840
~2.9 X 108
Gamma Photon(is
electromagn-
etic wave)
0 Easily travels
through
most objects
Least
ionising
Several cm of
dense
metal(eg
lead) or
several m of
concrete
0 3 X 108

4. Brief description of half-life
 The average time taken by half of the atoms in a radioactive sample to decay is
known as its half life.
 This concept is extremely useful to demonstrate the rate of decay, since we can
never measure the point where all the atoms in a sample would have decayed.
 However, knowing the half-life doesn’t assist us in finding the particular atoms that
would decay in a particular time.
 Therefore, we say that radioactive decay is an entirely random process.

5. Biological effects of radioisotopes.
Intense radiation
Cells get highly ionised and die
(RADIATION BURNS)
Suitable and timely treatment may
lead to tissue regrowth.
Cancer
Uncontrolled cell
division
And tumour forms
If DNA is
Damaged by radiation
Gamete affected
by radiation
Damaged DNA
and/or genes
pass on to
offspring
Genetic
mutation(harmful)
Death of fertilised
egg cell or baby
born with genetic
disorder

6. Biological effects of radioisotopes(contd.)
Alpha radiation and
humans
Inside
Highly ionising(eg: radon
and thoron gases)
Radon and thoron
Irradiate us from within
upon inhaling
Lung Cancer
outside
Absorbed by dead cells of
the skin.
Virtually harmless

7. Uses related to penetrating power
Penetrating power
Smoke Detectors
Americium-241 (alpha emitter)
used
If radiation falls on the detector,
circuit is complete and no alarm
When smoke is present, alpha
radiation ionises it and there is no
radiation on the detector
Alarm goes off
Thickness measurements
Beta radiation is used to measure
thickness of paper/plastic sheet
Radiation passes through
paper/plastic
And detector measures the
amount of radiation
If too low, then adjuster reduces
the thickness of paper
Medical diagnosis
Gamma radiation emitting
chemical is injected into the
patient’s body, where it
accumulates in the target area.
A camera then detects the
radiation and gives an image of
tissue under investigation.
Fault diagnosis
Engineers place a gamma emitter
on the inside of a pipe and a
photographic film on the outside
The developed image resembles a
X-ray image and shows the faults.

8. Uses related to cell damage
Cell Damage
Radiation therapy
Gamma/X-rays directed
At tumour
Other tissues suffer minimum
damage
Often used with
chemotherapy(using chemical
drugs)
Food irradiation
Uses Gamma rays to kill
unicellular microbes and preserve
food
Used for astronauts’ food and for
some patients whose resistance
to microbes is very low
Sterilisation
Gamma rays used to sterilise
medical equipment like syringes
and scalpels which are enclosed
in plastic bags
Also used for sanitary towels and
tampons

9. Uses related to detectability
Detectability
Radioactive Tracing
Uses radioactive substance to trace flow of
liquid/gas, or to detect position of
cancerous tissues in the body.
Engineers may inject Gamma emitting substance
into water and then monitor how it moves
through the cracks using Geiger Counter at the
ground level.
Radioactive labelling and genetic
fingerprinting
Radioactively labelled chemicals can be used to monitor complicated sequence of
reactions. Similarly, a genetic fingerprint can be labelled to show up ‘bands’ or specific
fragments of DNA on a photographic film.

10. Uses related to radioactive decay
 All living organisms contain carbon. Most of this is Carbon-12( non-radioactive) but there are
traces of the radioactive Carbon-14 as well.
 C-14 has a half life of 5370 years and is a beta-emitter.
 In a dead living organism, the remaining amount of carbon-14 can be measured to estimate
when the organism was alive/its age.
 This can be done using a Geiger Counter to detect the activity or a mass spectrometer to count
the remaining atoms.
 A mass spectrometer is a machine that that uses magnetic fields to separate atoms according to
their mass and charge.
 This is called radiocarbon dating.
 It can be affected by the atmospheric levels of C-14, making objects seem younger than they
really are.

11. Other Radioactive Dating Techniques
 Geologists use Radioactive dating to measure age of rocks.
 K-40, is an radioactive isotope that decays by beta emission to Ar-40 and is
contained within most rocks.
 Geologists study the proportions of these two isotopes in solidified rocks .
 Greater the proportion of Argon, older the rock.

12. Some important radioisotopes
Name Emits Decays to form
Carbon-14(C-14) Beta Radiation Nitrogen-14(N-14)
Americium-241(Am-241) Alpha Radiation Uranium-237(U-237)
Potassium-40(K-40) Beta Radiation Argon-40(Ar-40)

13. Thank You!