This document provides an overview of radioactivity and some key concepts. It explains that radioactive decay occurs when an unstable atomic nucleus releases energy by emitting particles or electromagnetic waves. The three main types of radioactive decay are alpha, beta, and gamma emissions, which have different levels of penetrability. It defines half-life as the time it takes for half of a radioactive sample to decay and describes how the radioactive decay law and exponential decay equation relate to the constant rate of decay over time.

2. Half life of Radio-active
source
• Introduction
• Radio-active elements
• Properties of 𝜶, 𝜷 𝒂𝒏𝒅 𝜸 ras
• Half life
• Decay Law
• Geiger Muller Counter
• Taking reading

3. Early Pioneers in
Radioactivity
The Curies:
Discoverers of
Radium and
Polonium 1900-
1908
Roentgen:
Discoverer of
X-rays 1895
Becquerel:
Discoverer of
Radioactivity
1896
Rutherford:
Discoverer
Alpha and Beta
rays 1897

4. What do we mean by
Radioactivity?
• Radioactive decay is the process in which an unstable
atomic nucleus loses energy by emitting radiation in
the form of particles or electromagnetic waves.
• There are numerous types of radioactive decay. The
general idea:
• An unstable nucleus releases energy to
become more stable

5. Important Aspects
Important aspects of radioactivity:
• Radioactivity is a quantum phenomenon. Radioactive
decay is a statistical process.
• The energy released in radioactive decay comes from
mass which is converted to energy.
• Elements transform into other, different elements.
• Radioactivity occurs because some nuclei are unstable
and spontaneously decay.

6. Some Key Definitions
Before We Move on
• Z = The Atomic Number. It’s the Number of
Protons in the nucleus of an Atom.
• Nucleus: It’s where the Protons and Neutrons
are located in an Atom.
• Protons: Positively Charged Particles in the
Nucleus of the atom. Mass = (approx) 1 AMU
• Neutrons: Neutrally charged particles in the
nucleus of an atom Mass = (approx) 1 AMU
• Mass Number of an atom: Number of Protons
+ Number of Neutrons in the nucleus of an atom.

8. Common types of
radioactive emissions

9. Kinds of Radioactivity
The three main decays are Alpha, Beta and
Gamma

10. Three Common Types of Radioactive
Emissions - Penetrability
• Alpha particles may
be completely
stopped by a sheet of
paper
• beta particles by
aluminum shielding.
• Gamma rays can only
be reduced by Heavy
substantial obstacles,
such as a very thick
piece of lead.

11. Half Life
• “The half-life of an element is the time it takes for
half of the material you started with to decay”
Remember, it doesn’t matter how much you start
with. After 1 half-life, half of it will have decayed.
• Each element decays into a new element
• C14 decays into N14 while U238 decays into Pb206
(lead), etc.
• The half-life of each element is constant.

16. Radioactive Decay law
• If the number of nuclei in a sample is N and the
number of radioactive decays per unit time Δt is
ΔN then,
•
ΔN
Δt
∝N
• or
ΔN
Δt
=λN,
• Where, λ is the constant of proportionality called
the radioactive decay constant or disintegration
constant.

17. • the number of radioactive decays ΔN is
reducing the total number present in the sample.
Convention tells us that this should be termed
negative.
•
𝑑𝑁
𝑑𝑡
=−λN
• Re-arranging this,
•
𝑑𝑁
𝑁
=−λdt
• Integration of both sides then results in,
• 𝑁0
𝑁 𝑑𝑁
𝑁
=−λ 𝑡0
𝑡
𝑑𝑡
• lnN−lnN0=−λ(t−t0)

18. • Here, N0 represents the original number of
nuclei in the sample at a time t0, i.e. t=0.
Applying that in the equation results in;
•
𝑑𝑁
𝑁0
=−λt
• This further leads to,
• N(t)=N0e−λt

19. Rate of Decay
• Getting back to the expression, to see
radioactive decays clearly, we should focus not
on the number but on the rates. Rate here is the
change per time. Calculating the rate of decay,
• R=−
𝑑𝑁
𝑑𝑡
• Substituting N(t) in the equation and
differentiating it,
• N(t)=N0e−λt

20. Differentiation result is’
R=−
𝑑𝑁
𝑑𝑡
=λN0e−λt
R=R0e−λt
R0 here represents the Radioactive decay
rate at time, t=0.
Substituting the original equation back here,
ΔN
Δt
=λN
We get,
R=λN

21. SI Unit of Radioactivity
The total decay rate R of a radioactive sample is
called the activity of that sample. SI unit of the
activity is Becquerel, in the honour of
Radioactivity’s discoverer, Henry Becquerel.
1 becquerel = 1 Bq = 1 decay per second
Another unit is the curie.
1 curie = 1 Ci = 3.7×1010Bq

22. What is half-life?
• In radioactivity, the life of a sample is measured using two different
measurements.
• Half-Life, T1/2: “Half-life is the time period in which both the
number of nuclei, N and the rate of decay, R have been reduced
to a half of the original value”.
• If we start with 100 nuclei, after one half-life the number left will
be 50. Second, 25. Third, 12.5. Fourth, 6.25 and so on.
• R=R0e−λt
• At the first half-life, R=1/2×R0 and t = T1/2. Substituting and
solving for T1
2
.
• T1/2=
ln2
λ
• =
0.693
λ