ICT Role in 21st Century Education & its Challenges.pptx
Radioactivity and laws of radioactivity
1. RADIOACTIVITY AND LAWS
OF RADIOACTIVITY
Dr. Jitendra Patil
Associate Professor
Dr, D.Y.Patil Medical College, Hospital and Research Institute
2. Discovery of Radioactivity
• Henri Bequerel (1852-1908)
• During his studies of phosphorescence (1896),
found a mineral (uranium) would darken a
photographic plate even if the plate was wrapped.
• Found that this mineral emitted a new kind of
radiation (X-rays needed an external stimulus)
3. Discovery of Radioactivity
• Marie (1867-1934) and Pierre (1859-1906) Curie
isolated two previously unknown radioactive
materials, polonium and radium
• Radioactivity was found to be unaffected by
chemical and physical testing, showing that the
radiation came from the atom itself – specifically
from the disintegration or decay of an unstable
nucleus
4. Discovery of Radioactivity
• 1898 – Ernest Rutherford began studying the
nature of the rays that were emitted
• Classified into three distinct types according to
their penetrating power.
• Alpha decay (α) – positively charged;can barely
penetrate a piece of paper
• Beta Decay (β) – negatively charged; pass
through as much as 3mm of aluminium
• Gamma Decay (γ) – neutral; Extremely
penetrating
5. Radioactivity
• The nuclei of naturally occurring heavy
elements like U,
unstable and
Th, Ra and Po are
keep on emitting
spontaneously invisible rays or radiations
and give more stable elements.
6. Radioactivity
• These heavy elements
radioactive elements.
are called
• The property of emitting these rays is
called radioactivity of the elements.
7. Radioactivity cont….
• It is the nucleus of an atom of an element
which spontaneously disintegrates to emit α,
β or γ-rays.
• The rays emitted by radioactive element are
called radioactive rays
8. Thus radioactivity can be defined as:-
The phenomenon in which the nucleus of the
atom of an element undergoes spontaneous
and uncontrollable disintegration (or decay)
and emit α, β or γ-rays.
9. Radioactivity cont….
The emitted α, β or γ-rays from unstable nuclei are
collectively called ionizing radiations.
Depending on how the nucleus loses this excess
energy either a lower energy atom of the same
form will result, or a completely different
nucleus and atom can be formed.
10. Radioactivity cont….
Ionization
is the addition or removal of an electron to create
an ion.
Ionizing radiation
is any type of particle (α, β) or electromagnetic
wave (γ) that carries enough energy to ionize or
remove electrons from an atom.
.
11. Radioactivity cont….
• These radiations are of such high energy
that when they interact with materials, they
can remove electrons from the atoms in
the material. This effect is the reason why
ionizing radiation is hazardous to health
12. • Radioactivity is of the following two types
which are:
a) Natural radioactivity
b)Artificial Radioactivity
13. Natural Radioactivity
is the process of spontaneous (i.e. without
external means, by it self) disintegration of the
nuclei of heavy elements with the emission of
radiation.
-these are unstable nuclei found in nature.
15. Natural radioactivity cont…..
• All heavy elements above Z=82 show the
phenomenon of radioactivity. the emission
of radiation changes the structure of the
nucleus and transforms the atom into a
lighter atom.
17. Artificial Radioactivity
• Is the process in which a stable (non-
nucleus is changed into an
(radioactive) nucleus by
radioactive)
unstable
bombarding it with appropriate atomic
projectiles like α, neutron, proton.
19. The differences between natural
and artificial radioactivity
Natural radioactivity Artificial radioactivity
Is spontaneous, since in natural
radioactivity, the nuclei of heavy
atom disintegrate on their own
accord, forming slightly lighter and
more stable nuclei and emitting α,β,ᵞ
radiations.
Is not spontaneous, since in it the
nuclei of the atoms have to be
bombarded by fast moving particles
like α, neutrons, protons, deuterons.
Is uncontrolled and hence it can not be
slowed down or accelerated by any
means.
Can be controlled by controlling the
speed of the bombarding particles used
for bringing about the artificial
radioactivity
Is usually shown by heavy elements. Can be induced even in light element.
20. Units of Radioactivity
The standard unit of radioactivity is CURIE (c)
It is defined as mass of radioactive substance that produces 3.7 x 1010
disintegrations per second
21. Equivalent dose
Is a dose quantity representing the stochastic health
effects of low levels of ionizing radiation on the human
body.
It is derived from the physical quantity absorbed dose,
but also takes into account the biological effectiveness of
the radiation, which is dependent on the radiation type
and energy.
The SI unit of measure is the Sievert (Sv).
22. Other Common Radiation Units – SI
1. Gray (Gy)
• To measure absorbed dose. (the amount of energy
actually absorbed in some material) and is used for any
type of radiation and any material (does not describe the
biological effects of the differentradiations)
• Gy = J / kg (one joule of energy deposited in one kg
of a material)
23. 2. Roentgen (R)
-Is used to measure exposure but only to
describe for gamma and X-rays, and only in
air.
• R = depositing in dry air enough energy
to cause 2.58 𝑥10−4 coulombsper kg
24. 3. Rem (Roentgen Equivalent
Man)
- to derive equivalent dose related the
absorbed dose in human tissue to the effective
biological damage of the radiation.
.
25. 4. Sievert (Sv)
• To derive equivalent dose related to the absorbed dose in human tissue to the effective Biological damage
of the radiation.
• Sv = gy x q
• (q= quality factor unique to the type of incident radiation)
• (Gy= Gray unit)
26. 5. Becquerel (Bq)
- to measure a radioactivity (the quantity of a radioactive
material that have 1 transformations /1s)
• Bq = one transformation per second, there are 3.7 x 1010 Bq
in onecurie.
27. Few conversions
1 curie = 3.7 x
10
10
disintegrati
ns per second
1 roentgen (R) =
0.000258
coulomb/
kilogram (C/kg)
1 megabecquerel
(MBq)
=
0.027 millicuries
(mCi)
1 gray (Gy) = 100 rad
1 sievert (Sv) = 100 rem
28. Detection and Measurement of
Radioactivity
• The radioactivity of
substance is detected
the radioactive
and measured by
instruments like:-
• Geiger-Muller (G-M) counter
• Wilson Cloud Chamber.
• Scintillation Counters.
• Dosimeter.
32. Fundamental laws of radioactivity
Rutherford Soddy Law of Radioactive
Decay
In 1902, Rutherford and Soddy studied the disintegrating of many radioactive
substance and found the conclusion regarding radioactive decay known as
Rutherford and Soddy Rules.
33. According to the fundamental law of radioactivity decay:
1. Radioactivity is a nuclear phenomenon and the rate of emission of
radioactive ray cannot be controlled by physical or chemical process that
mean neither can it be extended nor can it be reduced.
2. The nature of the disintegration of radioactive substance is statistical, this
is, it very difficult to say which nucleus will be disintegrated and which
particle will emit α,β and γ With the emission of α,β and γ rays in the process
of disintegration one element change into another new element, its
chemical and radioactive quantities are completely new.
3. At any time the rate of decay of radioactive atom is proportional to the
number of atoms present at that time.
