Transcript IONIZING RADIATION AND RADIONUCLIDS AS THE SOURSES …

ORIGIN
OF IONIZING RADIATION
AND RADIONUCLIDS
Historical background
Humans have evolved in an
environment of ionizing radiation
Discovery of X rays (1895)
Wilhelm Conrad Roentgen
Discovery of uranium’s
natural radioactivity (1896)
Antoine Henri Becquerel
Discovery of polonium
and radium (1898)
Marie Curie
Discovery of harmful effects
of ionizing radiation
• First report about local radiation injuries (1896)
and radiation-induced skin cancer (1902)
• First report about radiation-induced sterility
(1903) and radiation-induced leukemia (1911)
• 1920s: bone cancer
radium dial painters
among
• 1930s: liver cancer and leukemia
due to Throtrast administration
• 1940s: excess leukemia among
first radiologists
Discovery of A-bomb’s effect
in Japan (1945)
Hiroshima, 6.08.1945
Nagasaki, 9.08.1945
Discovery of radiation
accidents consequences
Coiania, Brazil (1987)
Chernobyl, USSR (1986)
Terrorist can use
of radioactive material
After September 11th, growing
apprehension that by shrouding a core of
conventional explosives around a
radioactive source….
…..contamination could be
spread over a wide area…
+
=
…and terror created!!
What is radiation?
Origin of ionizing radiation
Ionizing radiation
Origin of radiation
is from atom anatomy
Electron
Proton
Neutron
Nucleons
Atomic symbols
A
Z
MASS NUMBER (the number of protons and neutrons)
XN
SYMBOL OF ELEMENT
The number of neutrons
ATOMIC NUMBER (the number of protons)
Example:
131
I
53 78
131I
or I-131
Isotopes
Why are some nuclides
radioactive?
The stable isotopes of elements have very definite ratios of
neutrons to protons in their nuclei.
As the atomic mass number increases, the ratio of neutrons to
protons increases according to a definite pattern. If isotopes
vary from this pattern, they are relatively unstable.
The most stable state of a nucleus is called the ‘ground’ state.
In an unstable nucleus the nucleons are in an ‘exited’ state
and must release energy to reach the ground state.
In the transformation of an unstable nucleus to a more stable
nucleus, energy is emitted in the form of particles such as
alpha and beta particles, and in some cases photons (gamma
rays). This is the process of radioactive decay.
Alpha (α++) decay
A X
Z
e.g. 23892U
4 He
Y
+
Z-2
2
A-4
234
90Th +
4 He
2
Beta (-) decay
p + e- + υ
n
A
A
- +
X
Y
+e
Z
Z+1
e.g.
131 I
53
 13154 Xe+e-+
Positron (+) decay
p
A
A
++ 
X
Y+e
Z
Z-1
n+
e.g.
+
e +
υ
18 F 18 O+e++
9
8
Electron capture
p+ + e- n + 
A
A
X
Z
Z-1 Y +
125 Te+
I

53
52
125
Gamma () emission
Nuclear energy levels:
gamma radiation
SIMPLIFIED NUCLEAR MODEL
Gamma ray
Activity
Radioactivity is the number of decaying
nuclei per unit of time
The System International (SI) unit of
radioactivity is the Becquerel (Bq)
1 Bq = one disintegration per second
Non-SI unit of radioactivity is the Curie (Ci)
1 Ci = 3,7 x 1010 radioactive disintegration per second
1 Bq = 2.7 x 10-11 Ci
1 Ci = 3.7 x 1010 Bq
Time of half-life
Electric generators
of ionizing radiation
Ionizing radiation can also be obtained by
subjecting matter to a sufficient amount of energy.
This is the principle of X-ray generators and
particle accelerators
X-rays can have two sources:


electron rearrangement: their energy is then specific to the
element considered but not to the isotope
the phenomenon of incident electron retardation
(Bremsstrahlung effect): their energy is non specific and
varies between zero and the maximum energy as a direct
function of the initial energy of the electron.
Comparison of the risks from radioactive
sources and electric generators

The emission of ionizing radiation by a
radioactive source behaves a law of decay
governing the time in which work can be done

Electric generators obey an “On/Off” effect
which is tied to the presence or absence of the
electricity supply
Forms of ionizing radiation
and its abilities
Excitation of atom or molecules
by ionizing radiation
Ionization of atom or molecules
by ionizing radiation
Forms of ionizing radiation
Directly ionizing
Particulate radiation
consisting
of
atomic
or
subatomic particles (electrons,
protons, etc.) which carry
energy in the form of kinetic
energy of mass in motion
Indirectly ionizing
Electromagnetic radiation
in which energy is carried by
oscillating electrical and magnetic
fields traveling through space at speed
of light
Specific ionization and
linear energy transfer (LET)
Penetrating power of radiation
Alpha particle interaction
Interaction of alpha radiation with
living matter: external deposition
 Alpha radiation is not
external hazard
 The maximum range
in tissue is < 0.1 mm
 All alpha radiation is
absorbed in stratum
corneum
Interaction of alpha radiation with
living matter: internal deposition
Prime danger is inhalation and ingestion
of alpha emitter
Beta interaction with matter
Interaction of beta radiation
with living matter
Cell
nucleus
Cell
diameter
100 cell
diameter
alpha
1.7 MeV beta
0.15 MeV beta
beta
5.3 MeV alpha
Auger
I
0.001
I
0.01
I
0.1
mm
I
1
I
10
ı
100
Interaction of beta radiation with living
matter: external and internal deposition

Beta radiation damages
epithelial basal stratum. High
energy ß-radiation may affect
vascular layer of derma, with
lesion like thermal burn
 Danger is inhalation and
ingestion of beta emitter
 Danger is external ßirradiation whole body
Neutron interaction
Interaction of neutron radiation
with living matter
Neutron radiation is only external hazard:
high danger of external irradiation whole body
Interaction of gamma radiation
with matter
In terms of ionization, gamma radiation
interacts with matter in three main ways:
1. Photoelectric effect
2. Compton scattering
3. Pair production
Gamma interaction
by photoelectric effect
Gamma interaction
by Compton scattering
Pair production
Difference between
X-rays and gamma rays
Interaction of gamma radiation with living
matter: external and internal deposition
 Gamma radiation is very
external hazard:
- high danger of external
irradiation whole body;
- danger of external irradiation
of skin
 Danger is inhalation and
ingestion of gamma emitter
Risk due to radiation exposure
Summary of lecture
• Ionizing radiation is radiation with enough energy so that during an
interaction with an atom, it can remove tightly bound electrons from
their orbits, causing the atom to become excitated or ionized.
• Ionizing radiation occurs in two forms – particles or waves.
• Alpha particles is not external hazard and can bee shielded against
by clothing. Internal deposition of alpha particles is of importance on
a long-term basis in terms of causing radiation injury.
• Beta irradiation causes damage to the epithelial basal stratum. The
lesion is similar to a superficial thermal burn. Beta particles shielding
requires solid materials, like a wall.
• Gamma and neutron radiation are the most biologically active, and
required lead equivalent shielding for protection.
• Fission products are the major radiation hazard, because a large
number emit penetrating gamma radiation. This can result in whole
body injuries, even at great distance.
Lecture is ended
THANKS FOR ATTENTION
In lecture materials
of the International Atomic Energy Agency (IAEA),
kindly given by doctor Elena Buglova, were used