Applications of the elements
Radioactivity
• Elements with unstable
nuclei are said to be
radioactive
• Eventually they break
down and eject energetic
particles and emit highfrequency electromagnetic
radiation
• Involves the decay of the
atomic nucleus, often
called radioactive decay
Radioactivity
• It is found in volcanoes, geysers and hot
springs
Alpha, Beta and Gamma Rays
• All elements with an atomic
number greater than 82 (after
Lead) are radioactive
• These elements emit 3
different types of radiation,
named α ß γ (alpha, beta and
gamma)
• α : carries positive charge
• ß : carries negative charge
• γ : carries no charge
• Can be separated by placing a
magnetic field
Alpha, Beta and Gamma Rays
• The alpha particle is the
combination of 2 protons, and
2 neutrons (nucleus of He)
• Large size, easy to stop
• Double positive charge (+2)
• Do not penetrate through light
materials
• Great kinetic energies
• Cause significant damage
Alpha, Beta and Gamma Rays
• A beta particle is an electron
ejected from a nucleus
• The difference from this and other
electrons is that it originates inside
the nucleus, from a neutron
• Faster than an alpha particle
• Carries only one negative charge
(-1)
• Not easy to stop
• They can penetrate light materials
• Harming to kill living cells
Alpha, Beta and Gamma Rays
• Gamma rays are the high•
•
•
•
•
•
frequency electromagnetic radiation
emitted by radioactive elements
It is pure energy
Greater than in visible light,
ultraviolet light or even X rays
No mass or electric charge
Can penetrate through almost all
materials
(except Lead)
Cause damage
Sources of radioactivity
• Common rocks and
minerals in the
environment
• People who live in brick,
concrete and stone building
are exposed to greater
amounts
• Radon-222 (gas arising
from Uranium deposits)
• Non natural sources –
medical procedures
• Coal and nuclear power
industries (wastes)
Radiation dosage
• Commonly measured in rads
(radiation absorbed)
• Equals to 0.01 J of radiant
energy absorbed per kilogram
tissue
• The unit to measure for
radiation dosage based on the
potential damage is the rem
• Dosage: # rads x factor of
effects
• Letal doses →begin at 500
rems
Radioactive tracers
• Radioactive isotopes are called tracers
• Medical imaging
The atomic nucleus and the strong
nuclear force
• Strong nuclear force:
attraction between
neutrons and protons.
• Strong in short
distances
• Repulsive electrical
interactions (strong
even in long distances)
• A small nucleus has
more stability
The atomic nucleus and the strong
nuclear force
• A nucleus with more than
82 protons are radioactive.
There are many repulsive
effects due to all the
protons interacting together
• The neutrons are like the
“nuclear cement” (hold the
nucleus together). Attract
p+ and nº
• The more p+, the more nº
needed to balance the
repulsive electrical forces
The atomic nucleus and the strong
nuclear force
• In large nucleus more nº are needed
• Neutrons are not stable when alone
• A lonely neutron is radioactive and
spontaneously transforms to a p+ and
e• Nº seems to need p+ to avoid this from
happening
• When the nucleus`size reaches a
certain point, the #nº> #p+→ nº
transform into p+
• More p+= stability decreases, repulsive
electric force increases, starts radiation
Half life and transmutation
• Half life: the rate of decay for a
radioactive isotope. The time it
takes for half of an original
quantity of an element to decay
• Example: radium-226 (half life of
1620 years), uranium- 238 (half
life of 4.5 billion years)
• Half lives are not affected my
external conditions, constant
• The shorter the half life, the
faster it desintegrates, and the
more radioactivity per amount is
detected
Half life and transmutation
• To determine the half life
is used a radiation
detector
• When a radioactive
nucleus emits alpha or a
beta particle, there is a
change in the atomic
number, which means
that a different element is
formed
• This change is called
transmutation (Could be
natural or artificial)
Natural transmutation
• Uranium- 238 (92 protons, 146 neutrons)
• Alpha particle is ejected (2 protons and 2 neutrons)
• No longer identified as Uranium- 238 but as
Thorium-234
• Energy is released (kinetic energy of the alpha
particle, kinetic energy of the Thorium atom and
gamma radiation
Natural transmutation
• When an element ejects a beta particle from its
nucleus, the mass of the atom is practically
unaffected, there`s no change in the mass number,
its atomic number increases in 1.
• Gamma radiation results in no change in either the
mass or atomic number
Artificial transmutation
• Ernest Rutherford was the
1st to succeed in
transmuting a chemical
reaction
• He bombarded nitrogen gas
with alpha particle from a
piece of radioactive element.
The impact of an alpha
particle on the nitrogen
nucleus transmutes Nitrogen
into Oxygen
• Other experiments are used
to make synthetic elements
Nuclear Fission
• Hahn and Strassmann (1938)
• Uranium has not enough
nuclear forces
• Stretches into an elongated
shape
• Electric forces push it into an
even more elongated shape
• Electric forces > strong nuclear
forces
• The nucleus splits
• U-235 released energy (kinetic
energy, ejects a neutron and
gamma radiation)
Nuclear Fission
Chain reaction
Self sustaining
reaction in which the
products of one
reaction even
stimulate further
reaction events
Nuclear fission reactors
• An important amount of energy in the world is
made up by the use of nuclear fission reactors
• Boil water to produce steam for a turbine
• The fuel is Uranium
Nuclear fission reactors
• BENEFITS
Plentiful electricity
Conservation of
fossil fuels
• DISADVANTAGES
Radioactive waste
products
Mass –Energy equivalence E=mc²
• Albert Einstein discovered the
mass is actually “congealed”
energy
• E= the energy in rest
• M= mass
• C= speed of light
• c²= constant of energy and mass
• This relation is the key in
understanding why and how
energy is released in nuclear
reactions
Mass –Energy equivalence E=mc²
• More energy →greater
mass in the particle
• Nucleons outside > inside
• More energy is required
to separate nucleons
Nuclear fusion
• Is the opposite to nuclear
fission, it is a combination of
nuclei
• Energy is released as
smaller nuclei fuse. Less
mass is obtained
• For a fusion reaction to
occur, the nuclei must collide
at a very high speed in order
to overcome the mutual
electric repulsion
• Examples: Sun and other
stars
Thermonuclear fusion
• Hydrogen →Hellium and radiation
• Less mass, more energy
• Depends on high temperatures
Atomic bomb
Hiroshima y Nagasaki Case
• Nuclear attacks near the
end of World War II against
the Empire of Japan by the
United States on August 6
and 9, 1945.
• “Little Boy” →Hiroshima
(U-235)
• “Fat Man” → Nagasaki
(Plutonium-239)
• Many people died due to
the radiation poisoning
Hydrogen bombs
Eniwetok case
• Marshall islands (Pacific
Ocean)
• 1952
• Nothing survived
• In the zero point of the
explotion (center of the
bomb) the temperature
was 15 million degrees
celsius