Applications of the elements

Radioactivity• Elements with unstable

nuclei are said to be radioactive

• Eventually they break down and eject energetic particles and emit high-frequency 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 FissionChain 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 bombHiroshima 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