Applications of the elements. Radioactivity Elements with unstable nuclei are said to be radioactive Eventually they break down and eject energetic particles.

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