Applications of the elements

1. Applications of the elements

2. Radioactivity • Elements with unstable nuclei are said to be radioactive • Eventuallythey break down and eject energetic particles and emit high-frequency electromagnetic radiation • Involves the decay of the atomic nucleus, often called radioactive decay

3. Radioactivity • It is found in volcanoes, geysers and hot springs

4. 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

5. 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

6. 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

7. 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

8. 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)

9. Radiation dosage • Commonly measured inrads (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

10. Radioactive tracers • Radioactive isotopes are called tracers • Medical imaging

11. 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

12. 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

13. 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

14. 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

15. 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 calledtransmutation(Could be natural or artificial)

16. 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

17. 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

18. 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

19. 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)

20. Nuclear Fission Chain reaction Self sustaining reaction in which the products of one reaction even stimulate further reaction events

21. 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

22. Nuclear fission reactors • DISADVANTAGES Radioactive waste products • BENEFITS Plentiful electricity Conservation of fossil fuels

23. 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

24. Mass –Energy equivalence E=mc² • More energy →greater mass in the particle • Nucleons outside > inside • More energy is required to separate nucleons

25. 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

26. Thermonuclear fusion • Hydrogen →Hellium and radiation • Less mass, more energy • Depends on high temperatures

27. 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

28. 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