Nuclear Chemistry. Transmutations and the Creation of Elements

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1 Nuclear Chemistry Transmutations and the Creation of Elements

2 Nuclear Fusion When two smaller elements are fused together to form a larger element.

3 Fusion is Hard! There are two competing forces in an atom: The electromagnetic force is pushing protons apart. The strong nuclear force is holding nucleons together. But, the strong nuclear force only works over a small distance (~ 2 proton radii). Thus, in order to make atoms fuse, you must have enough energy to exceed the repulsive force of the electromagnetic force. You need to achieve temperatures over 1 million C to make fusion occur!

energy to overcome the repulsive forces of the electromagnetic

4 Particle Accelerators Particles need to be accelerated at velocities approaching the speed of light to have enough kinetic energy to overcome the repulsive forces of the electromagnetic force. Protons can then be attached to each other with the strong nuclear force.

5 Normal Stars Fuse Hydrogen to form Helium Helium can be fused to form larger elements, including the main elements of planets; Carbon, Nitrogen, Oxygen, Silicon, & Magnesium

6 Our Sun 91.2% of all atoms are hydrogen, 8.7% Helium, 0.1% other elements. Normal stars can fuse elements up to Iron in their core, especially as they grow larger and hotter.

But, when giant stars collapse on themselves and then explode in the universe

8 Supernovae Normal stars can not fuse anything larger than iron, which is why iron is the largest common metal present on most planetary bodies. But, when giant stars collapse on themselves and then explode in the universe s largest explosions, the energy released is great enough to fuse atoms larger than iron.

9 Supernovae All elements on Earth between Cobalt and Uranium formed from interstellar dust that came from the explosion of supernovae.

10 Fission Large atoms being split apart. Occurs naturally, but is a very slow process (millions of years). Can be sped up with the addition of high velocity neutrons.

11 Nuclear Reactor A controlled chain reaction in which emitted neutrons split the next uranium atom.

12 Nuclear Rods Contain materials that can absorb excess neutrons to slow the rate of fission so that it produces just the right amount of heat.

14 How Nuclear Power Works Use fission to produce energy to boil water. Steam will turn a turbine to generate electricity.

15 Controlled vs. Uncontrolled

16 How Atomic Bombs Work Fission Reactions

17 Let s See Some Historic Footage

18 What is a Nuclear Meltdown? Fukishima Nuclear Disaster. Chernobyl Nuclear Meltdown

19 Extent of Major Radiation Release Chernobyl 1986

20 Types of Radioactivity Alpha particles Beta particles Gamma rays Neutron emission Positron emission Electron capture Plutonium Glows in the dark

Radioactive Things Often Glow The release of

Radium was used in glow in the dark watches.

21 Radioactive Things Often Glow The release of energy from decay can make them glow. Uranium was used in glass and Fiestaware for many years. Radium was used in glow in the dark watches. Production only stopped once the dangers of radioactivity were better understood.

They were told it was harmless Radium is very similar

22 Radium Girls The Radium Girls painted radium on watches. Many of them died from years of exposure to the substance. They were told it was harmless Radium is very similar chemically to calcium and thus it entered their bones and they died of bone cancer.

23 Alpha Particle (α +2 ) 2 protons and 2 neutrons Equivalent to the 4 He +2 atom All Helium on Earth originates from radioactive decay of large atoms (Uranium, Thorium, etc). Low penetration (can be stopped by skin or air). Biggest danger: Eating them Drinking them Breathing them

24 Beta Particle (β - ) Equivalent to an electron leaving nucleus Converts a neutron into a proton. Changes element up one But doesn t change overall mass. Medium penetration (can penetrate skin)

25 Gamma Ray Radiation (γ) Unstable atoms sometimes simply need to release energy to calm down. This is often in the form of highly ionizing gamma rays. This is the most deadly form of radiation! It does not result in any change in mass or element type.

26 Neutron Emission (n) Sometimes extra neutrons are released from atoms, especially following fission or fusion reactions. These do not change the element type, only the mass. It is extremely ionizing and dangerous.

27 Positron (β + ) Equivalent to a positively charged electron leaving nucleus Converts a proton into a neutron. Changes element back one But, doesn t change overall mass. Medium penetration (can penetrate skin)

28 Antimatter Annihilation When matter (electron) and antimatter (positron) meet, they destroy each other and are converted into pure energy, in the form of gamma rays. Thus, positron emissions are almost always followed up with Gamma Ray emissions

29 Antimatter Annihilation What this annihilation looks like! Another Look

30 Electron Capture An electron is captured by a proton in the nucleus to form a neutron. It makes the atom go back one. Very rare form

31 Penetrating Power of Radiation

32 Nuclear Transmutations Any time a new element or isotope is created, it is called a transmutation. They can be naturally formed through radioactive decay. They can be fission products. They can be formed through particle accelerators by slamming atomic nuclei with various subatomic particles.

33 Uranium-235 vs. Uranium-238 The two most common isotopes of Uranium are 238 U at 99.28% and 235 U at 0.72% But, 238 U is not fissile, while 235 U is. Nuclear reactors need between 3-5% of 235 U Nuclear bombs need at least 85% or more of 235 U So, how do you get enough 235 U to make nuclear fuel rods and or nuclear bombs?

It is then rotated in a centrifuge at high velocity, such that it separates by

34 Isotope Separation Using Centrifuges Uranium Hexaflouride sublimates to a gas at 56.5 C. It is then rotated in a centrifuge at high velocity, such that it separates by mass. 235 UF 6 is only 1.6% lighter than 238 UF 6, so it takes a lot of energy to separate them. UF 6 crystals sublimate at relatively low temperatures

35 Transmutation Practice

36 Transmutation Practice

Nuclear Chemistry. Chapter 24

Nuclear Chemistry. Chapter 24 Nuclear Chemistry Chapter 24 Radioactivity Radioisotopes are isotopes that have an unstable nucleus. They emit radiation to attain more stable atomic configurations in a process called radioactive decay.