Fission & Fusion

Radioactive Elements Any element over atomic number 83 is radioactive. Radioactive materials have unstable nuclei (too few or too many neutrons). When an unstable nucleus decays, it breaks apart emitting particles and energy as it decays. Three types of nuclear radiation: Alpha particles Beta particles Gamma radiation electromagnetic wave

Fission The process used to release nuclear energy by splitting nuclei is called fission. + ENERGY

What nuclei can split during nuclear fission? Only large nuclei like U or plutonium can split apart during nuclear fission. Click on image for animation

What nuclei can split during nuclear fission?                                                U-236 is so unstable that it immediately splits into barium & krypton nuclei, several neutrons & a large amount of energy

Chain Reaction Free neutrons produced by fission can hit other nuclei emitting more neutrons repeating the reaction over and over. A series of fission reactions is called a chain reaction. Can only be slowed by using materials that will absorb the neutrons.

Chain Reaction An uncontrolled chain reaction releases a huge amount of energy in a short time & requires a critical mass of starting material to produce more reactions.

Fusion The sun is powered by nuclear fusion. In a nuclear fusion reaction, two small, light nuclei combine to form one larger, heavier nucleus. Two hydrogen atoms combine under extreme heat and pressure to form a helium atom. (H-2 + H-2→He-4)

Fusion Why would we want to use the fusion reaction in a nuclear power plant? 1. Hydrogen is the most common element in the universe. 2. Could meet energy demands for millions of years

How are temperature & fusion related? How can two nuclei get close enough to combine? They must be moving very fast. All nuclei positively charged Thus repel each other KE must overcome electric force to push them close enough to combine KE increases as temperature increases Temp must be millions of °C like Sun & other stars

How does the Sun produce energy? The Sun, made mostly of H produces its energy by fusion of H nuclei 2 protons (H-1) fuse to make a H isotope (H-2); then H-1 + H-2 form an isotope of He-3. positron Light light neutrino The emission of a positron or a positive electron is referred to as beta decay. The positron is accompanied by a neutrino, a massless and chargeless particle. Positrons are emitted with the same kind of energy spectrum as electrons in negative beta decay because of the emission of the neutrino.

How does the Sun produce energy? To complete the process, 4 H nuclei combine into 1 He nucleus during which a small amount of matter changes into a huge amount of energy.

Fusion on the Sun The heat & light Earth receives comes from this process. About 1% of the Sun’s hydrogen has been changed into energy. Sun has enough H to continue fusion reactions for another 5 billion years.

Fusion vs. Fission Comparison Chart Fission vs. Fission

Radiation Background radiation can come from Sun Water Plants ***Radon is the largest source of radiation in the earth’s crust.***

Radiation Damage Mutate hemoglobin Mutate cells, lose function Destroy immune system Burn skin, destroy bone

Radioactive Tracer What is a radioactive tracer? - short lived isotope that can be observed with a sensitive detector

Radioactive Tracer How are they used? - Agriculture – measure water flow - Medicine – locate tumors - Medical research – trace drug paths thru body - Geology – trace underground water flow