Chapter 16 Nuclear Energy

Radioactive Atoms that have an excess of neutrons are “radioactive”. Radioactive means that the atoms are unstable due to the excess neutrons. Atoms will, over time, release or give off those extra neutrons. That is what radioactivity is.

Misconceptions about radioactivty Radioactivity is not a new concept. Radioactivity is as old as the universe Some radioactivity is due to human activity, but most is NOT! Much radioactivity is natural For example: cosmic radiation from space Radiation at the Earth’s core that generates heat (volcanoes)

3 Types of radiation Alpha rays Beta rays Gamma rays

Alpha rays An alpha particle is the combination of 2 protons and 2 neutrons. (What element is that?) Alpha particles are easy to shield due to their relatively large size and their positive charge (+2) Alpha particles cannot penetrate light weight materials but can cause damage to skin if not protected Most helium in the atmosphere forms from Alpha particles picking up electrons

Beta radiation Beta radiation is a stream of beta particles A beta particle is a fast-flying electron Beta particles are faster than an Alpha particle Beta particles can penetrate more deeply than alpha particles Beta particles can penetrate light materials (clothing or paper) and can penetrate deeply into the skin, causing cell damage Beta particles CANNOT penetrate more dense materials (Aluminum for example)

Gamma rays Gamma rays are very high frequency, high energy radiation Gamma rays can penetrate most materials, except materials that are very dense (lead) Gamma rays may be used in medicine (radiation treatments for cancer)

Comparison of alpha, beta, and gamma rays

Electromagnetic spectrum

Environmental radiation (Can radiation make you sick?) Most radioactivity we experience originates in nature and is natural Very common is radon-222 which comes from uranium deposits in the soil. Radiation from space (cosmic radiation) Radiation can damage cells. Duration and intensity may determine damage level.

Radiation in perspective

Radiation and people Radiation can both cure sickness and cause sickness X rays for broken bones are a type of radiation Radiation treatments are used to fight cancer Extreme radiation can cause cancer Extreme doses of radiation can cause DNA in cells to be altered, thus causing long term negative changes in cells Common sense says to avoid radiation whenever possible

transmutation The changing of one element to another is called transmutation U-238 ejects an alpha particle (2 protons & 2 neutrons) and converts to Th-234 and He-4 Th-234 ejects a beta particle, leaving behind coming protactinium (Atomic number 91)

Thorium Transmutation Th-234 ejects a beta particle, leaving behind coming proactinium (Atomic number 91)

Uranium turning into lead Overtime U-238 will decay to Pb-206

Half-life is a measurement of radioactivity Half-life is the time needed for ½ of a radioactive material to decay. Radium-226 has a half life of 1620 years. U-238 has a half life of 4.5 billion years Short half life means the element is very radioactive. Long half life means the element is less radioactive.

Carbon dating C-12 and C-14 are isotopes of carbon C-14 makes up a very small % of carbon in the atmosphere C-14 is radioactive and will decay to C-12 over time Half life of C-14 is 5730 years The atoms that result from radioactive decay are called “daughter isotopes” Using the half life of C-14, scientists can calculate the age of carbon based artifacts (bones or wooden tools for example

Dating of non-living things The age of rocks can be calculated using radioactive dating of elements other than carbon (U-238 for example) This is how scientists were able to calculate how old moon rocks are.

Nuclear fission Nuclear fission means the “splitting” of a nucleus. When a nucleus splits, neutrons are released that can then split more nuclei, This is the start of a nuclear “chain reaction”.

Nuclear chain reaction (fission) http://www.youtube.com/watch?v=tQa4LONy9XM http://www.youtube.com/watch?v=Pmy5fivI_4U

Critical mass Critical mass is the minimum amount of a radioactive material needed to sustain a chain reaction Fuel rods in a nuclear reactor are made of enriched nuclear material.

Nuclear reactor

Nuclear explosion (fission) E=mc2

Nuclear fusion Nuclear fusion is the opposite of nuclear fission When fusion occurs, nuclei of atoms are forced together For example: 2 hydrogen isotopes fusing to form a helium isotope. Very high levels of heat are needed to force atoms together, but large amounts of energy are given off in the process

Fusion on the sun Thermonuclear fusion occurs on the sun and many stars. Hydrogen is fused to form helium and energy is released