Nuclear ChemistryGAVS Module

Radiation & Radioactive Decay pg. 2

• This sign means that radioactive materials are present and special safety precautions need to be taken.

• Nuclear power uses the energy released from a process called nuclear fission to turn water into steam, which turns a turbine and generates electricity.

• Nuclear reactions involve changes to the nuclei of atoms, whereas ordinary chemical reactions only involve rearrangements of electrons and atoms.

Radiation & Radioactive Decay pg. 2

• Alchemists, who lived during the Middle Ages, were people who strived to turn lead into gold.

• Tried all sorts of chemical reactions involving lead, but they were never able to produce gold.

• Today, scientists know that one element cannot be changed into another by chemical processes. However, there is a way that some elements can change into others.  • For an atom of one element to change into a different element, the number of protons

in its nucleus must change. • For example, lead atoms always have 82 protons, and gold atoms always have 79

protons.  

• In order to understand nuclear chemistry, there is specific terminology you must know.

Radiation & Radioactive Decay pg. 2

• Radioactivity is the ability of an atom to emit, or give off, charged particles and energy from its nucleus.

• The charged particles and energy are called by the general term radiation.

• To distinguish the difference between radioactivity and radiation, think about radioACTIVITY as an action. This is what the unstable nuclei does in order to become stable (emits particles and energy).

• What is being emitted from the nucleus is the radiation.

Radiation & Radioactive Decay pg. 2

• Only unstable nuclei emit radiation. They are unstable because they have too much energy, too many protons, or an unstable ratio of protons to neutrons. • For example, all elements with more than 83 protons—such as

uranium, radium, and polonium—have unstable nuclei. They are called radioactive elements. The nuclei of these elements must lose protons to become more stable. When they do, they become different elements.

Radioactive Decay pg. 3

• Did you know? (you don’t have to copy this slide )• Have you seen the symbol to the left?  Are you familiar with food

irradiation? Food irradiation is a sensitive subject for many people. The practice involves exposing the food to ionizing radiation in order to kill harmful bacteria (such as salmonella) that cause sickness. The food is essentially unchanged and does not lose any nutritive value. Parasites and insect pests are easily destroyed by this process, while bacteria take longer to kill. Viruses are not affected by the radiation treatment. But don't worry - the food is not radioactive and you will not glow in the dark if you eat it.  

Radioactive Decay pg. 3

• Unstable nuclei spontaneously emit radiation in the form of particles and energy. This generally changes the number of protons and/or neutrons in the nucleus, resulting in a more stable nucleus.

• A nuclear reaction is a reaction that affects the nucleus of an atom.

• One type of a nuclear reaction is radioactive decay, a reaction in which a nucleus spontaneously disintegrates into a slightly lighter nucleus, accompanied by the emission of particles, energy, or both.

Alpha Decay pg. 3

Beta Decay pg. 3

Beta Decay pg. 3

Gamma Ray Emission pg. 3

Detecting Radiation pg. 3

• You generally can't see, smell, taste, hear, or feel radiation. Fortunately, there are devices such as Geiger counters that can detect radiation.

• A Geiger counter contains atoms of a gas that is ionized if it encounters radiation. When this happens, the gas atoms change to ions that can carry an electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation.

Uses of Radiation pg. 3

• In the module, go to pg. 3 then scroll down to “Using Radiation.” Write a few uses of radiation.

• Then, go to the summary and review activities at the bottom. Complete these activities to review this material.

Half Life pg. 4

• The rate of radioactive decay is different for every radioactive isotope as seen in the table below. Less stable nuclei decay at a faster rate than more stable nuclei.

Half Life pg. 4

• A radioactive isotope has atoms with unstable nuclei. Unstable nuclei naturally decay, or break down. They lose energy and particles and become more stable.

• The original, unstable nucleus is called the parent nucleus. After it loses a particle (alpha or beta particle), it forms a daughter nucleus, with a different number of protons.

• The nucleus of a given radioisotope decays at a constant rate that is unaffected by temperature, pressure, amount of original size, or other conditions outside the nucleus.

• This rate of decay is called the half-life. The half-life (t1/2) is the length of time it takes for half of the original amount of the radioisotope to decay to another element .

Half Life pg. 4

Half Life pg. 4

Decay Curves pg. 4

• What can we interpret from a radioactive decay curve? • First, you can determine the half-life.

This is seen by looking at the red line on the graph above. On the y-axis, you will find the 50% remaining and then where the graphed line hits on the decay curve determine how much time as elapsed. The time it takes for half of the substance to decay is the half-life.

• Continuing, you can determine the percent remaining over time. As you can see, the activity decreases by one-half during each succeeding half-life.

Radioactive Dating pg. 6

• Radioactive dating is a process by which the approximate age of an object is determined through the use of certain radioactive nuclides. For example, carbon-14 has a half-life of 5,730 years and is used to measure the age of organic material. The ratio of carbon-14 to carbon-12 in living things remains constant while the organism is alive because fresh carbon-14 is entering the organism whenever it consumes nutrients. When the organism dies, this consumption stops, and no new carbon-14 is added to the organism. As time goes by, the ratio of carbon-14 to carbon-12 in the organism gradually declines, because carbon-14 radioactively decays while carbon-12 is stable. Analysis of this ratio allows archaeologists to estimate the age of organisms that were alive many thousands of years ago. The ages of many rocks and minerals are far greater than the ages of fossils. Uranium-containing minerals that have been analyzed in a similar way have allowed scientists to determine that the Earth is over 4 billion years old.

Fission pg. 6

• Nuclear fission is the splitting of the nucleus of a radioactive atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. Fission occurs so that large nuclei can become more stable by splitting into smaller fragments.

• Because the fission process produces more neutrons, a chain reaction can result. A chain reaction is a reaction in which the material that starts the reaction is also one of the products and can start another reaction. Illustrated below is a nuclear chain reaction for the fission of uranium-235.

Fission pg. 6

• All elements beyond bismuth in the periodic table are radioactive.

• Bombarding an atom with neutrons can alter its nuclear and atomic structure.

• In the process of nuclear fission, an unstable nucleus splits into two smaller atoms in a reaction that releases energy.

• A nuclear chain reaction occurs when one reaction causes additional reactions. For example, a neutron can cause a uranium atom to undergo fission, which releases energy and several more neutrons, which then split more uranium atoms and release more energy and neutrons. The process continues until all the uranium is spent.

Atomic Bomb pg. 6

• In an atomic bomb, or fission bomb, the nuclear chain reaction is designed to be uncontrolled, releasing huge amounts of energy in a short amount of time.

• A critical mass of fissionable plutonium is contained within the bomb, but not at a sufficient density. Conventional explosives are used to compress the plutonium, causing it to go critical and trigger a nuclear explosion.

Fusion pg. 7

Fusion pg. 7

• Nuclear fusion is a process in which light-mass nuclei combine to form a heavier and more stable nucleus. Fusion produces even more energy than fission. In the sun and other stars, four hydrogen nuclei combine at extremely high temperatures and pressures to produce a helium nucleus.

• Fusion is even more appealing than fission as an energy source because no radioactive waste is produced and the only reactant needed is hydrogen. However, fusion reactions only occur at very high temperatures—in excess of 40,000,000°C. No known materials can withstand such temperatures, so there is currently no feasible way to harness nuclear fusion for energy production, although research is ongoing.

Nuclear Energy pg. 8

• Nuclear energy is the energy released in nuclear reactions.  If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb.

• However, if a nuclear chain reaction is controlled, it produces energy much more slowly. This is what occurs in a nuclear power plant.

Nuclear Energy pg. 8

• Use guided video notes to help with watching the video.

• Then, go to pg. 9 of the module to read about the pros and cons of nuclear energy and the use of nuclear energy in Georgia.

Nuclear Energy Discussion ~ Class Chatter

• In this lesson, you have read about how nuclear power plants operate, the importance of using nuclear energy in regards to climate change, and the pros and cons of nuclear energy. You have also watched a number of videos with more information as well as examples of why nuclear energy is beneficial and what are some of the drawbacks. The video below describes Germany's reaction to the Fukushima nuclear disaster and their controversial decision to end its nuclear energy program.

• Write a paragraph summarizing your opinions on nuclear power plants. Include information such as the benefits of nuclear, if you think the benefits outweigh the drawbacks and why or why not, and if you think Germany is making the right decision or not and why.