Radioactivity Henri Becquerel discovered Xrays in 1896 As

Radioactivity Henri Becquerel discovered X-rays in 1896. As a result of his experiments, he also discovered other forms of rays that could be emitted that had not previously been detected. If you are interested in his research, read pages 266 – 267 in your textbook.

The Nature of Nuclear Radiation cannot be seen, but they have certain characteristics Radiation alters photographic film Radiation produces fluorescence Electric charge can be detected Radiation damages cells in most organisms

Radioactivity is the release of nuclear radiation in the form of particles and rays from a radioactive element. Types of Radiation Alpha particles Beta particles Gamma rays

Brain Break Turn to your partner and list the 3 types of radiation.

Alpha Particles Nucleus of a helium atom with 2 protons and 2 neutrons Has a positive charge because it has no electrons Weakest form of nuclear radiation Alpha particles can burn skin Alpha particles can be stopped by a piece of paper Uses the symbol α

Beta Particles Beta particles are an electron that is formed inside the nucleus when a neutron breaks apart Can penetrate 100 times greater than alpha particles Can pass through 3 mm of aluminum Uses the symbol β

Gamma Rays Gamma rays are electromagnetic waves of extremely high frequency and short wavelength Gamma rays carry much more energy than visible light Most penetrating radiation given off by radioactive elements Can pass through several centimeters of lead Uses the symbol ɣ

Brain Break Tell your partner one thing about alpha particles, beta particles, and gamma rays.

Nuclear Stability Nuclear strong force holds protons and neutrons together in the nucleus. The energy associated with this is called binding energy. This energy is essential to the stability of an atom. Some elements do not have stable nuclei. The unstable nucleus will come apart. These elements are referred to as radioactive.

Nuclear Stability An unstable nucleus can become stable by undergoing a nuclear reaction or change. There are 3 types of radioactive decay. Alpha decay Beda decay Gamma decay

Alpha Decay Occurs when a nucleus releases an alpha particle (2 protons and 2 neutrons) This decreases the mass by 4 but the number of protons is only reduced by 2. Because of this, the original element is no longer the same. Example: Uranium 238 undergoes alpha decay. The 238 represents the mass. The atomic number of uranium is 92. When it undergoes alpha decay, it becomes thorium (Th) which is the element with the atomic number 90 since uranium lost 2 protons.

Beta Decay A beta particle is an electron formed inside the nucleus when a neutron breaks apart. A proton also is produced when a neutron breaks apart. Beta decay occurs when a beta particle is released from a nucleus. When beta decay occurs an element with a mass number one higher is formed because during beta decay, the element gains a proton. The process in which one element is changed into another as a result of changes in the nucleus is called transmutation.

Gamma Decay When a gamma ray is emitted by a nucleus, the nucleus does not change into a different nucleus. A gamma ray is an extremely high-energy wave. In gamma decay, the nucleus makes a transition to a lower energy state.

Brain Break When radium-226 undergoes alpha decay, what does it become? When radium-226 undergoes beta decay, what does it become?

Radioactive Half-Life Half-life is the fixed rate of decay of a radioactive element. Carbon-14 has a half-life of 5, 730 years. If I had a 22 g sample of carbon-14, I would only have 11 g left after 5, 730 years. I would then after 11, 460 years, I would only have 5. 5 g left. Barium-139 has a half-life of 86 minutes. If I had 20 g of barium-139, after 86 minutes, I would only have 10 g left. After 172 minutes, I would only have 5 g left. After 258 minutes, I would only have 2. 5 g left.

Nuclear Fission Nuclear fission is the splitting of an atomic nucleus into two smaller nuclei of almost equal mass. Fission does not occur spontaneously like radioactive decay. When an atom undergoes fission, the amount of energy released from one atom is not that great. The neutrons released, however, are capable of splitting other atoms. This creates a nuclear chain reaction in which billions of fission reactions can occur each second. This produces huge amounts of energy. Nuclear power plants use controlled fission reactions to produce energy.

Nuclear Fusion Nuclear fusion is the joining of two atomic nuclei of smaller masses to form a single nucleus of larger mass. For fusion to occur, the temperature must be well over a million degrees Celsius. At temperatures this hot, plasma is formed. Plasma consists of positively charged ions, which are the nuclei of original atoms, and free electrons. The energy released in fusion reactions is far greater than that released in fission reactions. Fusion reactions produce less radioactive waste, and possible fuels for fusion are more plentiful. Fusion reactions are more difficult to begin, to control, and to maintain than fission reactions.

Brain Break Define fission Define fusion Calculating half life: The half-life of Pa-234 is 6. 75 hours. How much of a 12. 5 g sample remains after 20. 25 hours?

Instruments to Detect Radioactivity Electroscope Geiger counter Cloud chamber Bubble chamber

Radioactivity in our Lives Carbon dating of organic materials Finding leaks or weak spots in metal pipes Medical testing MRI scans Used to destroy unhealthy cells that cause cancer Killing bacteria that cause food to spoil

Dangers of Radiation The same radiation used to treat diseases can also cause diseases. Damage to biological tissue—especially DNA Reddening of the skin and a drop in white blood cell count, nausea, fatigue, and loss of hair. Exposure can be fatal—this was the cause of Marie Curie’s death in 1934. Metal structures can be weakened.