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Chapter 18 Radioactivity and Nuclear Reactions

Section One: Radioactivity

Vocabulary: strong force: causes protons and neutrons to be attracted to each other radioactivity: process that occurs when a nucleus decays and emits alpha, beta, and gamma radiation

Reading Check: The strong force. The number of protons in a nucleus.

Picture Questions: No because an electric force will still act on them. H-3 ratio of 2:1 H-4 ratio of 2:2 or 1:1

Section Review: 1. Describe the properties of the strong force. The strong force is about 100 times stronger than the electric force and it attracts protons to neutrons in the nucleus. The protons and neutrons must be close together for this force to act. 2. Compare the strong force between protons and neutrons in a small nucleus and in a large nucleus. The force will be greater in the smaller nucleus because more strong force acts in smaller places. The protons and neutrons will also be held less tightly in a larger nucleus. 3. Explain why large nuclei are unstable. Large nuclei are unstable because the protons and neutrons only exert a repulsive electric force on some of the others around them not on all like in a small nuclei. The ratio of neutrons to protons also effects the stability. 4. Identify the contributions of the three scientists who discovered the first radioactive elements. The three scientists hypothesized about radiation and slowly tested their thoughts. Their research helped others take over in the future. 5. Think Critically What is the ratio of protons to neutrons in lead-214? Explain whether you would expect this isotope to be radioactive or stable. 82:132 41:66 This varies from 3:2 so the lead could be radioactive. 6. What is the ratio of neutrons to protons in a nucleus of radon-222? 86:136 43:68 7. Calculate the percentage of each isotope in the rod. 31.76 TOTAL g silicon-28 95% silicon-29 .05% silicon-30 .032%

Section Two: Nuclear Decay

Vocabulary: alpha particle: made of two protons and two neutrons transmutation: the process of changing one element to another through nuclear decay beta particle: the electron emitted from the nucleus gamma ray: electromagnetic waves with the highest frequencies and the shortest wavelengths half-life: amount of time it takes the isotope for half the nuclei in a sample to decay

Reading Check: Two protons and two neutrons The portion that does not decay when half-life occurs.

Picture Questions: They do equal each other. The mass numbers are constant yet the atomic number increase by one. one because it went form 4 to 2 to ? must be 1.

Section Review: 1. Infer how the mass number and the atomic number of a nucleus change when it emits a beta particle. The atomic number is one greater and the mass number is the same. 2. Determine the daughter nucleus formed when a radon - 222 nucleus emits an alpha particle. Polonium because it has a atomic number 2 less than radon - 222. 3. Describe how each of the three types of radiation can be stopped. Alpha Particles: A sheet of paper Beta Particles: A sheet of aluminium foil Gamma Rays:thick blocks of dense materials 4. Think Critically After 3 half-lives pass for each sample, which sample contains more of the original nuclei? Since they both started with the same amount of nuclei and both undergo three half lives they would be the same. ???????????????????????????????????????????????????? 5. What percentage of radioactive nuclei left after 3 half lives pass. 12.5% 6. If the half-life of iodine 131 is 8 days, how much of a 5-g sample is left after 32-days.

__131__ __X__ 8X = 4192 8 32 X = 524

Section Three: Detecting Radioactivity Vocabulary: cloud chamber:can be used to detect alpha or beta particle radiation bubble chamber: holds a superheated liquid which does boil because the pressure in the chamber is too high. Geiger counter: a device that measures the amount of radiation by producing an electric current when it detects a charged particle. Reading Check: The charged particles knock electrons off the atoms in the air creating ions which then leave a trail. With a clicking sound or blinking light.

Picture Questions: None

Section Review: 1. Describe why a charged electroscope will discharge when placed near a radioactive material. Nuclear radiation creates positive ions and negative charges move from the leaves to the positively charged ions. The electroscope then lose than negative charge and come together. 2. Compare and contrast cloud and bubble chambers. A cloud chamber can be used to detect alpha or beta particle radiation and a bubble chamber holds a superheated liquid which does boil because the pressure in the chamber is too high. 3. Describe that process that occurs in a Geiger counter when a click is produced. Electron move to the positively charged wire in the device. This causes current to flow in the wire. The current is used to produce a click. 4. Explain why background radiation never can be completed eliminated. Background radiation is all around us and in our bodies so it cannot be destroyed. 5. Think Critically How can radon - 222 gas be coninually present inside houses? Radon is being produced and destroyed so it is always present. 6. What is the amount of the average background radiation in millirems? __8__ __25__ 8x = 2500 100 x x = 312.5 Applying Math: [1.21 + 1] (1.44 x 4.5)1n 2.21 (6.48)1n 2.21 (1.86) 4.13 billion years

Section Four: Nuclear Reactions

Vocabulary: nuclear fussion: the process of splitting a nucleus into several smaller nuclei chain reaction: the series ofrepeated fission reactions caused by the release of nuetrons in each reaction critical mass: the amount of material needed so that each fission reaction produces one more fission reaction nuclear fusion: two nuclei with low masses are combined to form one nucleus of larger mass tracer: a radioisotope is used tp fond pr keep track of molecules in an organism

Reading Check: The nucleus splits into two smaller nuclei. By detecting the radiation they emit.

Picture Questions: It can detect tumors and see if the thyroid is healthy.

Section Four Review: 1. Infer whether mass is converted in a nuclear reaction. Yes becasue a small amount of mass is converted into a huge amount of energy. 2. Explain why fusion reactions can occur inside stars. A great amount of heat is needed and stars have that heat. 3. Explain how a chain reaction can be controlled. Materials that absorb neutrons can be added. 4. Describe two properties of a tracer isotope used for monitoring the functioning of an organ in the body. Carbon-11 and Iodine -131 5. Think Critically Explain why high temperatures are needed for fusion reactions to occur, but not for fission reactions to occur? In fusion two become one so heat is needed. In fission one splits so not as much heat is needed. 6. How many nuclei will have been split after the fifth step? 63