How can the three types of radiation. Which is the thinnest material that absorbs: What is a gamma ray? a) alpha-rays b) beta-rays c) gamma-rays?

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1 How can the three types of radiation be separated? What is a nucleon? Which is the thinnest material that absorbs: a) alpha-rays b) beta-rays c) gamma-rays? What is a gamma ray? Why are heavier nuclei less stable than lighter nuclei? What is an alpha particle? Explain how a nuclear fission can be initiated and what happens in a nuclear fission. What is radiotherapy?

2 Collective name for neutron or proton Positive charges (alpha-particles) and negative charges (betaparticles) bend in different directions when they travel perpendicular to a magnetic field. High frequency electromagnetic radiation (like light, but with much more energy) emitted by atomic nuclei. Alpha part. are already absorbed by thin layer of paper, betapart. by mm-thick aluminum layer, gamma-part. by a thick block of lead Nucleus of a helium atom. It consists of two protons and two neutrons. It is ejected by certain radioactive nuclei. Because the nucleons are further apart, thus the nuclear force, which attracts the nucleons but acts only over a short distance, is weakened by the electrical force (which repels) Use of radiation as a medical treatment to kill cancer cells. A slow neutron hits a heavy nucleus like 235 U. It deforms. The electric repulsion between the protons becomes stronger than the attractive nuclear force which acts only over short distances.

3 What is the nuclear force? What is a nuclear reactor? What are its constituent parts? What is the critical mass? What is a beta particle? What is a chain reaction? What is mass defect? Describe what happens in a nucleus while alpha radiation is emitted. Which equation describes an alpha decay? Describe what happens in a nucleus while beta radiation is emitted. Which equation describes a beta decay?

4 Apparatus in which a controlled nuclear fission takes place. Fuel rods: Contain 235 U. This isotope undergoes nuclear fission if hit by a slow neutron Moderator: Material which slows down the neutrons, usually heavy water. Coolant: High pressurized water, absorbs the heat generated in a reactor. It then passes a heat exchanger where the heat energy is passed onto water to generate steam. Control rods: Material like Borium which absorbs neutrons. They are used to control the chain reaction. The deeper they are lowered into the reactor the more neutrons they catch. Strong attractive force which holds the nucleons in a nucleus together, however it acts only over very short distances. An electron which is emitted by a radioactive nucleus. (It can be a positron as well. This is a particle which has the same mass as an electron but is positively charged. The radiation is then called beta plus ) Minimum mass of fissable material in a nuclear reactor or bomb which will sustain a chain reaction. In a smaller mass too many neutrons will escape from the material without causing a fission. The mass of the nucleus is less than the total mass of all particles it contains. The difference m of masses is equivalent to energy (Einstein s equation E = m c², where c is the speed of light.) In each fission are 3 neutrons emitted. These can cause new fissions. The number of fissions grows exponentially. This energy is the binding energy which is smaller (per nucleon) in heavier nuclei. In a nuclear fission where a heavier nucleus is divided in lighter nuclei is thus energy released. A neutron is transformed into a proton and an electron, which is being ejected. Thus the atomic number decreases by one. Equation: A Z X Z A + Y e 4 The nucleus ejects a 2 He -nucleus. Thus its mass number decreases by 4 and its atomic number by 2. Equation: A Z A 4 X Z Y e

5 What is the atomic number? What is the mass number? What is an isotope? Why is radioactive radiation dangerous? Which radiation is the most dangerous? In which units are the doses of radiation measured? (E.g. to define a maximum yearly dose of radiation which must not be exceeded.) What are the unsolved problems of nuclear power plants? Why are many nations still building nuclear power plants?

6 The mass number is the total number of protons and neutrons in the nucleus. 4 2 He consists of 2 protons and 2 neutrons, thus its mass number is 4. The atomic number gives the number of protons in the nucleus. It determines the chemical element. 4 2 He consists of 2 protons and 2 neutrons, thus its atomic number is 2. The rays can destroy or damage cells. A destroyed cell can be substituted by the organism. But if the number of killed cells is too great severe burnings or death occur. Even worse is the damage of cells. The alteration of DNA molecules can cause cancer or if it is a reproductive cell genetic defects, which lead to mutations in following generations. The definition of 1 Sievert (Sv) is complicated.* Just remember that the yearly dose due to natural causes is Sv. (Eg. oversea flight Sv per hour) (*It tells you how much radiation energy is absorbed in a mass of 1 kg, multiplied by a factor, which represents the harmfulness of the radiation) Atoms with the same atomic number but different mass numbers are called isotopes. 1 1 H, 2 1 H, 3 1 H are hydrogen isotopes Alpha radiation is the most hazardous, because it is highly ionizing. Alpha radiation has only a short range is already absorbed in paper. But if inhaled or swallowed alpha emitters are dangerous. Beta and Gamma radiation are less harmful but it is more difficult to shield a body from these rays. Nuclear power plants are less harmful to the nature because they do not emit as much CO 2 as carbon, gas or oil power plants. If the oil /gas prices are high (which is currently the case!) the costs of nuclear power are lower than those of fossil fuel driven power plants. Radioactive waste remains active and thus dangerous over thousand or millions of years. The chosen destinations for the storage of radioactive waste can t be guaranteed to be save over such long periods. Although being very unlikely the danger of nuclear accidents is always present.