Reading 3-E
Radiation Facts
You are going to read five paragraphs about radiation. Choose the most suitable heading from the list A-F for each part (1-5). There is one extra heading which you do not need to use.
A.Radium Girls
B.X-Ray Shoe Fitter
C.Living in a Radioactive World
D.The Ironic Death of Marie Curie
E.Your Superheroes Can Be Radioactive
F.Radiation Can Be Good for You
1. We know today that overexposure to X-rays is dangerous. However, from the 1930s to the 1950s, salesmen in shoe shops actually used X- ray machines for fitting shoes. It was estimated that there were 10,000 of these devices in use. The device consisted of an x-ray tube with a fluorescent (светящийся) screen above it. In use, the customer placed his or her feet between the two, and an X-ray image of the customer's feet with shoes on them appeared on the screen. In reality, the shoe-fitting machine was just a way to attract potential customers. In 1949, the dangers of radiation became widely known, and the machines disappeared from the shops during the 1950s.
2.Radiation exposure has always attracted comic book writers. We think it is because radiation can change DNA and cause mutations and superpowers. Here is just a short list of some comic book characters affected by radioactivity: Spider-Man, Radioactive Man, Godzilla, X-ray, Doctor Phosphorus. There are dozens more, and who knows how many are living in the minds of tomorrow's comic book writers?
3.Before you lock yourself down in your nuclear shelter, remember that some radiation is actually beneficial to your health. Ultraviolet (UV) radiation, for example, is necessary for the body to stimulate production of vitamin D. Yes, a little bit of sunlight is actually good for you. But experts say that five to 15 minutes a day, three times a week, is more than enough to keep your vitamin D levels high.
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4.In the 1920s, a watch company used the newly discovered substance radium to make its watches glow in the dark. Thousands of girls went to work in the watch factory to paint watch dials with glow-in-the- dark paint which contained radium. Thinking that the paint was harmless, the girls licked their paintbrushes to keep them sharp. For fun, the girls painted their teeth and lips and turned off the lights. Although managers regularly tested the girls for radioactivity, the women never received the results of these tests. Many of the workers became sick. Many others died over the years, but a link was never proved and the company never took responsibility.
5.Sadly, the very thing that made Marie Curie famous is what eventually killed her. In the late 1890s, both Marie and her husband Pierre began suffering from various diseases. Marie suffered several cataracts (a side effect of radiation) and eventually got leukaemia caused by exposure to large amounts of radiation from her research. After her death, Marie's family gave her lab journals to the Bibliotheque Nationale in Paris, where they are still kept. Some of these papers were so radioactive that they required years of decontamination before anyone could handle them.
Nuclear Radiation Quiz
This nuclear radiation quiz will test your knowledge of radiation and radioactivity facts.
1. What makes something radioactive?
A. An unstable nucleus
B. Elements with an atomic number higher than 83
C. Equal number of neutrons and protons in the atomic nucleus
2. Which of the following events would expose you to the most radiation?
A.Living next to a nuclear power plant for a year
B.Talking over your cell phone 15 minutes a day
C.Getting an X-ray examination of your chest
3. How does radioactive material generate electricity?
A.The heat generated during fission creates steam that powers electricity generating turbines.
B.The decay of uranium creates enough force to turn turbines directly.
C.To quote Joe Dirt, "How exactly does the sun set? It just does."
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4. Which of the following typically poses the biggest health threat to humans?
A.Alpha particles
B.Beta particles
C.Gamma rays
5. Which of the following household devices might contain radioactive material?
A.Smoke detectors
B.Thermometers
C.Microwave ovens
6. How do you neutralize the radioactivity of a substance?
A.Burn the material
B.Pass a high-voltage current through the material
C.It cannot be done.
7. Who was the first person to discover radioactivity?
A. Ernest Rutherford
B. Henri Becquerel
C. Albert Einstein -- he pretty much discovered everything, right?
8. Who invented the term «radioactivity»?
A.Marie Curie
B.Pierre Curie
C.Wilhelm Roentgen
9. What does the term "half-life" mean in reference to radioactive material?
A.The amount of time it takes for a radioactive atom to decay
B.The amount of time it takes for half of a given sample of a radio-
active material to decay
C. Half-life? That's one of my favorite computer games!
10. Which of the following IS NOT true?
A.The radioactive element polonium was used as a minor component of a toy bicycle in the 1950s.
B.Before the first nuclear bomb was detonated, scientists took bets on whether or not it would destroy the entire world.
C.X-ray machines were once used in shoe stores to help the shoe fitting process before the dangers of radiation were well-known.
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UNIT 4
Reading 4-А
Nuclear Fission and Chain Reaction
Q: What did the Nuclear Physicist have for lunch?
A: Fission Chips.
Nuclear fission is a nuclear reaction in which the nucleus of a heavy atom splits into lighter atoms, producing free neutrons and large amounts of energy. If it occurs without neutron bombardment, as a type of radioactive decay, this type of fission is called spontaneous fission. However, most nuclear fission occurs as a "nuclear reaction" (called induced fission) in a nuclear reactor as a result of the bombardment of heavy nuclei by neutrons. In nuclear reactions, a subatomic particle (a neutron) collides with an atomic nucleus and causes it to split. The splitting nucleus releases two or three new neutrons which cause more fissions in the neighbouring uranium atoms. This makes possible a selfsustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.
The isotopes that can sustain a fission chain reaction are called nuclear fuels, and are said to be fissile or fissionable. Uranium is the most common nuclear fuel. The two most important isotopes of uranium are uranium-238 and uranium-235. Uranium-238 (U-238) undergoes spontaneous fission very slowly and has an extremely long half-life (the time it takes for half of its atoms to decay) of 4.5 billion years. It goes through many stages of decay in its life span, eventually forming a stable isotope of lead.
U-238 makes up 99 percent of the uranium on Earth, while urani- um-235 (U-235) makes up about 0.7 percent of the remaining uranium found naturally. Uranium-235 is the most important of all the uranium isotopes. Like U-238, U-235 decays naturally, by emitting alpha radiation. However, U-235 is one of the few materials that can undergo induced fission. If a free neutron runs into a U-235 nucleus, the nucleus will absorb the neutron, become unstable and split immediately.
The splitting of an atom releases tremendous heat. The decay of a single U-235 atom releases approximately 200 MeV (million electron volts). That may not seem like much, but there are a lot of uranium at-
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oms in a pound (0.45 kg) of uranium. So many, in fact, that a pound of highly enriched uranium used to power a nuclear submarine is equal to about a million gallons of gasoline. The energy released by a single fission comes from the fact that the fission products and the neutrons, together, weigh less than the original U-235 atom. The difference in weight is convert-
ed directly to energy at a rate given by Einstein’s equation E = mc2. However, for all of this to work, uranium must be enriched so that it
contains 3 to 5 percent U-235. Three-percent enrichment is sufficient for nuclear power plants, but weapons-grade uranium is composed of at least 90 percent U-235.
Note: Fissionable materials can be either fissile or fertile. A fissile material is one that will undergo fission when bombarded by neutrons of any energy. The isotope uranium-235 is fissile. A fertile material is one that will capture a neutron, and transmute by radioactive decay into a fissile material. Uranium-238 is a fertile material. Fertile isotopes may also undergo fission directly, but only by fast, high-energy neutrons.
Exercise 1. Match the two parts to make expressions from Reading 4-A. Read the text again if necessary.
1. spontaneous |
a) induced fission |
2. undergo |
b) chain reaction |
3. half |
c) uranium |
4. self-sustaining |
d) weapon |
5. at a controlled |
e) fission |
6. nuclear |
f) life |
7. weapons-grade |
g) rate |
Now complete these sentences using the expressions above. Uranium-238 (U-238) undergoes ______ very slowly and has an ex-
tremely long ______.
1.U-235 is one of the few materials that can ______.
2.A _______ releases energy______ in a nuclear reactor or at a very rapid uncontrolled rate in a _____.
3.Three-percent enrichment is sufficient for nuclear power plants, but _______ is composed of at least 90 percent U-235.
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