radioactivity

introduction to radioactivity

Radioactivity is the ability of an atom to emit, or give off, charged particles and energy from the nucleus. The charged particles and energy are called by the general term radiation. Only unstable nuclei emit radiation. When they do, they gain or lose protons. Then the atoms become different elements. (Be careful not to confuse this radiation with electromagnetic radiation, which has to do with the light given off by atoms as they absorb and then emit energy.)

discovery of radioactivity

Radioactivity was discovered in 1896 by a French physicist named Antoine Henri Becquerel. Becquerel was experimenting with uranium, which glows after being exposed to sunlight. Becquerel wanted to see if the glow was caused by rays of energy, like rays of light and X-rays. He placed a bit of uranium on a photographic plate. The plate was similar to film thats used today to take X-rays. You can see an example of an X-ray in Figure 11.1. As Becquerel predicted, the uranium left an image on the photographic plate. This meant that uranium gives off rays after being exposed to sunlight. Becquerel was a good scientist, so he wanted to repeat his experiment to confirm his results. He placed more uranium on another photographic plate. However, the day had turned cloudy, so he tucked the plate and uranium in a drawer to try again another day. He wasnt expecting the uranium to leave an image on the plate without being exposed to sunlight. To his surprise, there was an image on the plate in the drawer the next day. Becquerel had discovered that uranium gives off rays without getting energy from light. He had discovered radioactivity, for which he received a Nobel prize. To learn more about the importance of Becquerels research, go to this URL: http://nobelprize.org/no Another scientist, who worked with Becquerel, actually came up with the term "radioactivity." The other scientist was the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won two Nobel Prizes for her discoveries. You can learn more about Marie Curie at this URL: http://nobelprize.or

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radioisotopes

Isotopes are atoms of the same element that differ from each other because they have different numbers of neutrons. Many elements have one or more isotopes that are radioactive. Radioactive isotopes are called radioisotopes. An example of a radioisotope is carbon-14. All carbon atoms have 6 protons, and most have 6 neutrons. These carbon atoms are called carbon-12, where 12 is the mass number (6 protons + 6 neutrons). A tiny percentage of carbon atoms have 8 neutrons instead of the usual 6. These atoms are called carbon-14 (6 protons + 8 neutrons). The nuclei of carbon-14 are unstable because they have too many neutrons. To be stable, a small nucleus like carbon, with just 6 protons, must have a 1:1 ratio of protons to neutrons. In other words, it must have the same number of neutrons as protons. In a large nucleus, with many protons, the ratio must be 2:1 or even 3:1 protons to neutrons. In elements with more than 83 protons, all the isotopes are radioactive (see Figure 11.2). The force of repulsion among all those protons overcomes the strong force holding them together. This makes the nuclei unstable and radioactive. Elements with more than 92 protons have such unstable nuclei that these elements do not even exist in nature. They exist only if they are created in a lab.

radiation in the world around us

A low level of radiation occurs naturally in the environment. This is called background radiation. It comes from various sources. One source is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things. A source of radiation that may be more dangerous is radon. Radon is a radioactive gas that forms in rocks underground. It can seep into basements and get trapped inside buildings. Then it may build up and become harmful to people who breathe it. Other sources of radiation are described in the interactive animation at this URL: http://w

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dangers of radiation

You may have seen a sign like the one in Figure 11.3. It warns people that there is radiation in the area. Exposure to radiation can be very dangerous. Radiation damages living things by knocking electrons out of atoms and changing them to ions. Radiation also breaks bonds in DNA and other biochemical compounds. A single large exposure to radiation can burn the skin and cause radiation sickness. Symptoms of this illness include extreme fatigue, destruction of blood cells, and loss of hair. Long-term exposure to lower levels of radiation can cause cancer. For example, radon in buildings can cause lung cancer. Marie Curie died of cancer, most likely because of exposure to radiation in her research. To learn more about the harmful health effects of radiation, go to this URL: . Nonliving things can also be damaged by radiation. For example, high levels of radiation can remove electrons from metals. This may weaken metals in nuclear power plants and space vehicles, both of which are exposed to very high levels of radiation.

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detecting radiation

One reason radiation is dangerous is that it cant be detected with the senses. You normally cant see it, smell it, hear it, or feel it. Fortunately, there are devices such as Geiger counters that can detect radiation. A Geiger counter, like the one in Figure 11.4, has a tube that contains atoms of a gas. If radiation enters the tube, it turns gas atoms to ions that carry electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation. You can see a video about the Geiger counter and how it was invented at the URL below.

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using radiation

Despite its dangers, radioactivity has several uses. It can be used to determine the ages of ancient rocks and fossils. This use of radioactivity is explained in this chapters "Radioactive Decay" lesson. Radioactivity can also be used as a source of power to generate electricity. This use of radioactivity is covered later on in this chapter in the lesson "Nuclear Energy." Radioactivity can even be used to diagnose and treat diseases, including cancer. Cancer cells grow rapidly and take up a lot of glucose for energy. Glucose containing radioactive elements can be given to patients. Cancer cells will take up more of the glucose than normal cells do and give off radiation. The radiation can be detected with special machines (see Figure 11.5). Radioactive elements taken up by cancer cells may also be used to kill the cells and treat the disease. You can learn more about medical uses of radiation at the URL below. MEDIA Click image to the left or use the URL below. URL:

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instructional diagrams

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questions

The scientist who discovered radioactivity was

a. Curie.

b. Geiger.

-->  c. Becquerel.

d. none of the above

All nuclei that emit radiation are

a. radioactive.

b. very large.

c. unstable.

-->  d. two of the above

The radioactive isotope of carbon is

a. carbon-12.

b. carbon-13.

-->  c. carbon-14.

d. none of the above

Which combination of protons and neutrons would most likely result in a stable nucleus?

a. 4 protons and 2 neutrons

-->  b. 4 protons and 4 neutrons

c. 4 protons and 6 neutrons

d. 4 protons and 8 neutrons

Rocks may release radiation due to

a. formation of radioactive gas in the rocks.

b. radioactive elements in the rocks.

c. carbon-12 in the rocks.

-->  d. two of the above

Some elements naturally change into different elements.

-->  a. true

b. false

Only unstable nuclei emit radiation.

-->  a. true

b. false

The radioactive isotope of carbon has fewer neutrons than other isotopes of carbon.

a. true

-->  b. false

Radon gas is harmful when it burns and causes pollution.

a. true

-->  b. false

Background radiation is generally considered to be safe for living things.

-->  a. true

b. false

There is no way to detect radiation.

a. true

-->  b. false

Radiation can break bonds in biochemical molecules.

-->  a. true

b. false

Radioactive isotopes can be used to determine the ages of fossils.

-->  a. true

b. false

Radiation is harmless to nonliving things such as metals.

a. true

-->  b. false

You cannot see radiation but you can always feel it.

a. true

-->  b. false

A single large exposure to radiation can burn the skin.

-->  a. true

b. false

Human activities are responsible for almost all the radiation in the environment.

a. true

-->  b. false

Radiation can be used to generate electricity.

-->  a. true

b. false

Any exposure to radiation causes burns and destroys blood cells.

a. true

-->  b. false

A Geiger counter works because radiation changes atoms of a gas to ions.

-->  a. true

b. false

radioactive gas that forms in rocks underground

a. radiation

b. background radiation

c. radioactivity

-->  d. radon

e. radioisotope

f. Antoine Becquerel

g. Marie Curie

scientist who discovered radioactivity

a. radiation

b. background radiation

c. radioactivity

d. radon

e. radioisotope

-->  f. Antoine Becquerel

g. Marie Curie

ability of an atomic nucleus to give off charged particles and energy

a. radiation

b. background radiation

-->  c. radioactivity

d. radon

e. radioisotope

f. Antoine Becquerel

g. Marie Curie

low level of radiation that occurs naturally in the environment

a. radiation

-->  b. background radiation

c. radioactivity

d. radon

e. radioisotope

f. Antoine Becquerel

g. Marie Curie

charged particles and energy emitted by an unstable nucleus

-->  a. radiation

b. background radiation

c. radioactivity

d. radon

e. radioisotope

f. Antoine Becquerel

g. Marie Curie

scientist who discovered polonium and radium

a. radiation

b. background radiation

c. radioactivity

d. radon

e. radioisotope

f. Antoine Becquerel

-->  g. Marie Curie

atom with an unstable nucleus that emits radiation

a. radiation

b. background radiation

c. radioactivity

d. radon

-->  e. radioisotope

f. Antoine Becquerel

g. Marie Curie

For an element to change to a different element, it must change its number of

a. energy levels.

b. electrons.

c. neutrons.

-->  d. protons.

Which statement about radioisotopes is false?

a. Radioisotopes have unstable nuclei.

b. Some elements exist only as radioisotopes.

-->  c. All elements have one or more radioisotopes.

d. Radioisotopes contribute to background radiation.

Radioactive elements include

a. radium.

b. uranium.

c. polonium.

-->  d. all of the above

Elements with more than 92 protons are

a. a source of radiation in rocks.

-->  b. too unstable to exist in nature.

c. the least radioactive elements.

d. the only radioactive elements.

Sources of background radiation include

a. medical X rays.

-->  b. cosmic rays.

c. nuclear power plants.

d. all of the above

Uranium can leave an image on a photographic plate because uranium

a. gives off X rays.

b. absorbs sunlight.

c. emits light rays.

-->  d. is radioactive.

diagram questions

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