Module 2: Nuclear Energy Flashcards
15.1 Radioactivity
The atomic nucleus is the source of a tremendous amount of energy, which poses both risks and benefits. Nuclear energy arises from the atomic nucleus. It is in the radioactivity that occurs naturally in the air we breathe, in the rocks around us, and even in the food we eat. Another source of nuclear energy is the nuclear power plant, which transforms nuclear energy into electricity. About 20% of the electricity produced in the United States comes from nuclear power plants. A nuclear bomb is another source of nuclear energy. However, the most significant source of nuclear energy is the Sun. Natural radioactivity accounts for over 80% of radiation exposure for an average American.
Most atoms have stable nuclei. This stability comes from having the correct balance of protons and neutrons, which is usually the same number of each. Other atoms, however, have nuclei that are unstable because they contain all “off-balance” number of protons and neutrons. For example, they may contain too many neutrons and not enough protons. Atoms with unstable nuclei are said to be radioactive. Sooner or later, they break down and eject energetic particles and emit electromagnetic radiation. This process is called radioactivity. Because it involves the decay of the atomic nucleus, it is often called radioactive decay.
started 19/08/24
Radioactivity has been around far longer than humans. It has always been in the soil we walk on and in the air that we breathe, and it warms Earth’s interior. In fact, radioactive decay in the Earth’s interior heats the water that spurts from a geyser or wells up from a natural hot spring.
Most of the radiation we encounter is natural background radiation that originates in Earth and in space. Even the cleanest air we breathe is radioactive as a result of bombardment by cosmic rays. These rays originate in the Sun and other stars. At sea level, the protective blanket of the atmosphere reduces this background radiation. But radiation is more intense at higher altitudes. In Denver, nicknamed the “Mile-High City”, as its official elevation is one mile (5,280 ft; 1,609 m) above sea level) a person receives more than 2x as much cosmic radiation as someone at sea level. A couple of round-trip airplane flights between New York and San- Francisco expose us to as much radiation as we receive in a chest X-ray at the doctor’s office. Because extended exposure to this level of radiation is dangerous, the flight time of pilots and flight crew is limited.
Nuclear radiation is focused on harmful tissue, such as a cancerous tumor, to kill cells selectively or to shrink the tissue in a technique known as radiation therapy. Without nuclear technology, we would not have medical X-rays, radiation treatments for fighting cancer, smoke detectors, nuclear power as a source of electricity, and other useful applications. Our responsibility is to safeguard nuclear material and dispose of it in such a way as to reduce danger to future generations.
15.1 Radioactivity
VIDEO 1: Radioactivity
So far we looked at atomic physics, the study of clouds of electrons that make up an atom. Now, we will go deeper into the atom: to the atomic nucleus, where available energies dwarf those available to electrons. This is nuclear physics.
The story of radioactivity goes back to the discovery of X-rays. In 1895, German physicist, Wilhelm Röntgen, discovered rays of an unknown nature, produced when a beam of electrons struck the glass surface of a glass discharge tube. They were named X-rays, because they were unknown at the time. They could pass through solid materials, could ionise the air and were undeflected by magnetic fields. Today, we know that X-rays are high-frequency electromagnetic waves usually emitted by the de-excitation of the innermost orbital’s electrons of atoms. The photos of X-rays show that these rays penetrate flesh more readily than bones.
A few months later, a French physicist, Antoine Henri Becquerel, stumbled upon a new kind of penetrative radiation. One night, he left a wrapped photographic plate in a drawer next to some crystals that contained uranium. The next day he discovered to his surprise that the photographic plate had been darkened, apparently by a spontaneous radiation from the uranium. He proceeded to show that this new radiation was like X-rays in that it could ionise air but was different and could be deflected by magnetic fields. Becquerel’s radiation emanated from the processes inside unstable atoms. Later, scientists found that this instability or radioactivity resides in the atomic nucleus. More than 99.9% of the atoms in our everyday environment are stable, but some kind of atoms are unstable. All elements with an atomic number > 82 (Pb, Lead) are radioactive.
It was soon found that there are 3 distinct types of radiation (named for the first 3 letters of the Greek alphabet): alpha, beta, and gamma. Alpha rays have a positive electric charge. Beta rays have a negative charge. And gamma rays have no charge at all. The three rays can be separated by placing a magnetic field across their paths. Further investigation showed that an alpha ray to be a stream of helium nuclei, a bera ray - a stream of electrons. We call them alpha particles and beta particles. A gamma ray is a stream of photons whose frequency is even higher than that of X-rays.
15.1 Radioactivity
VIDEO 1: Radioactivity (cont’d)
Notice that in a magnetic field, alpha rays bend one way, while beta rays bend the other way. Alpha particles are positively charged, beta particles are negatively charged. Beta rays are streams of electrons ejected from the atomic nuclei, not electrons coming from orbits outside the nucleus. Gamma rays do not bend at all, having no electric charge. The combined beam comes from a radioactive source placed at the bottom of a hole drilled in a lead block.
Alpha particles are the least penetrating and can be stopped by a few sheets of paper. Beta particles will pass through the paper but not through a sheet of aluminum. Gamma rays will penetrate several centimeters into the solid lead block. These radiations were also encountered by Marie and Pierre Curie, when investigating the emissions of radiation by thorium, actinium and two new elements discovered in the process, polonium and radium.
It turned out that gamma rays were the result not of changes in the electric energy states of the atom, but of the changes occurring within the central atomic core, the nucleus. The term “radioactivity” was coined by Marie Curie. Because it involves the decay of the atomic nucleus, it is often called “radioactive decay.” Radiation is measured with various detectors. The most common is a Geiger counter and a more sensitive scintillation counter. Inside the glass-filled tube of the Geiger counter, incoming radiation ionizes gas and triggers sharp pulses of current. The scintillation counter registers incoming radiation by flashes of light, produced when beta or gamma rays pass into a photosensitive crystal.
We all know that the Earth’s interior is a hot place, but why? It’s hot due to extensive radioactive processes on the Earth’s interior. The lava is hot mostly due to radioactivity beneath. Radioactive decay in the Earth’s interior heats the water that feeds hot springs. Radioactivity is not something to be afraid of, its dangers are overblown.
Question: Is radioactivity something new or it goes back to the beginnings of the Earth’s history?
15.1 Radioactivity
15.1 Radioactivity
VIDEO 2: Atomic nucleus
Did you know that Hawaiian Islands formed because of radioactivity? Deep beneath the Earth surface it is hot, because there is a lot of radioactive activity down there. This heat causes the rock to melt and in certain areas, this molten rock is able to pass through the Earth surface where it forms lava. Over time, lava accumulates to form mountains, In the Hawaiian Islands, mountains are high enough to rise above sea level.
If there is one thing to remember from this Chapter, it is that radioactivity is a natural phenomenon, it’s been on this planet since day one. It is in the air, in the water and in the food we eat. Our bodies consist of radioactive isotopes. Studis suggest that natural amounts of radioactivity are beneficial for our health, because it stimulates our immune system. Radioactivity arises from atomic nucleus, which is a source of fantastic amount of energy. In the 20th century, we learned how to release this energy, called nuclear energy, for both destructive and constructive purposes. How much radioactivity should we be exposed to? Should we build nuclear power plants? What should we do with radioactive waste? Let’s answer these questions, based on knowledge.
VIDEO 3: The Discovery of Radioactivity
VIDEO 4: Three Different Types of Radiation
VIDEO 5: Penetrating Powers of Radiation
15.2 Alpha, Beta, and Gamma Rays
