Atoms and Radioactivity
Atoms are the basic building blocks of matter, composed of a nucleus containing protons and neutrons, surrounded by electrons. Radioactivity is the spontaneous emission of radiation from the nucleus of an unstable atom, often resulting in the transformation of the atom into a different element. This process can release energy in the form of alpha, beta, or gamma radiation.
8 Key excerpts on "Atoms and Radioactivity"
eBook - ePubRadiation Detection
Concepts, Methods, and Devices
- Douglas McGregor, J. Kenneth Shultis(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
...The spontaneous emission of alpha and beta particles led to the concept that atoms are composed of smaller fundamental units. Likewise, the scattering of alpha particles led to the idea of the nucleus, which is fundamental to the models used in atomic physics. The discovery of isotopes resulted from the analysis of the chemical relationships among the various radioactive elements. The bombardment of the nucleus by alpha particles caused the disintegration of nuclei and led to the discovery of the neutron and the present model for the composition of the nucleus. The discovery of artificial, or induced, radioactivity started a new line of nuclear research and hundreds of artificial nuclei have been produced by many different nuclear reactions. The investigation of the emitted radiations from radionuclides has shown the existence of nuclear energy levels similar to the electronic energy levels. The identification and the classification of these levels are important sources of information about the structure of the nucleus. A number of radioactive nuclides occur naturally on the earth. One of the most important is 19 40 K, which has an isotopic abundance of 0.0118% and a half-life of 1.28 × 10 9 y. Potassium is an essential element needed by plants and animals, and is an important source of human internal and external radiation exposure. Other naturally occurring radionuclides are of cosmogenic origin. Tritium (1 3 H) and 6 14 C are produced by cosmic ray interactions in the upper atmosphere, and also can cause measurable human exposures. 6 14 C (half-life 5730 y), which is the result of a neutron reaction with 7 14 N in the atmosphere, is incorporated into plants by photosynthesis. By measuring the decay of 14 C in ancient plant material, the age of the material can be determined. Other sources of terrestrial radiation are uranium, thorium, and their radioactive progeny. All elements with Z > 83 are radioactive...
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...Chapter 14 Nuclear Chemistry Fundamentals of Nuclear Chemistry Nuclear chemistry involves chemical reactions that deal with the loss and gain of particles found within the nucleus—protons and neutrons. In these reactions, the nucleus undergoes a fundamental change that alters its identity. In radioactive atoms, the nuclei are unstable and may emit particles or energy called radiation. You should know that only certain isotopes of elements are radioactive (radioisotopes). There is also a variety of decay processes that can occur that transform an unstable nucleus in a high energy state into a more stable nucleus. These decay processes result in a net release of energy and occur as first-order rate expressions. DID YOU KNOW? Without a doubt, you have a manmade radio-active material in your house: americium-241. Americium is used in smoke detectors to emit alpha particles, which, when blocked by smoke particles in the air, activates an alarm to warn occupants of danger. Types of Decay Processes Alpha Decay Alpha decay involves the emission of an alpha (α) particle, which is essentially a helium nucleus: or. This type of decay occurs for unstable radioisotopes having an atomic number greater than 82. Alpha particles are relatively harmless and cannot even penetrate a piece of paper. EXAMPLE: Beta Decay Beta decay involves the emission of a beta (β) particle,. This type of decay process occurs when the proton-to-neutron ratio within the nucleus is too low for the radioisotope. Beta particle emission involves the splitting of a neutron into a proton and high-speed electrons that are ejected from the nucleus. As a result, the emission of the beta particle will cause the number of neutrons to decrease and the number of protons to increase. Beta particles have more penetrating power than alpha particles, but are stopped readily by dense materials such as lead. EXAMPLE: For beta decay, the mass number will stay the same but the atomic number (# of protons) will increase...
eBook - ePub- Suzanne Easton(Author)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
...Chapter 3 Inside the Atom Chapter contents Atoms, elements and other definitions The ‘Make-Up’ of an atom – atomic structure Shells and energy The periodic table Radioactivity The effects of an electron changing orbits Electromagnetic radiation Frequency and wavelength Further reading Key points An atom is the smallest unit within an element having all the properties of the element. It is made up of a nucleus containing neutrons and protons surrounded by electrons A compound is a combination of different elements The periodic table contains details of all elements known to man and provides their proton and nucleon number Electrons orbit around the nucleus in shells. These hold a certain number of electrons per shell. If the shell is not complete, the atom will react differently to an atom with a full outer shell Radioactivity is the emission of particles from an atom with an unstable nucleus with the aim of becoming stable. This emission is called radioactive decay Ionisation is the interaction of radiation with matter. This involves the removal of an electron from an atom. The ejected electron and the positive atom are called an ion pair The electromagnetic spectrum consists of a collection of different types of radiation with a range of energy levels. This includes visible light, radio waves and X-rays Constituents of the electromagnetic spectrum move in a wave The wavelength is the distance from crest to crest of the wave The rate of rise and fall of a wave (electromagnetic radiation travels in waves) is called the frequency. It is measured in hertz (Hz) If the frequency is high, the wavelength is short Introduction The concepts and ideas discussed in this chapter can prove daunting at first. If the concepts are thought of as a miniature solar system, something that can actually be visualised, then the theory will become more manageable and less of a difficulty...
eBook - ePub- Simon R. Cherry, James A. Sorenson, Michael E. Phelps(Authors)
- 2012(Publication Date)
- Saunders(Publisher)
...chapter 2 Basic Atomic and Nuclear Physics Radioactivity is a process involving events in individual atoms and nuclei. Before discussing radioactivity, therefore, it is worthwhile to review some of the basic concepts of atomic and nuclear physics. a Quantities and Units 1. Types of Quantities and Units Physical properties and processes are described in terms of quantities such as time and energy. These quantities are measured in units such as seconds and joules. Thus a quantity describes what is measured, whereas a unit describes how much. Physical quantities are characterized as fundamental or derived. A base quantity is one that “stands alone”; that is, no reference is made to other quantities for its definition. Usually, base quantities and their units are defined with reference to standards kept at national or international laboratories. Time (s or sec), distance (m), and mass (kg) are examples of base quantities. Derived quantities are defined in terms of combinations of base quantities. Energy (kg · m 2 /sec 2) is an example of a derived quantity. The international scientific community has agreed to adopt so-called System International (SI) units as the standard for scientific communication. This system is based on seven base quantities in metric units, with all other quantities and units derived by appropriate definitions from them. The four quantities of mass, length, time and electrical charge are most relevant to nuclear medicine. The use of specially defined quantities (e.g., “atmospheres” of barometric pressure) is specifically discouraged. It is hoped that this will improve scientific communication, as well as eliminate some of the more irrational units (e.g., feet and pounds)...
eBook - ePubThe Amazing Story of Lise Meitner
Escaping the Nazis and Becoming the World's Greatest Physicist
- Andrew Norman(Author)
- 2021(Publication Date)
- Pen and Sword History(Publisher)
...In the process, a radioactive nuclide spontaneously transforms into a daughter nuclide, which may or may not be radioactive, with the emission of one or more subatomic particles or photons. This daughter nuclide will usually contain a different number of protons and therefore, by definition, be a different chemical element to the parent. If the daughter nuclide is also unstable (radioactive), the process is repeated until stability occurs. In the case of natural radioactivity, the decay is a slow process. Uranium-235, for example (which consists of 92 protons, 92 electrons, and 143 neutrons), has a half-life of 700 million years (and is only weakly radioactive). Types of radioactive decay Alpha decay Put simply, an alpha particle (helium nucleus) is emitted from the nucleus. Alpha decay typically occurs in the heaviest nuclei. Beta (negative) decay Put simply, this involves the conversion of a neutron into a proton and a beta particle (electron). This electron is emitted from the atomic nucleus (and is not one of the electrons surrounding the nucleus). In the process, a new element is formed, the daughter isotope having a different number of protons from the parent. Gamma decay The nucleus emits radiation (short-wavelength electromagnetic waves) without changing its composition. The decay curve The radioactivity of a material refers to the rate at which it emits radiation. Radiation is the energy or particles that are released during radioactive decay. Radioactive decay occurs each time a nucleus ejects particles or energy, and each radioactive isotope decays at its own unique rate, i.e. each radioactive nuclide has its own characteristic half-life. By measuring the number of disintegrations per unit of time, a decay curve may be constructed. This is useful when it comes to the identification of isotopes...
eBook - ePub- Alan Martin, Sam Harbison, Karen Beach, Peter Cole(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
...2 Radioactivity and radiation 2.1 Introduction It is found that a few naturally occurring substances consist of atoms which are unstable, that is they undergo spontaneous transformation into more stable product atoms. Such substances are said to be radioactive, and the transformation process is known as radioactive decay. Radioactive decay is usually accompanied by the emission of radiation in the form of charged particles and gamma (γ) rays. The fact that some elements are naturally radioactive was first realized by Becquerel in 1896. He observed the blackening of photographic emulsions in the vicinity of a uranium compound. This was subsequently attributed to the effect of radiation being emitted by the uranium. In the following 10 years, the experimental work of Rutherford and Soddy, Pierre and Marie Curie, and others established the fact that some types of nuclei are unstable and decay by emitting radiations of three main types, called alpha, beta and gamma radiation. During the same period, scientists in several countries were experimenting with electrical discharge tubes known as Crookes tubes and investigating the fluorescence that occurred in the glass walls of the tubes. In 1895, the German physicist Wilhelm Conrad Rontgen discovered that the tubes were emitting invisible rays, which he named X-rays, that were capable of penetrating solid objects. The potential importance of this discovery, particularly in the medical field, was quickly appreciated and within weeks investigators in many countries were developing equipment and techniques to exploit the discovery. The first medical X-ray was taken by Rontgen himself and was of his wife’s hand (see Figure 2.1). When Frau Rontgen saw the photograph, she exclaimed ‘I have seen my death!’ Figure 2.1 The first medical X-ray. 2.2 Alpha, beta and gamma radiation Alpha (α) radiation was shown by Rutherford and Royds to consist of helium nuclei, which themselves consist of two protons and two neutrons...
- Rachel A. Powsner, Matthew R. Palmer, Edward R. Powsner(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
...This process is referred to as radioactive decay. The type of decay depends on which of the following rules for nuclear stability is violated. Excessive Nuclear Mass Alpha Decay: Very large unstable atoms, atoms with high atomic mass, may split into nuclear fragments. The smallest stable nuclear fragment that is emitted is a particle consisting of two neutrons and two protons, equivalent to the nucleus of a helium atom. Because it was one of the first types of radiation discovered, the emission of a helium nucleus is called alpha radiation, and the emitted helium nucleus an alpha particle (Figure 1.13). Figure 1.13 Alpha decay. Fission: Under some circumstances, the nucleus of an unstable atom may break into larger fragments, a process usually referred to as nuclear fission. During fission, two or three neutrons are emitted (Figure 1.14). Figure 1.14 Fission of a 235 U nucleus. Unstable Neutron–Proton Ratio Too Many Neutrons: Beta Decay: Nuclei with excess neutrons can achieve stability by a process that amounts to the conversion of a neutron into a proton and an electron. The proton remains in the nucleus, but the electron is emitted. This is called beta radiation, and the electron itself a beta particle (Figure 1.15). The process and the emitted electron were given these names to contrast with the alpha particle before the physical nature of either was discovered. The beta particle generated in this decay will become a free electron until it finds a vacancy in an electron shell in another atom. Figure 1.15 β − (negatron) decay. Careful study of beta decay suggested to physicists that the conversion of a neutron to a proton involved more than the emission of a beta particle (electron). Beta emission satisfied the rule for conservation of charge in that the neutral neutron yielded one positive proton and one negative electron; however, it did not appear to satisfy the equally important rule for conservation of energy...
eBook - ePubParticles, Fields, Space-Time
From Thomson's Electron to Higgs' Boson
- Martin Pohl(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...Another often used measure is the half-life, the time at which half the nuclei have decayed. If nuclei were not independent of each other, terms inversely proportional to N(N-1), the number of pairs, or N(N-1)(N-2), the number of triplets, etc. would have to be taken into account. If radioactivity were not a random process, the decaying fraction would not be constant. In a recent long term test, Dobrivoje Novkovi and collaborators have measured the decay rate of 198 Au, a radioactive isotope of gold, over more than two months [ 560 ], close to twenty times its lifetime. They found no deviation from the exponential decay law and λ to be constant within the statistical errors of their measurement. Focus Box 4.4: Radioactive decay law In 1907, Rutherford moved to the Victoria University of Manchester. He and Thomas Royds proved in 1909 that alpha particles are doubly ionised helium [ 129 ]. In parallel, Hans Geiger and Ernest Marsden started investigating the scattering of these particles by matter. They found that while the scattering angles were small in general, a tiny fraction of the alpha particles, of the order of one in several thousand, was scattered by large angles, even reflected backwards [ 127 ]. This is inconceivable, if the positive charge in an atom were smeared out over the atomic volume. The qualitative observation thus triggered Ernest Rutherford to propose a configuration of the atom where the positive charge is concentrated in a small nucleus at the centre of the atom [ 140 ], surrounded by only as many electrons as necessary to balance the central charge. The negative charge density of the electrons, small since they are few and take up the whole atomic volume, does not contribute to large angle scattering. He thus calculated the rate of scatters off the compact nucleus alone using classical electrodynamics...
