Physics
Radioactivity
Radioactivity is the spontaneous emission of radiation from the nucleus of an unstable atom. This process can result in the transformation of the atom into a different element. The three main types of radiation emitted during radioactivity are alpha particles, beta particles, and gamma rays.
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11 Key excerpts on "Radioactivity"
eBook - PDFIsotopes in Nanoparticles
Fundamentals and Applications
- Jordi Llop, Vanessa Gomez-Vallejo, Jordi Llop, Vanessa Gomez-Vallejo(Authors)
- 2016(Publication Date)
- Jenny Stanford Publishing(Publisher)
In the latter state, the nucleus has an excess of internal energy and tends to move to a more stable state. The process by which the atomic nucleus moves from an unstable to a more stable state is called radioactive decay. Radioactive decay is spontaneous and is accompanied by the emission of particles and/or electromagnetic radiation. The unstable nucleus is called a radioactive atom or radionuclide. 145 During radioactive decay, the unstable atoms can become a different element via a process known as transmutation. This is the case in radioactive processes that result in the emission of alpha particles ( a , or 4 He 2+ ), electrons ( b – ), or positrons ( b + ). As an example, fluorine-18 ( 18 F) has nine protons and nine neutrons in its nucleus and is a positron emitter; on spontaneous decay a positron is emitted and, consequently, one of the protons becomes a neutron. The newly formed element, which has eight protons and ten neutrons, is oxygen-18 ( 18 O). Radioactive decay can also occur via electron capture (when a nucleus captures an orbiting electron, thereby converting a proton into a neutron with consequent transmutation), by emission of gamma ( g ) rays, by emission of a neutron, or by ejection of an orbital electron due to interaction with an excited nucleus in a process called “internal transition”. In the latter three decay modalities, the atoms before and after radioactive decay correspond to the same element because the number of protons remains unchanged and transmutation does not occur. Radioactive atoms exist in nature (and indeed are continuously produced naturally) and can be found in air, water, soil, or even living organisms. They can also be produced artificially using different technologies. Over 1500 radionuclides, both natural and artificial, have been identified. 6.2.2 Radioactive Decay Equations Radioactive decay is a stochastic process in which, according to quantum theory, it is impossible to predict when a specific atom will decay.
eBook - PDF- B. Zemel(Author)
- 1995(Publication Date)
- Elsevier Science(Publisher)
Radioactivity Basics Radioactivity Some combinations of protons and neutrons result in unstable nuclei. Such nuclides undergo spontaneous disintegration with time. This decay, accompanied by the emission of nuclear particles and/or electromagnetic radiation, is termed Radioactivity. Emission of particles from the nucleus also results in the formation of a new nuclide if there is a net change in the number of protons in the new nucleus as a result of the decay. Statistically, decay of a given radioactive nucleus is a random, unpredictable event; however if a sufficient number of radioactive nuclides is present, the rate of decay, dN/dT, becomes proportional to the number of nuclides (N) present. The greater the number of radioactive nuclides, the more closely this rule is followed. The rate of decay per unit time, dN/dt, is a measure of the amount of radio- activity (A) present and has the dimensions of events per second. This is shown below, where k is a proportionality constant, known as the decay constant, which is specific to each isotope. dN A= -d-~-= LN (1.2) Activity and half-life In modern (SI) nomenclature, the basic unit for the amount of Radioactivity present, A, is the becquerel (Bq), which is equal to a decay rate of one disin- tegration per second (dps). An older unit still widely used in the industry is the curie (Ci), which is equal to 3.7 x 1010 dps. The Bq and the Ci are normally used in multiples and submultiples, respectively, of these units as can be seen in Table 1.2. TABLE 1.2 Unit multipliers Prefix Symbol Multiple Example femto f 10-15 fj = femtojoule pico p 10 -12 pCi = picocurie nano n 10-9 nCi = nanocurie micro ~t 10-6 ~tSv = microsievert milli m 10-3 mGy = milligray kilo k 103 kr = kilorad mega M 106 MBq = megabecquerel giga G 109 GeV = gigaelectron volt tera T 1012 TBq = terabecquerels
eBook - PDF- Morris Hein, Susan Arena, Cary Willard(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
In other words, the genetic effects of increased radiation exposure are found in future generations, not only in the present generation. Because radioactive rays are hazardous to health and living tissue, special precautions must be taken in designing laboratories and nuclear reactors, in disposing of waste materi- als, and in monitoring the radiation exposure of people working in this field. 18.1 Discovery of Radioactivity • Radioactivity is the spontaneous emission of particles and energy from the nucleus of an atom. • Protons and neutrons are known as nucleons. • In nuclear chemistry isotopes are also known as nuclides. • Radioactive elements undergo radioactive decay to form different elements. • Radioactivity is not affected by changes in temperature, pressure, or the state of the element. • Principal emissions: • Alpha particles • Beta particles • Gamma rays • The half-life of a nuclide is the time required for one-half of a specific amount of the nuclide to disintegrate. 18.2 Alpha Particles, Beta Particles, and Gamma Rays • Alpha particles: • Consist of 2 protons and 2 neutrons with mass of 4 amu and charge of +2 • Loss of an alpha particle from the nucleus results in • Loss of 4 in mass number • Loss of 2 in atomic number • High ionizing power, low penetration • Beta particles: • Same as an electron • Loss of a beta particle from the nucleus results in • No change in mass number • Increase of 1 in atomic number • Moderate ionizing power and penetration • Gamma rays: • Photons of energy • Loss of a gamma ray from the nucleus results in • No change in mass number (A) • No change in atomic number (Z ) • Almost no ionizing power, high penetration 18.3 Radioactive Disintegration Series • As elements undergo disintegration, they eventually become stable after the loss of a series of particles and energy. • The disintegration series can be used to determine the age of geologic deposits. • Transmutation of an element can occur spontaneously or artificially.
eBook - PDF- Philip Palin Dendy, Brian Heaton(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
1 1 Fundamentals of Radiation Physics and Radioactivity P P Dendy and B Heaton SUMMARY • Why some atoms are unstable is explained. • The processes involved in radioactive decay are presented. • The concepts of physical and biological half-life and the mathematical expla-nation of secular equilibrium are addressed. • The basic physical properties of X and gamma photons and the importance of the K shell electrons in diagnostic radiology are explained. • The basic concepts of the quantum nature of electromagnetic (EM) radia-tion and energy, the inverse square law and the interaction of radiation with matter are introduced. CONTENTS 1.1 Structure of the Atom ............................................................................................................ 2 1.2 Nuclear Stability and Instability ......................................................................................... 4 1.3 Radioactive Concentration and Specific Activity .............................................................. 6 1.3.1 Radioactive Concentration ....................................................................................... 6 1.3.2 Specific Activity ......................................................................................................... 7 1.4 Radioactive Decay Processes ................................................................................................ 7 1.4.1 β – Decay ....................................................................................................................... 7 1.4.2 β + Decay ....................................................................................................................... 7 1.4.3 α Decay ........................................................................................................................ 8 1.5 Exponential Decay .................................................................................................................
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 1 Radioactive Decay Alpha decay is one example type of radioactive decay, in which an atomic nucleus emits an alpha particle, and thereby transforms (or 'decays') into an atom with a mass number 4 less and atomic number 2 less. Many other types of decays are possible. Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). The emission is spontaneous, in that the atom decays without any interaction with another particle from outside the atom (i.e., without a nuclear reaction). Usually, radioactive decay happens due to a proceses confined to the nucleus of the unstable atom, but occasionally (as with the different proceses of electron capture and internal conversion) an inner electron of the radioactive atom is also necessary to the process. Radioactive decay is a stochastic (i.e. random) process on the level of single atoms, in that according to quantum theory it is impossible to predict when a given atom will decay. However, given a large number of identical atoms (nuclides) the decay rate for the collection is predictable. The decay, or loss of energy, results when an atom with one type of nucleus, called the parent radionuclide , transforms to an atom with a nucleus in a different state, or a different nucleus, either of which is named the daughter nuclide . Often the parent and daughter are different chemical elements, and in such cases the decay process results in nuclear transmutation. In an example of this, a carbon-14 atom (the parent) emits radiation (a beta particle, antineutrino, and a gamma ray) and transforms to a nitrogen-14 atom (the daughter). By contrast, there exist two types of radioactive decay processes (gamma decay and internal conversion decay) that do not result in transmutation, but only
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 1 Radioactive Decay Alpha decay is one example type of radioactive decay, in which an atomic nucleus emits an alpha particle, and thereby transforms (or 'decays') into an atom with a mass number 4 less and atomic number 2 less. Many other types of decays are possible. Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). The emission is spontaneous, in that the atom decays without any interaction with another particle from outside the atom (i.e., without a nuclear reaction). Usually, radioactive decay happens due to a proceses confined to the nucleus of the unstable atom, but occasionally (as with the different proceses of electron capture and internal conversion) an inner electron of the radioactive atom is also necessary to the process. Radioactive decay is a stochastic (i.e. random) process on the level of single atoms, in that according to quantum theory it is impossible to predict when a given atom will decay. However, given a large number of identical atoms (nuclides) the decay rate for the collection is predictable. The decay, or loss of energy, results when an atom with one type of nucleus, called the parent radionuclide , transforms to an atom with a nucleus in a different state, or a different nucleus, either of which is named the daughter nuclide . Often the parent and daughter are different chemical elements, and in such cases the decay process results in nuclear transmutation. In an example of this, a carbon-14 atom (the parent) emits radiation (a beta particle, antineutrino, and a gamma ray) and transforms to a nitrogen-14 atom (the daughter). By contrast, there exist two types of radioactive decay processes (gamma decay and internal conversion decay) that do not result in transmutation, but only
eBook - PDF- John H. Lawrence, Joseph G. Hamilton, John H. Lawrence, Joseph G. Hamilton(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
A radioactive atom may best be regarded as one whose existence is liable to sudden and unannounced termination by a spontaneous nuclear transformation. Its existence up to the instant of such decay is no different, chemically or physically, from that of its stable brethren, except for the slight differences due to its increased or diminished mass (and perhaps to difference in spin). Radioactivity, occur-ring in the natural and in the artificial or induced radioisotopes, is con-sidered as evidence of nuclear instability which, in turn, depends upon the forces and particles in the particular nucleus under consideration. (c) Nuclear Particles. Although high speed electrons or /3-rays (termed negatrons if negative and positrons if positive, and denoted by the symbols ß~~ and respectively) are known to be ejected in many radio-active disintegrations, it is currently believed that protons and neutrons are the fundamental building blocks of atomic nuclei, and that the afore- ARTIFICIAL Radioactivity 119 mentioned particles are formed at the instant of decay. The proton is the nucleus of the light hydrogen atom (mass number Ξ A = 1) carrying a charge equal to that of the electron and positive in sign. The neutron is essentially the same particle but electrically uncharged. The mass number is defined as the integral number nearest the actual mass^ of the nucleus in question and is, therefore, by definition, the sum of the number of neutrons and the number of protons. The number of protons in a nucleus defines the total positive charge of that nucleus, which decides the number of extranuclear electrons in the neutral atom; this, in turn, defines the chemical identity of the atom. The number of protons is given by the atomic number of the element, sym-bolized by Z.
eBook - PDF- David Ucko(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
u ear e str and rad at n So far, you have learned about the chemistry of elements and compounds. Their properties and reactions d e p e n d mainly on the number and arrange-ment of valence electrons of the atoms involved. In contrast, nuclear chemis-try deals with changes in the nuclei of atoms, their number of protons and neutrons. These nuclear changes can create a large amount of energy as d e m -onstrated by the explosion of an atomic b o m b . T h e y also provide valuable methods for the diagnosis and treatment o f disease, such as cancer. ad a t t Certain atoms are unstable: Their nuclei break d o w n , giving off particles or energy known as radiation. This process of nuclear decomposition or disinte-gration is called Radioactivity. Many elements are naturally radioactive, most commonly w h e n the atomic number is larger than 83. For example, uranium (atomic number 92) is a radioactive element. W h e n a radioactive atom decomposes, the radiation it gives off can have three possible forms, called alpha radiation, beta radiation, and gamma radia-tion. Alpha radiation is symbolized b y the Greek letter a, for which it is named. It consists of particles, called alpha particles, that have two protons and two neutrons; they comprise the nuclei o f helium atoms. Thus, alpha par-ticles have a mass of 4 amu and a charge o f 2 + . T h e y are easily stopped b e -cause of their large size and cannot even penetrate the layer of dead cells on the surface of the skin. Beta radiation, symbolized by the Greek letter β, simply consists of electrons given off with high speed and energy. These beta particles thus have a charge of 1 - and a very small mass (1/1827 amu), which is usually ignored and called zero. Because they are smaller than alpha particles, beta particles can p e n e -176
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
γ rays are high-energy photons emitted by a radioactive nucleus. The gen- eral form for γ decay is Z A P* Z A P + γ decay does not cause a transmutation of one element into another. 31.5 The Neutrino The neutrino is an electrically neutral particle that is emitted along with β particles and has a mass that is much, much smaller than the mass of an electron. 31.6 Radioactive Decay and Activity The half-life of a radioactive iso- tope is the time required for one-half of the nuclei present to disintegrate or ⏟ ⏟ ⏟ ⏟ ⏟ ⏟ ⏟ ⏟ ⏟ Parent nucleus Daughter nucleus α particle (helium nucleus) ⏟ ⏟ ⏟ Parent nucleus ⏟ ⏟ ⏟ Daughter nucleus ⏟ ⏟ ⏟ β − particle (electron) ⏟ ⏟ ⏟ Excited energy state ⏟ ⏟ ⏟ Lower energy state ⏟ ⏟ ⏟ ray Reasoning We can use Equation 31.5 to calculate the ratio of remain- ing 90 Sr atoms (N) to the original number (N 0 ). To find this ratio, we will need the decay constant (λ) for 90 Sr, which is related to its half-life (T 1/2 ) by Equation 31.6. Solution Beginning with Equation 31.5, we have: N = N 0 e −λt ⇒ N N 0 = e −λt . To find the decay constant, we use Equation 31.6: λ = 0.693 T 1/2 = 0.693 29.1 yr = 0.0238 yr −1 . Plugging this into the expression above, we can calculate the ratio of remaining atoms: N N 0 = e −(0.0238 yr −1 )(50.0 yr) = 0.304 = 30.4% . The half-life of 90 Sr is a significant fraction of a typical lifespan. Thus, even after 50 years, there is a considerable percentage of atoms remaining. FIGURE 31.19 Cross-section of a human femur bone showing a malignant tumor known as osteosarcoma. This is an aggressive form of cancer that can result from 90 Sr replacing Ca in the bone. CNRI/Science Source Focus on Concepts 907 decay. The activity is the number of disintegrations per second that occur. Activity is the magnitude of ΔN/Δt, where ΔN is the change in the number N of radioactive nuclei and Δt is the time interval during which the change occurs.
- Basim A. Almayah(Author)
- 2019(Publication Date)
- IntechOpen(Publisher)
The positron decay 5. Alpha decay Figure 5. For proton numbers (Z) up to 20, N = Z could be a straight line. For all nuclei with Z > 20, stable nuclei have less protons than neutrons; the line bends upwards. Unsteady nuclei over the soundness bend are called neutron-rich [1]. 27 Basic Modes of Radioactive Decay DOI: http://dx.doi.org/10.5772/intechopen.85502 2.2.1 Beta decay Beta decay or ( β � decay ) is a process in which the neutron in the nucleus is essentially transformed into a proton and electron: n ! p þ β � þ υ þ energy Beta decay is also the decay of one of the neutrons to a proton via the weak interaction: A Z X ! β � A Z þ 1 Y Z þ 1 The electron is called β � particle ( υ ), meanwhile the neutrino is a particle that has no mass or electrical charge. It does not virtually undergo interactions with matter and therefore is essentially undetectable. The energy released in β � decay is shared between β � particle and neutrino ( υ ). This sharing of energy is more or less random from one decay to the next. As shown in Figure 6 , the plot displays the distribution of β � particle energy. It is also noticed that beta particles are not monoenergetic for a particular radionuclide, but they are released at varying energy levels over a continuous range (spectrum). The average energy of beta emission can be estimated as one-third of the maximum energy of emission: E avg = 1/3E max (as shown in Figure 6 ) [1]. 2.2.2 Gamma decay It is a mechanism for an excited nucleus to release energy. Emanation could be a sort of Radioactivity in which a few unsteady nuclear nuclei disseminate excess energy by an unconstrained electromagnetic radiation. Within the most common form of gamma decay, which is called gamma emis-sion, gamma rays (photons or bundles of electromagnetic vitality, of highly short wavelength) are radiated. Gamma rays are electromagnetic radiation (high-energy photons) with an extreme frequency and a high energy.
eBook - PDFIsotopic Tracers in Biology
An Introduction to Tracer Methodology
- Martin D. Kamen, Louis F. Fieser, Mary Fieser(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
This possibility leads to the existence of a nuclide in simultaneous isomeric states. Such states with average lives of 10~ 7 sec. to several months are known. An excited isomeric state can decay either by a transition to a lower energy state (isomeric transition) with 7 -ray emis-sion, or to a neighboring isobar by a β decay or Κ capture. An example is Mn 5 2 , which exhibits isomeric transition, Κ capture, and positron emission. The phenomenon of nuclear isomerism introduces some limitations in the use of radioactive isotopes as tracers which are discussed in a later section. 3. Alpha Decay. This type of radioactive transformation is of limited importance because no tracer elements of major interest exhibit radioactive isotopes which decay by emission of a particles. It should be remarked only that the a particle is emitted with a discrete energy forming a sharp distribution and that concomitant emission of 7 rays with their accompany-ing secondary radiations is possible when the daughter atom is left in an excited state. B . F U N D A M E N T A L D E C A Y L A W The rate at which radiation is emitted is a function of nuclear consti-tution and is not alterable by ordinary chemical or physical means. 3 The process whereby radioactive transformation takes place is governed by chance. Studies of statistical theory and its application to numerous cases of radioactive decay have been made by a number of workers, 4 and it has been shown conclusively that radioactive decay is a statistical process. Hence, it is permissible to assume that the probability of decay at any time is proportional to the number of atoms. Experimentally the rate of decay is seen to follow an exponential course with fluctuations governed by the Poisson distribution law (see pp. 96, 97). 8 Two reports have appeared which indicate that under very special conditions, as in Κ capture by a light nucleus (Be 7 ), chemical bonding can affect radioactive decay rate to a small but significant extent.
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