Traveling at a speed close to the speed of light causes time to slow down significantly, relative to the stationary observer. For instance, a number of radioactive atoms shot through a tube at high speed in the lab will have their half-life lengthened relative to the lab because of time dilation. This effect has been verified many times using particle accelerators. Time can also be dilated by applying a very strong gravitational field. For instance, placing a bunch of radioactive atoms near a black hole will also extend their half-life relative to the distant observer because of time dilation.
The half-life of radioactive decay can also be altered by changing the state of the electrons surrounding the nucleus. In a type of radioactive decay called "electron capture", the nucleus absorbs one of the atom's electrons and combines it with a proton to make a neutron and a neutrino.
The more the wavefunctions of the atom's electrons overlap with the nucleus, the more able the nucleus is to capture an electron. Therefore, the half-life of an electron-capture radioactive decay mode depends slightly on what state the atom's electrons are in.
By exciting or deforming the atom's electrons into states that overlap less with the nucleus, the half-life can be reduced. Since the chemical bonding between atoms involves the deformation of atomic electron wavefunctions, the radioactive half-life of an atom can depend on how it is bonded to other atoms. Linear attenuation coefficient is the sum of individual linear attenuation coefficients for each type of interaction:.
In diagnostic energy range, m decreases with increasing energy except at absorption edges e. For a given thickness of material, the probability of interaction depends on the number of atoms which the X-rays or gamma rays encounter per unit distance. For a given thickness, the probability of interaction relies on the number of atoms per volume. Dependency can be overcome by normalizing linear attenuation coefficient for thickness of material:.
In radiology, we usually differentiate between regions of an image that correspond to irradiation of adjacent volumes of tissue. Coherent scattering is vital for low kilo voltage photons as it increases with atomic number. The mass photoelectric attenuation coefficient is commensurate to the cube of the atomic number Z 3 and inversely proportional to the cube of the beam energy E 3.
The mass incoherent scattering attenuation coefficient is comparative to most values of Z, but it diminishes gradually with the expanding of beam energy. It is most dependent on the electron density [ 10 ]. Pair production happens only with higher beam energies over 1. The mass attenuation coefficient for pair production is linearly related to the atomic number.
Increasing beam energy also raises the attenuation from pair production in a logarithmic style [ 11 ]. The attenuation of gamma radiation can be achieved using a wide range of materials. Understanding the basic principles involved in the physical interactions of gamma radiation with matter that lead to gamma attenuation can help in the choice of shielding for a given application. Utilizing this understanding and considering the physical, chemical, and fiscal constraints of a project will lead to better application of resources to develop the most appropriate type of shielding [ 1 ].
Both of these methods are prime methods of inquiry in science. An advantage of both is that the experimental and analytical methods should be objective. Radiation has always been present around us. Life has evolved in a world containing significant levels of ionizing radiation. We are also exposed to fabricated radiation from sources such as medical treatments and activities involving radioactive materials. Because dangers of radiation on the well-being are known, it must be carefully utilized and entirely controlled.
It can be confirmed that ionizing radiation has long been vital in medicine and industry. Modern medicine would be impossible without ionizing radiation. X-ray imaging, computed tomography scans, diagnostic and therapeutic nuclear medicine, the gamma knife, and linear accelerators are a few of the technologies that have revolutionized medical diagnosis and treatment.
Indeed in spite of the fact that the utilization of ionizing radiation in medicine offers gigantic benefits, in any case, it moreover postures potential dangers to patients, restorative faculty, and the public. The diagnostic and helpful devices that remedy moreover can cause intestinal wounds and chronic illness such as cancer.
In expansion to the gamma rays, the attenuation of gamma radiation can be accomplished by employing a wide range of materials. Understanding the fundamental standards included within the physical interactions of gamma radiation with matter that lead to gamma radiation can offer assistance within the choice of protecting for a given application.
Utilizing this understanding and considering the physical and chemical limits of a project will lead to a better application of resources to develop the most suitable type of shielding. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.
Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications. Edited by Basim Almayahi. Edited by Waldemar Alfredo Monteiro. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Some radionuclides go through a series of transformations before they reach a stable state.
For example, uranium ultimately transforms into a stable atom of lead. But in the process, several types of radioactive atoms are generated. This is called a decay chain. When uranium decays, it produces several isotopes of:. As a result of this natural process, all of these radioactive atoms are part of our natural environment.
Certain radioactive nuclei emit alpha particles. Alpha particles generally carry more energy than gamma or beta particles , and deposit that energy very quickly while passing through tissue. Alpha particles can be stopped by a thin layer of light material, such as a sheet of paper, and cannot penetrate the outer, dead layer of skin.
Therefore, they do not damage living tissue when outside the body. When alpha-emitting atoms are inhaled or swallowed, however, they are especially damaging because they transfer relatively large amounts of ionizing energy to living cells. See also beta particle , gamma ray , neutron , x-ray. Atom — The smallest particle of an element that can enter into a chemical reaction. Beta Particles — Electrons ejected from the nucleus of a decaying atom. Although they can be stopped by a thin sheet of aluminum, beta particles can penetrate the dead skin layer, potentially causing burns.
They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if beta-emitting atoms are ingested or inhaled.
See also alpha particle , gamma ray , neutron , x-ray. Decay Chain Decay Series — The series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with uranium U ends in lead Pb , after forming isotopes, such as uranium U , thorium Th , radium Ra , and radon Rn Gamma Rays — High-energy electromagnetic radiation emitted by certain radionuclides when their nuclei transition from a higher to a lower energy state.
These rays have high energy and a short wave length. However, we generally refer to isotopes of a particular element e. The number associated with an isotope is its atomic mass i.
The element itself is defined by the atomic number i. Only certain isotopes are radioactive and not all radioactive isotopes are appropriate for geological applications -- we have to choose wisely. Those that decay are called radioactive or parent isotopes; those that are generated by decay are called radiogenic or daughter isotopes. The unit that we use to measure time is called half-life and it has to do with the time it takes for half of the radioactive isotopes to decay see below.
Half-life is a very important and relatively difficult concept for students. Mathematically, the half-life can be represented by an exponential function, a concept with which entry-level students may not have much experience and therefore may have little intuition about it.
I find that entry-level students in my courses get stuck on the term "half-life". Even if they have been given the definition, they interpret the term to mean one-half the life of the system. Instead, it is really the lifetime of half of the isotopes present in the system at any given time.
Problem solving in the geosciences was forever changed with the discovery of radioactivity. Radioactive elements can be used to understand numerical age of geological materials on time scales as long as and even longer than the age of the Earth. In order to determine the age of a geologic material, we must understand the concept of half-life.
Half-life is a term that describes time. The definition is: The time required for one-half of the radioactive parent isotopes in a sample to decay to radiogenic daughter isotopes.
The units of half-life are always time seconds, minutes, years, etc. If we know the half-life of an isotope and we can measure it with special equipment , we can use the number of radiogenic isotopes that have been generated in a rock since its formation to determine the age of formation.
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