Radioisotope: Applications, Effects, and Occupational Protection

Principles and Applications in Nuclear Engineering - Radiation Effects, Thermal Hydraulics, Radionuclide Migration in the Environment

Edited by Rehab O. Abdel Rahman and Hosam El-Din M. Saleh

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Abstract

This chapter presents a brief introduction to radioisotopes, sources and types of radiation, applications, effects, and occupational protection. The natural and artificial sources of radiations are discussed with special reference to natural radioactive decay series and artificial radioisotopes. Applications have played significant role in improving the quality of human life. The application of radioisotopes in tracing, radiography, food preservation and sterilization, eradication of insects and pests, medical diagnosis and therapy, and new variety of crops in agricultural field is briefly described. Radiation interacts with matter to produce excitation and ionization of an atom or molecule; as a result physical and biological effects are produced. These effects and mechanisms are discussed. The dosimetric quantities used in radiological protection are described. Radiological protections and the control of occupational and medical exposures are briefly described.

Keywords

• radioisotopes
• sources of natural and artificial radiation
• radiation dose
• biological effect
• dosimetric units
• radiation protection
• radiation application
• environment

Author Information

Sannappa Jadiyappa *

• Department of Studies and Research in Physics, Kuvempu University, Shivamogga, Karnataka, India

*Address all correspondence to: sannappaj2012@gmail.com

1. Introduction

Radiation and radioactivity existed long before life evolved on the earth and are indispensable parts of the environment. We are continuously exposed to natural and artificial radiations. In addition to these, some of the radionuclides such as polonium and radium are present in our bones; our muscle contains radiocarbon and radiopotassium, radon, thoron, and their progeny in our lungs, and they emit ionizing radiation. The radiation coming from the sun is due to the nuclear fusion; it is very essential for the existence of life on earth. Therefore we live in a natural radioactive world. All organisms including human beings on the earth are getting benefits from radiation in a direct way without realizing it. Therefore, without radiation life does not exist. Scientific understanding of radiation and radioactivity and their benefits and effects on humans, that’s back almost century to the pioneering work of Roentgen (1895) and Becquerel (1896). Further investigation by M. Curie and P. Curie (1898) and Rutherford (1911) showed that radioactivity is exhibited by heavy elements such as uranium, thorium, and radium. The discovery of isotope was one of the results of work on the radioactive elements. The name “isotope” was first suggested by Soddy in 1913. The radioactive decay law was also proposed by him. More than thousand natural radioisotopes are present in our nature. At present more than 200 radioisotopes were produced from nuclear reactors and accelerators. The application of radioisotopes in medical, industry, and research field has served human civilization over a several decades. The radioisotopes have been a valuable gift to many braches of medicine and biology. Shorter half-lives of radioisotopes are used in medicine because they decay quickly and they are suitable for medical diagnosis and therapy. The World Health Organization (WHO) and International Atomic Energy Agency (IAEA) jointly coordinated a research program on radioactive tracers in cardiovascular diseases and searched for clues to this widespread health problem [1]. There are numerous applications of radioisotopes in medical fields; one of the revolutionized techniques is radioimmunoassay; this is used to detect and quantify minute levels of tissues components such as hormones, enzymes, or serum proteins by measuring the components ability to bind to an antibody or other proteins in competition with a standard amount of the same component that had been radioactivity tagged in the laboratory. For this technique, Rosalyn Sussman Yalow was awarded Nobel Prize in 1977 [2]. The precise dose is a life-and-death matter; therefore the IAEA has several program components to assist institutions in the members of the countries and aspect of radiation therapy and diagnosis. The IAEA in cooperation with the WHO offers on intercomparison service to check and improve accuracy of radiation dosimetry due to increase in the effectiveness of the radiotherapy [1]. The release of radioisotopes from nuclear fuel cycles, naturally occurring radioactive materials (NORM) from mining activity, mishandling of radioisotopes in industries and laboratories, and accidental release of radioactive materials could enter into the atmosphere. Therefore, it is necessary to require an urgent decision for protective actions. Therefore, the main objective is to focus on the applications and effects of radioisotopes and radiological protection.

2. Radioisotopes and radiation

The atom is the basic building block of matter. The concept of atoms and molecules was first introduced by John Dolton in 1811, and he proposed the atomic theory. The atom consists of positively charged nucleus and surrounded by a number of negatively charged electron, so that atom as a whole is electrically neutral. The electron had been discovered by J. J. Thomson in 1897. The nucleus consists of positive-charged proton and neutral-charged neutron referred as nucleons. The nucleus and proton were discovered by Rutherford in 1911, and neutron was discovered by James Chadwick in 1932. The number of proton present in the nucleus is called atomic number (Z), and total number of neutrons and protons present in the nucleus is called mass number (A). The atomic number of an element is the same, but different mass numbers are called isotope of an element. If the nucleus contains either excess of neutrons or protons, the force between these constituents will be unbalanced leading to unstable nucleus. An unstable nucleus will continuously vibrate and will attempt to reach stability by undergoing radioactive decay. The number of neutrons determines whether the nucleus is radioactive or not. The radioactive isotopes of an element are called radioisotopes; they are natural and artificially produced by nuclear reactors and accelerators. The discovery of radioisotope was one of the result works on the radioactive element. The way in which isotope arises in the radioactive element can be understood in terms of effects of radioactive decay on the atomic number Z and mass number A. In the year 1902, Rutherford and Soddy established that radioactivity is directly connected to the state of atomic nucleus.

The unstable nuclei of an element can undergo the variety of processes resulting in the emission of radiation in two forms, namely, radioactivity and nuclear reactions. In a radioactive decay, the nucleus spontaneously disintegrates to different species of nuclei or to a lower energy state of the same nucleus with the emission of alpha (α), beta (β), and gamma (γ) radiation is called radioactivity. The radioactivity was discovered by Henry Becquerel in 1896. Alpha, beta, and their ionizing property were discovered by Rutherford in 1899, and gamma was discovered by Villard in 1900. In nuclear reaction, the nucleus interacts with another particle or nucleus with subsequently emission of radiation as one of its final products. In some cases, the final product is also radioactive. The radiation emitted in both these processes may be electromagnetic (X-rays and γ-rays) or particle-like α, β, and neutrons. The nuclear reactions were discovered by Rutherford in 1917.

2.1. The type of emission of ionizing radiations

The ionizing radiations such as α, β, and γ except neutron are originated from unstable nuclei of an atom in an element undergoing radioactive decay.

2.1.1. Alpha radiation

Some naturally occurring heavy nuclei with atomic number 82 < Z < 92 and artificially produced transuranic element Z >92 decay by alpha emission, in which the parent nucleus loses both mass and charge. The alpha particle is emitted in preference to other light particles such as deuteron ( 2 H), tritium ( 3 H), and helium ( 3 He). Because energy must be released in order for decay to take place at all. The alpha particle has very stable and high binding energy, has tightly bound structure, and can be emitted spontaneously with positive energy in alpha decay, whereas 2 H, 3 H, and 3 He decay would require an input energy. The parent nucleus (Z, A) is transformed via

It has less penetrating and high ionizing power.

2.1.2. Beta radiation

Beta particles are fast electron or positron; these are originated from weak interaction decay of a neutron or proton in nuclei, which contains an excess of the respective nucleon. In a neutron-rich nucleus, neutron can transform itself in to a proton by emission of beta particles and antineutrino. Similarly, in the nuclei with rich proton, it transforms into neutron by emission of neutrino and positron. These radiations are high penetrating and less ionizing power:

Similarly in the nuclei with rich proton, the decay is

2.1.3. Gamma radiation

The emission of gamma rays is usually the most common mode of nuclear excitation and also occurs through internal conversion.

2.1.4. X-ray radiation

X-rays arises from the electron cloud surrounding the nucleus. They were discovered by Roentgen in 1895. X-rays are produced in X-ray tube by fast moving electron which is suddenly stopped by target.

2.1.5. Neutron radiation

It is a neutral particle that produces ionization indirectly by emission of γ-rays and charged particles when interacting with matter. These charged particles produce the ionization. It has more penetrating than gamma ray and can be stopped by thin concrete or paraffin barrier. They are produced by nuclear reaction and spontaneous fission in nuclear reactors. The characteristic emission of α, β, γ, and neutron sources is given in Table 1 [3].

Table 1.

Characteristics of some α, β, and γ emitters and neutron (sources).

2.2. Classification of radiation

Depending on its effects on matter and its ability to ionize the matter, radiation is classified in two main categories: ionizing and nonionizing radiations.

2.2.1. Ionizing radiation

Radiation passing through the matter which breaks the bonds of atoms or molecules by removing the electron is called ionization radiation. It passes through the matter or living organisms, and it produces various effects.

Ionizing radiation is produced by radioactive decay, nuclear fission, and fusion, by extremely hot objects, and by particle accelerators. The emission of ionizing radiation is explained in Section 2.1. The ionizing radiation is again divided into two types: direct and indirect ionizing radiation.

2.2.1.1. Direct ionizing radiation

Directly ionizing radiation deposits energy in the medium through direct Coulomb interaction between the ionizing charged particles and orbital electrons of atoms in the medium, for example, α, β, protons, and heavy ions.

2.2.1.2. Indirect ionizing radiation

Indirectly ionizing radiation deposits energy in the medium through a two-step process; in the first step, charged particles are released in the medium. In the second step, the released charged particles deposit energy to the medium through direct coulomb interaction with orbital electron of the atoms in the medium, for example, X-rays, photons, γ rays, and neutrons.

2.2.2. Nonionizing radiation

Nonionizing radiation is part of the electromagnetic radiation where there is insufficient energy to cause ionization. But it has sufficient energy only for excitation and not to produce ions when passing through matter [4]. Radiowaves, microwaves, infrared, ultraviolet, and visible radiation are the examples of nonionizing radiations. Nonionizing radiation is essential to life, but excessive exposures will cause biological effects.

3. Sources of natural and artificial radiation

There are two important sources of radiation: they are natural and man-made.

3.1. Natural background radiation

The radiation that exits all around us is called natural background radiation. All living organisms including man have been continuously exposed to ionizing radiations emitted from different sources, which always existed around us. The sources of natural radiation are cosmic rays and naturally occurring primordial radionuclides such as 238 U, 232 Th, 235 U, and their decay products as well as the singly occurring natural radionuclides like 40 K and 87 Rb, which are present in the earth crust, soil, rocks, building materials, ore, and water in the environment [5, 6]. Background radiation is a constant source of ionizing radiation present in the environment and emitted from a variety of sources. Natural radiations originated from three major sources: terrestrial, extraterrestrial, and internal (intake of natural radionuclides and their daughter product) sources of radiation.

3.1.1. Terrestrial sources of radiations

Terra means earth; the radiation originated from the earth crust is called terrestrial radiation. The primordial radionuclides ( 238 U, 232 Th, and 40 K) present in varying amounts in soil, rocks, water, and atmosphere are the sources of terrestrial radiation. The bulk of the natural radiation is mainly due to 40 K and 238 U, 232 Th, and their decay products [7]. Natural uranium consists of three isotopes 234 U, 235 U, and 238 U. 238 U is present in an abundance of 99.28% with a half-life of 4.5 × 10 9 years and 235 U in abundance 0.72% with a half-life of 0.7 × 10 9 years. Thorium is one of the important natural primordial radionuclides with a half-life of 1.4 × 10 9 years. It is about four times more abundant in nature than uranium. Average crustal abundance of 232 Th is 7.2 ppm [7]. All substances found in the terrestrial system contain variable amounts of 238 U and 232 Th; they undergo radioactive decay until they become stable isotopes. The two main important radioactive series are given in Tables 2 and 3.

The bulk of natural radiation comes from the primordial radionuclides such as 238 U, 235 U and 235 Th. They decay into other radioactive isotope as a part of radioactive series. These series are naturally occurring radioactive series, which have existed since the earth was formed. The nuclei in each series decay by emitting α, β and γ particles until stable (lead). These radioisotopes are chemically bound to minerals in rocks and soils and pose no biological hazards except radon, thoron and its progeny. Radon and thoron are noble radioactive gases, the higher concentrations of these gases and progenies are inhaled to produce lung cancer. According WHO and UNSCEAR, radon and their progeny are the second leading lung cancer after tobacco smoking.

Table 2.

Decay series of uranium ( 238 U) [8].