2. Radio Isotopes


Nowadays radiotracer has become an indispensable and sophisticated diagnostic tool in medicine and radiotherapy purposes.

Diagnostic purpose

The most common radioactivity isotope used in radioactive tracer is technetium (99Tc). Tumors in the brain are located by injecting intravenously 99Tc and then scanning the head with suitable scanners.

131I and most recently 132I and 123I are used to study malfunctioning thyroid glands. Kidney function is also studied using compound containing 131I. 33P is used in DNA sequencing. Tritium (3H) is frequently used as a tracer in biochemical studies. 14C has been used extensively to trace the progress of organic molecule through metabolic pathways.

A most recent development is positron emission tomography (PET), which is a more precise and accurate technique for locating tumors in the body. A positron emitting radionuclide (e.g., 13N, 15O, 18F, etc.) is injected to the patient, and it accumulates in the target tissue. As it emits positron which promptly combines with nearby electrons, it results in the simultaneous emission of two γ-rays in opposite directions. These γ-rays are detected by a PET camera and give precise indication of their origin, that is, depth also. This technique is also used in cardiac and brain imaging.

Compound X-ray tomography or CT scans. The radioactive tracer produces gamma rays or single photons that a gamma camera detects. Emissions come from different angles, and a computer uses them to produce an image. CT scan targets specific area of the body, like the neck or chest, or a specific organ, like the thyroid.

2. Radio Isotopes

Radioisotope production

The sustainability of radioisotope production is one of the critical areas that receive great attention. There are more than 160 different radioisotopes that are used regularly in different fields; these isotopes are produced either in a medium or in high-flux research reactors or particle accelerators (low or medium energy). Some of the radioisotopes produced by the reactor and particle accelerators and their applications are given in Table.

Reactor radioisotopeHalf-lifeApplications
Radioisotopes produced by reactors
Bismuth-21345.59 minIt is an alpha emitter (8.4 MeV). Used for cancer treatment, e.g., in the targeted alpha therapy (TAT)
Cesium-1319.7 daysIt emits photon radiation in the X-ray range (29.5–33.5 keV). Used in brachytherapy of malignant tumors
Cesium-13730 yearsUsed in medical devices (sterilization) and gauges (661.64 keV)
Chromium-5128 daysUsed in Diagnosis of gastrointestinal bleeding and to label platelets (320 keV)
Cobalt-605.27 yearsUsed for controlling the cancerous growth of cells (1173.2 keV)
Dysprosium-1652 hUsed for synovectomy treatment of arthritis (95 keV)
Erbium-1699.4 daysUsed for relieving arthritis pain in synovial joints (8 keV)
Holmium-16626 hDiagnosis and treatment of liver tumors (81 keV)
Iodine-12560 daysUsed in cancer brachytherapy and radioimmunoassay (35 keV)
Iodine-1318 daysWidely used in treating thyroid cancer and in imaging the thyroid, diagnosis, and renal blood flows (284 keV)
Iridium-19274 daysUsed as an internal radiotherapy source for cancer treatment. Strong beta emitter for high-dose rate brachytherapy (317 keV)
Iron-5946 daysUsed in studies of iron metabolism in the spleen (1095 keV)
Lead-21210.6 hUsed in TAT for cancers (239 keV)
Molybdenum-9966 hUsed as the parent in a generator to produce technetium-99 m (740 keV)
Palladium-10317 daysUsed to make brachytherapy permanent implant seeds for early-stage prostate cancer. Emits soft X-rays (362 keV)
Potassium-4212.36 hUsed for potassium distribution in bodily fluids and to locate brain tumors (1524 keV)
Radium-22311.4 daysUsed to treat prostate cancers that have spread to the bones
Rhenium-1863.71 daysUsed for therapeutic purpose to relief pain in bone cancer. Beta emitter with weak gamma for imaging (137 keV)
Samarium-15347 hEffective in relieving the pain of secondary cancers lodged in the bone, sold as Quadra met. Beta emitter (103 keV)
Selenium-75120 daysUsed to study the production of digestive enzymes (265 keV)
Sodium-2415 hUsed for studies of electrolytes within the body (2754 keV)
Ytterbium-16932 daysUsed for cerebrospinal fluid studies in the brain (63 keV)
Radioisotopes produced by accelerators
Cobalt-57272 daysUsed as a marker to estimate organ size and for in vitro diagnostic kits (122 keV)
Copper-6413 hUsed for PET imaging studies of tumors and also cancer therapy (511 keV)
Copper-672.6 daysBeta emitter, used in therapy
Fluorine-18110 minUsed as fluorothymidine (FLT)
Gallium-6778 hUsed for tumor imaging and locating inflammatory lesions (infections)
Indium-1112.8 daysBrain studies, infection, and colon transit studies
Iodine-12313 hUsed for diagnosis of thyroid function
Rubidium-821.26 minConvenient PET agent in myocardial perfusion imaging
Strontium-8225 daysUsed as the parent in a generator to produce Rb-82
Thallium-20173 hUsed for location of low-grade lymphomas


Some of the radioisotopes produced by the reactor and particle accelerators and their applications.

2. Radio Isotopes

Radiotracer (radioisotopes)

Radiotracers are widely used in medicine, agriculture, industry, and fundamental research. Radiotracer is a radioactive isotope; it adds to nonradioactive element or compound to study the dynamical behavior of various physical, chemical, and biological changes of system to be traced by the radiation that it emits. The tracer principle was introduced by George de Hevesy in 1940 for which he was awarded the Nobel prize.

2. Radio Isotopes

Applications of radioisotope

The applications of radioisotopes have played a significant role in improving the quality of life of human beings. The whole world is aware of the benefits of the radiation, but the phobia of nuclear weapons on Hiroshima and Nagasaki (August 6 and 9, 1945) and the nuclear accidents occurred in Chernobyl in Russia (April 25–26, 1986) and Fukushima in Japan (March 2011) was so deep in the mind of the common man that we can still struggle to come out of it. Major problems arrived by workers in nuclear fields are due to lack of legalization, shortage of resources, and knowledge about nuclear society and safe guards. To minimize these problems the international organization such as International Atomic Energy Agency (IAEA) and International Commission on Radiation Protection (ICRP), identify requirements and provide the infrastructure that can support nuclear technology.

2. Radio Isotopes

Uranium decay series

The decay series of uranium and the type of radiation and range of energy of decay products are shown in Table 2. The important daughter product of uranium series is radon and its progenies. Radon is a naturally occurring radioactive gas. This was discovered by F.E. Dorn in 1900. It is found everywhere as part of our environment (i.e., in soil, water, and air). The ubiquitous radioactive gas is formed by radioactive decay of radium (226Ra), which is the daughter product of uranium decay series. The half-life of radon is 3.82 days; it decays by emission of alpha particle to form radon decay products or progeny, which are divided into short-lived and long-lived progeny. These are the significant contributor of natural radiation. On the basis of the epidemiological studies, it has been established that the enhanced levels of indoor radon in dwellings can cause health hazards and may lead to serious diseases like lung cancer in human beings .

Thorium decay series

The decay series of thorium and types of radiation with range of energies of decay products are as shown in Table 3. The important daughter products in this series are thoron and its progenies. The thoron progeny has relatively long half-life than that of radon progeny; therefore thoron progeny would give a significant dose to the lungs [11, 12, 13]. The decay of thorium 232Th leads to the subsequent formation of thoron (220Rn), its half-life 55 seconds. It is more abundant than 238U, but the short half-life of 220Rn allows only a fraction to escape into the atmosphere. The 222Rn is the one of the most significant isotope and it contributes significant dose to publics as ionizing radiation.

2. Radio Isotopes

Sources of natural and artificial radiation

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

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 238U, 232Th, 235U, and their decay products as well as the singly occurring natural radionuclides like 40K and 87Rb, which are present in the earth crust, soil, rocks, building materials, ore, and water in the environment. 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.

Terrestrial sources of radiations

Terra means earth; the radiation originated from the earth crust is called terrestrial radiation. The primordial radionuclides (238U, 232Th, and 40K) 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 40K and 238U, 232Th, and their decay products. Natural uranium consists of three isotopes 234U, 235U, and 238U. 238U is present in an abundance of 99.28% with a half-life of 4.5 × 109 years and 235U in abundance 0.72% with a half-life of 0.7 × 109 years. Thorium is one of the important natural primordial radionuclides with a half-life of 1.4 × 109 years. It is about four times more abundant in nature than uranium. Average crustal abundance of 232Th is 7.2 ppm. All substances found in the terrestrial system contain variable amounts of 238U and 232Th; 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 238U, 235U and 235Th. 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.

Parent nuclideHalf-life T1/2Decay mode (% branch)Decay energy (MeV)% IntensityDaughter nuclideγ-emission energy (keV)% γ-emission intensity
238U4.5 × 109 yearsα (100)4.19879.0234Th49.550.063
234Th24.10 daysΒ (100)0.19970.3234Pa63.284.1
234Pa1.17 mβ (99.84)2.26998.2234U1001.030.837
IT (0.16)*234Pa73.92*
234Pa6.70 hβ (100)0.64219.4234U131.300.029
234U2.5 × 105 yearsα (100)4.774671.38230Th53.200.123
230Th7.5 × 104 yearsα (100)4.687076.3226Ra67.6720.373
226Ra1600 yearsα (100)4.784394.45222Rn186.213.59
222Rn3.8235 daysα (100)5.489499.92218Po511.000.076
218Po3.10 mα (99.98)6.0024100.0214Pb**
β (0.02)*218At
218At1.60 sα (100)6.0024100.0214Bi*
214Pb26.8 mβ (100)0.67148.9214Bi351.9335.1
214Bi19.9 mβ (99.98)3.27218.2214Po609.3144.6
α (0.02)5.45253.9210Tl1238.115.78
214Po164.30 μsα (100)7.686899.99210Pb799.70.0104
210Tl1.30 mβ (100)4.20930.0210Pb*
210Pb22.3 yearsβ (100)0.01660.0631210Bi46.544.25
210Bi5.013 daysβ (100)1.1615100210Po**
210Po138.376 daysα (100)5.304399.99206Pb803.100.00122
206PbStable end product

Table 2.

Decay series of uranium (238U)

No gamma rays observed.

Parent nuclideHalf-life T1/2Decay mode (% branch)Decay energy (MeV)% IntensityDaughter nuclideγ-emission energy (keV)% γ-emission intensity
232Th1.4 × 1010 yearsα (100)4.012378.2228Ra63.810.263
228Ra5.75 yearsβ (100)0.039240.0228Ac13.521.6
228Ac6.15 hβ (100)1.15829.9228Th911.2025.8
228Th1.9116 yearsα (100)5.423272.2224Ra84.3731.22
224Ra3.66 daysα (100)5.685494.92220Rn240.994.10
220Rn55.6 sα (100)6.288199.87216Po549.760.114
216Po0.145 sα (100)6.7783100212Pb804.90.0019
212Pb10.64 hβ (100)0.33582.5212Bi238.6343.3
212Bi60.55 mβ (64.06)2.24886.57212Po727.336.58
α (35.94)6.050869.19208Tl39.861.06
212Po0.299 μsα (100)8.7849100.0208Pb**
208Tl3.053 mβ (100)1.79648.7208Pb2614.5335.64
208PbStable end product

Table 3.

Decay series of thorium (232Th)

2. Radio Isotopes

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.

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.

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.

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.

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 . 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.

2. Radio Isotopes

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.

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 (2H), tritium (3H), and helium (3He). 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 2H, 3H, and 3He decay would require an input energy. The parent nucleus (Z, A) is transformed XZA→XZ−2A−4+αXZA→XZ−2A−4+αE1

It has less penetrating and high ionizing power.

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:

n → p + e− + ν− E2

Similarly in the nuclei with rich proton, the decay is

p → n + e+ + E3

Gamma radiation

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

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.

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.

Source/isotopeHalf-lifeEnergy (MeV)
433 years
138 days
163 days
7.4 × 103 years
2.4 × 104 years
12.26 years
5730 years
3.08 × 105 years
92 years
3.81 years
5.2 years
30 years
2.6 years
5.2 years
8 × 105 years
48 years
330 days
2 k.6 years
3.690 keV
SourceHalf-lifeEnergy MeVYield × 106
24,000 years
138 days
87.4 years
433 years


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

2. Radio Isotopes

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. Radio Isotopes


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.

. 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.

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. 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.