When I was doing my Ph.D. none of the teachers were ready to teach me course of Radio Tracer Techniques. The reason was it includes basis of molecular physics, application in various disciplines and laboratory equipments their principles and usage. This was considered as a tough subject. I preferred to study it only because it was a tough task. A dummy teacher was nominated and I started preparing this course. I was standing in the library even up to eight hours, canning over the racks of books in various disciplines in the library. Ultimately 45 standard books and several dozen back volumes of world class journals were selected and I brood over it continuously for four months and the first manuscript of this book was ready before 20 years. The compilation at the vary initial stage received wide coverage. My handouts were circulated in several universities. By chance I joined as a faculty in the same department where I was once a student. Automatically, I shouldered the responsibility of teaching Radio Tracer Technique. I am teaching this subject since last 20 years. Every year my students also suggested so many points and we were enriching the content of our manuscript. My students have taken keen interest in this particular subject. Rather they have been instrumental in shaping this script during two decades. It rarely happens that any book before coming into black and white takes such a long incubation period. While during the years long interaction this text has become more palatable, lucid and interesting. We hope this collection is a time tested work and will be appreciated by students and teachers as well.

Even though we are now in the atomic age, the idea of the atom is not new. More than 2,000 years ago, the Greek philosopher Democritus suggested that any matter is composed of tiny indestructible particles called Atoms. The word atom is derived from the Greek word Atoms meaning something that can not be cut further. However not much attention was paid to this concept till 1808, when Dalton proposed the famous “Atomic theory”. According to this theory, “all matter is composed of tiny indivisible particles called ‘Atom’. Combining the ideas of Lavoisier, Boyle and his own, Dalton proposed that atoms of elements combine together to make molecules of a compound. This was a great step in the concept of the atom and compounds, since this gave a clear picture of how the supposedly smallest particles of matter called atoms could be put together to form the various familiar substances found in nature.

2.1 Isotopes In 1913, J.J. Thomson and Aston introduced atmospheric neon into the positive ray apparatus and got two parabolas corresponding to masses 20 and 22, with the intensities of the tracks corresponding to the ratio of 9:1, irrespective of the condition of discharge and pressure. This indicated that neon existed in two forms having atomic weights 20 and 22, and at the same time it could not be distinguished chemically. These two types are known as isotopes of neon (iso = same, topas = place in the periodic table). When the average atomic weight of the ordinary neon was calculated based on the abundance of these two forms in the ordinary neon, it was found to be 20.2 which agreed the chemical methods. Thus the existence of isotopes of a given element was discovered. Formerly isotopes were defined chemical properties but with different atomic weights, the same atomic number and occupying the same position in the periodic classification. Later this definition was slightly modified and now isotopes are defined as nuclides with the same number of protons but differing in the number of neutrons, for example, ordinary hydrogen (also called protium ; proton =1 and neutron =0), deuterium (heavy hydrogen ; proton =1 and neutron = 1), and tritum super heavy hydrogen (proton =1 and neutron =2). Investigations using mass spectrographs have revealed more than 280 isotopes which are stable artificially radioactive isotopes.

Radioactivity The discovery of radioactivity, in general, actually came about on a few different fonts. First was the discovery of x-ray radiation that was artificially generated in a laboratory, followed by the discovery of several elements that naturally emit radiation when the nucleus of the atoms disintegrates or decay. These are the elements that today are called radioactive elements and are said to have unstable nuclei.

4.1 Selection of Isotopes for Tracer Studies In radioisotopes we have all the essentials of a powerful research tool, a non-destructive means by which atoms could be followed and detected in the organism. Application mainly depends on the fact that chemical properties of the isotope of an element are essentially identical. The basic requirement of a tracer is that it be 1.Chemically and physically, virtually equivalent to the substance it represents or displaces and that it, in no appreciable way, affect the system differing from its normal counterpart. 2.Radioactivity could be detected directly and 3.Unaffected by the physical or chemical treatments that are given. Hence, this has been used widely in the investigations of the various problems in biology, chemistry, physics and other fields like agriculture.

Carbon dating uses the half-life of Carbon-14 to find the approximate age of an object that is 40,000 years old or younger. 5.1 What is radiocarbon dating ? Radiocarbon dating is a method of estimating the age of organic material. It was developed right after World War II by Willard F. Libby and coworkers, and it has provided a way to determine the ages of different materials in archeology, geology, geophysics, and other branches of science. Some examples of the types of material that radiocarbon can determine the ages are wood, charcoal, marine and freshwater shell, bone and antler, and peat and organic-bearing sediments. Age determinations can also be obtained from carbonate deposits such as calcite, dissolved carbon dioxide, and carbonates in ocean, lake, and groundwater sources.

Although a number of radioactive isotopes are found in nature, most of the isotopes used as radioactive tracers are produced artificially. Methods for producing radioactive isotopes include nuclear fission and the bombardment of selected materials by neutrons or positively charged particles. 6.1 Production of Radioactive Nuclides Nuclear Reactors In a nuclear reactor, a fissionable nuclear fuel such as 235U or 239Pu is placed in a defined geometry within the reactor core. Fast moving neutrons released as the 235U or 239Pu nuclei fission are slowed to thermal energy (0.025 eV) by a low-Z moderator such as water, heavy water, beryllium, or graphite surrounding or mixed intimately with the nuclear fuel. The slowly moving neutrons are absorbed by addition of 235U or 239Pu nuclei, and a chain reaction is maintained. The rate of absorption of slow neutrons by fissionable nuclei determines the fission rate for the reactor and is controlled by placing inert neutron absorbers in the reactor core. Typical neutron absorbers, usually termed control roads include boron and calcium. Heat generated in the reactor is removed by a coolant such as water or one of a variety of gases or liquid materials.

7.1 Measurement of Radiation Dose Radiation dosimetry involves the measurement of the energy actually absorbed in a substrate exposed to ionizing radiation. The radiation may be either electromagnetic or corpuscular in nature. The passage of electromagnetic radiation through a substrate causes ionization by virtue of the secondary electrons released. Particle radiations on the other hand, ionize directly because they are charged, or indirectly through the charged particle resulting from a collision with a substrate. Alpha, beta particles, and protons yield primary ionization. Gamma rays and neutrons produce ionizing radiation by their interaction with the substrate in passage through it.

Although some forms of electromagnetic energy, such as light and heat, can be detected by the human senses. One of the greatest draw backs to high energy radiation is the inability to detect it. We cannot see, feel, taste, smell, or hear the various forms of ionizing radiation. Fortunately, ionizing radiation interacts with matter which makes detection and measurement possible by utilizing specialized equipment. In this section we want to introduce you to the various ways and means of detecting and measuring ionizing radiation. As mentioned previously, Becquerel discovered radioactivity because it left marks on photographic film as a means of detecting radiation. However, there are more definitive means commonly used by scientists and technicians who study and work with radiation. The equipment utilized for the detection and measurement of radiation commonly employs some type of a substance or material that responds to radiation. Many common methods use either an ionization process or molecular excitation process as a basis. Remember that we stated earlier that radiation interacts with matter. For detection and measurement purposes the process of ionization is the most commonly employed technique, based on the principle of charged particles producing ion pairs by direct interaction. These charged particles may collide with electrons, which remove them from their parent atoms, or transfer energy to an electron by interaction of electric fields.

9.1 Potential Tracer Difficulties and their Corrections In radioactive measurements, the observed counting rate is not equal to the true disintegrations rate of the sample since a number of factors like nature of detectors tend to increase it or, in a majority of cases, decrease the actual counts. Some of the important factors responsible for this are 1.Background, 2.Backscattering 3.Absorption 4.Self absorption 6.Geometry 7.Instrument efficiency

Radionuclides are used in two major ways: for their chemical properties and as sources of radiation. Radionuclides of familiar elements such as carbon can serve as tracers because they are chemically very similar to the non-radioactive nuclides, so most chemical, biological, and ecological processes treat them in a near identical way. One can then examine the result with a radiation detector, such as a Geiger counter, to determine where the provided atoms ended up. For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that had laid down atmospheric carbon would be radioactive. In medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays that can provide diagnostic information about a person’s internal anatomy and the functioning of specific organs. This is used in some forms of tomography single emission computed tomography and positron emission tomography scanning. Radioisotopes are also a promising method of treatment in hemopoietic forms of tumors, while the success for treatment of solid tumors has been limited so far. More powerful gamma sources are used to sterilize syringes and other medical equipment. About one in two people in Western countries are likely to experience the benefits of nuclear medicine in their lifetime. In biochemistry and genetics, radionuclides are used to label molecules and allow tracing chemical and physiological processes occurring in living organisms, such as DNA replication or amino acid transport.

In the Radiochemical Laboratory The following are some illustrative recommendation which may be used selected as a guide for setting up working rules : General No unnecessary materials should be brought into the laboratory. No unnecessary work should be done there. Eating, drinking, and the use of cosmetics in the laboratory should be forbidden. Radioactive materials should not be place in milk bottles, soft drink bottles, or other vessels that might be inadvertently used for food purposes. Record should be kept of radioactivity brought into the building and of its disposition.

Glossary and Abbreviation