By:RAHUL MALIKDECEMBER, 2015

RadiopharmaceuticalsDISCOVERY - A. H. Becquerel (1896)

http://www.umich.edu/~radinfo/images/beq.jpgDuring the course of his experiments in 1896, on the fluorescence of uranium salts, Antoine Henri Becquerel left a wrapped photographic plate in a drawer. On developing the plate Becquerel found that it had been exposed. He concluded that as no light could have possibly penetrated the wrapping, the plate must have been fogged by rays from a sample of uranium salt which was stored in the same drawer.For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903, sharing the other half with Pierre and Marie Curie for their further study and experimentation of the Becquerel radiation.

WHAT MAKES A SUBSTANCE RADIOACTIVE?

Radioactivity is the random spontaneous disintegration of an atom of an element. The stability of the nucleus depends on the relative numbers of protons and neutrons present. The most stable nuclides tend to have an even number of protons and an even number of neutrons as each group of two protons and two neutrons, in the nucleus, makes an especially stable combination. A number of elements have atoms or nuclei which are unstable and consequently split up to form smaller atoms. This is due to all elements wanting to achieve equilibrium or stability in the nucleus.A substance is said to be radioactive if it contains unstable nuclei and is able to naturally release energy in the process of shedding high speed charged particles, in an attempt to reach a stable state. With this, a non-radioactive substance will remain intact indefinitely unless acted upon by an external force.In the process of transmutation, known as decay, the radioactive nuclei emits charged particles or electromgnetic rays depending on the nature it's instability. This results in a daughter nuclide being produced which may be radioactive or stable, but if it is radioactive it will in turn decay into a daughter nuclide, continuing to do so until it reaches the point of stability, an isotope of lead.NUCLEAR REACTIONS AND RADIOACTIVE DECAY.http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/imgnuc/alprad2.gifA nuclear reaction differs to that of a chemical reaction. In chemical reactions, the nuclei of the atoms from the reactants to the products is unchanged. In nuclear reactions, the protons and neutrons are rearranged in the nucleus of the atom to form new elements. Radioactive substances give off three types of radiation; alpha particles, beta particles and gamma rays.ALPHA DECAY:-When the nucleus of an atom has too many protons it results in disequilibrium of the nucleus due to the excessive repulsion. In order to reduce the repulsion the atom emits an alpha particle. An alpha particle consists of 2 protons and 2 neutrons and is identical to a Helium nucleus. If an atom emits an alpha particle the atomic number is reduced by two and the molar mass by four.http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/imgnuc/betarad.gifBETA DECAY:-When the neutron to proton ratio in the nucleus is too great a beta particle is emitted. In basic beta decay a neutron is transformed into a proton and an electron. The electron is then emitted as a beta particle which increases the atomic number by one and the molar mass is unchanged.http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/imgnuc/gamrad.gifGAMMA DECAY:-When the nucleus of an atom is at too high an energy it reaches equilibrium by emitting an electromagnetic photon of energy known as a gamma ray. The loss of a gamma ray does not alter the atomic number or the molar mass of the element, the atom simply passes to a lower state of energy.

NATURAL AND ARTIFICIAL RADIOACTIVITY.

NATURAL RADIOACTIVITY:-Nuclear reactions which occur spontaneously are said to be an example of natural radioactivity. There are three naturally occurring radioactive series among the elements in the periodic table. These are known as the uranium series, the actinium series and the thorium series, each named after the element at which the series start (except the actinium series which starts with a different uranium isotope). Each series decays through a number of unstable nuclei by means of alpha and beta emmission, until each series end on a different stable istope of lead.ARTIFICIAL RADIOACTIVITY:-Not all nuclear reactions are spontaneous. These reactions occur when stable isotopes are bombarded with particles such as neutrons. This method of inducing a nuclear reaction to proceed is termed artificial radioactivity. This meant new nuclear reactions, which wouldn't have been viewed spontaneously, could now be observed. Since about 1940, a set of new elements with atomic numbers over 92 (the atomic number of the heaviest naturally occurring element, Uranium) have been artificially made. They are called the transuranium elements.

USES of radiopharmaceuticals

The uses of radioactive isotopes are forever becoming more widespread as new methods of adaptation are being devised. Here are just a few of the ways in which radioactive isotopes are used today.Cancerous tissue can be destroyed by radioactivity in preference to healthy tissue. A cobalt-60 source which is a gamma emitter with a half life of 5 years is used to irradiate the cancer patient. The dose which the patient receives must be carefully calculated to destroy only the cancer cells without harming the patient's healthystissues.Surgical instruments can be sterilised more effectively with the use of radioactivity compared to that of boiling.Underground leaks in water or fuel pipes can be detected by introducing a short-lived radioisotope into the pipe. The level of radioactivity on the surface can be monitored. A sudden increase of surface radioactivity shows where water/fuel is escaping.Carbon-14 dating can be used to calculate the age of plant and animal remains. Living plants and animals take in carbon, which includes a small proportion of the radioactive isotope carbon-14. When a plant or animal dies, it takes in no more carbon-14, and that which is already present decays. The rate of decay decreases over the years, and the activity that remains can be used to calculate the age of the plant or animal material.Tracer studies use radioactive isotopes to track the path of an element through the body. Radioactive iodine(iodine-131) is administrated to patients with defective thyroids to enable doctors to follow the path of iodine through the body. As the half-life is only 8 days, the radioactivity soon falls to a low level.

Method of DetectionIonization Chamber

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Proportional Counterhttp://large.stanford.edu/courses/2012/ph241/lam1/images/f1big.png

The Geigercounterhttp://book.transtutors.com/cmsimg/4101_nuclear%20radiation%20instrumentation.jpg

Scintillation counter

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