Protons- plus charge In the nucleus Neutrons- neutral Electrons - negative charge Outside the nucleus

Definition:In nature there are nearly 300 nuclei, consisting of different elements and their isotopes. Isotopes are different nuclei of an element having the same number of protons but differ in the number of neutrons.

They are elements having the same atomic number but different mass numbers.

Some isotopes are stable, however, some isotopes of an element may be unstable. To attain stability they give up energy in the form of radiation hence they are known as radioisotopes. They disintegrate, with the emission of three main types of radiation.

The unstable nuclei decay by emission of or particles or radiation. Some very heavy nuclei decay also by fission.

Radioisotopes, because of their radiation characteristics and the energy they posses, can be utilized in industry, agriculture, healthcare and research applications. While natural radioactivity is common in heavy elements, it is rather rare in light elements exception being 19 40K, 37Rb, V, 87 23 50 etc.

OriginNaturally occurring radionuclides fall into three categories:Primordial These radionuclides originate mainly from the interiors of stars and, like uranium and thorium, are still present because their half-lives are so long that they have not yet completely decayed.Secondary radionuclides are radiogenic isotopes derived from the decay of primordial radionuclides. They have shorter half-lives than primordial radionuclides. Cosmogenic isotopes, such as carbon-14, are present because they are continually being formed in the atmosphere due to cosmic rays.Terrestrial radioactivity

MAN MADEManmade radioactive sources are produced by introducing an extra neutron to atoms of the source material. As the material rids itself of the neutron, energy is released in the form of gamma rays. Radioisotopes produced with nuclear reactors exploit the high flux of neutrons present. The neutrons activate elements placed within the reactor. A typical product from a nuclear reactor is thallium-201 and iridium-192. The elements that have a large propensity to take up the neutrons in the reactor are said to have a high neutron cross-section

Two of the more common industrial gamma-ray sources for industrial radiography are iridium-192 and cobalt-60. These isotopes emit radiation in a few discreet wavelengths. Cobalt-60 will emit a 1.33 and a 1.17 MeV gamma ray, and iridium-192 will emit 0.31, 0.47, and 0.60 MeV gamma rays.In comparison to an X-ray generator, cobalt-60 produces energies comparable to a 1.25 MeV X-ray system and iridium-192 to a 460 keV X-ray system. These high energies make it possible to penetrate thick materials with a relatively short exposure time. This and the fact that sources are very portable are the main reasons that gamma sources are widely used for field radiography. Of course, the disadvantage of a radioactive source is that it can never be turned off and safely managing the source is a constant responsibility.

Cyclotron was devised by Lawrence and Livingston in 1932 to accelerate charged particles like protons, deuterons and alpha. 1. Particle accelerators such as cyclotrons accelerate particles to bombard a target to produce radionuclides. Cyclotrons accelerate protons at a target to produce positron emitting radioisotopes, e.g., fluorine-18.

1. Radionuclides are produced as an unavoidable side effect of nuclear and thermonuclear explosions.

These particles are accelerated to high energy levels and are allowed to impinge on the target material. 11C, 13N, 18F, 123I etc are some of the isotopes that can be produced in a cylotron

ISOTOPE "COWS"

Radionuclide generators contain a parent isotope that decays to produce a radioisotope. The parent is usually produced in a nuclear reactor. A typical example is the technetium-99m generator used in nuclear medicine. The parent first produced in the reactor is Molybdenum-99 (66 h)*: these parent compounds are known as radioisotope cows.

Technetium-99m (6 h): Used in to image the skeleton and heart muscle in particular, but also for brain, thyroid, lungs (perfusion and ventilation), liver, spleen, kidney (structure and filtration rate), gall bladder, bone marrow, salivary and lacrimal glands, heart blood pool, infection and numerous specialised medical studies.

They have to possess well-defined characteristics, and, ideally, the radioactivity should be eliminated from the body as soon as the study has been completed.

A radioisotope, or any compound that contains a radioisotope, is said to be radiolabeled and is called a radionuclide

Properties;Penetrability

Gamma rays -they are stopped by 2 meters of concrete or 40 cm. of lead. Very dense materials, such as lead, are commonly used as shielding to slow or stop gamma photons.

IonizationWhen radio isotopes pass through matter they tend to ionize the material in their path

Blackening of photographic paperPhotographic film can be exposed by all types of radiation, and is used to monitor exposure of personnel working with high energy emitters. A visible track in a cloud or bubble chamber can pick up radioactivity, as can a calorimeter if the energy emitted is quite high. This property is used for auto-radiography DecayRadioactive decay by radioisotopes includes the emission of particles and/or electromagnetic radiation.Half life : When the product of an atomic disintegration is a stable isotope, atomic decay leaves less radioactive material behind. Therefore, as time passes, the amount of activity declines logarithmically. The half-life of a radioisotope is the time it takes for one-half of the unstable atoms to disintegrate.

Each radioisotope has a characteristic rate of decay and pattern of radiation. For example, 14-C is a low energy beta emitter with a half life of 5500 yearsIsotope Half life15C-2.4 secRa-2243.6 daysRa-22312 daysI-12560 daysU-235710, 000, 000 years (71 crore years)

1. Alpha emitters release a particle composed of 2 neutrons and 2 protons. The atomic number is therefore reduced by 2, and the atomic mass by 4.

Alpha particles are so heavy that even with low velocity their momentum is high. They don't travel far, but when they collide with other molecules they do a lot of damage, therefore alpha emitters are considered to be quite hazardous.

When a beta particle emitter decays, one of its extra neutrons is converted to a proton, increasing its atomic number by 1 without changing its atomic mass.

The breakdown is accompanied by the emission of a negatively charged particle of low mass, called the beta particle, and an uncharged particle of low mass, called a neutrino.

For example, hydrogen consists of just one proton and one electron. Deuterium (2-H), a component of "heavy water," consists of a proton, an electron, and one neutron, and is a stable isotope. Tritium (3-H) is an unstable isotope of hydrogen, consisting of a proton, an electron, and two neutrons.

When an atom of tritium decays, one of the neutrons is converted to a proton, one beta particle and one neutrino are released, and a helium isotope (3-He) remains. Tritium is called a "soft" beta emitter, because its beta particles have relatively low velocities

Gamma raysGamma emission does not consist of particles, but is an electromagnetic wave of high energy emitted from an unstable atom.

Gamma irradiation is similar to X rays, but with a slightly higher energy. Gamma irradiation travels at very high speeds (the speed of light).

They interact with matter in eight known ways, of which the three most important lead toproduction of secondary electrons, which in turn cause excitation and ionization.

Energy is transferred to atomic particles such as electrons (which are essentially the same as betaparticles). These energized particles then interact with tissue to form ions, in the same wayradionuclide-emitted alpha and beta particles would.

An example of a gamma emitter is 131-I (iodine). Gamma radiation may accompany alpha and beta particles

X raysX rays are electromagnetic rays with photons of very high energy. They are physically identical with gamma rays.

Methods of detectionThe method employed to detect radiation depends on the type of emitter and the intended purpose of detection. The most well known method of detecting radiation is with an ionization chamber A high energy particle can dislodge electrons from the atoms it strikes, producing pairs of ions. Particles are allowed to pass between parallel plates, one with a positive charge and one with a negative charge. As ionization takes place the ions each move to the plate with the opposite charge, producing a current. The current is read on a meter. The Geiger-Mueller counter is based on the ionization detection principle

A Geiger counter, also called a Geiger-Mller counter, is a type of particle detector that measures ionizing radiation.

They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a Geiger-Mller tube. Each particle detected produces a pulse of current, but the Geiger counter cannot distinguish the energy of the source particles.

Geiger counters are popular instruments used for measurements in health physics, industry, geology and other fields, because they can be made with simple electronic circuits.Scintillation counterA scintillation counter measures ionizing radiation. The sensor, called a scintillator, consists of a transparent crystal, usually phosphor, plastic (usually containing anthracene), or organic liquid (see liquid scintillation counting) that fluoresces when struck by ionizing radiation. A sensitive photomultiplier tube (PMT) measures the light from the crystal. The PMT is attached to an electronic amplifier and other electronic equipment to count and possibly quantify the amplitude of the signals produced by the photomultiplier.

When a charged particle passes through the phosphor, some of the phosphor's atoms get excited and emit photons. The intensity of the light flash depends on the energy of the charged particles. Cesium iodide (CsI) in crystalline form is used as the scintillator for the detection of protons and alpha particles; sodium iodide (NaI) containing a small amount of thallium is used as a scintillator for the detection of gamma waves.

Liquid scintillation countingThe amount of kinetic energy in a beta particle differs from one decay to the next. However, each radioisotope has a typical energy spectrum, that is, a predictable range of energies. In liquid scintillation counting, the material containing radioisotopes is dissolved in an organic solvent containing an aromatic solute (the scintillant).When radioactive decay takes place, the energy of a beta particle is transferred by collision to an electron in the shell of the scintillant, exciting that electron.The electron then returns to its ground state, releasing a photon. The number of photons emitted following each atomic disintegration is proportional to the energy of the released beta particle. The vial is lowered into a dark chamber with photoelectric detectors on each side. Each "flash" received by the detectors corresponds to one atomic disintegration. The detectors are connected, via photomultiplier tubes, to a microprocessor unit that records not only each event, but also the number of photons detected during each event (brightness of the flash).

Gamma-Ray Spectroscopy and Applications0. 0. Most radioisotopes emit gamma rays and almost all elements have isotopes that emit gamma rays 0. 0. Used for detection, identification, and assay of naturally occurring radioisotopes (e.g. in geology, mining, and oil exploration).0. 0. Detection, identification, and assay of man-made radioisotopes (effluents from nuclear power and other sources of radioisotopes such as cyclotrons, e.g. in geology, homeland security)

Measuring of tracers in biology, medicine, physics, chemistry, and engineering.

Gamma-ray imaging e.g. in nuclear medicine and drug development, recently in homeland security and nuclear non-proliferation as well.

Elemental analysis by gamma rays emitted in induced nuclear reactions.

Elemental analysis by nuclear (e.g. neutron) activation.

Gamma-ray spectroscopy to study the structure of nuclei.

Gamma-ray spectroscopy to study astrophysical processes.

X-ray fluorescence

Units of measurement:Magnitude of radioactivity is measured in Becquerels (Bq), which is the SI unit or Curies-(Ci).

One Becquerel is equal to one disintegration per second.

Curie is the quantity of radioactive material in which the number of nuclear disintegrations per minute is the same as that in 1g of Radium i.e. 2.2 X1012.

37 kBq = 37 000 Bq = 1 Ci37 MBq = 37 000 000 Bq = 1 mCi

RAD - unit of absorbed dose (100 rad = 1 Gy)- Radiation adsorbed dose

The rad is a unit of absorbed radiation dose.The rad was first proposed in 1918 as "that quantity of X rays which when absorbed will cause the destruction of the malignant mammalian cells in question..." It was defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by one gram of matter. It was restated in SI units in 1970 as the dose causing 0.01 joule of energy to be absorbed per kilogram of matter.The older quantity and unit of radiation exposure (ionization in dry air) is the "roentgen" (R), where 1 R is equal to 2.58 10-4 C/kg. To convert absorbed dose to dose equivalent, or "rem," the biological effects in man are now considered, which is done by modifying with a quality factor. For practical scenarios, with low "linear energy transfer" (LET) radiation such as gamma or x rays, 1 R = 1 rad = 1 rem. [2]The Systme International has introduced as a rival unit, the gray (Gy); the rad is equal to the centigray and 100 rads are equal to 1 Gy. RBE- Relative biological efficacy- LD 50 of radiation : human 400 RAD; amoeba- 1-2 Lakh/ parmoecium ; Frog- 700 RAD

REM ( RBE x RAD) unit of dose equivalent (100 rem = 1 Sv) ( R equivalent to man)

Gray (Gy) a measurement of absorbed dose (energy) deposited in any medium by any typeof radiation.

Sievert (Sv) For protection purposes, the term Dose Equivalent has been introduced.

The Dose Equivalent is expressed in Sieverts (Sv) and dose limits that are given in this unit are ameasure of human absorbed dose, with corrections made for the type of radiation.

In biological systems, the same degree of damage is not necessarily produced by the sameabsorbed dose of different types of radiation.

Until recently, other units for absorbed radiation were used:

A radioisotope, or any compound that contains a radioisotope, is said to be radiolabeled and is called a radionuclide. Radioisotopes and their formulations find varied applications in diagnosis, therapy and healthcare. Bhaba Atomic Research Centre (BARC) supplies reactor produced radioisotopes and radionuclides for medical use. The radioisotopes processed and supplied by Board of Radiation & Isotope Technology (BRIT), Mumbai to medical uses across the country, include radiopharmaceuticals, brachy-therapy wires, radio-immunoassay (RIA) kit

Agricultural Uses Radiations from certain radioisotopes are used for killing insects which damage the food grains.

Certain seeds and canned food can be stored for longer periods by gently exposing them to radiations.

Better yields of milk from cows, and more eggs from hens have been obtained on the basis of information gained by mixing radioisotopes with their diet.

Radioisotopes are used for determining the function of fertilizer in different plants.

Radioisotopes are also used for producing high yielding crop seeds. Thus the agricultural yield is increased

Industrial Uses There are many different uses to which radioisotopes are put in industry. These include radiography, gamma scanning of process equipment, use of radiotracers to study sediment transport at ports and harbours, flow measurements, hydrology and water resource management.

The isotope related services like sediment transportation, gamma scanning leakage detection and others have led to considerable monetary savings to the nation. By -ray photography we can find out wearing of cutting tools and lathes and can locate internal cracks in stones.

MEDICAL USESDiagnostic There are nearly one hundred radioisotopes whose beta and/or gamma radiation is used in diagnosis, therapy, or investigations in nuclear medicine.

Nuclear medicine uses radiation to provide diagnostic information about the functioning of a person's specific organs, or to treat them. Diagnostic procedures are now routineThe most used radioisotopes were discovered before World War II using the early cyclotrons of Ernest Lawrence, with the initial applications to medicine being developed by his brother John Lawrence. Some of the most well known radioisotopes, discovered by Glenn Seaborg and his coworkers, are 131I (discovered in 1938), 60Co (1937), 99mTc (1938), and 137Cs (1941).

By 1970, 90 percent of the 8 million administrations per year of radioisotopes in the United States utilized either 131I, 60Co, or 99mTc. Today, 99mTc, with a half-life of 6 hours, is the workhorse of nuclear medicine. It accounts for more than 10 million diagnostic procedures a year in the United States. It is used for brain, bone, liver, spleen, kidney, lung and thyroid imaging as well as for blood-flow studies.131I, with a half-life of 8 days, is used to diagnose and treat thyroid disorders. Seaborgs mother was one of the first to benefit from the use of this radioisotope that her son had discovered. Fatally ill from hyperthyroidism, (a related condition from which her sister died), diagnosis and treatment with 131I led to her complete recovery and a long life. Former President George Bush and First Lady Barbara Bush are some notable people who were successfully treated for Graves' disease, a thyroid disease, with 131I. Radioactive iodine treatment is so successful that it has virtually replaced thyroid surgery.

Scintigraphy is the science, or art, of using radioactive materials to produce a picture of their distribution within the human body.

Medical radioisotope scintigraphy makes use of the capability of certain organs to accumulate either for a short time or permanently some radioactive substances after they have been administered to a patient by mouth or by injection.

Scintillation cameras, autofluoroscopes or spark chambers, view the region of interest as a whole rather than scan it point by point.

As a result the doses to the patient could be lowered considerably or, when these were already acceptable, the time for the examination reduced to sometimes a few minutes.

In addition the high sensitivity of these techniques now made it possible not only to record the distribution of radioactivity fixed in a particular organ but to follow its movements (usually with the passage of the blood) through a number of organs such as the kidneys, the heart and lungs or the liver

A very effective role for radioisotopes in nuclear medicine is the use of short-lived positron emitters such as 11C, 13N, 15O, or 18F in a process known as Positron Emission Tomography (PET). Incorporated in chemical compounds that selectively migrate to specific organs in the body, diagnosis is effected by detecting annihilation gamma raystwo gamma rays of identical energy emitted when a positron and an electron annihilate each other. These gamma rays have the very useful property that they are emitted in exactly opposite directions. When both are detected, a computer system may be used to reconstruct where the annihilation occurred. By attaching a positron emitter to a protein or a glucose molecule, and allowing the body to metabolize it, we can study the functional aspect of an organ such as the human brain. The PET image shows where the glucose has been absorbed (Fig. 13-3a).Positron Emission Tomography (PET) which is a more precise and sophisticated technique using isotopes produced in a cyclotron. A positron-emitting radionuclide is introduced, usually by injection, and accumulates in the target tissue. As it decays it emits a positron, which promptly combines with a nearby electron resulting in the simultaneous emission of two identifiable gamma rays in opposite directions. These are detected by a PET camera and give very precise indication of their origin. PET's most important clinical role is in oncology, with fluorine-18 as the tracer, since it has proven to be the most accurate non-invasive method of detecting and evaluating most cancers. It is also well used in cardiac and brain imaging.PET imaging becomes even more valuable when we can observe the functional image compared to the anatomical image. Magnetic Resonance Imaging (MRI)originally known as Nuclear Magnetic Resonance Imagingcan provide very detailed images of the anatomy as shown in the second image shown in Fig. 13-3b. These techniques provide researchers a better understanding of what is healthy tissue versus what is diseased. Positioning of the radiation source within the body makes the fundamental difference between nuclear medicine imaging and other imaging techniques such as x-rays. Gamma imaging by either method described provides a view of the position and concentration of the radioisotope within the body. Organ malfunction can be indicated if the isotope is either partially taken up in the organ (cold spot), or taken up in excess (hot spot). If a series of images is taken over a period of time, an unusual pattern or rate of isotope movement could indicate malfunction in the organ.Radio isotopes used for diagnostic purposeChromium-51 (28 d): Used to label red blood cells and quantify gastro-intestinal protein loss.Holmium-166 (26 h): Being developed for diagnosis and treatment of liver tumours.Iodine-131 (8 d)*: Widely used in treating thyroid cancer and in imaging the thyroid; also in diagnosis of abnormal liver function, renal (kidney) blood flow and urinary tract obstruction. A strong gamma emitter, but used for beta therapy.Iron-59 (46 d): Used in studies of iron metabolism in the spleen.Potassium-42 (12 h): Used for the determination of exchangeable potassium in coronary blood flow.Selenium-75 (120 d): Used in the form of seleno-methionine to study the production of digestive enzymes.Sodium-24 (15 h): For studies of electrolytes within the body.Technetium-99m (6 h): Used in to image the skeleton and heart muscle in particular, but also for brain, thyroid, lungs (perfusion and ventilation), liver, spleen, kidney (structure and filtration rate), gall bladder, bone marrow, salivary and lacrimal glands, heart blood pool, infection and numerous specialised medical studies. Xenon-133 (5 d)*: Used for pulmonary (lung) ventilation studies.Ytterbium-169 (32 d): Used for cerebrospinal fluid studies in the brain.Carbon-11, Nitrogen-13, Oxygen-15, Fluorine-18: These are positron emitters used in PET for studying brain physiology and pathology, in particular for localizing epileptic focus, and in dementia, psychiatry and neuropharmacology studies. They also have a significant role in cardiology. F-18 in FDG (fluorodeoxyglucose) has become very important in detection of cancers and the monitoring of progress in their treatment, using PET.Gallium-67 (78 h): Used for tumour imaging and localisation of inflammatory lesions (infections).Gallium-68 (68 min): Positron emitter used in PET and PET-CT units. Derived from germanium-68 in a generator.Copper-64 (13 h): Used to study genetic diseases affecting copper metabolism, such as Wilson's and Menke's diseases, and for PET imaging of tumours, and therapy.Cobalt-57 (272 d): Used as a marker to estimate organ size and for in-vitro diagnostic kits.Indium-111 (2.8 d): Used for specialist diagnostic studies, eg brain studies, infection and colon transit studies.Iodine-123 (13 h): Increasingly used for diagnosis of thyroid function, it is a gamma emitter without the beta radiation of I-131.Iodine-124: tracer.Krypton-81m (13 sec) from Rubidium-81 (4.6 h): Kr-81m gas can yield functional images of pulmonary ventilation, e.g. in asthmatic patients, and for the early diagnosis of lung diseases and functionRubidium-82 (1.26 min): Convenient PET agent in myocardial perfusion imaging.201 Thallium- (73 h): Used for diagnosis of coronary artery disease other heart conditions such as heart muscle death and for location of low-grade lymphomas.Radio-cobalt (60Co) is used in the treatment of brain tumour, radio-phosphorous (32P) in bone diseases and radio-iodine (131I) in thyroid cancer.

Bacteria and other disease-carrying organisms can be destroyed by irradiating them with -rays. The process is used to sterilise medical instruments, plastic hypodermic needles, packets of antibiotics, and hospital blankets

Radionuclide therapy (RNT)Rapidly dividing cells are particularly sensitive to damage by radiation. For this reason, some cancerous growths can be controlled or eliminated by irradiating the area containing the growth.External irradiation (sometimes called teletherapy) can be carried out using a gamma beam from a radioactive cobalt-60 source, though in developed countries the much more versatile linear accelerators are now being utilized as a high-energy x-ray source (gamma and x-rays are much the same).An external radiation procedure is known as the gamma knife radiosurgery, and involves focusing gamma radiation from sources of cobalt-60 sources on a precise area of the brain with a cancerous tumour. Worldwide, over 30,000 patients are treated annually, generally as outpatients.Internal radionuclide therapy is by administering or planting a small radiation source, usually a gamma or beta emitter, in the target area. Short-range radiotherapy is known as brachytherapy, and this is becoming the main means of treatment. Iodine-131 is commonly used to treat thyroid cancer, probably the most successful kind of cancer treatment. It is also used to treat non-malignant thyroid disorders. Iridium-192 implants are used especially in the head and breast. They are produced in wire form and are introduced through a catheter to the target area. After administering the correct dose, the implant wire is removed to shielded storage. This brachytherapy (short-range) procedure gives less overall radiation to the body, is more localized to the target tumour and is cost effective. Treating leukaemia may involve a bone marrow transplant, in which case the defective bone marrow will first be killed off with a massive (and otherwise lethal) dose of radiation before being replaced with healthy bone marrow from a donor.Many therapeutic procedures are palliative, usually to relieve pain. For instance, strontium-89 and (increasingly) samarium 153 are used for the relief of cancer-induced bone pain. Rhenium-186 is a newer product for thisA new field is Targeted Alpha Therapy (TAT) or alpha radioimmunotherapy, especially for the control of dispersed cancers.The short range of very energetic alpha emissions in tissue means that a large fraction of that radiative energy goes into the targeted cancer cells, once a carrier such as a monoclonal antibody has taken the alpha-emitting radionuclide to exactly the right placeLaboratory studies are encouraging and clinical trials for leukaemia, cystic glioma and melanoma are under way. TAT using lead-212 is said to show promise for treating pancreatic, ovarian and melanoma cancers.An experimental development of this is Boron Neutron Capture Therapy using boron-10 which concentrates in malignant brain tumours. The patient is then irradiated with thermal neutrons which are strongly absorbed by the boron, producing high-energy alpha particles which kill the cancer. This requires the patient to be brought to a nuclear reactor, rather than the radioisotopes being taken to the patient.Radionuclide therapy has progressively become successful in treating persistent disease and doing so with low toxic side-effects. With any therapeutic procedure the aim is to confine the radiation to well-defined target volumes of the patient. The doses per therapeutic procedure are typically 20-60 Gy.

Although radiotherapy is less common than diagnostic use of radioactive material in medicine, it is nevertheless widespread, important and growing. An ideal therapeutic radioisotope is a strong beta emitter with just enough gamma to enable imaging, eg lutetium-177. This is prepared from ytterbium-176 which is irradiated to become Yb-177 which decays rapidly to Lu-177. Yttrium-90 is used for treatment of cancer, particularly non-Hodgkin's lymphoma, and its more widespread use is envisaged, including for arthritis treatment. Lu-177 and Y-90 are becoming the main RNT agents.Iodine-131 and phosphorus-32 are also used for therapy. Iodine-131 is used to treat the thyroid for cancers and other abnormal conditions such as hyperthyroidism (over-active thyroid). In a disease called Polycythemia vera, an excess of red blood cells is produced in the bone marrow. Phosphorus-32 is used to control this excess.For targeted alpha therapy (TAT), actinium-225 is readily available, from which the daughter bismuth-213 can be obtained (via 3 alpha decays) to label targeting molecules. The bismuth is obtained by elution from an Ac-225/Bi-213 generator similar to the Mo-99/Tc-99 one. Bi-213 has a 46-minute half-life. The actinium-225 (half-life 10 days) is formed from radioactive decay of radium-225, the decay product of long-lived thorium-229, which is obtained from decay of uranium-233, which is formed from Th-232 by neutron capture in a nuclear reactor.Another radionuclide recovered from used nuclear fuel is lead-212, with half-life of 10.6 hours, which can be attached to monoclonal antibodies for cancer treatment. Its decay chain includes the short-lived isotopes bismuth-212 by beta decay, polonium-212 by beta decay and thallium-208 by alpha decay of the bismuth, with further alpha and beta decays respectively to Pb-208, all over about an hour.Considerable medical research is being conducted worldwide into the use of radionuclides attached to highly specific biological chemicals such as immunoglobulin molecules (monoclonal antibodies). The eventual tagging of these cells with a therapeutic dose of radiation may lead to the regression - or even cure - of some diseases.Reactor Radioisotopes (half-life indicated)Bismuth-213 (46 min): Used for targeted alpha therapy (TAT), especially cancers, as it has a high energy (8.4 MeV).Cobalt-60 (5.27 yr): Formerly used for external beam radiotherapy, now used more for sterilizingDysprosium-165 (2 h): Used as an aggregated hydroxide for synovectomy treatment of arthritis.Erbium-169 (9.4 d): Use for relieving arthritis pain in synovial joints.Iodine-125 (60 d): Used in cancer brachytherapy (prostate and brain), also diagnostically to evaluate the filtration rate of kidneys and to diagnose deep vein thrombosis in the leg. It is also widely used in radioimmuno-assays to show the presence of hormones in tiny quantities.Iodine-131 (8 d)*: Widely used in treating thyroid cancer and in imaging the thyroid; also in diagnosis of abnormal liver function, renal (kidney) blood flow and urinary tract obstruction. A strong gamma emitter, but used for beta therapy.Iridium-192 (74 d): Supplied in wire form for use as an internal radiotherapy source for cancer treatment (used then removed).Lead-212 (10.6 h): Used in TAT for cancers, with decay products Bi-212, Po-212, Tl-208.Lutetium-177 (6.7 d): Lu-177 is increasingly important as it emits just enough gamma for imaging while the beta radiation does the therapy on small (eg endocrine) tumours. Its half-life is long enough to allow sophisticated preparation for use. It is usually produced by neutron activation of natural or enriched lutetium-176 targets.Molybdenum-99 (66 h)*: Used as the 'parent' in a generator to produce technetium-99m.Palladium-103 (17 d): Used to make brachytherapy permanent implant seeds for early stage prostate cancer.Phosphorus-32 (14 d): Used in the treatment of polycythemia vera (excess red blood cells). Beta emitter.Rhenium-186 (3.8 d): Used for pain relief in bone cancer. Beta emitter with weak gamma for imaging.Rhenium-188 (17 h): Used to beta irradiate coronary arteries from an angioplasty balloon.Samarium-153 (47 h): Sm-153 is very effective in relieving the pain of secondary cancers lodged in the bone, sold as Quadramet. Also very effective for prostate and breast cancer. Beta emitter.Strontium-89 (50 d)*: Very effective in reducing the pain of prostate and bone cancer. Beta emitter.Ytterbium-177 (1.9 h): Progenitor of Lu-177.Yttrium-90 (64 h)*: Used for cancer brachytherapy and as silicate colloid for the relieving the pain of arthritis in larger synovial joints. Pure beta emitter and of growing significance in therapy.Radioisotopes of caesium, gold and ruthenium are also used in brachytherapy.* Fission productCyclotron RadioisotopesCopper-67 (2.6 d): Beta emitter, used in therapy.Fluorine-18 as FLT (fluorothymidine), F-miso (fluoromisonidazole), 18F-choline: tracer.Germanium-68 (271 d): Used as the 'parent' in a generator to produce Ga-68.Strontium-82 (25 d): Used as the 'parent' in a generator to produce Rb-82.Uses in archeologyRadiometric dating (often called radioactive dating) is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.[1] It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.[2] Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts.Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years (e.g., tritium) to over 100 billion years (e.g., Samarium-147).In general, the half-life of a nuclide depends solely on its nuclear properties; it is not affected by external factors such as temperature, pressure, chemical environment, or presence of a magnetic or electric fieldRadioisotope PoisonsIn 2006 Britain witnessed the apparent murder of one of its newer citizens, a former Russian intelligence official, by poisoning with radioactive polonium. His death was slow and excruciating.Polonium has about 26 isotopes, all of which are radioactive. Webelements periodic table says that it is 250 billion times more toxic than hydrocyanic acid. It is readily soluble in weak acid. (It was the first element discovered by Marie Curie, in 1898, and named after her native Poland. Her daughter Irene was contaminated with polonium in a laboratory accident and died of leukemia at the age of 59.)Polonium-210 is the penultimate decay product of U-238, before it alpha decays to become stable lead. It results from the beta decay of Pb-210 (in the U-238 decay series) to Bi-210 which rapidly beta decays to Po-210. This gives rise to its occurrence in nature, where uranium is ubiquitous. However, because of its short (138 day) half life, very little Po-210 would be found in uranium ore or mill tailings (Webelements suggests 0.1 mg/tonne). Po-210 levels in soil would be even less, but it is concentrated in tobacco and traces of it can be found in smokers' urine.Po-210 can also be made by neutron irradiation of Bi-209, and that is most likely source of any significant quantity. Russia has used Po-210 as a heat source in short-life spacecraft and lunar rovers. It also operates reactors using lead-bismuth cooling, which becomes contaminated with Po-210 due to neutron bombardment.Because its half-life is so short, a gram of Po-210 is about 5000 times as radioactive as a gram of radium - which sets the standard of activity. But at 138 days its half life is long enough for it to be manufactured, transported and administered before its loses its potency. It would not put the carrier at much risk, since alpha radiation is only really a hazard inside the body - a layer of skin is protection. About 10 micrograms (2 GBq) was said to have been used, administered in a cup of tea (it would be warm due to the decay).However, simply dosing someone with polonium might not have much effect if it simply went in one end and out the other in a day or two without being absorbed from the gut. It would probably need to be complexed on to an organic carrier which would enter the bloodstream and take it to vital organs where it would stay. (This is what happens with targeted alpha therapy (TAT) using very low levels of alpha-active radioisotopes: the carriers take them to dispersed cancerous tissues where they are needed.)In Mr Litvinenko's case the intense alpha radiation was reportedly in vital organs and sufficient to destroy them over three weeks. It was apparently over one hundred times the dose used in TAT for cancer treatment and the Po-210 is much longer-lived than isotopes used for TAT. It could have been attached to something as simple as a sugar.

But in general, the half-life of any nuclide is essentially a constant. Therefore, in any material containing a radioactive nuclide, the proportion of the original nuclide to its decay product(s) changes in a predictable way as the original nuclide decays over time. This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclide(s) into a material to the present.

The precision of a dating method depends in part on the half-life of the radioactive isotope involved. For instance, carbon-14 has a half-life of 5,730 years. After an organism has been dead for 60,000 years so little carbon-14 is left that accurate dating can not be established. On the other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades

Basic Physics of Radiocarbon Dating

Three carbon isotopes are found in atmosphere: C-11 (98.89%), C-12 (1.11%), and radioactive C-14 (10-10%) with T1/2 = 5730 +/-40 yrC-14 is constantly formed through cosmic-ray produced neutrons and its (n,p) reaction on N-14. C-14 oxidizes to 14CO2and enters the plant and animal life cycle through photosynthesis and food chain.

C-14 can be found in all living organism on earth with constant C-14/C-total ratio Death of living organism sets the clock and C-14 is depleted by radioactive decay

Research Uses

Various molecular biology techniques e.g. dotblot assay, restriction fragment length polymorphism (RFLP), single stranded conformationalpolymorphism (SSCP), amplified fragment length polymorphism (AFLP), mismatch cleavageassay, heteroduplex tracking assay (HTA), DNA sequencing, microsatellite detection,scintillation proximity assay (SPA), macroarray chip technology, isotope coded affinity tags(ICAT), etc. may use isotopes.

Microarrays can be used to detect thousands of genes using a single glass chip withimmobilized probes, and fluorescence-based detection. However, this technology remains outof the reach of academic laboratories, due to the prohibitive cost of equipment (about $200000). In such settings, a relatively cost-effective method using nylon macroarray chips andradioisotopic (autoradiography) detection is a viable alternative. This is amenable to smallscaleautomation, with probes to a couple of hundred genes immobilized on each nylon chip

Telomerase assayChromosomal telomere shortening is associated with cell aging and senescence. Numerousstudies on telomerase, an enzyme which can elongate the telomere ends of chromosomes ledto the increasing evidence that the presence of telomerase in cells that normally lack it maycontribute to the uncontrolled cell growth of cancer. The TRAP (telomeric repeatamplification protocol) assay, allowing amplification of the telomerase reaction product byPCR, has advantages like speed and sensitivity, and involves the analysis of 32P-labeledreaction products by polyacrylamide gel electrophoresis [58].

Effects of radiation on humansRadiation can have severe effects when it interacts with human cells. Different types of tissuerespond differently to radiation; e.g. bone marrow and gonads are much more sensitive toradiation than brain or the skin. Cytological and molecular damage caused by radiation maymanifest in the form of cancers, genetic mutations, skin reddening and epilation. Oneimportant hazard is the internal deposition in body tissues. Radioactive materials cause mostdamage when internalized by inhalation of aerosols, and by ingestion via contaminated hands,food, drink, and cigarettes. The exposure hazard depends upon the complexity of theprocedure, the activity and the radiotoxicity of the nuclide. Terms used to describeradioactivity are detailed in Appendix I. Radionuclides can be classified in one of four groupsbased on their relative radiotoxicity.Very high radiotoxicity This group includes plutonium and other alpha-emittingradionuclides. These materials are not commonly used in biomedical research laboratories.High radiotoxicity Radionuclides include 125I, 131I, 45Ca, 60Co and 137Cs, all of which arenot so commonly used in molecular research laboratories.Moderate radiotoxicity (1 mCi to 1 Ci or 37 MBq to 37 GBq). Most nuclides used inthe molecular biology research laboratory fall into the moderate radiotoxicity class,including 14C, 32P and 35S.Low radiotoxicity (10 mCi to 10 Ci or 370 MBq to 370 GBq) This group includes 3H,99mTc, natural uranium and natural thorium. Only the former is relevant to the molecularbiology laboratory.The biological effect of a given dose of radiation depends on a number of factors such as thetotal time during which the various doses of radiation are received, the dose rate duringirradiation and the type of irradiation. It is therefore necessary to take stringent precautions toprotect users from suffering from these severe effects of radiation exposure. The followingunits have been defined to evaluate/quantify this exposure