2.  Radioactive decay, also known as nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting particles of ionizing radiation.  A material that spontaneously emits this kind of radiation - which includes the emission of energetic alpha particles, beta particles, and gamma rays - is considered radioactive.  An example of spontaneous radioactive decay is that of carbon-14, which takes place by loss of a beta particle to give nitrogen-14  Basic characteristics:  Spontaneous and irreversible emission  Highly penetrating, can pass through thin sheets of glass and metals  Can ionize the air or gas through which they pass  Can produce black spots on photographic plates

3.  A decay results when an atom with one type of nucleus, called the parent radionuclide, transforms to an atom with a nucleus in a different state, or to a different nucleus containing different numbers of protons and neutrons. Either of these products is named the daughter nuclide.  In some decays the parent and daughter are different chemical elements, and thus the decay process results in nuclear transmutation (creation of an atom of a new element).  Some elements are radioactive because of the configuration of the protons and neutrons in the nucleus produces an unstable structure.  During the process of spontaneous transformation the ratio of neutrons to protons changes. After one or more decay processes, a stable nucleus is formed.

4.  When a radioactive isotope decays, it does so with the emission of certain particles or quantities of energy those are characteristics of particular isotopes involved.  The major decay particles of interest include:  Alpha particles  Beta particles including negatrons and positrons  Gamma rays  X- rays  More recent work has shown that the decay of some nuclei involves the emission of other particles:  Neutrino  Antineutrino etc.

5.  Alpha (α) particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is generally produced in the process of alpha decay, but may be produced also in other ways.  Alpha radiation is emitted only from elements having atomic number greater than 82.  Isotopes emitting alpha particles will decay to the elements having a mass number of four less and an atomic number of two less than the original isotope  The low penetrating power of alpha particles makes isotopes emitting this radiation useless for biological applications because these particles can not penetrate tissue.

6.  Alpha particles are by far the heaviest and slowest of all radioactive emissions.  It is the most highly charged nuclear species with a charge of +2  Produce intense ionization. Their ionizing power is 100 times greater than beta ray and 10000 times greater than gamma ray.  Alpha particles move at a relatively low speed, about 0.1 the speed of light.(the speed of light is 3 × 10 10 cm/sec.)  Their penetrating power is inversely proportional to their ionizing power. They can be stopped by a sheet of paper or a very thin sheet of aluminum foil. These particles will travel only 3 to 8 cm in air.

7.  Beta ray is a flow of electron (more specifically negatron or positron). So, after this decay the nuclear charge of the element changes, resulting a new element having a different atomic number.  Beta plus decay  Beta minus decay  In β − decay, the weak interaction converts an atomic nucleus into a nucleus with one higher atomic number while emitting an electron (e − ) and an electron antineutrino (ν e ). An example of β − decay is shown when carbon-14 decays into nitrogen-14: 14 6 C → 14 7 N + e − + ν e  In β + decay, or "positron emission", the weak interaction converts a nucleus into its next-lower neighbor on the periodic table while emitting a positron (e + ) and an electron neutrino(ν e ). An example of positron (β + decay) is shown with magnesium-23 decaying into sodium-23: 23 12 Mg → 23 11 Na + e + + n + ν e

8.  Velocity is 99% of light’s velocity.  Their ionizing power is 1/100 times of alpha ray. The ionization is not continuous like the alpha ray.  Can penetrate large thickness of matter, eg. they can easily pass through1 cm thickness of Al foil sheet.  They affect photographic plates more strongly than alpha ray.  Rays are deflected by electric and magnetic field.

9.  An electromagnetic ray.  The nucleus lowers its internal energy by emitting a neutron-gamma ray.  The original element doesn’t change here.  Gamma radiation emission occurs when the nucleus of a radioactive atom has too much energy. It often follows the emission of a beta particle.

10.  γ rays are not deflected by electric and magnetic field.  Velocity same as light, 3 × 10 10 cm/s.  Their ionizing power is 1/10000 times of alpha ray.  Their penetrating power is very high eg. can easily penetrate through 30 cm thickness of iron.  They affect photographic plates more intensely than beta ray.  Produces fluorescence.

11. Penetrating Distances  < 4cm air, will not penetrate skin.  - several meters in air, penetrates skin ~ 0.8 cm, use ~ 6 mm plastic shielding. X – penetrating tissue, use lead shielding.  - more penetrating than X-rays, use lead or concrete shielding.

12.  The SI unit of radioactive activity is the becquerel (Bq), in honor of the scientist Henri Becquerel.  One Bq is defined as one transformation (or decay or disintegration) per second.  Since sensible sizes of radioactive material contains many atoms, a Bq is a tiny measure of activity; amounts giving activities on the order of GBq (gigabecquerel, 1×10 9 decays per second) or TBq (terabecquerel, 1×10 12 decays per second) are commonly used.  Another unit of radioactivity is the curie, Ci.  At present it is equal to the activity of any radionuclide decaying with a disintegration rate of 3.7×10 10 Bq, so that 1 curie (Ci) = 3.7×10 10 Bq.  Low activities are also measured in disintegrations per minute (dpm).

13.  The decay rate, or activity, of a radioactive substance is characterized by:  Constant quantities : The half-life—t 1/2, is the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value. The decay constant— λ (lambda), the inverse of the mean lifetime. The mean lifetime— τ (tau), the average lifetime of a radioactive particle before decay.

14.  Time-variable quantities: Total activity— A, is the number of decays per unit time of a radioactive sample. Number of particles—N, is the total number of particles in the sample.  These are related as follows:

16. Given a sample of a particular radioisotope, the number of decay events −dN expected to occur in a small interval of time dt is proportional to the number of atoms present N, that is

17.  Relation between initial and final amount of nuclides and time  Equation of half-life  Relation between half-life and average life period

18.  Not all living cells are equally sensitive to radiation. Those cells which are actively reproducing are more sensitive than those which are not.  This means that different cell systems have different sensitivities. Lymphocytes (white blood cells) and cells which produce blood are constantly regenerating, and are, therefore, the most sensitive.  Reproductive and gastrointestinal cells are not regenerating as quickly and are less sensitive. The nerve and muscle cells are the slowest to regenerate and are the least sensitive cell.  Cells, like the human body, have a tremendous ability to repair damage. As a result, not all radiation effects are irreversible. In many instances, the cells are able to completely repair any damage and function normally.  If the damage is severe enough, the affected cell dies. In some instances, the cell is damaged but is still able to reproduce. The daughter cells, however, may be lacking in some critical life-sustaining component, and they die.

19.  The other possible result of radiation exposure is that the cell is affected in such a way that it does not die but is simply mutated. The mutated cell reproduces and thus perpetuates the mutation. This could be the beginning of a malignant tumor.  Biological effects of radiation are typically divided into two categories.  ACUTE : The first category consists of exposure to high doses of radiation over short periods of time producing acute or short term effects.  CHRONIC : The second category represents exposure to low doses of radiation over an extended period of time producing chronic or long term effects.  High doses can kill so many cells that tissues and organs are damaged. This in turn may cause a rapid whole body response often called the Acute Radiation Syndrome (ARS).  Low doses spread out over long periods of time don’t cause an immediate problem to any body organ. The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years.

20.  Main organs affected by radioactivity:  Blood Forming Organs  Reproductive and Gastrointestinal Tract Organs  Skin  Muscle and Brain  So, the effects can be summarized below  Somatic effect: Damage to the organism itself resulting in either sickness or death. Effects may appear immediately or years later, usually in the form of cancer  Genetic damage: Damage to the genetic machinery of the body Produces malfunction in the offspring of the organism

21.  Total Dose  Type of Cell  Type of Radiation  Age of Individual  Stage of Cell Division (M Phase is the most sensitive)  Part of Body Exposed  General State of Health  Tissue Volume Exposed  Time Interval over which Dose is received

22.  Diagnostic Radiopharmaceuticals  Every organ in our bodies acts differently from a chemical point of view. Doctors and chemists have identified a number of chemicals which are absorbed by specific organs. The thyroid, for example, takes up iodine, the brain consumes quantities of glucose, and so on.  With this knowledge, radiopharmacists are able to attach various radioisotopes to biologically active substances. Once a radioactive form of one of these substances enters the body, it is incorporated into the normal biological processes and excreted in the usual ways.  Diagnostic radiopharmaceuticals can be used to examine blood flow to the brain, functioning of the liver, lungs, heart or kidneys, to assess bone growth, and to confirm other diagnostic procedures. Another important use is to predict the effects of surgery and assess changes since treatment.

23.  The amount of the radiopharmaceutical given to a patient is just sufficient to obtain the required information before its decay. The radiation dose received is medically insignificant.  A radioisotope used for diagnosis must emit gamma rays of sufficient energy to escape from the body and it must have a half- life short enough for it to decay away soon after imaging is completed.  The radioisotope most widely used in medicine is technetium- 99m, employed in some 80% of all nuclear medicine procedures for eg. Imaging of brain, thyroid, heart, etc.  Myocardial Perfusion Imaging (MPI) uses thallium-201 chloride or technetium-99m.  For PET imaging, the main radiopharmaceutical is Fluoro-deoxy glucose (FDG) incorporating F-18

24.  Therapeutic Radiopharmaceuticals  For some medical conditions, it is useful to destroy or weaken malfunctioning cells using radiation. The radioisotope that generates the radiation can be localized in the required organ in the same way it is used for diagnosis. This is radionuclide therapy (RNT) or radiotherapy.  Short-range radiotherapy is known as brachytherapy, and this is becoming the main means of treatment.  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.

25.  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.  A new and still experimental procedure uses boron-10, which concentrates in the tumor. The patient is then irradiated with neutrons which are strongly absorbed by the boron, to produce high-energy alpha particles which kill the cancerous cells.  For targeted alpha therapy (TAT) for killing metastatic cells, actinium-225 is readily available.

26. Universal Toxic sign Radiation sign Ionizing radiation sign