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Basic Radiation Physics - Mr. D.S. Patkulkar.pdf

This document provides an overview of basic radiation physics for radiation safety officer (RSO) certification. It defines ionizing radiation and different types including alpha, beta, gamma, x-rays and neutron radiation. It describes the composition of atoms and isotopes. Unstable nuclei undergo radioactive decay through emission of particles or photons. Radiation has sufficient energy to ionize atoms. The document covers radiation quantities, units of measurement, radiation interactions with matter and shielding. Understanding basic radiation physics is essential for RSOs to safely control and use radioactive sources.

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Basic Radiation Physics For RSO certification Course DS Patkulkar Coordinator IARP, GCTC RP&AD, BARC 022-25598660, 9967528343 patkulkards@gmail.com
To achieve an understanding of ionizing radiation and its properties. Successful completion of this training will qualify you a Radiation Safety Officer (RSO) RSO is responsible for control of radioactive sources all the time (during procurement, transportation, storage, use, disposal) ensuring radiation safety of self, employees, public & the environment. Understanding ionizing radiation and its properties i.e. Basic Radiation Physics and radiation protection is essential for RSO. Objective : -
We are constantly exposed to unavoidable Natural Background Radiation – coming from universe - cosmic, terrestrial due to daughters products of Uranium Thorium series present in rocks, walls, and also few nuclides, K-40, C-14, etc.. seated in our body. Radiation exposure, however small, involves some risk. Radiation has become an indispensable tool in Industries, Agriculture, medical (diagnosis, treatment, sterilization, food preservation, Research Applications, etc… This involves additional exposure & risk. Decision to use Radiation is taken when benefits overweigh risk (Justification). Radiation exposure should be As Low As Reasonably Achievable (ALARA), social and economic factors taken into consideration (Optimization) and always below prescribed limits. Basic radiation physics help use radiation tool safely. Introduction
Radiation Radiation is a process of transfer of energy without a medium. Radiation is in the form of electromagnetic waves including x-rays and Gamma rays or fast moving particles (such as Alpha, Beta, neutron). Wave photon energy E= hƴ where ƴ is frequency in Hertz Moving particle energy E = ½ mv2 where v & m is particle velocity & mass. Units of energy is electron-Volt (eV = 1.6 x 10-19 Joules) eV, keV, MeV, GeV, are multiples
If radiation has energy sufficient to knock out electron from atom to form +ve and –ve ion pair we call it Ionizing Radiation Ex. X-rays, gamma rays, Alpha, Beta, neutron. Non Ionizing radiation can excite electrons to higher energy orbits, and up on de-excitation, release excess energy in the form of X-rays. Ex. Radio Frequency, Microwave, Infra red, Visible light waves, Ultra violet waves
Ionizing radiation has enough energy to knock out electron from Atom and ionize it.
Electromagnetic wave spectrum Presence of some types of radiation can be detected by the human senses. e.g. light from the sun or from a light bulb can be seen and the heat can be felt. Other radiation can only be detected by special equipment. e.g. a television or radio receiver.
• Atomic structure • Subatomic particles and their properties • Stability of nucleus •Transformations in unstable nuclides •Radiation & types •Ionizing and non-ionizing radiation •Properties of Radiation • Radioactivity & laws of radioactive decay •Principles of Radiation protection •Radiation sources Basic Radiation Physics
The Atom All mater in nature is made up of elements and compounds. Each element is represented by its Chemical Symbol such as H, C, O, etc… Atom is a building block of element. It consists of a nucleus at its centre and electrons (e-) revolve around the nucleus in fixed orbits like planets in our solar system. An atom is so tiny that it cannot be seen by naked eye or even under a microscope. Its diameter is of the order of 10-8 cm and that of the nucleus is of the order of 10-12 - 10-13 cm. Atom is mainly empty space. Nucleus contain Protons (P) & Neutrons(N). Number of protons (P) in the nucleus is its Atomic Number (Z). Sum of Protons and Neutrons number is its Mass Number (A = P+N) Neutral Atom has same number of protons and electrons
Building Blocks of Atom (Subatomic Particles) Sub-atomic particle Symbol Charge Mass (amu) Proton p +1 1 Neutron n 0 1 Electron e -1 or + 1 1/1840 Since the electrons have negligible mass, the mass of an atom is concentrated in the nucleus with contributions entirely from protons and neutrons. The mass of a Proton = 1.6723 x 10-27kg and The mass of a Neutron = 1.6775 x 10-27kg
There are 92 elements in nature. These were formed at the time the earth They progressively contain an increasing number of protons, neutrons, and electrons. Hydrogen is the simplest of the elements. It has only one proton (and no neutron) in the nucleus and one electron in its orbit. Hydrogen H Atomic no. Z=1, Atomic mass A = 1 1 1H Helium has 2 protons and two neutrons in its nucleus & two electrons in orbit Helium He Atomic no. Z=2, Atomic mass A = 4 4 2He Lithium has three protons and three neutrons Lithium Li Atomic no. Z=3, Atomic mass A = 6 6 3Li An element is specified by using its chemical symbol, the mass number, and atomic number.
Proton Neutron Electron 2He4 Chemical symbol – He Atomic Number Z = ??? Mass Number A = ???
13 Isotopes may be radioactive or stable. Radioactive, Isotope is called “radioisotope”. Examples 3H, 60Co, 137Cs, 192Ir, 123I, 131I, 241Am. Isotopes 1 1H 2 1H 3 1H STABLE STABLE UNSTABLE and RADIOACTIVE All atoms of the same element have the same number of protons and electrons and thus the same atomic number Z. They can, however, have different numbers of neutrons . They are then called isotopes of that element. Thus isotopes of an element have the same atomic number, but different mass numbers. Isotopes of an element are chemically identical.
Stability of the nucleus/Atom The stability of the nucleus depends on the ratio of number of neutrons to number of protons present in the nucleus. The ratio is 1 for lighter nuclides and increases to 1.5 for heavier nuclides. A stable atom can be converted into unstable atom if the nuclear forces in side the nucleus are disturbed by some means. In nature, atom with excess number of neutrons or protons in the nucleus are found to be unstable.
The stability of an element depends upon the ratio of neutrons to protons in the nucleus. In elements of lower atomic number, except hydrogen, this ratio is generally one. In heavier elements i.e., elements having higher atomic number, this ratio tends to be more than unity, resulting in some degree of instability in the nucleus. An unstable nucleus, which has excess energy, tries to attain stability by releasing this energy in the form of radiation. Henry Becquerel, a French Physicist, discovered in 1996, that a compound of uranium emitted some invisible radiant energy. Madame Curie studied a large number of such substances and gave the name “Radioactivity” to this property. Radioactivity
Radioactivity is a phenomenon in which an unstable nucleus of an element disintegrates with the emission of energy and becomes a new element. It is a spontaneous process unaffected by physical and chemical agents. Radioactivity exists in nature among heavier elements. However, many lighter elements can be rendered radioactive by bombardment with charged particles or neutrons in Reactor or accelerators. This is called artificial radioactivity. Radioactivity
Radioactive transformation (or decay), whether natural or artificial can occur only in a limited number of ways with the emission of 1) Alpha particles, 2) Beta particles, 3) Positrons or by 4) Electron capture. However, the first two modes of decay are the most commonly observed. It may also be noted that in a number of cases the decay process is followed by the emission of gamma-rays or characteristic X-rays. MODES OF RADIOACTIVE DISINTEGRATION or X-ray   neutron
The table below shows the daughter produced by the alpha, beta or gamma disintegration of a parent with atomic number Z and mass number A Decay Parent Daughter  Z, A Z - 2, A- 4 - Z, A Z +1, A + Z, A Z - 1, A  Z, A Z, A
RADIOACTIVITY It is the process by which an Unstable radio-nuclide changes to another nuclide by emitting particles or energy in the form of radiation. RADIOACTIVE MATERIAL Matterial containing unstable nuclides is called radioactive material. Natural radioactive material: Uranium, Thorium, Radium, etc.. Man-made/Artificial radioactive material : Cobalt-60, Ceasium-137, Irdium-192,etc RADIOACTIVE DECAY Transformations are continuously taking place in unstable nuclides, New nucleus is formed along with emission of radiation. Parent nuclide = Daughter nuclide + Radiation NUCLEAR RADIATION Energetic particles or electromagnetic rays released/ emitted from the nucleus of the unstable nuclide/atom during its transformation is called nuclear radiation. Example: 88Ra226  86Rn222 +  (alpha) 27Co60  28Ni60 +  (Beta) + (Gamma)
Alpha Particle  An alpha particle is a swiftly moving particle consisting of two neutrons and two protons. It is identical with a helium nucleus. The Greek letter  is used to represent alpha radiation  Range : 2 to 8 cm in air  Velocity : 5% of that of light  Alpha particles are emitted upon the disintegration of principally those of heavy radioactive elements, e.g. U235, U238, Ra226 and Th230  Over 150 alpha emitting radionuclides have been discovered
21 Alpha () radiation: • is comprised of 2 protons and 2 neutrons (the nucleus of a helium atom); • is not very penetrating and can be shielded by a few centimetres of air or a sheet of paper; • is a significant internal exposure hazard; • but can be difficult to detect because of the low penetrating power. • Example • 88Ra226 ----- 86Rn222 +  Alpha () radiation
Range (cm) Energy (MeV) 7 6 5 4 3 4 5 6 7 8 Range of Alpha Particles in Air
Beta Particle A beta particle is a swiftly moving electron which has been emitted by a nucleus. The Greek letter  is used to represent beta radiation. Most fission products are beta emitters and in most cases the daughters and grand daughters are also. The most energetic beta particles have a velocity which is almost equal to the speed of light, e.g. the beta particle emitted by Rh106 (rhodium) has a velocity of 0.97c One neutron with in the nucleus of the parent atom changes into a proton and an electron, which is being ejected as ß- particle. Such a transformation will leave the mass number of the daughter atom unchanged i.e the same of the parent atom. The atomic number of the daughter nuclide increases by 1 as one more protons created in the nucleus of daughter nuclide. When beta particles have lost their velocity, they become ordinary electrons and join the free electron population
24 Beta () radiation – in most cases are negatively charged electrons; – is more penetrating than alpha but still can be shielded by thick plastics or thin sheets of metal; – is an external eye and skin exposure hazard; – is an internal exposure hazard; The degree of detection depends on the energy of the beta particles. Example 27Co60 ----- 28Ni60 +  + neutrino Beta () radiation
Beta Disintegration  In beta decay, a neutron divides into a proton and an electron (beta particle). The proton remains in the nucleus and the beta particle is emitted. - - n P n 1H3 - P P n 2He3 P P n 2He3 91Pa234 92U234 - + 82Pb214 83Bi214 - + 19K40 20Ca40 - +
Positron Emission  Positron is a particle exactly equal in mass to the electron, but it carries an opposite (positive) charge. Some radionuclides decay by positron emission.  This process is opposite to beta decay ; a proton changes to a neutron by the emission of a positron. 8O15 7N15 + +
12 10 6 8 4 2 0.1 0.2 0.3 0.4 0.5 0.6 Kinetic Energy (MeV) Relative Number Emax = 0.54MeV The Beta Energy Spectrum of Sr90
28 Gamma () radiation • has no mass and no charge but can be extremely penetrating; • must be shielded by heavy or massive material such as steel, lead, or concrete (or a combination); • is both an external and internal exposure hazard; • can be readily detected. • Excited nuclei or Isomers give Rise to gamma radiation Gamma () radiation
Gamma Rays Gamma Rays (or photons): Result when the nucleus releases energy, usually after an alpha, beta or positron transition
Gamma Radiation Visible light, Radio waves, Microwaves, UV rays, IR rays, X-rays and gamma rays are all electromagnetic radiations All the electromagnetic radiations have the velocity 3 x 1010 cm/sec. They differ from one another only in their frequencies. X-rays and Gamma rays have the highest frequencies and therefore they are also the most energetic and are ionising radiations Gamma rays are emitted from the nuclei of radioactive atoms, while X-rays are produced by X-ray tubes and similar apparatus. X-rays are not emitted from nuclei. Electron volt (eV) is the unit of radiation energy, keV, MeV
27Co60 28Ni60 28Ni60  28Ni60  320 KeV - 1.17 MeV  1.33 MeV  Gamma Disintegration  When a daughter nucleus is formed by radioactive decay, some energy is carried away from the nucleus by the particle emitted. After some disintegrations, however the daughter still possesses more energy than is normal for that nucleus, and such nucleus is said to be in excited state. A nucleus in an excited state promptly gets rid of excess energy by emitting a gamma photon
32 X-rays: • are generated electrically rather than originating from the decay of radioactive material; • have properties that can be considered to be almost identical to gamma rays, except that they usually have lower energies. X-ray radiation
X-Rays X-Rays: Occur whenever an inner shell orbital electron is removed and rearrangement of the atomic electrons results with the release of the elements characteristic X-Ray energy
Difference between X rays and Gamma ray
35 Neutron (n) radiation Free neutrons can exist as a type of radiation. • Uncharged themselves, neutrons may be absorbed by other nuclei rendering such nuclei unstable and therefore radioactive. • This process is called activation. • Neutrons are very penetrating and can cause significant biological damage. • Neutrons can be shielded by hydrogenous material e.g. water, polyethylene. • Cf-252, Am-Be, nuclear reactor
The penetrating power of any type of radiation depends partly on its energy, the greater the energy, the greater the penetrating power Alpha particles are generally less penetrating than beta particles, which in turn are less penetrating than gamma rays Alpha particles and gamma rays are emitted with a constant energy level from their respective nuclides, whereas beta particles are emitted with a range of energies. The half-value layer is the thickness of absorber required to reduce gamma radiation to half its former level. The tenth-value layer is the thickness of absorber required to reduce gamma radiation to 1/10thits former level.
+- -+-+-+ -+-+-+ -+-+-+ -+-+-+-+ - +-+ -+- -+ -+ -+ -+ -+ 100 1cm 50000 Alpha Source Beta Source Alpha particle Beta particle Specific Ionisation in Air +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Radiation (Symbol) Relative Mass in amu (1.66x10-27 kg) Electric charge (1.6x10-19 C) Range in Air Suitable Absorber Changes in Daughter Nuclide Alpha () 4 amu ++ Few cms Paper. Z reduces by 2 A reduces by 4 Beta () Positron (+) Mass of electron is Negligible (9.11 x 10–31 kg) Beta = -ve Positron = +ve Few metre Few mm Plastic or Aluminium Z increases by 1 A does not change Z reduces by 1 A does not change Gamma () No mass Neutral Very large Lead, Water or Concrete A & Z does not change Neutron (0n1) 1 amu. Neutral Very large Cd, B for thermal, Paraffin, B, Cd for fast neutrons. A reduces by 1 Important Properties of Radiations
Rate of Disintegration  The activity of a radioactive source is the number of nuclie disintegrating per unit time  The half-life of a radioactive substance is the time required for it to lose 50% of its activity by decay. Half life of a nuclide is constant. (Range from a fraction of a second for some radio nuclides to many millions of years for others)  Curie (Ci) is that quantity of a radioactive nuclide which is disintegrating at the rate of 3.7 x 1010 atoms per second.  It is relatively large unit. Its sub multiples, milli curie (mCi = 10-3 Ci) and micro curie (Ci = 10-6 Ci) are preferred in practice.  The SI unit of radioactivity is Becquerrel (Bq). One Bq is equal to one dps.
Radionuclide Mass requiredfor 1 Ci Half-life of radionuclide Nitrogen-16 1 x10-11 g 7.35 seconds Iodine-131 8 x10-6 g 8.14 days Cobalt-60 9 x10-4 g 5.3 years Tritium 1 x10-4 g 12.4 years Radium-226 1 g 1620 years Uranium-238 3 x106 g or 3 tons 4.5 x109 years Quantities of Radionuclides for one Curie
Radioactive decay Law Universal Radioactive Decay Law Number of atoms decaying is proportional to number present in the sample at that time     693 . 0 2 2 log 2 1 ) 0 ( ) ( dt dN Sample in Number time Events of Number 2 1 2 1            T e e t N t N N T t Half Life of a decay process of radioactive isotopes is the time taken for the total number in the sample to reduced to one half of its initial value
42 For example, Cobalt-60 has a half-life of 5.2 years. i.e. the activity initially present will halve over 5.2 years and halve again over a further 5.2 years. i.e. after 10.4 years, the remaining activity will be ¼ of that originally present. Note: The radiation output (the gamma radiation emitted by the 60Co) also will fall as the radionuclide decays. To ensure the correct dose is delivered to the patient during radiotherapy, treatment times must be adjusted regularly for the decay of the source. Radioactive Decay and Half-life (T½)
43 • Capable of ejecting an electron from the atom and producing positive and negative ions • Ionizing radiation cannot be detected by the human senses (hearing, sight, smell or taste). • Special equipment is required to detect and measure ionizing radiation. Properties of Ionizing Radiation
Protons and Neutrons in Nucleus are held together by very strong but short range nuclear forces. Electrons orbit its nucleus in fixed shells (k, L, M, N – shells) due to electro- static forces which are long range weak forces. (Binding energy of electron BE) Excitation - If energy transferred to orbital electron from a striking photon/particle < BE, electron climbs up higher orbit and we say the atom is in excited state. The atom is still electrically neutral. Ionization If energy transferred to orbital electron from a striking photon/particle > BE, then electron leaves the atom, ion pairs is formed. The atom is ionized. Radiation effects Ionisation Neutral Atom Ion Pair
Radiation effects Effect Ionizing Radiation changes chemical properties and ultimately the Biological state of living cell and cause them to become a non functional cell (dead cell) or mal-functional cell (Carcinogenic cell). If the rate of cell killing is more than cell reproduction rate, tissue function is lost. This can happen at high dose (beyond threshold dose). This type of effect is called Deterministic effect. Ex. Cataract, NVD Syndrome, CNS Cell malfunction can occur at any dose, it is probabilistic and known as Stochastic effect. Ex. Cancer, genetic effect. Radiation protection is aimed at preventing deterministic effects by keeping doses below threshold dose limits and minimise stochastic effect by keeping exposure ALARA
46 Alpha emitters polonium-210, americium-241 Beta emitters krypton-85, strontium-90, hydrogen-3 (tritium), phosphorus-32 Gamma emitters cobalt-60, iridium-192, caesium-137; iodine-131, Tc-99m Neutron emitters americium-241 mixed with beryllium, Cf-252, Nuclear Reactor X Rays x-rays are emitted by electrically powered devices such as x-ray equipment and linear accelerators; some linear accelerators also emit electrons for therapeutic use.
47 Half lives of commonly used radiation sources: Radioisotope Practice Half Life (T1/2) Cobalt 60 Gamma Irradiators, Radiotherapy, gauges 5.3 years Iridium 192 Industrial radiography 74 days Cesium 137 Radiotherapy, Gauges 30.2 years Americium 241 Well logging 458 years Am-Be neutron source Well logging 458 years Cf- 252 neutron source Industrial radiography, research 2.65 years
Summary • Radiation are of two types – ionizing and non-ionizing. • Ionizing radiation has capability to remove an electron from an atom resulting in ionization. • Atom as a whole is neutral. • Atom contains nucleus surrounded by orbits containing electrons having negative charge. • Nucleus contains protons (positive charge) and neutrons (neutral). • Atomic number is equal to number of protons whereas mass number is sum of protons and neutrons. • Isotypes differ in their mass number. • Unstable atoms emit radiation and known as radioisotopes. Depending upon type of instability, radioisotope may emit alpha, beta, neutron or gamma radiation. • In alpha decay, daughter product has mass number less by 4 and atomic number less be 2. Alpha particle is helium nucleus having two protons and two neutrons. • After beta emission, atomic number of daughter product is increased by 1 and mass number remains the same. • In gamma emission or isomeric transition, change in mass number or atomic number of daughter product. Only excess energy is released by emission of gamma rays. • Neutron sources are either spontaneous fission sources or alpha n sources. • Radioisotopes decay with time and has characteristic half life in which its activity is reduced to half. • There are natural radioisotopes and man made radioisotopes. 48
50 The Periodic Table lists all known elements

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Basic Radiation Physics - Mr. D.S. Patkulkar.pdf

  • 1.
    Basic Radiation Physics ForRSO certification Course DS Patkulkar Coordinator IARP, GCTC RP&AD, BARC 022-25598660, 9967528343 [email protected]
  • 2.
    To achieve anunderstanding of ionizing radiation and its properties. Successful completion of this training will qualify you a Radiation Safety Officer (RSO) RSO is responsible for control of radioactive sources all the time (during procurement, transportation, storage, use, disposal) ensuring radiation safety of self, employees, public & the environment. Understanding ionizing radiation and its properties i.e. Basic Radiation Physics and radiation protection is essential for RSO. Objective : -
  • 3.
    We are constantlyexposed to unavoidable Natural Background Radiation – coming from universe - cosmic, terrestrial due to daughters products of Uranium Thorium series present in rocks, walls, and also few nuclides, K-40, C-14, etc.. seated in our body. Radiation exposure, however small, involves some risk. Radiation has become an indispensable tool in Industries, Agriculture, medical (diagnosis, treatment, sterilization, food preservation, Research Applications, etc… This involves additional exposure & risk. Decision to use Radiation is taken when benefits overweigh risk (Justification). Radiation exposure should be As Low As Reasonably Achievable (ALARA), social and economic factors taken into consideration (Optimization) and always below prescribed limits. Basic radiation physics help use radiation tool safely. Introduction
  • 4.
    Radiation Radiation is aprocess of transfer of energy without a medium. Radiation is in the form of electromagnetic waves including x-rays and Gamma rays or fast moving particles (such as Alpha, Beta, neutron). Wave photon energy E= hƴ where ƴ is frequency in Hertz Moving particle energy E = ½ mv2 where v & m is particle velocity & mass. Units of energy is electron-Volt (eV = 1.6 x 10-19 Joules) eV, keV, MeV, GeV, are multiples
  • 5.
    If radiation hasenergy sufficient to knock out electron from atom to form +ve and –ve ion pair we call it Ionizing Radiation Ex. X-rays, gamma rays, Alpha, Beta, neutron. Non Ionizing radiation can excite electrons to higher energy orbits, and up on de-excitation, release excess energy in the form of X-rays. Ex. Radio Frequency, Microwave, Infra red, Visible light waves, Ultra violet waves
  • 6.
    Ionizing radiation hasenough energy to knock out electron from Atom and ionize it.
  • 7.
    Electromagnetic wave spectrum Presenceof some types of radiation can be detected by the human senses. e.g. light from the sun or from a light bulb can be seen and the heat can be felt. Other radiation can only be detected by special equipment. e.g. a television or radio receiver.
  • 8.
    • Atomic structure •Subatomic particles and their properties • Stability of nucleus •Transformations in unstable nuclides •Radiation & types •Ionizing and non-ionizing radiation •Properties of Radiation • Radioactivity & laws of radioactive decay •Principles of Radiation protection •Radiation sources Basic Radiation Physics
  • 9.
    The Atom All materin nature is made up of elements and compounds. Each element is represented by its Chemical Symbol such as H, C, O, etc… Atom is a building block of element. It consists of a nucleus at its centre and electrons (e-) revolve around the nucleus in fixed orbits like planets in our solar system. An atom is so tiny that it cannot be seen by naked eye or even under a microscope. Its diameter is of the order of 10-8 cm and that of the nucleus is of the order of 10-12 - 10-13 cm. Atom is mainly empty space. Nucleus contain Protons (P) & Neutrons(N). Number of protons (P) in the nucleus is its Atomic Number (Z). Sum of Protons and Neutrons number is its Mass Number (A = P+N) Neutral Atom has same number of protons and electrons
  • 10.
    Building Blocks ofAtom (Subatomic Particles) Sub-atomic particle Symbol Charge Mass (amu) Proton p +1 1 Neutron n 0 1 Electron e -1 or + 1 1/1840 Since the electrons have negligible mass, the mass of an atom is concentrated in the nucleus with contributions entirely from protons and neutrons. The mass of a Proton = 1.6723 x 10-27kg and The mass of a Neutron = 1.6775 x 10-27kg
  • 11.
    There are 92elements in nature. These were formed at the time the earth They progressively contain an increasing number of protons, neutrons, and electrons. Hydrogen is the simplest of the elements. It has only one proton (and no neutron) in the nucleus and one electron in its orbit. Hydrogen H Atomic no. Z=1, Atomic mass A = 1 1 1H Helium has 2 protons and two neutrons in its nucleus & two electrons in orbit Helium He Atomic no. Z=2, Atomic mass A = 4 4 2He Lithium has three protons and three neutrons Lithium Li Atomic no. Z=3, Atomic mass A = 6 6 3Li An element is specified by using its chemical symbol, the mass number, and atomic number.
  • 12.
    Proton Neutron Electron 2He4 Chemical symbol –He Atomic Number Z = ??? Mass Number A = ???
  • 13.
    13 Isotopes may beradioactive or stable. Radioactive, Isotope is called “radioisotope”. Examples 3H, 60Co, 137Cs, 192Ir, 123I, 131I, 241Am. Isotopes 1 1H 2 1H 3 1H STABLE STABLE UNSTABLE and RADIOACTIVE All atoms of the same element have the same number of protons and electrons and thus the same atomic number Z. They can, however, have different numbers of neutrons . They are then called isotopes of that element. Thus isotopes of an element have the same atomic number, but different mass numbers. Isotopes of an element are chemically identical.
  • 14.
    Stability of thenucleus/Atom The stability of the nucleus depends on the ratio of number of neutrons to number of protons present in the nucleus. The ratio is 1 for lighter nuclides and increases to 1.5 for heavier nuclides. A stable atom can be converted into unstable atom if the nuclear forces in side the nucleus are disturbed by some means. In nature, atom with excess number of neutrons or protons in the nucleus are found to be unstable.
  • 15.
    The stability ofan element depends upon the ratio of neutrons to protons in the nucleus. In elements of lower atomic number, except hydrogen, this ratio is generally one. In heavier elements i.e., elements having higher atomic number, this ratio tends to be more than unity, resulting in some degree of instability in the nucleus. An unstable nucleus, which has excess energy, tries to attain stability by releasing this energy in the form of radiation. Henry Becquerel, a French Physicist, discovered in 1996, that a compound of uranium emitted some invisible radiant energy. Madame Curie studied a large number of such substances and gave the name “Radioactivity” to this property. Radioactivity
  • 16.
    Radioactivity is aphenomenon in which an unstable nucleus of an element disintegrates with the emission of energy and becomes a new element. It is a spontaneous process unaffected by physical and chemical agents. Radioactivity exists in nature among heavier elements. However, many lighter elements can be rendered radioactive by bombardment with charged particles or neutrons in Reactor or accelerators. This is called artificial radioactivity. Radioactivity
  • 17.
    Radioactive transformation (ordecay), whether natural or artificial can occur only in a limited number of ways with the emission of 1) Alpha particles, 2) Beta particles, 3) Positrons or by 4) Electron capture. However, the first two modes of decay are the most commonly observed. It may also be noted that in a number of cases the decay process is followed by the emission of gamma-rays or characteristic X-rays. MODES OF RADIOACTIVE DISINTEGRATION or X-ray   neutron
  • 18.
    The table belowshows the daughter produced by the alpha, beta or gamma disintegration of a parent with atomic number Z and mass number A Decay Parent Daughter  Z, A Z - 2, A- 4 - Z, A Z +1, A + Z, A Z - 1, A  Z, A Z, A
  • 19.
    RADIOACTIVITY It is theprocess by which an Unstable radio-nuclide changes to another nuclide by emitting particles or energy in the form of radiation. RADIOACTIVE MATERIAL Matterial containing unstable nuclides is called radioactive material. Natural radioactive material: Uranium, Thorium, Radium, etc.. Man-made/Artificial radioactive material : Cobalt-60, Ceasium-137, Irdium-192,etc RADIOACTIVE DECAY Transformations are continuously taking place in unstable nuclides, New nucleus is formed along with emission of radiation. Parent nuclide = Daughter nuclide + Radiation NUCLEAR RADIATION Energetic particles or electromagnetic rays released/ emitted from the nucleus of the unstable nuclide/atom during its transformation is called nuclear radiation. Example: 88Ra226  86Rn222 +  (alpha) 27Co60  28Ni60 +  (Beta) + (Gamma)
  • 20.
    Alpha Particle  Analpha particle is a swiftly moving particle consisting of two neutrons and two protons. It is identical with a helium nucleus. The Greek letter  is used to represent alpha radiation  Range : 2 to 8 cm in air  Velocity : 5% of that of light  Alpha particles are emitted upon the disintegration of principally those of heavy radioactive elements, e.g. U235, U238, Ra226 and Th230  Over 150 alpha emitting radionuclides have been discovered
  • 21.
    21 Alpha () radiation: •is comprised of 2 protons and 2 neutrons (the nucleus of a helium atom); • is not very penetrating and can be shielded by a few centimetres of air or a sheet of paper; • is a significant internal exposure hazard; • but can be difficult to detect because of the low penetrating power. • Example • 88Ra226 ----- 86Rn222 +  Alpha () radiation
  • 22.
    Range (cm) Energy (MeV) 7 6 5 4 3 45 6 7 8 Range of Alpha Particles in Air
  • 23.
    Beta Particle A betaparticle is a swiftly moving electron which has been emitted by a nucleus. The Greek letter  is used to represent beta radiation. Most fission products are beta emitters and in most cases the daughters and grand daughters are also. The most energetic beta particles have a velocity which is almost equal to the speed of light, e.g. the beta particle emitted by Rh106 (rhodium) has a velocity of 0.97c One neutron with in the nucleus of the parent atom changes into a proton and an electron, which is being ejected as ß- particle. Such a transformation will leave the mass number of the daughter atom unchanged i.e the same of the parent atom. The atomic number of the daughter nuclide increases by 1 as one more protons created in the nucleus of daughter nuclide. When beta particles have lost their velocity, they become ordinary electrons and join the free electron population
  • 24.
    24 Beta () radiation –in most cases are negatively charged electrons; – is more penetrating than alpha but still can be shielded by thick plastics or thin sheets of metal; – is an external eye and skin exposure hazard; – is an internal exposure hazard; The degree of detection depends on the energy of the beta particles. Example 27Co60 ----- 28Ni60 +  + neutrino Beta () radiation
  • 25.
    Beta Disintegration  Inbeta decay, a neutron divides into a proton and an electron (beta particle). The proton remains in the nucleus and the beta particle is emitted. - - n P n 1H3 - P P n 2He3 P P n 2He3 91Pa234 92U234 - + 82Pb214 83Bi214 - + 19K40 20Ca40 - +
  • 26.
    Positron Emission  Positronis a particle exactly equal in mass to the electron, but it carries an opposite (positive) charge. Some radionuclides decay by positron emission.  This process is opposite to beta decay ; a proton changes to a neutron by the emission of a positron. 8O15 7N15 + +
  • 27.
    12 10 6 8 4 2 0.1 0.2 0.30.4 0.5 0.6 Kinetic Energy (MeV) Relative Number Emax = 0.54MeV The Beta Energy Spectrum of Sr90
  • 28.
    28 Gamma () radiation •has no mass and no charge but can be extremely penetrating; • must be shielded by heavy or massive material such as steel, lead, or concrete (or a combination); • is both an external and internal exposure hazard; • can be readily detected. • Excited nuclei or Isomers give Rise to gamma radiation Gamma () radiation
  • 29.
    Gamma Rays Gamma Rays(or photons): Result when the nucleus releases energy, usually after an alpha, beta or positron transition
  • 30.
    Gamma Radiation Visible light,Radio waves, Microwaves, UV rays, IR rays, X-rays and gamma rays are all electromagnetic radiations All the electromagnetic radiations have the velocity 3 x 1010 cm/sec. They differ from one another only in their frequencies. X-rays and Gamma rays have the highest frequencies and therefore they are also the most energetic and are ionising radiations Gamma rays are emitted from the nuclei of radioactive atoms, while X-rays are produced by X-ray tubes and similar apparatus. X-rays are not emitted from nuclei. Electron volt (eV) is the unit of radiation energy, keV, MeV
  • 31.
    27Co60 28Ni60 28Ni60  28Ni60  320 KeV - 1.17MeV  1.33 MeV  Gamma Disintegration  When a daughter nucleus is formed by radioactive decay, some energy is carried away from the nucleus by the particle emitted. After some disintegrations, however the daughter still possesses more energy than is normal for that nucleus, and such nucleus is said to be in excited state. A nucleus in an excited state promptly gets rid of excess energy by emitting a gamma photon
  • 32.
    32 X-rays: • are generatedelectrically rather than originating from the decay of radioactive material; • have properties that can be considered to be almost identical to gamma rays, except that they usually have lower energies. X-ray radiation
  • 33.
    X-Rays X-Rays: Occur wheneveran inner shell orbital electron is removed and rearrangement of the atomic electrons results with the release of the elements characteristic X-Ray energy
  • 34.
    Difference between Xrays and Gamma ray
  • 35.
    35 Neutron (n) radiation Freeneutrons can exist as a type of radiation. • Uncharged themselves, neutrons may be absorbed by other nuclei rendering such nuclei unstable and therefore radioactive. • This process is called activation. • Neutrons are very penetrating and can cause significant biological damage. • Neutrons can be shielded by hydrogenous material e.g. water, polyethylene. • Cf-252, Am-Be, nuclear reactor
  • 36.
    The penetrating powerof any type of radiation depends partly on its energy, the greater the energy, the greater the penetrating power Alpha particles are generally less penetrating than beta particles, which in turn are less penetrating than gamma rays Alpha particles and gamma rays are emitted with a constant energy level from their respective nuclides, whereas beta particles are emitted with a range of energies. The half-value layer is the thickness of absorber required to reduce gamma radiation to half its former level. The tenth-value layer is the thickness of absorber required to reduce gamma radiation to 1/10thits former level.
  • 37.
    +- -+-+-+ -+-+-+ -+-+-+-+-+-+-+ - +-+ -+- -+ -+ -+ -+ -+ 100 1cm 50000 Alpha Source Beta Source Alpha particle Beta particle Specific Ionisation in Air +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  • 38.
    Radiation (Symbol) Relative Mass in amu (1.66x10-27kg) Electric charge (1.6x10-19 C) Range in Air Suitable Absorber Changes in Daughter Nuclide Alpha () 4 amu ++ Few cms Paper. Z reduces by 2 A reduces by 4 Beta () Positron (+) Mass of electron is Negligible (9.11 x 10–31 kg) Beta = -ve Positron = +ve Few metre Few mm Plastic or Aluminium Z increases by 1 A does not change Z reduces by 1 A does not change Gamma () No mass Neutral Very large Lead, Water or Concrete A & Z does not change Neutron (0n1) 1 amu. Neutral Very large Cd, B for thermal, Paraffin, B, Cd for fast neutrons. A reduces by 1 Important Properties of Radiations
  • 39.
    Rate of Disintegration The activity of a radioactive source is the number of nuclie disintegrating per unit time  The half-life of a radioactive substance is the time required for it to lose 50% of its activity by decay. Half life of a nuclide is constant. (Range from a fraction of a second for some radio nuclides to many millions of years for others)  Curie (Ci) is that quantity of a radioactive nuclide which is disintegrating at the rate of 3.7 x 1010 atoms per second.  It is relatively large unit. Its sub multiples, milli curie (mCi = 10-3 Ci) and micro curie (Ci = 10-6 Ci) are preferred in practice.  The SI unit of radioactivity is Becquerrel (Bq). One Bq is equal to one dps.
  • 40.
    Radionuclide Mass requiredfor1 Ci Half-life of radionuclide Nitrogen-16 1 x10-11 g 7.35 seconds Iodine-131 8 x10-6 g 8.14 days Cobalt-60 9 x10-4 g 5.3 years Tritium 1 x10-4 g 12.4 years Radium-226 1 g 1620 years Uranium-238 3 x106 g or 3 tons 4.5 x109 years Quantities of Radionuclides for one Curie
  • 41.
    Radioactive decay Law UniversalRadioactive Decay Law Number of atoms decaying is proportional to number present in the sample at that time     693 . 0 2 2 log 2 1 ) 0 ( ) ( dt dN Sample in Number time Events of Number 2 1 2 1            T e e t N t N N T t Half Life of a decay process of radioactive isotopes is the time taken for the total number in the sample to reduced to one half of its initial value
  • 42.
    42 For example, Cobalt-60has a half-life of 5.2 years. i.e. the activity initially present will halve over 5.2 years and halve again over a further 5.2 years. i.e. after 10.4 years, the remaining activity will be ¼ of that originally present. Note: The radiation output (the gamma radiation emitted by the 60Co) also will fall as the radionuclide decays. To ensure the correct dose is delivered to the patient during radiotherapy, treatment times must be adjusted regularly for the decay of the source. Radioactive Decay and Half-life (T½)
  • 43.
    43 • Capable ofejecting an electron from the atom and producing positive and negative ions • Ionizing radiation cannot be detected by the human senses (hearing, sight, smell or taste). • Special equipment is required to detect and measure ionizing radiation. Properties of Ionizing Radiation
  • 44.
    Protons and Neutronsin Nucleus are held together by very strong but short range nuclear forces. Electrons orbit its nucleus in fixed shells (k, L, M, N – shells) due to electro- static forces which are long range weak forces. (Binding energy of electron BE) Excitation - If energy transferred to orbital electron from a striking photon/particle < BE, electron climbs up higher orbit and we say the atom is in excited state. The atom is still electrically neutral. Ionization If energy transferred to orbital electron from a striking photon/particle > BE, then electron leaves the atom, ion pairs is formed. The atom is ionized. Radiation effects Ionisation Neutral Atom Ion Pair
  • 45.
    Radiation effects Effect IonizingRadiation changes chemical properties and ultimately the Biological state of living cell and cause them to become a non functional cell (dead cell) or mal-functional cell (Carcinogenic cell). If the rate of cell killing is more than cell reproduction rate, tissue function is lost. This can happen at high dose (beyond threshold dose). This type of effect is called Deterministic effect. Ex. Cataract, NVD Syndrome, CNS Cell malfunction can occur at any dose, it is probabilistic and known as Stochastic effect. Ex. Cancer, genetic effect. Radiation protection is aimed at preventing deterministic effects by keeping doses below threshold dose limits and minimise stochastic effect by keeping exposure ALARA
  • 46.
    46 Alpha emitters polonium-210, americium-241 Betaemitters krypton-85, strontium-90, hydrogen-3 (tritium), phosphorus-32 Gamma emitters cobalt-60, iridium-192, caesium-137; iodine-131, Tc-99m Neutron emitters americium-241 mixed with beryllium, Cf-252, Nuclear Reactor X Rays x-rays are emitted by electrically powered devices such as x-ray equipment and linear accelerators; some linear accelerators also emit electrons for therapeutic use.
  • 47.
    47 Half lives ofcommonly used radiation sources: Radioisotope Practice Half Life (T1/2) Cobalt 60 Gamma Irradiators, Radiotherapy, gauges 5.3 years Iridium 192 Industrial radiography 74 days Cesium 137 Radiotherapy, Gauges 30.2 years Americium 241 Well logging 458 years Am-Be neutron source Well logging 458 years Cf- 252 neutron source Industrial radiography, research 2.65 years
  • 48.
    Summary • Radiation areof two types – ionizing and non-ionizing. • Ionizing radiation has capability to remove an electron from an atom resulting in ionization. • Atom as a whole is neutral. • Atom contains nucleus surrounded by orbits containing electrons having negative charge. • Nucleus contains protons (positive charge) and neutrons (neutral). • Atomic number is equal to number of protons whereas mass number is sum of protons and neutrons. • Isotypes differ in their mass number. • Unstable atoms emit radiation and known as radioisotopes. Depending upon type of instability, radioisotope may emit alpha, beta, neutron or gamma radiation. • In alpha decay, daughter product has mass number less by 4 and atomic number less be 2. Alpha particle is helium nucleus having two protons and two neutrons. • After beta emission, atomic number of daughter product is increased by 1 and mass number remains the same. • In gamma emission or isomeric transition, change in mass number or atomic number of daughter product. Only excess energy is released by emission of gamma rays. • Neutron sources are either spontaneous fission sources or alpha n sources. • Radioisotopes decay with time and has characteristic half life in which its activity is reduced to half. • There are natural radioisotopes and man made radioisotopes. 48
  • 50.
    50 The Periodic Tablelists all known elements