Types of radiation


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Types of radiation

  1. 1. Different forms of radiation may be emitted from an unstable radioactive nucleus. Energy is released and a new, more stable nucleus is formed.
  2. 2. Alph a Beta Gamm a
  3. 3. Particulate Radiation  Electromagnetic Radiation 
  4. 4. -can be classified as particulate if they are in motion and possess sufficient kinetic energy. Principal Types: • Alpha •Beta
  5. 5. Ernest Rutherford, an English scientist, discovered alpha particles in 1899 while working with uranium. Rutherford's studies contributed to our understanding of the atom and its nucleus through the RutherfordBohr planetary model of the atom.
  6. 6. Alpha Particle An alpha particle can be considered as a helium nucleus. Helium has 2 protons and 2 neutrons in its nucleus. If both of its electrons were removed, the result would be an alpha particle: 4 2 He or They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α.
  7. 7. Alpha decay is a radioactive process in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom. Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very “neutron rich” (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible.
  8. 8. After an atom ejects an alpha particle, a new parent atom is formed which has two less neutrons and two less protons. Thus, when uranium-238 (which has a Z of 92) decays by alpha emission, thorium-234 is created (which has a Z of 90). Since there are two protons and no electrons, alpha particles are positively charged. Alpha particles are not very penetrating. Paper, clothing or a few centimeters of air can effectively shield against alpha particles. However, if ingested or inhaled, alpha particles can be hazardous.
  9. 9. Henri Becquerel is credited with the discovery of beta particles. In 1900, he showed that beta particles were identical to electrons, which had recently been discovered by Joseph John Thompson.
  10. 10. Beta Particle Beta particles are high-speed electrons emitted from the nuclei of decaying radioisotopes. Since these are electrons, they have a negative charge and a small mass, approximated as 0 amu. 0 e or -1 The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β− and β+, which respectively give rise to the electron and the positron
  11. 11. Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom, along with an unusual particle called an antineutrino (almost massless particle that carries away some of the energy). Like alpha decay, beta decay occurs in isotopes which are “neutron rich” . When a nucleus ejects a beta particle, one of the neutrons in the nucleus is transformed into a proton.
  12. 12. Two forms of Beta decay 1. β− decay (electron emission) - An unstable atomic nucleus with an excess of neutrons may undergo β− decay, where a neutron is converted into a proton, an electron and an electrontype antineutrino (the antiparticle of the neutrino): n → p + e− + ν Ex. Carbon-14 Nitrogen-14 6 protons 7 protons + Electron + Antineutron 8 neutrons 7 neutrons
  13. 13. 2. β+ decay (positron emission) -Unstable atomic nuclei with an excess of protons may undergo β+ decay, also called positron decay, where a proton is converted into a neutron, a positron and an electron-type neutrino: p → n + e+ + ν Ex. Carbon-10 6 protons 4 neutrons Boron-10 5 protons + Neutrino + Positron 5 neutrons
  14. 14. Since the number of protons in the nucleus has changed, a new daughter atom is formed which has one less neutron but one more proton than the parent. For example, when rhenium-187 decays (which has a Z of 75) by beta decay, osmium-187 is created (which has a Z of 76). Beta particles have a single negative charge and weigh only a small fraction of a neutron or proton. As a result, beta particles interact less readily with material than alpha particles. Beta particles will travel up to several meters in air, and are stopped by thin layers of metal or plastic. Beta particles may travel 2 or 3 meters through air. Heavy clothing, thick cardboard or one-inch thick wood will provide protection from beta radiation.
  15. 15.  X-rays – are produced outside the nucleus in the electron shell.  Gamma rays – emitted from the nucleus of a radioisotopes and are usually associated with alpha or beta emission. Often called Photons (have no mass and no charge) Travel at the speed of light (c= 3x10^8 m/s) and considered energy disturbances in space.  Once emitted, they have an ionization rate approximately 100 ion pairs per centimeter, about equal to beta particles.
  16. 16. Physicists credit French physicist Henri Becquerel with discovering gamma radiation. In 1896, he discovered that uranium minerals could expose a photographic plate through a heavy opaque paper. Roentgen had recently discovered x-rays, and Becquerel reasoned that uranium emitted some invisible light similar to x-rays. He called it "metallic phosphorescence”.
  17. 17. Gamma Radiation - Gamma radiation is very much like x rays. It has no charge, a very short wavelength and high energy. Gamma radiation is the most penetrating form of radiation considered in this section. It travels great distances through air (500 meters). To be protected from a gamma emitter, thick sheets of lead or concrete are required. The positron is represented by the symbol: 0 e +1 After a decay reaction, the nucleus is often in an “excited” state. This means that the decay has resulted in producing a nucleus which still has excess energy to get rid of. Rather than emitting another beta or alpha particle, this energy is lost by emitting a pulse of electromagnetic radiation called a gamma ray. The gamma ray is identical in nature to light or microwaves, but of very high energy.
  18. 18. Like all forms of electromagnetic radiation, the gamma ray has no mass and no charge. Gamma rays interact with material by colliding with the electrons in the shells of atoms. They lose their energy slowly in material, being able to travel significant distances before stopping. Depending on their initial energy, gamma rays can travel from 1 to hundreds of meters in air and can easily go right through people. It is important to note that most alpha and beta emitters also emit gamma rays as part of their decay process. However, there is no such thing as a “pure” gamma emitter.
  19. 19. NAME CHARGE SYMBOL SHIELD DISTANCE TRAVELED alpha positive or paper or clothing 2-4 cm beta negative or heavy clothing 2-3 m gamma neutral lead or concrete 500 m
  20. 20. -is any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity. In equation form: Where I is the intensity of the radiation and d is the distance.
  21. 21. If I1 and I2 are intensities of light at distances d1 and d2 respectively. Then Inverse square law is given by: Inverse square law formula is useful in finding distance or intensity of any given radiation. The intensity is given in Lumen or candela and distance s expressed in meters. It has wide applications in problems based on light.
  22. 22. 1m 2m 3m 4m 5m 1 4 9 16 25 1 ¼ 1/9 1/16 1/25
  23. 23. Example 1) Use Newton's Inverse Square Law to calculate the intensity of a radioactive source at a different distance than the distance it was originally measured. If the intensity of a Iridium 192 source was found to be 62 milliroentgen/hour 100 feet, what is the exposure at a distance of 1 foot.
  24. 24. Example 2) A source is producing an intensity of 456 R/h at one foot from the source. What would be the distance in feet to the 100, 5, and 2 mR/h boundaries. Convert Rem per hour to mRem per hour 456R/h x 1000 = 456,000 mR/h D2= 67.5 feet
  25. 25. Question 1: The intensity of a monochromatic light are in the ratio 16:1. Calculate the second distance if the first distance is 6m? Solution: Given: I1 : I2 = 16 : 1, d1 = 6m, d2 = ? Distance d2 = I1d21I2−−−√ = 16×6m1−−−−−√ d2 = 9.8 m.
  26. 26. Question 2: Calculate the intensity of radio active source antimony 124 if it has intensity of 80 milliroentgen/hour for 50 feet. What will be its intensity at 10 foot? Solution: Given: I1 = 80 milliroentgen/hour, d1 = 50 feet, I2 = ? d2 = 10 feet. Intensity I2 = I1d21d22 = 80×502102 = 40 milliroentgen/hour.
  27. 27. Inverse square law is applied to: Gravitational strength with distance. Electrostatic force with distance. Light intensity from a point object. Sound intensity from a point source. Nuclear radiation from a point source.