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Radiobiology2

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  • Part 2. Radiation Physics Radiation Protection in Nuclear Medicine
  • Part 2. Radiation Physics Radiation Protection in Nuclear Medicine
  • Part 2. Radiation Physics Radiation Protection in Nuclear Medicine This is an insertion to help make sure all participants are at the same level.
  • Part 2. Radiation Physics Radiation Protection in Nuclear Medicine
  • Part 2. Radiation Physics Radiation Protection in Nuclear Medicine
  • Part 2. Radiation Physics Radiation Protection in Nuclear Medicine
  • Transcript

    • 1. Prof.Dr.Tarek Elnimr L 2 Presented to the Biology Departments in Faculty of Sciences on February 15 , 2009
    • 2.
      • It is found that a few naturally occurring substances consist of
      • atoms which are unstable.
      • -that is they undergo spontaneous transformation Into more stable product
      • Such substances are said to be radioactive
      • and the transformation process is known as radioactive decay.
      • Radioactive decay is usually accompanied by the emission of
      • charged particles and gamma rays .
      • As a result of that transformation process , these unstable nuclei
      • emit radiations of three main types , called alpha , beta and gamma radiation.
    • 3. Fission The nucleus is divided into two parts, fission fragments. and 3-4 neutrons. Examples: Cf-252 (spontaneous), U-235 (induced)  -decay The nucleus emits an  - particle (He-4). Examples: Ra-226, Rn-222  -decay Too many neutrons results in   -decay. n=>p + +e - +  . Example:H-3, C-14, I-131. Too many protons results in   -decay p + =>n+ e + +  Examples: O-16, F-18 or electron capture (EC). p + + e - =>n+  Examples: I-125, Tl-201
    • 4.
      • If there are initially N atoms, the initial rate of decay will be N/t
      • This change in the decay rate can be expressed as - dN/dt , being negative as it is decreasing
      • With time, whereas,
      • - dN/dt =  N ........................(1)
      • This equation can be rearranged
      • dN/Ndt =  N/N , - dN. dt / N. dt =  N . dt/N
      • - dN / N =  dt , N = No exp(-  t) , where
      • No is the number of nuclei present initially
      • N is the number of nuclei present at time t
      • -  is the radioactive decay constant
      Part 2: Radiation Physics
    • 5.
    • 6. Part 2: Radiation Physics It is impossible to know at what time a certain radioactive nucleus will decay. It is, however possible to determine the probability l of decay in a certain time. In a sample of N nuclei the number of decays per unit time is then:
    • 7. Nuclear Activity
      • Radioactive decay is described by
      • N(t), N 0 : number of radionuclide at time t = 0 and t , resp.
      •  : decay constant [ 1/ t ]
      • Activity A = average decay rate [decays per second]
      • Nuclear activity is measured in curie: 1 [Ci] = 3.7  10 10 decays/sec ( orig.: activity of 1 g of 226 Ra )
      • Practical: 1 mCi,  Ci. SI unit is becquerel [Bq] = 1 decay/second
      99m Tc
    • 8. Part 2: Radiation Physics A C B λ 1 λ 2
    • 9. Part 2: Radiation Physics Secular equilibrium T B <<T A ≈ ∞ Transient equilibrium T A ≈ 10 T B No equilibrium T A ≈ 1/10 T B
    • 10. 99 Mo- 99m Tc Part 2: Radiation Physics 99 Mo 87.6% 99m Tc  140 keV T½ = 6.02 h 99 Tc ß - 292 keV T½ = 2*10 5 y 99 Ru stable 12.4% ß - 442 keV  739 keV T½ = 2.75 d
    • 11. Alpha  Decay 4 He Nucleus Ejected from 222 Rn Nucleus +2 4 He + 218 Po + + + + + + + + + Radon - 222
    • 12. Alpha Decay...
      • Alpha decay is a common radioactive process encountered with heavier isotopes. The alpha particle is a helium nucleus having a mass of 4 and a charge of +2. Isotopes with mass numbers less than about 150 (Z 60) seldom yield alpha particles. Alpha particles progressively lose their energy as a result of collisions as they pass through matter and are ultimately converted into helium atoms through capture of two electrons from their surroundings .
    • 13. Radioactive Decay Radon 222 Polonium 218  Radiation  Radiation
      • Occurs spontaneously
      • Due to change in # of protons, atom becomes -2 charge
      • Radiation released
    • 14. a
      • Alpha Radiation (  )
        • Particle released when the nucleus kicks out 2 neutrons and 2 protons
        • Relatively massive
        • Relatively slow
        • Total charge of +2
      Mass number changes by 4 and atomic number changes by 2
    • 15. b
      • Beta Radiation (  )
        • Particle released when the nucleus changes a neutron into a proton and a beta particle
        • Relatively small mass
        • Relatively fast moving
        • Total charge of -1
      Atomic Mass Number remains constant  P N
    • 16. g
      • Gamma Radiation (  )
        • Pure energy. Released from the nucleus when an alpha or a beta is emitted
        • No mass
        • Speed of light
        • No charge
      NO CHANGE
    • 17.    Penetrating Power
    • 18.  
    • 19. Beta Decay...
      • Beta decay is a radioactive process in which, the atomic number changes but the mass number stays the same
      • There are types of  decay are encountered: negatron formation
      • positron formation
      • electron capture
    • 20.  
    • 21. Beta Radioactivity
      • Beta particles are just electrons from the nucleus, the term &quot;beta particle&quot; being an historical term used in the early description of radioactivity . The high-energy electrons have greater range of penetration than alpha particles , but still much less than gamma rays . The radiation hazard from betas is greatest if they are ingested
    • 22. Beta Radioactivity
      • The emission of the electron's antiparticle, the positron , is also called beta decay. Beta decay can be seen as the decay of one of the neutrons to a proton via the weak interaction . The use of a weak interaction Feynman diagram can clarify the process
    • 23. Gamma Decay...
      • Gamma rays are produced by nuclear relaxations. Gamma-ray emission is the result of a nucleus in an excited state returning to the ground state in one or more quantized steps with the release of monoenergetic gamma rays. Gamma rays, except for their source, are indistinguishable from X-rays of the same energy.
    • 24. X-Ray Emission...
      • X-Ray emission are formed from electronic transitions in which outer electrons fill the vacancies created by the nuclear process. One of the processes is electron capture. A second process which may lead to X-rays is internal conversion, a type of nuclear process that is an alternative to gamma-ray emission.
    • 25. Radioactive Half Life...
      • It is time taken for the radioactive substance to reduce to half its activity. Mathematically it is given by:
      • t1/2 = ln 2/Decay Constant
    • 26. Radioactive Half Life
      • Radioactivity is measured by means of a detector that produces a pulse of electricity for each atom undergoing decay
      • Quantitative information about decay rates is obtained by counting these pulses for a specific period
      • table with decay data obtained by successive one-minute counts is shown on next slide…
    • 27.   Total counts = 2004 Average counts/min = 167   Minutes Counts Minutes Counts 1 180 7 168 2 187 8 170 3 166 9 173 4 173 10 132 5 170 11 154 6 164 12 167
    • 28. Part 2: Radiation Physics Ques-tions?