Understanding Radiopharmaceuticals & Contrast Media: Atomic Structure & Radioactivity, Lecture notes of Pharmaceutical Analysis

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Radiopharmaceuticals and

contrast media

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An atomic structure The electrons move in orbits around the nucleus

• (^) A nucleus consists of a number of protons and neutrons
• (^) Protons and neutrons also known as nucleons
• (^) A proton has a unit positive charge
• (^) A neutron is an uncharged particle of about the same mass # There are lot of empty spaces within atom # 2

Nuclide NUCLIDE NOTATION Proton Neutron Electron Example Proton number of carbon = 6 , carbon nucleus has 6 protons. The nucleon number is 12. so the number of neutrons in carbon nucleus is 12-6= A= nucleon number (mass no.) Z=proton number (atomic no.) X=chemical symbol of the element 4

Isotopes ISOTOPES Example: hydrogen deuterium tritium Isotopes are atoms with the same proton number but different nucleon number.  (^) Isotopes of an element contain the same number of protons and the same number of electrons. So isotopes have the same chemical properties and chemical reactions involve the electrons in an atom  (^) However they have different physical properties because their mass is different  (^) Some isotopes exist naturally. Isotopes can also be made artificially

ISOTOPES

Isotopes are atoms with the same pr but different nucleon number.  (^) Isotopes of an element contain the of protons and the same number o isotopes have the same chemical chemical reactions involve the e atom  (^) However they have different phys because their mass is different  (^) Some isotopes exist naturally. Isot be made artificially 5

Radioactivity RANDOM PROCESS

• (^) There is no way to tell which nucleus will decay, and cannot predict when it is going to decay. SPONTANEOUS PROCESS
• (^) The process is not triggered by any external factors such as temperature and pressure Three different types of radiation

Alpha

Beta

Gamma

radiation

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Radioactivity

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Since alpha particles cannot penetrate the dead layer of the skin, they do not present a hazard from exposure external to the body. However, due to the very large number of ionizations they produce in a very short distance, alpha emitters can present a serious hazard when they are in close proximity to cells and tissues such as the lung. Special precautions are taken to ensure that alpha emitters are not inhaled, ingested or injected. 11

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 electron-type antineutrino (the antiparticle of the neutrino): n → p + e− + ν Ex. Carbon-14 Nitrogen- 6 protons 7 protons 8 neutrons 7 neutrons

• Electron + Antineutron

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 Boron- 6 protons 5 protons 4 neutrons 5 neutrons

• Neutrino + Positron

Beta particles are much less massive and less charged than alpha particles and interact less intensely with atoms in the materials they pass through, which gives them a longer range than alpha 16

3- Gamma ray:

 (^) Gamma rays are waves, not particles. This means that they have no mass and no charge.  (^) in Gamma decay:  (^) atomic number unchanged  (^) atomic mass unchanged.  (^) Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead to reduce them.  (^) Gamma rays do not directly ionise other atoms, although they may cause atoms to emit other particles which will then cause Ionisation.  (^) We don't find pure gamma sources - gamma rays are emitted along side alpha or beta particles. 17

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 (^) 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 centimetre, about equal to beta particles. Electromagnetic radiation