Radiation Biophysics 1 Radiation and Radioactivity Decay Scheme Types of ionizing radiation Interaction of Radiation with Matter The inverse square law Absorption processes Health and biophysical effect
IAEA Training Course: Radiation Protection in Radiotherapy slide 12 Photons are part of the Photons are part of the electromagnetic spectrum electromagnetic spectrum Visible light X-rays & Gamma rays UV Infrared Radio Enough energy to cause ionization
Radiation and Radioactivity The fact that some elements are naturally radioactive was first realized by Becquerel in 1896. He observed blackening of photographic emulsions in the vicinity of a uranium compound. The fact that certain nuclei, like Uranium, are not completely stable. Such substances are said to be Radioactive and the transformation process is known as radioactive decay . These unstable nuclei emit radiation of three main types called alpha (α), beta (β) and gamma (γ) radiation.
Alpha Particles (α) The nuclei of atoms of the element Helium consists of two protons and two neutrons. They are easily stopped and do not penetrate the skin. Radioactive material that emits alpha particles can only be hazardous if swallowed or breathed into the body, or if they enter the body through a break in the skin. The decay process may be represented as follows:
Alpha Particles Alpha particles High mass (4 amu) = 2 protons + 2 neutrons High charge (+2) High linear energy transfer (cause great biological damage) Travel a few centimeters in air Stopped by a sheet of paper or protective layer of skin Not an external hazard Concern would be for ingestion or inhalation
Z Z-2 2 Y + α A-4 4 A X Where: A = Atomic Weight (Mass) Z = Atomic Number Alpha Particle (α) has a mass of 4 and two units of positive charge.
OR 238 4 234 U α + Th 92 2 90
Beta Particles (β) Consists of high speed electrons which originate in the nucleus, they have a mass of 1/1840v and carry one unit of negative charge. Beta radiation has greater penetrating powers than alpha particles, however they are stopped by thin layer of water, glass or metal. They also can be hazardous if taken into the body. Another type of beta radiation was discovered in 1932 which consists of particles of the same mass as electron but having one unit of positive charge, and known as positron radiation β+.
Beta Particles Low mass (0.0005 amu) Low charge - can be positively or negatively charged (+/- 1) Travel 10 - 20 feet in air Stopped by a book Shield betas with low density materials such as lucite or plexiglass Shielding high energy betas like P-32 with lead can generate more radiation than it shields due to Bremsstrahlung X-rays
The nucleus 234 Th formed by the α-decay of 238 U, (previous example) undergoes further decay by β- emission to Protactinium 234 Pa.