Radiation Samar El-Sayed

Radiation Radiation is an energy in the form of electro-magnetic waves or particulate matter, traveling in the air.

The structure of the atom ELECTRON negative, mass nearly nothing PROTON positive mass (“1”) NEUTRON neutral mass (“1”)

The structure of the atom ParticleRelative MassRelative Charge Proton1+1 Neutron10 Electron0 MASS NUMBER = number of protons + number of neutrons SYMBOL ATOMIC NUMBER = number of protons

Isotopes An isotope is an atom with a different number of neutrons Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. Notice that the mass number is different.

Radioactivity Spontaneous emission of particles and/or electromagnetic radiation from an unstable nucleus. Radiation The nucleus is more stable after emitting some radiation – this is called “radioactice decay”.

Half life The time required for radioactive matter to decrease by one half (lose 50% of its activity). The decay of radioisotopes can be used to measure the material’s age. … At start there are 16 radioisotopes After 1 half life, half have decayed (that’s 8) After 2 half lives, another half have decayed (that’s 12) = radioisotope= new atom formed

Physical half life Time required for the radioactive substance to lose 50% of its activity by radioactive decay Time required for the radioactive substance to lose 50% of its activity by radioactive decay Biological half life Time required by the body to eliminate 50% of internally deposited quantity of radioactive substance Time required by the body to eliminate 50% of internally deposited quantity of radioactive substance Effective half life Time required for radionuclide in body to decrease by 50% as a result of biological elimination & radioactive decay Time required for radionuclide in body to decrease by 50% as a result of biological elimination & radioactive decay

Linear energy transfer (LET) linear collision stopping power The ionization density (e.g., ion pairs/cm of tissue) along the path of the radiation. The energy a charged particle imparts to matter per unit length as it traverses the matter Depends on: ChargeVelocity High LET : alpha Low LET: beta particles, x-ray, gamma ray

Ionizing Radiation Ionizing Radiation Radiation that has sufficient energy to dislodge orbital electrons Radiation that has sufficient energy to dislodge orbital electrons Non-Ionizing Radiation Non-Ionizing Radiation Radiation that does not have the ability to dislodge electrons, but can still cause biological damage by causing chemical changes or by heating (vibrating) molecules. Radiation that does not have the ability to dislodge electrons, but can still cause biological damage by causing chemical changes or by heating (vibrating) molecules. Examples are ultraviolet light, microwaves. Examples are ultraviolet light, microwaves. Types of Radiation

Ionizing radiation

Ionization Radiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons.

particulate Ionizing radiation Short wave electromagnetic uncharged Charged -ve beta neutrons gamma rays x-ray alpha +ve Types of ionizing radiation

X and gamma radiation are penetrating radiation and an EXTERNAL HAZARD. stopped by lead naturally present in soil and cosmic radiation found in medical uses

can’t penetrate skin internal hazard stopped by paper found in soil, radon and other radioactive materials Alpha Radiation It is only a hazard when inside body (internal hazard)

Beta Radiation is a Skin, Eye and Internal Hazard skin, eye and internal hazard stopped by plastic found in natural food, air and water

The Penetrating Power of Radiation Alpha Beta Gamma/ X-ray

Dangers of radioactivity OUTSIDE the body  and  are more dangerous as  radiation is blocked by the skin. INSIDE the body an  source causes the most damage because it is the most ionising. Alpha Beta Gamma

Measurement units Air Exposure in air Radioactivity Absorbed dose in matter Absorbed dose in tissue (Dose equivalent)

Radioactivity Number of disintegration nuclei / unit time (sec). Disintegration : spontaneous transformation in number or internal arrangement of protons, neutrons in the nucleus. Units: Becquerel (Bq) = 1 disintegration/second (dps) Becquerel (Bq) = 1 disintegration/second (dps) Curie (Ci) 1 Ci = 3.7 X Bq Curie (Ci) 1 Ci = 3.7 X Bq

Exposure A measure of what is emitted Charge (number of ions) produced in air from ionization by gamma and x-rays Units: –coulomb/ Kg air –Roentgen (R)

Absorbed Dose The amount of energy absorbed by a given mass (e.g. water or tissue ) Units: Gray (Gy) Gray (Gy) Rad (Roentgen Absorbed Dose) Rad (Roentgen Absorbed Dose) 1 Gy = 100 rad 1 Gy = 100 rad

Dose Equivalent Risk adjusted absorbed dose. The absorbed dose is weighted by the radiation type and tissue susceptibility to biological damage Takes into account the biological effect of the various types of radiation = absorbed dose X Radiation Weighting Factor = absorbed dose X Radiation Weighting FactorUnits Sievert (Sv) 1 Sv = 100 rem Sievert (Sv) 1 Sv = 100 rem rem rem

The Radiation Weighting Factor (RWF) Reflects differences in the amount of each type of radiation necessary to produce the same biologic effect Type of radiation RWF X-ray, gamma, or beta 1 Neutrons and High-energy protons 10 Alpha particles 20

What is an individual's dose equivalent from 10 mrad of gamma rays, 5 mrads of Beta particles and 10 mrads of neutrons? (m = milli = 1/1000) Dose Equivalent = mrads X RWF = mrems Dose Equivalent = mrads X RWF = mrems Gamma dose equivalent = 10 x 1 = 10 Gamma dose equivalent = 10 x 1 = 10 Beta dose equivalent = 5 x 1 = 5 Neutron dose equiv. = 10 x 10 = 100 Total 115 mrems

An exposure to 1 mrad of gamma, 10 mrad of Beta particles, and 5 mrad of fast neutron radiations would give an individual a dose equivalent of: 16 mrem 16 µ Ci 61 mrem 61 mrads

What dose of X-ray would produce the same biologic effect as 50 mrad of gamma or beta radiation? The RWF for X-ray is also one; The RWF for X-ray is also one; therefore, a dose of 50 mrads of X-ray radiation would produce the same biologic effect as 50 mrads of gamma or beta radiation. therefore, a dose of 50 mrads of X-ray radiation would produce the same biologic effect as 50 mrads of gamma or beta radiation.

If the radioactive material in the case study had been an alpha-emitter instead of a beta and gamma emitter, would the biologic effects be greater? Explain. if the radioactive material was emitting alpha particles the biologic effectiveness would be greater. if the radioactive material was emitting alpha particles the biologic effectiveness would be greater. The RWF for alpha particles is 20, which indicates a given dose of alpha radiation is twenty times more biologically effective than the same dose of beta or gamma radiation. The RWF for alpha particles is 20, which indicates a given dose of alpha radiation is twenty times more biologically effective than the same dose of beta or gamma radiation.

If a physician calculates that a young boy at the scene of an accident received a maximum beta or gamma radiation radiation dose of 50 millirads (mrad). Express this dose in millirems (mrem) and Sieverts (Sv). The RWF for beta or gamma radiation is one; therefore, a dose of 50 mrads of beta or gamma radiation is equivalent to 50 mrem or 0.05 rem. One Sievert = 100 rem; therefore, 0.05 rem = (5×10−4) Sv The RWF for beta or gamma radiation is one; therefore, a dose of 50 mrads of beta or gamma radiation is equivalent to 50 mrem or 0.05 rem. One Sievert = 100 rem; therefore, 0.05 rem = (5×10−4) Sv

Sources of radiation Natural Sources Artificial sources

Exposure to ionizing radiation Internal contamination (i.e., radionuclide deposited within the body) External contamination (i.e., radionuclide deposited on the body surface) External exposure (Irradiation by an external source. External Exposure Internal Contamination External Contamina tion