Introduction to Free Air Ionization Chamber
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Added on 2020-05-08
Introduction to Free Air Ionization Chamber
Added on 2020-05-08
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Running head: PHYSICS1
PHYSICS2Solutions1a) a free air ionization chamber is a chamber that is freely open to the atmosphere where the fill gas is ambient air in order to produce perfect charged particle equilibrium. In principle the walls of the chamber do not play any role in its response whereas a thimble air-walled chamber is a compacted free air chamber where the wall is made of an air equivalent material that has the same effective atomic number as air. Commonly used for radiation therapy measurements[ CITATION SAk16 \l 1033 ].b) Equivalent dose is the dose that represents the stochastic health effects of low levels of ionizing radiation on the human body. It is denoted by a quantity H. the unit of measure in the SI system of units is the Sievert (Sv). On the other hand effective dose is the level of radiation exposure that is sufficient enough to achieve the desired clinical improvement in all specified tissues[ CITATION JWa15 \l 1033 ]. It is denoted by quantity E and the SI unit is the Sievert (Sv)c) Stopping power is the retarding force acting on charged particles, e.g. alpha particles, that results in loss of particle energy due to its interaction with matter. It is normally applied in areas that require radiation protection. Whereas, linear energy transfer is the amount of energy that is deposited by radiation per unit length of travel, normally expressed in keV per micron. It usually describes the amount of energy transferred by an ionizing particle to the material traversed per unit distance[ CITATION PMe17 \l 1033 ].d) Radioactive half-life for a given radio-isotope is the measure of the tendency of the nucleus to decay or disintegrate. It describes the time required for one half the atoms of the given radio-isotope to disintegrate. Contrary to that, biological half-life of a substance e.g. radio-active
PHYSICS3substance is the time the substance takes to lose one half of its radiologic or physiologic activity. Also called terminal half-life.e) Deterministic effect of radiation is an effect that can be related directly to the radiation dose received. Deterministic effect has a threshold below which the effect will not occur. The dose is directly proportional to the severity. Stochastic effects of radiation are effects that usually occur by chance and can occur without a threshold of dose e.g. cancer. The severity of stochastic effectis independent of the dose[ CITATION DBu09 \l 1033 ].2a) Absolute dosimetry is a direct measure of ionization or absorbed dose under standard conditions. For example, things like electron release in an ionization chamber and calorimetry. Absolute dosimetry informs a standard because of the need for accuracy. Relative dosimetry, on the other hand, refers to the use of a dosimeter that has a secondary standard for example, film dosimetry that is accurate but relies on the production of a known dose somewhere on the film[ CITATION ZZh17 \l 1033 ].b)Since 24Na is cleared exponentially at an effective rate λE, the amount of activity in the source organ is expressed as: As(t) = As(0) × e-λEt, Where As(0) is the initial activity in the source.Ã=∫0∞As(t)dt = As(0) ∫0∞e−λEtdt = As(0)λESince λE = 0.693(TR∗TB)/(TR+TB)
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