Физика - Помощь и решение домашних заданий по физике - 157

Short te xt c) Radiation shielding (protection of ionizing radiation). Practically three types of protection of ionizing radiations are discussed: protection by time, distance and material. This is obviously from the formula (4): X=K_(Y)ADelta t/r^2. Protection by time. The less the time period of ionizing radiations action the more protection is. Protection by distance. The further you are posed from the source of radiation, the less the dose of radiation. Protection by material. This kind of protection is based on different ability of materials to absorb different types of ionizing radiation. The sheet of paper or a layer of air in the same centimeters can protect from a-particles. Metallic aluminum plate or glass can become protection from beta - particles. The protection of the y-radiation and neutrons is the most complex , since these kinds of radiation have minor probability of interaction with particles of material and get deeper into it. Material in the end of the periodic tables of elements (lead) can protect us from x- and y- rays. Neutron radiation requires specifically complex protection Firstly, high-velocity neutrons are slowed down, for instance, in water. Then, materials, capable to absorb the neutrons are used: (}_{48)^113Cd+_(0)^1narrow ^114_(48)Cd Energy and, accordingly, a velocity of neutrons are necessary to be taken into account. The less velocity of neutrons is, the more probable a capture of the neutrons by an atom or a molecule of the material is. So it is necessary to decelerate neutrons . It can be made with interaction neutrons and an absorber.

Short this text 1. The absorbed dose (irradiation dose) At hit ionizing radiations on any body it is important to value the action of this radiation. Energy of the ionizing radiations partly converts in energy of molecular heat motion of bodies. The absorbed dose (irradiation dose) is a main physical value, accepted in dosimetry to estimate influence of the ionizing radiations on all objects including living organisms); D=Delta E/m, (1) D is the absorbed dose (irradiation dose), AE - energy, m =the mass of a body. The unit of measurement of the absorbed dose is Gy (gray) in SI: 1Gy=(1J)/(1kg) . This unit of measurements has a name of the English radiobiologist Gray. In a real experiment another unit is used - rad: 1 rad=10^-2Gy. Abbreviation rad means "radiated absorbed dose". We often want to know the absorbed dose in a unit of time. So there is a power of dose.It is a ratio the dose to time interval of irradiation -D/Delta t. The main unit of this value is Gy/s in SI; the other unit of dose power is rad/s. 2. Exposure (air) dose for the photon radiation. There is a very important problem about calculation of energy of the ionizing radiations, which absorbed by a body . The absorbed dose isn't convenient for this purpose.The bodies, absorbing the ionizing radiations, are not homogenous.Both absorption and reflection of the falling ionizing radiations occur so it is difficult to determine the true dose. The ionizing effect, caused by the ionizing radiation in the air, surrounding a body, is easier to take into account The exposure (air) dose is used for the effectiveness photon radiations (X. ray and y-radiations). Exposure (air) dose X is valued by the charge of ions of the same sign, which are formed midair, surrounding a body, under the action of X-ray and y-radiations. X=dQ/dm, dQ - a total charge of ions of the same sign, created in the air under the action of photon radiations in the elementary volume; dm the mass of air in this volume. The unit of measure of the exposure dose is C/kg in SI. 1 C/kg - is such an exposure (air) dose, when all ions, formed by photons in I kg of dry air, carry electric charge IC (Coulomb) for each sign. Non-SI unit of measure is Roentgen (R) Roentgen corresponds to the charge, forming in 1cm^3 of dry air. 1R=2.58times 10^-4 C/kg. There is a straight proportional dependency between the air dose and the absorbed dose: D=fX, (3) f - factor, which depends on material and kind of radiation f=1 for soft tissues and water, if D is expressed in rad, X-in Roentgen . For air ff=0,88 N/M-power of an air dose. It's a unit of measure in SI is C/(kgtimes s) or A/kg The power of an exposure dose is connected with the activity of a radioactive substance (A): X/Delta t=K_(y)A/r^2, K, - is a y-constant.depends on a type of the substance (radioactive nuclide). A-is activity of the substance. r= is a distance from the source of radiations to the place, where the air dose is measured, Delta t-is time of influence ionizing radiations on object Hence: X=K_(r)ADelta t/r^2

Hypothe rmia I s the temp erature rise: Select one: a.no b.yes

3. Tewog kouisavui =7, V=(1)/(T)

Task 5. Find the minimum thickness of matter Silicon in which protons with energy 3 MeV, 30 MeV, and 300 MeV will lose all their energy. For these energies, are collisions with electrons or with nuclei predominant?

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