Interaction of X-ray radiation with substance.

Radiation is partially reflected from a surface at falling R-rays on a body. The basic part of radiation is absorbed, photons of x-ray radiation cooperate with electrons and atoms of molecules of substance passing through a body. Thus occurs:

1. Coherent dispersion;

2. Photoeffect

3. Kompton - effect

1 . If - coherent (classical) dispersion takes place (А_exit - work of an output electron from substance). The direction of movement of photons changes owing to influence of photons with electrons the internal level, strong connected with a nuclear. Energy and length of a wave remain constant. It does not cause biological action.

2. If the photon is absorbed, electron comes off atom: the substance is ionized (substance turns to a positive ion), the photoeffect occurs.

3. If , then where The part of energy of a photon is spent for fulfillment of work for an output of electron from the substance, other part is spent for kinetic energy free electron, the third part is radiated in the form of secondary radiation ( ), which dissipates in every possible directions.

Secondary radiation with length of a wave more, than length of a wave of excitation and with smaller energy is formed. This phenomenon is not coherent dispersion or Kompton-effect. Secondary radiation dissipates in every possible directions.

The photoeffect is characteristic for photons with rather low energy and occurs mainly on electronах internal level of atoms. Photons with the energy changing in enough wide limits cause Kompton - effect at interaction of photons with electrons the external levels poorly connected with a kernel. The Kompton-effect occurs in substance in parallel (and it is independent) to a photoeffect.

In medicine use x-ray radiation with energy of photons from 60 up to 200 Кelectronvolt.

Х- rays is weakened at interaction with substance. Buger’s law determines this weakening. Buger’s law for x-rays radiation looks like

- Stream of radiation, the past through substance

- Stream of the radiation, falling on substance

- linear factor of easing,

Linear factor of easing of x-ray radiation depends upon natures of substance.

Where - factor of true absorption,

- factor of dispersion of primary radiation

Radiation with the same length of a wave absorbs the more strongly, than it is more density and more nuclear number Z. The bone absorbs Х-beams more strongly, than soft tissues of the person. If a non-uniform body to place on a way of a bunch of the x-ray radiation, the fluorescing screen to place before it the shadow is formed on the screen because of non-uniform absorption. This shadow allows to judge an internal structure of a body. The bones, consisting in basic from , almost in 150 times absorb more strongly, than soft tissues (consisting basically from water ).

Radioactivity radiation Radioactive disintegration Structure of a nucleus

The nucleus of atoms consists of elementary particles - protons and the neutrons, which are named nucleons. Protons and neutrons - independent particles in a free condition, but they can transformation earth other in a nucleus and then they are considered as various conditions of the same particles. Quantity Z of protons in a nucleus is equal to atomic number of an element. The mass number A is the integer number approximately equal to atomic mass of element (isotope).

The quantity of neutrons in nucleus is equal to a difference between mass number and atomic number of element (isotope):

N = A - Z

The radius of a nucleus is determined by approximately formula: R=1.5 ^-13, it has the order 10^-13 sм (in 10⁵ times less then order of radius of atom).

Nuclear forces. Properties of nuclear forces. Models of nuclear forces

Nucleons in a nucleus are connected by special forces of a mutual attraction - nuclear forces. The nature of nuclear forces is not enough studied; however its basic properties are installed authentically.

1. Nuclear forces is short-range

2. Nuclear forces is strong

3. Nuclear forces operate act between nucleons irrespective of their electric charge. Nuclear forces act between two neutrons, and between a neutron and a proton or two protons.

4. Nuclear forces have properties of saturation, i.e. each nucleon interaction with only limited quantity of nucleons surrounding it, therefore if to increase quantity of nucleons in a nucleus, then nuclear forces do not increase, as it takes place for forces of electrostatic pushing away between protons. Stability of a nucleuses is weakened in process of increase of the general quantity of nucleons in nucleus (quantity of neutrons more then quantity of protons - N/Z>1.6). Nucleus such chemical elements have the spontaneous disintegration.

We have two kings of structure of atomic nucleus. Nucleons unbrokenly exchange special particles in a nucleus, which are named π-meson or quantum of a nuclear field, according to the theory accepted now. This is very difficult to determine independent to existence of these particles in nucleus, because the exchange to π-meson happens very quickly (during 10^-23), therefore π-meson is named virtual.

Energy of connection of nucleons.

There is definition of energy of connection E_c. The energy of connection is a difference between general potential energy Е all free nucleons and potential energy Е_n of nucleons, which there are inside nucleus Е_c=Е-Е_n. Energy of connection is an energy, which is allocated at formation of a nucleus from free nucleons, or accordingly energy, which is spend if action of external forces to destroy a nucleus. Energy of connection of a nucleus is proportional to quantity of nucleons, therefore we can use average value of energy the connections, falling one nucleon, which is named specific energy E_s of connection

Е_s = Е_c/A (A - mass number).