Sources of X-ray radiation.

Sources of x-ray radiation it is possible to divide on two groups: natural and artificial. Natural sources of radiation. Some radioactive isotopes can serve as sources of X-rays. Intensity of X-rays of isotope sources is less than intensity of radiation of a X-ray tube. The sun is source of X-ray radiation also. Its X-ray radiation is so huge, that is capable to destroy in a few minutes all alive on the Earth. But the x-ray quantum on is many times absorbed and let out by particles of plasma to road to the Earth. As a result it comes on a surface of the Earth weakened. So rigid radiation of a sunlight becomes soft and turns to ultra-violet radiation, visible and infra-red.

There are "X -ray" stars though they are rare enough. 200 x-ray stars have been found out by 1977. Presumably the further searches will increase this number up to thousand. Presumably x-ray and optical (visible) radiation of x-ray stars represents a continuous spectrum of thermal radiation of gas, разогретого up to tens millions degrees.

Pulsars - the "beacons" invisible in a usual telescope. They change intensity of the radiation, radio wave or X-ray on a regular basis, quite often with surprising correctness through different time intervals. What is the pulsar? It is a neutron star which operates not alone, and together with the partner similar to our Sun, only it is many times more.

It super dense and rather massive, it incessantly draws on herself substance of the partner - the heated gaseous sphere. Thus the huge quantity of radiant energy is allocated in a x-ray range. The neutron star rotates about the axis, X-rays blink.

Artificial sources of radiation.

Artificial sources of radiation is x-ray tube. X-ray tube represents glass flask with high vacuum, with the cathode and the anode, at oblique which end face there is a plate - a pocket mirror from heavy metal. The heated spiral cathode (1) (fig 1.) is a source of electrons. The stream of electrons (4) is accelerated in the strong electric field created between the cathode and the anode (2). The accelerated stream of electrons is broken by substance of the anode and causes occurrence X – rays (3). This is brake radiation. Brake x-ray radiation is formed at sharp braking of electrons by electric field of atoms of the anticathode. The part of electrons gets into substance of the anode (fig. 2) and causes characteristic radiation. A feed of a x-ray tube is provided with two sources: a source of a high pressure for an anode circuit and a source of a low pressure (6 -8 V) for heat. Change of an anode pressure allows to adjust rigidity radiation, change of heat - force of a current in an anode circuit and capacity of radiation. The anode circuit eats a direct current. In some cases probably use of an alternating current. Then the tube serves simultaneously both the generator of X-ray radiation and the rectifier of a feeding pressure.

It is possible to explain occurrence of electromagnetic radiation as follows: the directed movement of electrons from the cathode to the anode represents an electric current. Around of an electric current there is a magnetic field. At braking of electrons or at sharp reduction of speed of movement of electrons, the electric current as sharply changes, in this connection the magnetic field will change too, electromagnetic brake radiation arises so. The therapeutic x-ray tube has high working pressure also works at small values of force of a current.

Spectrum of the brake radiation

1. Spectrum of the brake radiation is continuous (fig. 3)

2. Spectrum has short-wave border

3. Spectrum has the wavelength corresponding the maximal energy at the given pressure.

4. Spectrum has short-wave border

Photons can get this energy at full braking of electrons, having the maximal energy equal to product of a charge of electron on a pressure, e - a charge of electron.

Experimental check of validity of this formula is calculation after it Planck's constant. Value of a constant of Planck, received by this method, most precisely and authentically.

The most typical for radiation is the wave on which it is necessary a maximum of energy of radiation

The length of a wave depends on energy of photons which defines getting ability of radiation. Therefore getting ability characterize in the length of a wave. More absorbed long-wave radiation is called soft, and less absorbed - short-wave is called rigid. Getting ability of rigid rays is more, than at soft rays. The length of a wave can be adjusted, changing a pressure of a tube. The above the pressure, the is more “rigid” radiation. At change of a pressure changes not only length of a wave, but also the general capacity of radiation. Absorption of x-ray radiation will be carried out more strongly by bone tissues.

S tream of energy of brake radiation -

U - the pressure enclosed between the cathode and the anode.

I - force of a current in a circuit of a tube.

Z - Nuclear number of substance of the anode (anticathode)

Except for brake, characteristic radiation exists, which has a linear spectrum. Characteristic x-ray radiation is formed at transitions of electrons on internal levels of atoms with a high serial number.

Characteristic radiation is a results of excitation of atoms by electrons with high energy, which get deep into atom and translate close to a nuclear electrons on higher power levels. The quantum is let out at the subsequent transitions removed from nuclear of electrons on a released level.

Characteristic radiation arises at transitions of electronоs on internal levels (K, L, M) look fig. 4) atoms with a high serial number. The substance is exposed to strong external influence (bombing by fast electrons or - particles). Electron of level K is removed from the own orbit and has passed to external level. Electron from any other, higher power level can pass to the released place. Thus a photon is radiated with the frequency corresponding a difference of energy of transition.

The empty place can arise on internal levels, and transition electronа can occur from any higher level. As a result radiation consisting of separate lines and specific to substance in which it is raised is formed. Lines in a spectrum of characteristic radiation are united in series K, L, M and correspond to transitions of electrons from higher levels on levels K- K-series, L - L-series. The frequencies corresponding lines of these series, are connected with nuclear number of substance in which radiation is raised. English physicist Mozli has established this communication experimentally in 1913 year.

Where - frequency of characteristic radiation;

R – Ridberg’s constant;

n - the main quantum number

We can write the Mozli’s law in following kind:

- frequency of characteristic radiation

Z - nuclear number of an element, A and B – special constant.

Value increases for the same size in each series at transition from Z to (Z +1). Therefore elements can be spread out in a number according to increase of nuclear number of substance of the anode. Linear spectrum - the passport of substance. Electrons are raised on the internal levels close to a kernel at excitation characteristic X-radiation. A structure of these level equally at all heavy elements, elements with a high serial number. Therefore characteristic X-ray radiation has a similar appearance at different elements, but frequency of characteristic radiation depends on nuclear number of substance.