A half-life period.
Half-life period T 1/2 determine speed of disintegration of various elements in practice. Half of initial number of radioactive nucleuses breaks up during this time. The half-life period T 1/2 can be found from following reasons. If
then quantity of not broken nucleuses is equal to
,
Whence
,
hence,
The half-life period of elements (isotopes) differs in wide limits - from millions years up to shares of second.
Activity. A unit of measure.
The general quantity of the disintegrations happening in unit of time has the major importance in practical use of sources of radioactive radiation. This quantity is named activity A of given source of radioactive radiation. Activity depends upon speed of disintegration and initual quantity of nucleuses, i.e. mass of isotope.
Activity determine absolute speed of disintegration of isotope in given source.
If we compare of formulas of the basic law and a half-life period then it follows:
Activity of an element is proportional to quantity of nucleuses (mass of isotope) and inversely proportional to its half-life period.
We have some kinds of units for determinate activity of radioactivity element. Quire is unit of measure of activity of such element, which gives 3.7 1010 disintegrations in a second. We can use unit of activity - Reserford also, which correspond 106 disintegrations in a second.
Radioactive elements in the nature.
Radioactive
elements there are in the nature, but in small quantities.
Radioactive elements contain mainly in uranium ores in an earth's
crust. There is a radioactive isotope of potassium
in
the ground contain and isotopes of hydrocarbon
14C
and
hydrogen
3H,
which
are formed in an atmosphere and penetrate from atmosphere to the
ground. There are the radioactive substances, which are washed away
from ground and rocks in natural waters. These sources are used for
the medical purposes. Plants acquire radioactive substances from
ground, waters and atmospheres. The isotope of carbon
is
formed in an atmosphere, from nitrogen
under
action of neutrons of space radiation. This process we can write with
help chemical equition:
It is acquired by plants at photosynthesis. The radioactive substances penetrate to animal organisms with food, water and air, but also are removed with excrement. Therefore their accumulation in an organism does not occur happen.
There is a radioactive radiation everywhere in the nature, where there are radioactive substances, which makes natural radioactive backgraund together with spase radiation. Plants and animals have adapted to this radioactive background, as well as to other physical factors of an environment.
Ionizing radioactive radiation and its biological action.
Radioactive radiations and rigid x-rays and as streams of protons and neutrons are united under the general name of an ionizing radiation. Speed and energy of the protons, which are thrown out at nuclear reactions, getting and ionizing ability of these particles same, as well as alpha - particles. Elastic dispersion can happen at impact of neutrons to nucleus, not elastic dispersion and capture of a neutron by a nucleus (radiating capture) can be also.
Action of ionizing radiation can cause infringement in structure of molecules of substances. For example: it is possible to specify distillict waters, which consists from ionization and the subsequent disintegration of the ionized molecule of water with formation of nonsaturated radicals Н and OH, not having electric charges, but having nonsaturated valencies and having exclusively high chemical activity, thus forms also connections of type Н2О2 or НО2, they are very strong oxidizers.