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Transcript
Radioactivity
overview
Rikhvanov Leonid P., professor,
DSc in Geology and Mineralogy
Nadeina Luiza V., associate professor,
PhD in Philology
TOMSK -2015
RADIOACTIVITY (from Latin radio — radiate the beam and
activus — active), spontaneous transformation unstable atom
nuclei in atom nuclei of other elements, conducting by emission
of particles or gamma quantum.
Definition. Conceptions.
«Radioactive elements are chemical elements cyaracterized by
spontaneous atom emission of so-called alpha-, beta- and gammarays. This radiation associated with atomic transformations.
Substances emitting Becquerel rays were called radioactive, and
new property discovered due to this emission was called
radioactivity. Elements including these properties were called
radioelements» (М. Curie «Radioactivity»).
ATOM CONCEPTION
As already mentioned, atom consists of nucleus with definite charge and equal to it
number of electrons located on the allowed energy levels.
Nucleus consists of protons determined its charge (Z), and neutrons these particles are called
nucleons and in sum Z + N = A determine mass number. Atoms with equal Z are called
isotopes.
Electron and proton are stable, their lifetime is not limited, lifetime of free neutron is limeted
1∙ seconds. Electron and proton have got corresponding antiparticles – positron and
anti-proton with lifetimes less s. Except these particles, should note another atomic
particle - photon (γ), which does not have rest mass and with unlimited lifetime. Atomic
nuclei are able to emit more than 25 elementary particles, but we would be limited by these
5 particles.
Atom – a particle of matter indivisible by chemical means. It is the fundamental building block
of elements. Constituent part of substance containing the same atoms, is called a chemical
element.
Atomic number Z is equal to number of protons in atom nucleus. There are Z electrons in
electron shell of electroneutral atom.
Mass number A is equal to number of photons Z and number of neutrons N in atom
nucleus; A = Z + N.
Nuclides – atoms with definite number of protons and neutrons.
Isotopes – atoms with equal Z, but different N.
Isobars – atoms with equal A, but different Z.
Isotones – atoms with equal N, but different A.
Atomic mass – approximately the sum of the number of protons and neutrons
found in the nucleus of an atom. Unit of atomic mass is equal 1/12 mass of
carbon-12 isotope.
Relative atomic mass is equal to atomic mass of element.
Relative atomic mass of element is equal to relative atomic mass of isotope.
Characteristics of radiation types