ation to produce chemical reactions.
The radiation used includes alpha
particles, electrons, neutrons, X-rays,
and gamma rays from radioactive
materials or from accelerators. Energy transfer produces ions and excited species, which undergo further
reaction. A particular feature of radiolysis is the formation of short-lived
solvated electrons in water and other
polar solvents.
radiometric dating (radioactive
dating) See dating techniques;
radioactive age.
radionuclide (radioactive nuclide)
A *nuclide that is radioactive.
radiopharmaceuticals Compounds used in medicine that have a
radioactive atom in the molecule. Radiopharmaceuticals are both for diagnostic purposes (as in radionuclide
imaging) or for therapy (e.g. certain
cancer treatments).
radium Symbol Ra. A radioactive
metallic element belonging to
*group 2 (formerly IIA) of the periodic table; a.n. 88; r.a.m. 226.0254;
r.d. ∼5; m.p. 700°C; b.p. 1140°C. It occurs in uranium ores (e.g. pitchblende). The most stable isotope is
radium–226 (half-life 1602 years),
which decays to radon. It is used as a
radioactive source in research and, to
some extent, in radiotherapy. The element was isolated from pitchblende
in 1898 by Marie and Pierre Curie.
A
• Information from the WebElements site
radon Symbol Rn. A colourless
radioactive gaseous element belonging to group 18 of the periodic table
(the *noble gases); a.n. 86; r.a.m. 222;
d. 9.73 g dm
–3 ; m.p. –71°C; b.p.
–61.8°C. At least 20 isotopes are
known, the most stable being
radon–222 (half-life 3.8 days). It is
formed by decay of radium–226 and
undergoes alpha decay. It is used in
radiotherapy. Radon occurs naturally,
particularly in areas underlain by
granite, where it is thought to be a
health hazard. As a noble gas, radon
is practically inert, although a few
compounds, e.g. radon Ûuoride,
can be made. It was Ürst isolated
by William Ramsey and Robert
Whytlaw-Gray (1877–1958) in 1908.
A
• Information from the WebElements site
rafÜnate A liquid puriÜed by solvent extraction.
rafÜnose A white solid carbohydrate, C 18 H 32 O 16 , m.p. 80°C. It is a
trisaccharide (a type of *sugar) consisting of fructose, galactose and glucose. It occurs naturally in sugar-beet
and cotton-seed residues.
r.a.m. See relative atomic mass.
Raman effect A type of scattering
of electromagnetic radiation in
which light suffers a change in frequency and a change in phase as it
passes through a material medium.
The intensity of Raman scattering is
about one-thousandth of that in
Rayleigh scattering in liquids; for this
reason it was not discovered until
1928. However, it was not until the
development of the laser that the effect was put to use.
In Raman spectroscopy light from a
laser is passed through a substance
and the scattering is analysed spectroscopically. The new frequencies in
the Raman spectrum of monochromatic light scattered by a substance
are characteristic of the substance.
Both inelastic and superelastic scattering occurs. The technique is used
as a means of determining molecular
structure and as a tool in chemical
analysis. The effect was discovered by
the Indian scientist Sir C. V. Raman
(1888–1970).
453
Raman effect
r
www.AzShimi.ir www.AzShimi.com
The radiation used includes alpha
particles, electrons, neutrons, X-rays,
and gamma rays from radioactive
materials or from accelerators. Energy transfer produces ions and excited species, which undergo further
reaction. A particular feature of radiolysis is the formation of short-lived
solvated electrons in water and other
polar solvents.
radiometric dating (radioactive
dating) See dating techniques;
radioactive age.
radionuclide (radioactive nuclide)
A *nuclide that is radioactive.
radiopharmaceuticals Compounds used in medicine that have a
radioactive atom in the molecule. Radiopharmaceuticals are both for diagnostic purposes (as in radionuclide
imaging) or for therapy (e.g. certain
cancer treatments).
radium Symbol Ra. A radioactive
metallic element belonging to
*group 2 (formerly IIA) of the periodic table; a.n. 88; r.a.m. 226.0254;
r.d. ∼5; m.p. 700°C; b.p. 1140°C. It occurs in uranium ores (e.g. pitchblende). The most stable isotope is
radium–226 (half-life 1602 years),
which decays to radon. It is used as a
radioactive source in research and, to
some extent, in radiotherapy. The element was isolated from pitchblende
in 1898 by Marie and Pierre Curie.
A
• Information from the WebElements site
radon Symbol Rn. A colourless
radioactive gaseous element belonging to group 18 of the periodic table
(the *noble gases); a.n. 86; r.a.m. 222;
d. 9.73 g dm
–3 ; m.p. –71°C; b.p.
–61.8°C. At least 20 isotopes are
known, the most stable being
radon–222 (half-life 3.8 days). It is
formed by decay of radium–226 and
undergoes alpha decay. It is used in
radiotherapy. Radon occurs naturally,
particularly in areas underlain by
granite, where it is thought to be a
health hazard. As a noble gas, radon
is practically inert, although a few
compounds, e.g. radon Ûuoride,
can be made. It was Ürst isolated
by William Ramsey and Robert
Whytlaw-Gray (1877–1958) in 1908.
A
• Information from the WebElements site
rafÜnate A liquid puriÜed by solvent extraction.
rafÜnose A white solid carbohydrate, C 18 H 32 O 16 , m.p. 80°C. It is a
trisaccharide (a type of *sugar) consisting of fructose, galactose and glucose. It occurs naturally in sugar-beet
and cotton-seed residues.
r.a.m. See relative atomic mass.
Raman effect A type of scattering
of electromagnetic radiation in
which light suffers a change in frequency and a change in phase as it
passes through a material medium.
The intensity of Raman scattering is
about one-thousandth of that in
Rayleigh scattering in liquids; for this
reason it was not discovered until
1928. However, it was not until the
development of the laser that the effect was put to use.
In Raman spectroscopy light from a
laser is passed through a substance
and the scattering is analysed spectroscopically. The new frequencies in
the Raman spectrum of monochromatic light scattered by a substance
are characteristic of the substance.
Both inelastic and superelastic scattering occurs. The technique is used
as a means of determining molecular
structure and as a tool in chemical
analysis. The effect was discovered by
the Indian scientist Sir C. V. Raman
(1888–1970).
453
Raman effect
r
www.AzShimi.ir www.AzShimi.com