tion in London, he initiated X-ray diffraction studies of organic molecules.
Bragg peak A peak in the scattering pattern in X-ray diffraction of a
crystal. The intensity of Bragg peaks
is proportional to the square of the
number of the scatterers. If X-ray
scattering from a solid produces
Bragg peaks this indicates that the
solid has long-range order. Bragg
peaks are named after Sir William
Lawrence *Bragg, who discovered
them in 1912. The scattering of Xrays from a set of planes in a crystal
that gives rise to Bragg peaks is
called Bragg scattering.
Bragg’s law When a beam of Xrays (wavelength λ) strikes a crystal
surface in which the layers of atoms
or ions are separated by a distance d,
the maximum intensity of the
reÛected ray occurs when sinθ =
nλ/2d, where θ (known as the Bragg
angle) is the complement of the
angle of incidence and n is an integer. The law enables the structure of
many crystals to be determined. It
was discovered in 1912 by Sir
William Lawrence Bragg.
branched chain See chain.
brass A group of alloys consisting
of copper and zinc. A typical yellow
brass might contain about 67% copper and 33% zinc.
Bravais lattice An inÜnite array of
lattice points. A Bravais lattice can
have only fourteen space groups divided into seven crystal systems. It is
named after Auguste Bravais
(1811–63).
Bremsstrahlung (German: braking
radiation) The *X-rays emitted when
a charged particle, especially a fast
electron, is rapidly slowed down, as
when it passes through the electric
Üeld around an atomic nucleus. The
X-rays cover a whole continuous
range of wavelengths down to a minimum value, which depends on the
energy of the incident particles.
Bremsstrahlung are produced by a
metal target when it is bombarded
by electrons.
brewing The process by which
beer is made. Fermentation of sugars
from barley grain by the yeasts Saccharomyces cerevisiae and S. uvarum (or
S. carlsbergenesis) produces alcohol. In
the Ürst stage the barley grain is
soaked in water, a process known as
malting. The grain is then allowed to
germinate and the natural enzymes
of the grain (the amylases and the
maltases) convert the starch to maltose and then to glucose. The next
stage is kilning or roasting, in which
the grains are dried and crushed. The
colour of a beer depends on the temperature used for this process: the
higher the temperature, the darker
the beer. In the next stage, mashing,
the crushed grain is added to water
at a speciÜc temperature and any remaining starch is converted to sugar;
the resultant liquid is the raw material of brewing, called wort. The
yeast is then added to the wort to
convert the sugar to alcohol, followed by hops, which give beer its
characteristic Ûavour. Hops are the
female Ûowers of the vine Humulus
lupulus; they contain resins (humulones, cohumulones, and adhumulones) that give beer its distinctive
bitter taste.
bridge An atom or group joining
two other atoms in a molecule. See
aluminium chloride; borane.
brighteners Substances added to
detergents or used to treat textiles or
paper in order to brighten the
colours or, particularly, to enhance
whiteness. Blueing agents are used in
laundries to give a slight blue cast to
white material in order to counteract
83
brighteners
b
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Bragg peak A peak in the scattering pattern in X-ray diffraction of a
crystal. The intensity of Bragg peaks
is proportional to the square of the
number of the scatterers. If X-ray
scattering from a solid produces
Bragg peaks this indicates that the
solid has long-range order. Bragg
peaks are named after Sir William
Lawrence *Bragg, who discovered
them in 1912. The scattering of Xrays from a set of planes in a crystal
that gives rise to Bragg peaks is
called Bragg scattering.
Bragg’s law When a beam of Xrays (wavelength λ) strikes a crystal
surface in which the layers of atoms
or ions are separated by a distance d,
the maximum intensity of the
reÛected ray occurs when sinθ =
nλ/2d, where θ (known as the Bragg
angle) is the complement of the
angle of incidence and n is an integer. The law enables the structure of
many crystals to be determined. It
was discovered in 1912 by Sir
William Lawrence Bragg.
branched chain See chain.
brass A group of alloys consisting
of copper and zinc. A typical yellow
brass might contain about 67% copper and 33% zinc.
Bravais lattice An inÜnite array of
lattice points. A Bravais lattice can
have only fourteen space groups divided into seven crystal systems. It is
named after Auguste Bravais
(1811–63).
Bremsstrahlung (German: braking
radiation) The *X-rays emitted when
a charged particle, especially a fast
electron, is rapidly slowed down, as
when it passes through the electric
Üeld around an atomic nucleus. The
X-rays cover a whole continuous
range of wavelengths down to a minimum value, which depends on the
energy of the incident particles.
Bremsstrahlung are produced by a
metal target when it is bombarded
by electrons.
brewing The process by which
beer is made. Fermentation of sugars
from barley grain by the yeasts Saccharomyces cerevisiae and S. uvarum (or
S. carlsbergenesis) produces alcohol. In
the Ürst stage the barley grain is
soaked in water, a process known as
malting. The grain is then allowed to
germinate and the natural enzymes
of the grain (the amylases and the
maltases) convert the starch to maltose and then to glucose. The next
stage is kilning or roasting, in which
the grains are dried and crushed. The
colour of a beer depends on the temperature used for this process: the
higher the temperature, the darker
the beer. In the next stage, mashing,
the crushed grain is added to water
at a speciÜc temperature and any remaining starch is converted to sugar;
the resultant liquid is the raw material of brewing, called wort. The
yeast is then added to the wort to
convert the sugar to alcohol, followed by hops, which give beer its
characteristic Ûavour. Hops are the
female Ûowers of the vine Humulus
lupulus; they contain resins (humulones, cohumulones, and adhumulones) that give beer its distinctive
bitter taste.
bridge An atom or group joining
two other atoms in a molecule. See
aluminium chloride; borane.
brighteners Substances added to
detergents or used to treat textiles or
paper in order to brighten the
colours or, particularly, to enhance
whiteness. Blueing agents are used in
laundries to give a slight blue cast to
white material in order to counteract
83
brighteners
b
www.AzShimi.ir www.AzShimi.com