tion in London, he initiated X-ray dif-
fraction studies of organic molecules.
Bragg peakA peak in the scatter-
ing 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 X-
rays 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 X-
rays (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 inte-
ger. 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% cop-
per and 33% zinc.
Bravais latticeAn inÜnite array of
lattice points. A Bravais lattice can
have only fourteen space groups di-
vided 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 min-
imum 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 Sac-
charomyces cerevisiae and S. uvarum (or
S. carlsbergenesis) produces alcohol. In
theÜrst 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 mal-
tose and then to glucose. The next
stage is kilningor roasting, in which
the grains are dried and crushed. The
colour of a beer depends on the tem-
perature 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 re-
maining starch is converted to sugar;
the resultant liquid is the raw ma-
terial of brewing, called wort. The
yeast is then added to the wort to
convert the sugar to alcohol, fol-
lowed by hops, which give beer its
characteristicÛavour. Hops are the
femaleÛowers of the vine Humulus
lupulus; they contain resins (humu-
lones, cohumulones, and adhumu-
lones) that give beer its distinctive
bitter taste.bridgeAn atom or group joining
two other atoms in a molecule. See
aluminium chloride; borane.brightenersSubstances 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 counteract83 brighteners
b