Geology Reference
In-Depth Information
Box 9.9 Radon
the heaviest of the noble gases, radon (rn,
Z
= 86), com-
prises four naturally occurring isotopes, all of which are
highly radioactive with half-lives from fractions of a sec-
ond to 3.8 days.
218
rn,
219
rn,
220
rn and
222
rn are all stages
in the decay chains leading from
232
th,
235
U and
238
U to
isotopes of lead (exemplified in Figure 3.3.1).
Uniquely among the many radioactive decay products of
U and th, radon's gaseous state allows it to escape read-
ily from U- and th-bearing minerals. radon thus constit-
utes a potential public health concern in areas underlain
by U- and th-rich rocks, such as granite and shale (and
some limestones and sandstones). radon gas seeping up
from bedrock in such areas (particularly
222
rn whose rel-
atively long half-life of 3.8 days facilitates migration) may
accumulate in poorly ventilated household basements and
under-floor cavities, where it constitutes a radiological haz-
ard to occupants who may breath it in.
radon isotopes undergo alpha-decay to short-lived iso-
topes of polonium (po,
Z
= 84), a solid element that may
lodge in lung tissue and decay to a succession of
α
-active
daughter nuclides. the
α
-particles emitted cause intense
tissue damage on account of their high mass and charge.
In the UK, radon is recognized as the second greatest
cause of lung cancer after tobacco-smoking, and it
accounts for about half the annual average human rad-
iation exposure.
the effects of radon can be mitigated by ensuring that
under-floor spaces are adequately ventilated, sometimes
with the aid of a pump venting to the outside air (where rn
is dispersed and diluted to safe levels). In some coun-
tries, radon risk maps are available (e.g.
www.ukradon.
Ferrous metals
Steel: Fe alloyed with C and other transition metals:
• stainless steel contains Cr and Ni.
• tool steel contains Cr, Mo and W.
Other alloys:
Alnico (Co, Ni, Al, Cu) is used for low-cost magnets.
Nichrome (Ni, Cr) is used for resistance wire in
electric heaters.
Titanium
TiO
2
is the white pigment
used in lead-free paints.
Ti is a strong, low-density
metal used in aerospace
applications.
Corrosion-resistant.
VIII
Group
IIIa
IVa a
VIa
VIIa
Ib
First
transition
series (3d)
27
Co
21
Sc
22
Ti
23
V
25
Mn
24
Cr
26
Fe
28
Ni
29
Cu
Second
transition
series (4d)
*
39
Y
40
Zr
41
Nb
42
Mo
44
Ru
45
Rh
46
Pd
47
Ag
Third
transition
series (5d)
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
Lanthanides
(58-71)
Refractory metals
Electrical filaments
and high-temperature
steels
Coinage metals
Electrical wiring (Cu) and
contacts (Cu & Au) where
high reliability is required.
Corrosion-resistant alloys
and plumbing (Cu).
Jewellery and decorative
uses (Ag, Au).
Other rare metals
Hf and Ta exemplify rare
metals that have found
important high-tech
applications.
E.g.
Ta, mixed with its oxide,
is used for capacitors in
mobile phones.
Platinum group
Catalysts in the chemical
industry and in low-emission
car exhausts ('catalytic con-
verters' using Pd, Pt and Rh).
Applications where chemical
inertness is required.
Figure 9.7
Transition metals and
their uses.
*Technetium (Tc,
Z
= 43) has no stable isotope and is not found in Nature - see Exercise 6.4(b).
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