USES OF RADIONUCLIDESto the malignant tissue without causing severe injury to the surrounding healthy
tissue.
- Radioisotopes as tracers
Radioisotopes have the same chemicalreactions as non-radioactive isotopes of the
same element, but they have the advantage that their position may be located using
suitable detection equipment, i.e. they can be traced. In medicine, tracers consisting
of compounds containing technetium^9943 Tc, are used to locate brain tumours. The
use of salt which contains radioactive^2411 Na allows doctors to follow movements of
sodium ions in the kidney. In positron emission tomography (PET)positron-
emitting nuclides, such as^158 O, are used to provide an image of the flow of blood in
the brain.
- Miscellaneous uses
These include the use of the beta emitter^24195 Am (t (^1) ⁄ 2 432 yr) in smoke detectors, the
sterilization of food using nuclear radiation, the use of gamma sources to estimate the
thickness of metal pipes, and the use of radioisotopes in an analytical technique called
neutron activation analysis(see Box 21.1).
409
BOX 21.1
Was Napoleon poisoned?
Emperor Napoleon was confined to the island
of St Helena in 1816. He died in 1821,
convinced that he was being poisoned by his
captives, the British authorities. Although a
post-mortem examination suggested that
Napoleon suffered from an advanced cancer
and from hepatitis, many people have since
speculated that he was slowly poisoned with
arsenic in order to prevent him from
re-emerging as a political force in Europe.
In more recent times it has been realized that
hair contains many chemical deposits which
reflect the health and diet of the individual.
Fortunately, several people obtained hair
cuttings from Napoleon’s body shortly after
his death, and these were carefully preserved
from generation to generation. In the 1960s
these samples were analysed by neutron
activation analysis. In this technique, the
sample is bombarded with neutrons, in this
case causing any arsenic-75 atoms to be
converted to radioactive arsenic-80 atoms:
75
33 As^5
1
0 n
80
33 As
Because arsenic-80 is radioactive, it may be
detected in tiny concentrations. The
concentration of arsenic-80 present is equal
to the initial concentration of arsenic-75
present in the hair sample.
Analysis of the arsenic content in the
Emperor’s hair samples did indeed show
much higher arsenic levels (about 10 mg kg^1
of hair) than would be regarded as healthy
today. However, the highest As levels (about
40 mg kg^1 ) were found in hair cuttings that
were almost certainly taken beforehis
imprisonment, and were probably caused by
the ingestion of arsenic-containing medicines
(which were popular in those days) before his
capture. In addition, hair cuttings from
unrelated individuals of the same period
suggest that the arsenic levels in many
people were very much higher than is the
case today. It was therefore concluded that it
was unlikely that the Emperor was poisoned
with arsenic. It is possible that some other
poison was used, but it seems most likely
that Napoleon died of natural causes.
In 1991 it was suggested that Zachary Taylor,
the 12th president of the United States, had
been murdered using arsenic because of his
antislavery views. However, neutron activation
analysis of Taylor’s hair revealed insignificant
levels of arsenic.