午夜福利1000集合

EVERY batch of paper has a characteristic chemical fingerprint that could
soon help to solve crimes as diverse as kidnapping, counterfeiting and fraud,
say Australian researchers.

Crime investigations sometimes hinge on identifying the source of paper used
for a ransom note, say, or to alter a business contract. But standard forensic
methods often fail to do this with white office paper, which is the commonest
type.

Now John Byrne of the University of Technology in Sydney and Lindsay Spence
of the Queensland Police Service in Brisbane have come up with a rapid way of
telling different white papers apart, using mass spectrometry to measure the
trace elements they contain.

鈥淚t鈥檚 only a small study, but they have an exceptionally high level of
discrimination,鈥� says forensic scientist Chris Lennard of the Australian Federal
Police in Canberra. Normally, a forensic scientist who wants to match two sheets
of paper has to examine their fibre structures under a microscope, or study the
thickness or colour. But this often doesn鈥檛 work with white paper.

The trace-element technique could be used to link paper made into counterfeit
banknotes with the paper found in a suspect鈥檚 home, or to spot when a page has
been inserted fraudulently into a will or other document.

Byrne and his colleagues tested for 23 elements in samples of 17 different
papers from around the world. They were able to reliably measure nine of these
elements, and found that they only required two of them鈥攎anganese and
strontium, measured to 60 parts per billion鈥攖o identify each paper type.
All nine, they say, should be enough to distinguish between hundreds of
different types of paper.

Trace-element analysis has already been used to fingerprint gunshot residues,
gold and paint. 鈥淓verything has got half the periodic table in it at some low
level,鈥� says Byrne. 鈥淭his technique has good long-term applications to a variety
of substances.鈥�

Byrne and his colleagues also showed that handling the paper or printing on
it didn鈥檛 upset the test. But Spence warns that more potential contaminants will
have to be tested before the technique can be used in a crime investigation. 鈥淎
piece of paper can have orange juice spilt on it, be dropped on the floor,
stored in dusty cabinets,鈥� he points out. Certain chemicals used to collect
human fingerprints might also affect the accuracy of the result.