The chronology of PT/35(b): 28/02/1992

28 February 1992 (Wilkinson – see also 2 March 1990)

According to their HOLMES statements, McAdam and Buwert went to the Wolfson
Centre and met Dr Rosemary Wilkinson by prior arrangement, and she attempted to
examine the whole of DP/347(a) in her scanning electron microscope but due to
technical difficulties this proved impossible, and she was authorised to remove a
sample from the circuit board at a place previously agreed with the fiscal depute. The
corner section was then removed (DP/494, Crown label 411) and put in the scanning
electron microscope.

At the conclusion of the tests Dr Wilkinson produced DP/495 (production 354), a computer disk containing plots of x-ray spectra and data sheet,and she also provided a roll of film containing photographic evidence of her findings, which were detailed in her statement S5579A.

MST13_BOARD

The police report records that Dr Wilkinson was of the opinion that the surface of
DP/347(a) was different from the surface of PT/35(b). She qualified this opinion by
saying that lead, which had a low boiling point, had been lost selectively if PT/35(b)
had suffered flash burning as a result of blast.

Dr Wilkinson’s manuscript statement (prod 364) records that the surface of the new
sample looked different from the fragment.

The fragment’s surface had contained bright “crystallites” 1/2 to 2 microns in diameter, but no such structure was present on DP/494, which contained bright and dark areas 5 to 15 microns in diameter which after analysis were associated with a lead rich metal for the bright areas and a tin rich metal for the dark areas.

No copper was found except at the edge exposed by the cutting of the sample. Dr Wilkinson suggested that this was because in DP/494 had a greater thickness of tin/lead metal covering the copper. She stated that, since the original fragment had been recovered from the scene of an explosion, it was possible that the coating material had been lost in the course of the explosion and that lead, which has a low boiling point, had been lost selectively but she said that this hypothesis should be tested by experiment.

In her CP Dr Wilkinson stated that, on examining the results (DP/495) of her testing
of the piece cut from DP/347(a), in the main areas of the sample tested, no significant
copper could be seen on any spectrum, although copper was noted at the edge cut
kom the sample, where it had been exposed. She stated that this indicated that there
was a consistent, thick layer of tin and lead across the copper base, which you would
expect when the board left the manufacturer. She stated that this supported the theory
she had about PT/35(b) that it had suffered a “loss” of tin and lead, thus exposing the
copper structure below. She was referred to DP/20, photos 1 and 2, which she
identified as photographs of the copper track area of PT/35(b). She had previously
described how these photos depicted patterns of crystals that demonstrated the
presence of copper oxide. She stated that DP/511 (which are not mentioned in her
police statement but which are, according to the police label she signed, photos and a
data sheet taken by her on 28 February 92) are images taken by the scanning electron
microscope. She stated that these images were of the pad area of DP/347(a), whereas
DP/20 was of the copper track area of PT/35(b), and she stated that “Accordingly, the
comments which I have made in my second Police statement in relation to “crystallites” are not appropriate.”

She stated that she would be happy to testify about the tests she carried out and the results, but that she did not believe she was qualified to comment on the reasons why PT/35(b) was in the condition it was in, as any such comments would be entirely speculative.

In her DP Dr Wilkinson referred to the return visit by police in 1992 and said that she
had been asked by them whether the control sample they had brought was the same as
the original sample she had examined, and that all she could say to them was that it
confirmed her original analysis “that the first sample was not a virgin sample”. She
said that one thing it did indicate was that the levels of solder were smooth and level
on the control sample, which was not the case with the original sample. In a note
relating to her comments, it is recorded by the defence to be of interest that she
thought the original fragment did not appear to be explosion damaged and that she did
not count for much given that she is not an expert in the field. She was reprecognosced
by the defence and re-stated that she saw differences between the fragment and the control sample, the latter very clearly showing itself to be a 2 phase alloy of bright and dark bits, being lead and tin, whereas this was not obvious from the fragment.

When asked to clarify why she said the first sample was different from
the second, she said “The first sample was not pristine. It was dirty in the electrical
sense. I spent a long time looking at the second sample – I had the photographs of the
first sample – but not the sample itself. The first sample was difficult it had bits on it
– it had been used – The copper in the second sample was less obvious – which
probably suggests the copper was thinner or the solder layer was thinner [sic – this
should possibly have read thicker].”

Dr Wilkinson did not give evidence. The defence considered calling Dr Wilkinson
because of her comments that she could not see any particles that might be indicative
of explosion damage, but in a filenote it is recorded that the defence felt it potentially
dangerous to call her, given her self-professed lack of expertise.

Comparison between control sample and fragment: on the fragment Dr Wilkinson
could find no trace of lead on the copper track she tested, only copper and tin, it
appears that the sample from DP/347(a) that she tested, DP/494, only contained an
area from the land and did not contain any sample from the copper tracks, hence her
comment in her CP that it had not been appropriate for her to say in her 1992 police
statement that the control sample did not have the crystallites – she had not tested the
corresponding area. She did find quite uniform tin and lead on the land of the control
sample but no copper, which was different from the fragment, where she found traces
of all three in differing proportions. She accepted herself that this could be accounted
for by the fragment losing some tin and lead, perhaps by partial melting, to expose the
copper below.

NB Wilkinson’s signature is visible on the label for DP/347(a).

 

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