Just to add to david's note. The technology has moved on somewhat and several firms now market truely hand-held XRF instruments using an X-ray tube and running off rechargable batteries. I've tested a couple of these and was impressed - For example, getting a visible the mercury "shoulder" on the Au peak for traces of firegilding on armour - something that our old Kevex instrument struggled with. Of course the usual cautions about air gaps and unprepared surfaces apply and the area of excitation is large at c 1cm dia (this can be reduced with colimators but with major reduction in counts and a difficulty in targetting small areas of interest). Another possible problem is that I believe they use an Ag target and I don't know how reliably this silver in the material under investigation can be quantified.
Dave
David Starley PhD
Science Officer
Royal Armouries Museum
Conservation Department
Armouries Drive
Leeds LS10 1LT
United Kingdom
Tel. 0044 (0)113 220 1919
Fax 0044 (0)113 220 1917
-----Original Message-----
From: Arch-Metals Group [mailto:[log in to unmask]]On Behalf Of
david killick
Sent: 17 September 2005 18:35
To: [log in to unmask]
Subject: Re: Handheld XRF
Our conservation department here has one of these, and I've made some
use of it. There are two types - the genuinely portable ones with
radioactive sources for excitation, and the semiportable types that
have a miniature x-ray tube and need to be plugged in to the mains or a
portable power supply. The one I've used has the radioactive source,
and I doubt that I would bother to buy one if I had $25,000 lying
around, which I don't. All handheld XRFs have an air gap between sample
and detector that absorbs weak x-rays, and thus can't detect anything
of lower atomic number than sodium, but there are additional
limitations with radioactive sources. None of them cover the whole
range of elements that I would want in analyzing slags, so one would
have to change sources to get a full listing of elements in the sample.
(The americium source is the most common, and will only give you
elements with atomic numbers from titanium up; from titanium down the
iron sources is used. The sources only last a few years, and are very
expensive to replace. Being radioactive, they are also a real pain as
far as permits are concerned - perhaps not a concern if only used in
Britain, but taking one abroad would require all sorts of permits.
Our conservation department make a lot of use of this instrument in
collections management - for example, it's a quick way of finding out
if older biological specimens have been conserved with arsenic. But I
frankly would not spend such a large amount for an instrument to be
used in the field. You can put together a little collection of field
tools for archaeometallurgy - an acid bottle, a charcoal block and
blowpipe, a short length of platinum wire, a few chemicals, a miniature
propane torch, a scratch plate, a magnet, a hand lens, a small short-
and long-wave UV lamp, and a copy of an old text (pre-1960's) on
determinative mineralogy (to tell you how to make effective use of the
first four items listed) for about $250. These will identify the major
elements in most samples that you will encounter in the field at
minimal cost.
Dave Killick
On Sep 16, 2005, at 4:38 PM, Evelyne Godfrey wrote:
> Dear All,
>
> I seem to recall messages about portable handheld XRF meters on this
> List
> some time ago... could someone remind me of what the bottom line was,
> in
> terms of cost, usefulness, whether there was one type more recommended
> than
> another? We're analysing archaeological and museum artefacts, and
> historic
> architectural samples of different materials, although primarily metal.
>
> Cheers,
> Evelyne
>
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