Newsgroups: sci.astro,sci.space.policy,sci.space.history,alt.thebird
From: henry@spsystems.net (Henry Spencer)
Subject: Re: [CASSINI] Re: A note from "Pro-Space"
Date: Sun, 1 Nov 1998 16:31:35 GMT

In article <71g2me$cnq$1@nntp.Stanford.EDU>,
Jonathan Stone <jonathan@DSG.Stanford.EDU> wrote:
>...I keep hearing that they use steel salvaged from
>second world war ships for NMR imaging, to avoid the rise in
>background radiation due to atmospheric nuclear tests;
>but that may well be an urban legend.

Yes and no.

For NMR it doesn't make any difference (to the best of my knowledge; it's
not equipment I know a lot about) because NMR does not use ionizing
radiation at all.

Where low radiation background does become important is for precision
radiation measurement, e.g. for research work that does use isotope
tracers.  For *that* application, there has indeed been considerable
interest in things like pre-1945 battleship armor plate, to try to
minimize trace radioisotopes in shielding.  Actually, probably the
ultimate in low-radiation shielding was when a European physics-research
group paid for the salvage of a sunken Roman trading vessel by
archaeologists, in exchange for 80% of its cargo of lead... lead which not
only was smelted before nuclear weapons, but which had also been shielded
from cosmic rays by 50m or so of water for nearly two millennia.
--
Mass-market software technology has |  Henry Spencer   henry@spsystems.net
been deteriorating, not improving.  |      (aka henry@zoo.toronto.edu)