Talk:Spallation
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What is the advantage of a neutron beam can be pulsed with relative ease?--Anthony Duff 01:18, 8 February 2006 (UTC)
I'm not a nuclear or accelerator physicist, but it is my impression that the advantage is "high time resolution" in regards to the products of the downstream nuclear reaction for which the beam is intended. At low to moderate energies, many of the products of a nuclear reaction (e.g. ones initiated by neutrons in the beam) will move at nonrelativistic speeds, i.e. speeds not close to that of light. Therefore, by clocking the time between a burst (pulse) of neutrons is known to have hit the target, and the time at which a counter records a reaction product, the speed of that product particle can be calculated and thus its energy. In fact, the very identification (determining what kind of particle it is) of detected reaction product may depend on its speed. For highly relativistic energies this will not work because all the products will travel at nearly the speed of light. At slower speeds, the energy :
can be found from the velocity v, but as v-> c the necessary accuracy that would be required in measuring v, to get a reliable value for E is impractical. Yet, there is a lot of nuclear physics that can be done at lower energies, where v reliably determines E. I am having trouble finding a simply described experiment using this method, but on [1] you can see they sell detectors for use in it. (Item D).
According to this paper: [2], time-of-flight techniques can also reduce background. This application is simpler than the one I just gave. One uses the time of flight of the neutron bursts themselves to determine when they hit the target. The observations are then made in a narrow time-window based on that "hit" time, so extraneous counts (e.g. from cosmic rays or local natural radioactivity can be reduced.
This paper: [3] deals with using the time of flight of the neutrons themselves to determine their energy. Carrionluggage 03:30, 8 February 2006 (UTC)
[edit] Overhaul needed
Spallation is a much more general term than nuclear spallation alone. I have updated the introductory paragraph to reflect this; but additional sections are needed to describe impact spallation and other processes. Some nice figures (e.g. of spalled impact sites such as meteor craters and spacecraft surfaces) would be helpful too. No time just now but I'll make an effort over the coming days/weeks to add at least something. zowie 17:05, 14 March 2006 (UTC)
