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- Path: sparky!uunet!gatech!mailer.cc.fsu.edu!sun13!ds8.scri.fsu.edu!jac
- From: jac@ds8.scri.fsu.edu (Jim Carr)
- Newsgroups: sci.physics.fusion
- Subject: Re: A stupid question about reaction cross-section, etc.
- Message-ID: <10043@sun13.scri.fsu.edu>
- Date: 31 Jul 92 14:01:54 GMT
- References: <6879@charon.cwi.nl>
- Sender: news@sun13.scri.fsu.edu
- Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
- Organization: SCRI, Florida State University
- Lines: 35
-
- In article <6879@charon.cwi.nl> jack@cwi.nl (Jack Jansen) writes:
- >The discussions on this group have long gone past the point where my
- >physics education went, so this is probably a stupid question, but
- >here goes anyway: I keep hearing about the reaction cross-section; is
- >this a number that rolls out of theory or is this an experimental
- >result?
-
- Both. The great triumphs of nuclear physics are when the two agree to
- better than a few percent. In general terms, cross sections at low
- energy have been measured in excruciating detail and cross sections
- for the basic n+p system have been measured very carefully at a wide
- range of energies. In addition, spin-dependent observables (where
- either the projectile or target or both are polarized and/or the spin
- of the ejectile or recoil or both are measured) have also been measured
- for the n+p system with excellent precision, providing the basis to
- calculate many things of relevance to the d+d system with confidence.
-
- The biggest weakness in the theoretical results for d+d is that no one
- bothered to calculate anything since about 1956 since the results seemed
- uninteresting and outside the possibility of being measured. The FPH
- claims changed *that* in a hurry!
-
- >The reason I ask is the following: if it is experimental, would it be
- >possible that the real chance of two deuterons fusing is actually a
- >lot bigger than we think, only that usually the end result of the
- >reaction is again two deuterons? ...
-
- This would not be fusion and would give no energy: d+d --> d+d has the
- same mass in the final state, hence no energy released.
-
- --
- J. A. Carr | "The New Frontier of which I
- jac@gw.scri.fsu.edu | speak is not a set of promises
- Florida State University B-186 | -- it is a set of challenges."
- Supercomputer Computations Research Institute | John F. Kennedy (15 July 60)
-