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Gold/Mining/Energy : A New Age In Gold Refining -- Ignore unavailable to you. Want to Upgrade?

To: Chuck Bleakney who wrote (451)	1/16/1998 2:21:00 PM
From: Bill Jackson	Read Replies (1) \| Respond to of 672

To: +Bill Jackson (445 ) From: +Chuck Bleakney Friday, Jan 16 1998 1:13PM EST Reply # of 451 >> Neutron activation assay will get all elements that will add neutrns to give a radioisotope, and gold and plat do that. << Not entirely true... Neutron activation works by the absorbtion of a neutron by a substance turning it into another isotope of that substance... Whether or not a substance will absorb that neutron depends upon a number of factors. If a strong absorber is present and effectively shields another element then the likelihood of activating that element is greatly diminished... this would give very skewed results in a standard neutron activation analysis. # qualifying tests are done to see qualitatively if strong absorbers are present, and if so the exposure is increased to compensate or the absorbers are removed by pretreatments. Elements have very different absorbtions depending upon the energy of the free neutrons. Most activation analysis is done with "thermal" neutrons. These are neutrons that have been slowed down by interactions with lighter elements (H,C,He, etc) until they are in equilibrium with the average thermal velocities of these elements. # usually a huge over excess of neutrons is provided to drive the absorption to some degree of steady state for the elements sought. Fast neutrons from reactors are harder to get, and the better assays cos arrange for their samples to be shipped and irradiated and returned for assays in a timely manner. Some places have their own irradiation on site, but these are rare. Usually LLNL or some such place that can do it has them jobbed in. Fast fluxes are harder to get and control but can allow one to do things you can't with a thermal flux because of how the absorbtion changes with the average energy of the flux. The bottom line is that Mike's comment about a cluster trapped inside not being able to be activated as it usually would be expected to by neutron activation is correct when the trapping element has a very high cross section for absorbtion. # these high absorption elements are known and the samples are pretested by chemical methods to see if those elements are present and liable to interfere. If so they are removed chemically. If you haven't already figured this I have a significant understanding in nuclear theory... this is required of anyone who has held a license to operate a nuclear reactor. I've done more than my share of neutron activation analysis's. Chuck Any assay procedure works fine on an optimal sample. It is the presence of interfering elements that challenge the labs. Mass spec can also be used to find interfering elements after they have been placed into an averaging mass state(such as a nickel sulfide pellet), a smallamount can be mass specced and the weights of all elements found and screened for interferers. I would like to think there is a huge mass of Plat/gold shielded in some way and I find it?? Bill