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Nuclear reactors are capable of delivering a large amount of neutrons to a sample. Typically we refer to this as "activation," but in general, we are delivering neutron radiation. Neutron radiation can include a lot of different things: Neutron Radiations Near the reactor, there is a huge gamma flux in addition to the neutron flux. Some of these gammas come directly from fission, while others come from decay products of fission. This mixed field is the most common form of irradiation we do. This means most of the samples we irradiate are resistant to damage from gamma radiation and the heat they generate when they interact with matter. Some researchers wish to expose material to a mixed field with a higher ratio of neutron fields to gamma fields. Placing a gamma shield (lead) between the reactor and the sample stops most of the gamma radiation with little effect on the neutrons. We have a large irradiation cell to accept almost any size sample. Past users include the Texas A&M Cyclotron Institute, which used the fields for radiation-testing components. Mixed neutrons for activation
Fission provides neutrons of various energies. Often these energies have different uses. For example, thermal (slow or low-energy) neutrons are best for activation since most elements prefer absorbing slow neutrons. In the reactor flux, there are more thermal neutrons than fast, so we can use this flux for most activations. The primary users for mixed neutron activation are
Pure thermal field The NSC has a heavy water box that will provide a higher thermal-to-fast neutron ratio than otherwise exists. This is a labor-intensive process that hasn’t been used for several years. Fast Neutron Flux For some jobs such as argon dating and gemstone irradiation, fast neutrons are preferable to slow neutrons. For these jobs, the NSC has devices that filter out the thermal neutrons leaving just the fast neutrons. Users include geophysics departments at New Mexico Tech, the University of Minnesota and the University of Nevada-Las Vegas. Gamma Irradiations The NSC can use the reactor to provide a multi-energetic gamma field at fairly high rates. We can sustain 2 MRad/hr neutron-free field and use the shutdown reactor as a source of neutron-free gammas at lower levels. Users include
Lanthanum Source The NSC has a large lanthanum (La) source that can provide a different energy spectrum than the reactor at lower levels. Fission Product Irradiation One company uses fission products to make micro-pore filters –– filters that are made after bombarding high-density plastic with massive nuclei and then undergoing an acid-etching process, which leaves microscopic holes in the plastic. Micropore filters are used to filter bacteria in food-manufacturing processes; to filter bloodworms in veterinary medicine; and as cell filters in cancer detection and identification. Other Services The NSC provides a place where researchers and industry partners can conduct a variety of experiments with radioactive materials –– ideal for organizations without the expertise or licenses necessary to handle and posses these materials. Previous users include various departments at Texas A&M and several private research institutions. Neutron Activation Analysis The NSC, individually or with the Center for Chemical Characterization and Analysis, uses neutron activation analysis to identify trace metals in various materials. Previous users include:
Radioassay The NSC houses a multi-million dollar counting lab with five high-purity germanium detectors. This lab gives us the ability to detect and identify extremely small amounts of radioactive material, ideal for various applications. |
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