Neutron source thermal reactor

The name NESTOR (neutron source thermal reactor) was chosen because in Greek mythology Nestor was one of the Argonauts led by Jason in the quest for the Golden Fleece. 

TNA PRO AB 16 961. Neutron Source Thermal Reactor NESTOR. See also TNA PRO AB 17/102. NESTOR, Neutron Source Thermal Reactor. TNA PRO AB 6/2312. Atomic Energy Establishment, Winfrith NESTOR (JASON type) neutron source reactor. TNA PRO AB 17/302. Reactors UK. 

This reaction offers the advantage of a superior neutron yield of in a thermal reactor system. The abiHty to breed fissile from naturally occurring Th allows the world s thorium reserves to be added to its uranium reserves as a potential source of fission power. However, the Th/ U cycle is unlikely to be developed in the 1990s owing both to the more advanced state of the / Pu cycle and to the avadabiHty of uranium. Thorium is also used in the production of the cx-emitting radiotherapeutic agent, Bi, via the production of Th and subsequent decay through Ac (20). 

Beryllium has a high x-ray permeabiUty approximately seventeen times greater than that of aluminum. Natural beryUium contains 100% of the Be isotope. The principal isotopes and respective half-life are Be, 0.4 s Be, 53 d Be, 10 5 Be, stable Be, 2.5 x 10 yr. Beryllium can serve as a neutron source through either the (Oi,n) or (n,2n) reactions. Beryllium has alow (9 x 10 ° m°) absorption cross-section and a high (6 x 10 ° m°) scatter cross-section for thermal neutrons making it useful as a moderator and reflector in nuclear reactors (qv). Such appHcation has been limited, however, because of gas-producing reactions and the reactivity of beryUium toward high temperature water. 

Vulpis (1973) added pure natural boron as H3B03, which contains about 19% B-10, to the blood culture. It was then irradiated with thermal neutrons from a reactor. The reaction of B-10(n,a)Li-7 within the culture served as alpha source. The dose range was 35 to 195 mGy according to her dose estimation which was complicated by subtracting the dose due to the reactor radiation alone. The dicentric chromosomes appeared to follow a linear response up to about 0.18 Gy and then leveled off to a plateau due to a "saturation effect. The relative biological efficiency (RBE) with respect to X-rays with the doses up to 5f1 Gy was found to be 23. v... 

The thermal neutron sources are radioactive isotopes which emit neutrons, acclerators, and nuclear reactors. The neutrons from the sources are moderated with materials such as paraffin, graphite, water, heavy water or beryllium. Some of the radioisotopes used as sources of thermal neutrons are antimony, polonium, americium curium and californium. The various sources have different half-lives, ranging from days to years. 

There are two types of neutron sources available for powder diffraction. One is the nuclear reactor, which provides a monochromatic beam of wavelength 1.0 A, selected by means of a crystal monochromator from the continuous wavelength spectrum of thermalized neutrons [481. The diffraction experiment uses the Bragg method as in X-ray single crystal diffractometry. 

For the thermal neutron activations, a lOmg Californium-252 ( Cf) source was utilized in a special assembly constructed from a Neutron Howitzer (Trademark of Reactor Experiments, Inc). The assembly is a 6-cu ft cylindrical Lucite tank filled with distilled water and containing three access ports (Fig 3). The large spherical container on the right is the shielded storage cask for the Cf neutron source when not in use... 

There are several types of neutron sources one can use for NAA, but megawatt nuclear reactors with their intense flux of 10 to 10 neutrons m s from uranium fission, offer the highest available sensitivities for most elements. Neutron energy distribution is quite broad, but for conventional NAA, low-energy neutrons (energies below 0.5 eV) are chosen that represent 90—95 per cent of the neutron flux. Sufficient levels of activation are reached in a few minutes, even if the isotope formed has a long half-life. The procedure imposes that the sample to be treated must be thermally stable. It is enclosed in a tube with a comparator standard of known concentration, before being introduced in a reactor beam port. 

Neutron sources include nuclear reactors, accelerators, and isotopic sources. Nuclear reactors are, by far, the most frequently used irradiation facilities. They provide high fluxes [upper limit 10 neutrons/(m s)] of mostly thermal neutrons E < I eV). Fast neutrons in the keV range are also available, but at lower flux levels. 

Nuclear reactors are the most common source of neutrons. Inside the reactor, a sustained nuclear reaction of fissile material produces fast neutrons. When is used as the reactor fuel, 2-3 MeV neutrons are produced, along with other neutrons at other energy ranges. A neutron moderator slows the fast neutrons to reduce their energies to the thermal level. This is required to continue the chain reaction by further absorption of neutrons by surrounding atoms of Other neutron energy ranges are the epithermal between 0.1 and 1 eV and resonances between 1 eV and 1 keV. 

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