Thermal swing absorption

Assessment of Thermal Swing Absorption Alternatives for Producing Oxygen Enriched Combustion Air, Report no. DOE/CE-040762T-H1, U.S. Department of Energy, Washington, D.C., April 1990. 

Answer The most important fission product to reactor operation is xenon-135 because of its large absorption cross-section - about 3.2 x 10 barns - for thermal neutrons. The effects of the xenon poison transients influence reactor operation in many ways. For example, although the saturated poison effect at equilibrium operation may cause a reactivity loss of 2 to 2-l/2 k (2000-2500 c-mk) in the usual power ranges, the decay of this amount of poison in the shutdown pile will represent a total swing of 4000 to 5000 c-mk from the initial xenon-free pile at startup. This delayed action effect in xenon formation and decay is the major cause for the scram transient, minimum downtime, and turnaround problems encountered in the operation of a hi power reactor. A detailed discussion on the effects of xenon poisoning on pile reactivity may be found in Chapter IV of this series. 

As mentioned above, the first radio detection of a comet was that of the 18-cm OH line. The study of this line has been an important component of cometary research for over 25 years. The 18-cm line is split into four transitions at 1612, 1665, 1667, and 1721 MHz. The observed intensity of the OH line is quite variable. The line is seen in emission or absorption depending on the comet s heliocentric velocity. The explanation of this effect is that it is due to pumping of the OH molecules by solar UV photons. If the comet s heliocentric velocity is such that Fraunhofer absorption lines from the Sun shift into the excitation frequency, the OH molecules are not excited. At all other times they are. This variation in excitation is known as the Swings effect. When OH is not excited, it is seen in absorption against the galactic background. If it is excited, the emission is actually maser emission rather than simple thermal emission. 

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