Emissions from embedded sources

Illustration 2.9 Laplace s Equation, Steady-State Diffusion in Three-Dimensional Space Emissions from Embedded Sources... 

The whole unit is accommodated in a fume cupboard fitted with a scrubber unit to remove the acidic fumes before emission to the atmosphere. The constructional materials of the fume cupboard should be able to withstand the heat radiated from the hotplate and heating blocks. A digestion tube containing a 350°C thermometer with the bulb embedded in a 2-cm layer of sand occupies one hole in each block. The hotplate can be connected to the power source via a time-switch, which can be set to come on approximately 1 hour before commencement of work this saves valuable time lost waiting for it to warm up. 

For the absorption process, the same conservation law should be satisfied. For the transition Eq — 14.4 keV in Fe, / is 1.9 X 10 eV which is 10 times large compared to the natural line width of the excited state and no resonance between source and absorber for the free nucleus can be expected. When the nucleus is bounded into the solid, the recoil energy can be dispersed by the excitation of the solid. When the source and absorber are the nuclei embedded into the solid, recoil energy R may be used for the excitation of phonon that is the vibration state of sohd. Phonon is quantized as discrete value in solid and in usual metals the excitation energy of phonon states is the order of 10 -10 eV and there is rather large probability to have a zero phonon excitation in emission and absorption process in other word, the recoilless emission and recoilless resonant absorption of photon. This is the most important characteristic feature of the Mossbauer effect. As a consequence, the y photon emitted by the decay from the first excited state that has a... 

In conventional Mossbauer spectroscopy one uses a single-line source, e.g. Co embedded in a rhodium matrix in the case of Fe spectroscopy, and the iron containing material under study as absorber. This technique is termed Mossbauer Absorption Spectroscopy (MAS) in order to distinguish it from the so-called source experiment, also known as Mossbauer Emission Spectroscopy (MES). In a MES... 

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