Slowing-down time

In positronium forming materials without optical phonons much longer Ps slowing-down times should be found. This may be tested by AMOC measurements in solid rare gases, crystallizing in the face centered cubic (fee) structure which, being a Bravais lattice, does not have optical phonon branches. 

The lineshape function 5 (t) of solid Neon (Figure 14.8) shows a maximum similar to PIB (Figure 14.6). The slowing-down times rth according to the two state model analysis are in the range of 20 ps to 40 ps [3, 4, 11] and thus are similar to Ah in materials with optical phonons. The process responsible for the shorter slowing-down times in Ne is not yet fully understood and requires further study. 

How does one stabilize the colloid suspension and slow down time-dependent changes in its state of dispersion, or, alternatively, measure the SERS fast enough ... 

At is the uncertainty in neutron slowing-down time if the source is surrounded by a moderator. 

The slowing down time must be very short compared to the mean life of the muon. Again this condition is well satisfied, the time span to achieve thermalization being loops or less in condensed matter. 

To compute the time required to slow down from w = 0 to w = w h we need only to sum the slowing-down times through all the intervals along the way. Then, if we call Ip the average time required to slow down to thermal, we have... 

In comparison to (9.22) it may be seen that in this approximation the effect of including the time-dependent behavior in the fast range is to add the average slowing-down time to the average thermal lifetime. 

The frame rate does not speed up or slow down time, only how it is measured. These are all various standards that have been used for different purposes over the years. For example, movies are twenty-four frames per second (fps), while color television in the United States is 29.97 fps. In audio, 30 fps is probably the most frequently used standard. More important than which particular standard you choose is that both of your devices (ACID and the other application) are using the same standard. MTC and other relevant timecodes are measured in hours, minutes, seconds, and frames (hh mm ss ff), with the number of frames in a second being the only difference. 

An important quantity in reactor kinetics is neutron lifetime, l, the average time between the release of a neutron in a fission reaction and its loss from the system by absorption or escape. For convenience of calculation, the lifetime in a thermal reactor may be divided into two parts (a) slowing down time, the mean time required for fission neutrons to slow down to thermal energies, and (b) diffusion time, the average time that thermal neutrons diffuse before being lost in some way. Table 3.6 provides values of these parameters for several different media. 

Generation time is the time between succeeding neutron generations and is the sum of fission time, slowing down time, and diffusion time. 

Lifetime = Slowing Down Time + Diffusion Time - 7. IxiO + 2.4xi0 sec = 2.47x10" sec Ji 1x1 C)- sec... 

Moderator 1/mfp 2,(cra"0 Slowing Down Time (sec) Diffusion Time (sec)... 

Hence, this approximation ignores the link between the energy changes and momentum (directional) changes induced by collisions. The slowing-down time of a positron from an initial energy E to a final energy E is... 

For a positron slowing-down time of Ir to an energy E -C Equation 4.44 yields... 

The resulting thermal-neutron population will rise to some maximum value. The time of rise depends on the average slowing-down time of the source neutrons and the time width of the neutron burst. This statement is true only if the slowing time of the medium is smaller than the diffusion time (thermal-neutron lifetime). 

If a burst of fast neutrons impinges on a moderating medium, the slowing-down time ( 10" sec) is very short compared with the diffusion time ( 10" -10 sec). Thus thermal neutrons are produced so rapidly by the slowing-down process that the time effect is much the same as if a burst of thermal neutrons had been received by the medium. The application of such a pulse of thermal neutrons will excite the fundamental and higher modes in the medium, the specific modes and their amplitudes being determined by the geometry of the experiment. 

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