Slowing-down length

While 8 is somewhat greater than 1, both p and / are somewhat smaller than 1. Therefore, for approximate calculations, epf can be set 1. The fission factor rj varies appreciably with the energy of the neutrons, as shown in Fig. 11.4 for The neutron losses in a reactor of finite dimensions can be taken into account approximately by the sum L +1 , where Ls is the mean slowing-down length of the fission neutrons in the moderator and L the mean diffusion length in the fuel-moderator mixture. For a spherical reactor of radius R the approximate relation is... 

The linear dependence of the average r u) on r u) is a general result. The constant of proportionality is determined by the source distribution. Thus, in general, the square root of the Fermi age is a measure of the slowing-down length of a neutron. 

Substance Moderating ratio Average slowing down length from fast to thermal (cm)... 

Slowing down length and diffusion length increase. Thermal non leakage, fast non leakage, and resonance escape probabilities decrease. As a secondary effect, rod worth increases. 

Slowing-down length is proportional to the straight-line distance that a neutron covers between the time it is emitted from the source at high energy to the time it reaches a much lower energy (Ellis et al., 2003). 

Slowing-down length and diffusion length are inversely proportional to the corresponding cross sections. 

At small driving forces a completely fiat interface cannot move at a constant speed. This is basically a result of the inherent scaling property of the diffusion equation, which scales lengths proportional to the square-root of time, so an advancing interface would slow down with time. 

Rouse behavior observed on PI homopolymer melts has to be modified if the labelled (protonated) PI species are replaced by diblock copolymers of proto-nated PI and deuterated polystyrene (PS) [46]. The characteristic frequency Q(Q) is slowed down considerably due to the presence of the non-vanishing X-parameter. Thus, the reduction is stronger at smaller Q-values or at larger length scales than in the opposite case. In addition, as a minor effect, Q(Q) becomes dependent on both friction coefficients per mean square monomer length, //2, valid for PI and for PS. 

Sometimes, extra chemicals are added to the main chemical as stabilizers. For example, formaldehyde is too reactive in its pure state to exist as formaldehyde for any length of time. It will dimerize or polymerize on standing. Formaldehyde is normally sold as a 40 vol% solution in water, with a methanol stabilizer (12 vol%) to slow down the polymerization. 

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