"The pulsed source technique consists of introducing repeated short bursts of neutrons into a subcritical assembly, and following the decay of the leakage flux as a function of time...It is noted that plotting the decay constant as a function of buckling gives an apparently accurate way to extrapolate to prompt critical. The pulsed source technique can also be used to calibrate control rod and poison worth, and will give some estimate of the prompt neutron lifetime."

Abstract. Monte Carlo methods using importance sampling and splitting are proposed for estimating the effectiveness of neutron shields. As usual, the aim is to increase the number of particles that go through or around the shield, this increase being compensated by a decrease in the weights of these particles. With suitable modifications, the ideas are applicable to to other Monte Carlo problems. One way of using splitting and Russian roulette is to require that the weight of each particle be approximately equal to a specified function of the coordinate; one such function is given in equation. The proposed form of importance sampling uses a cross-section for particle collisions that is the product of the neutron cross-section (or its square root) with a linear function of the cosine of the angle between the particle direction and some preferred direction. The probability density of this cosine itself is taken proportional to the reciprocal of this same linear function. This function is adjustable on both a regional and an overall basis.

From abstract: " The interaction of positive K mesons having energies between 20 to 220 Mev with the nuclei of photographic emulsion has been investigated."