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DYNAMIC NUCLEAR REACTION MODELS THOMAS E. VAN DAM, P. HOLLOWAY, LAWRENCE SHAPIRO, and RAYMOND HECTOR University of Dlinois, Chicago, Illinois
ATA N annual open house of thc University
of Illinois at Chicago, t,lre department of physical sciences exhibited to lay people two dynamic models illustrating nuclear chain reactions. Initially a unique mouse trap model illustrated controlled and uncontrolled multinuclear reactions while a model of an atomic pile portrayed the practical use of t,he controlled nuclear reaction. The mouse trap model consists of several mouse traps so arranged and modified that the firing of one trap initiates the firing of one or two other traps, each of which is responsible for successive firings. The actual firing mechanism is a cork ball attached to the release levers of the traps; as the first trap is released, the released spring causes the lever and connected ball to swing back. I t is this ball which sets off the second succession of traps. These secondary traps must be so interlocked as to achieve proximity of their releasesallowing both to be set off by the initiating t,rap. Incisions are consequently made on the wooden base of the traps; these incisions-of two types-are illustrated for 90" and 120' divergencies in Figure 1. The placement of these arrangements within the model is shown. The multiplication effect increases through two, four, and eight traps-along eight separate paths.. Only one of these eight is designed for continuance. It is of value to examine the parallelism between the model and the actual mechanism of chain reactions. ~h~ spring simulates the energy of the splitting nuclei
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r i m 2. Model of Atomic Pile
and also imparts enerffy to the cork balls. These cork balls then in effect become fission neutrons. The absorption of neutrons is illustrated by the seven dead paths, and the continuing eighth path with its several dead subpaths as multiplication is averted. The preparation of the traps and balls is evident from the figure. A flexible base to absorb shock (weatherboard), tmo bolts per trap, and appropriate paint mill tend to increase the effectiveness and life of the model. An additional refinement of loosening the trap springs will result in diminished striking force of the trap, and wear on the cork balls, releases, and lever arms is greatly lessened. This model is easier to construct than that of Slabaugh.' I t also permits faster (4 minutes) and more frequent loading, and illustrates both branched and unbranched nuclear reaction chains. The atomic pile is constructed from scrap lumber and standard electrical equipment. A wooden cube, partially cut away, is the primary step of construction. This cube (a bottom face is unnecessary) is made t o resemble a concrete shell hy the a ~ ~ l i c a t i oof n a suitable stucco-like ~ a i n t(Serotex grand). An insert cube to this shell is made of scored
' SI.ABAU(:~, W. H., J. Cnam. EDTTC., 25, 679 (1948).
~ odd P of NU&^ chain fission ~aastion
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(by sawing) and flat black painted stock to simulate the carbon moderator blocks. This insert needs no bottom or back faces. Sections of aluminum painted doweling are inserted into drilled depressions on the face of this inner box. At least one dowel should be lengthy and actually inserted into the model. A centrally placed section of small bore doweling represents the entrance for chemicals to be irradiated in the center of the pile. Glass tubing filled with colored liquid and attached t,hrough t,he concrete shield suggests the cooling and heat transfer system of the pile.
JOURNAL OF CHEMICAL EDUCATION
The general nature and importance of the cadmium control rods for real-life pile operation is illustrated by the following electrical feature. A ring stand steel rod, employed as the control rod, may be lowered or raised through the core of an assembly of choke coils, with the concomitant change of current impedance affecting the brightness of a glowing light bulb and the deflection of an ammeter needle. Wired in series with the choke coils the lowering of the rod reduces the intensity of the light bulb and meter reading, simulating neut,ron absorpt,ion and decrease of power of the pile.
