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Critical Assembly Simulator v.1.1

by Alex Wellerstein, 2015

The red atoms split when hit by neutrons (fission). The blue atoms absorb the neutrons. Can you get all of the red atoms to split? Click on an atom to cause it to fission. Click the "initiator" button to shoot a few neutrons into the center. Play with the settings below to see how they change your rate of success (click "Apply" or "Reload" to make them active). Note: Sometimes the neutrons will just bounce off of the atoms (scattering).

Click here to learn more about this simulator and critical assemblies.





The implode option is not available unless you enable the "neutron reflector" in the options below.



Total atoms:

Total atoms of all kinds. Warning! Too many atoms will slow down your web browser. Enrichment percent (0-100):

Percentage of atoms that can fission if a neutron hits them (red). Other atoms (blue) will absorb neutrons. Neutron reflector:

Adds a neutron reflector around the atoms. Original density:

Initial density of atoms (1 = fills the window equidistantly; 2 = twice the density of 1, etc.). Atom radius:

Size of the atoms. Neutron radius:

Size of the neutrons. Neutron lifetime:

How many frames until a neutron decays/vanishes. Show splitting animation:

Shows fissioning as an animation. Warning! Can slow down your web browser. Repulsive effect:

Controls whether fissioning moves nearby atoms. Show repulsive effect:

Makes a small animation showing the radius that a fissioning atom is pushing others. Spontaneous fission:

If enabled, all atoms have a small chance of randomly fissioning at any time.

Maximum neutrons per fission:

Sets the upper possibility of neutrons randomly created after a fission event. Neutron speed:

Default speed of a neutron. Neutron scatter speed:

Differential speed of a neutron after it scatters off of something (multiplies by base neutron speed). Neutron scatter size:

Differential size of a neutron after it scatters (multiplies by base neutron size). Graph current fissions:

Controls whether the number of fission events per frame are graphed on the bottom of the frame in red. Graph total fissions:

Controls whether the cumulative total of fission events is graphed on the bottom of the frame in green. Export data Scattering chance:

Percentage chance that a neutron will just bounce off of an atom, rather than cause a fission or absorption event. Repulsive effect radius:

The distance by which fission events push nearby atoms. Repulsive effect force:

The amount of momentum imparted to nearby atoms when they are pushed by nearby fission events. Neutrons created by the initiator:

The number of neutrons created when the initiator button is clicked. Implosion amount:

The factor by which the implosion button reduces the size of the reflector (2 = reduced by half). Spontaneous fission chance for fissile atoms:

Chance of a fissile (red) atom fissioning spontaneously per frame (out of 1,000,000). Spontaneous fission chance for inert atoms:

Chance of an insert (blue/purple) atom fissioning spontaneously per frame (out of 1,000,000). Canvas size: x

Changes the size of the application window. Frame rate:

Maximum frames per second of the animation (default 60). Export reaction data

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