Uranium-235 undergoes fission to produce two neutrons per fission event. A neutron-absorbing material is mixed in with this sample. This causes the number of neutrons that can initiate fission events to decrease. Which of the following will be effective at achieving a critical mass? Check all that apply.

A critical mass sustains a chain reaction, with enough neutrons causing further fissions. Surrounding the sample with deflective material can reflect neutrons back into it, reducing neutron loss; compressing the uranium increases its density and the chance that neutrons cause fission. Adding more absorbent material would capture even more neutrons, making criticality harder to achieve.

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