Question

a) The rate constant for Cr decay is 2.89×10^-7 s-¹. Calculate the time required for 87.5% decay. b) Explain the method of determining the age of an organic material. c) Explain the following terms: i) Moderator and ii) Breeder reactor.

Answer 1

a)

$$N(t) = N_0e^{-\lambda t}$$

$$875 = 1000e^{-2.89*10^{-7} t}$$

$$8.75 = 10e^{-2.89*10^{-7} t}$$

$$-2.89*10^{-7}t = ln0.875$$

$$-2.89*10^{-7}t = − 0.13$$

$$t = -0.13/(-2.89*10^{-7}) = 0.045*10^7 = 4.5*10^5 s$$

b) Carbon dating - measuring the content of the radioactive isotope ¹⁴C in the material.

c)

i) Moderator - the process of reducing the kinetic energy of free neutrons as a result of their multiple collisions with the atomic nuclei of matter.

ii) Breeder reactor - nuclear reactor, allowing to produce nuclear fuel in quantities exceeding the needs of the reactor itself.