Question

a) ²²₁₁ Na is radioactive. Is it a ?^- or ?⁺ emitter?

b)Write down the decay reaction, and estimate the maximum KE of the emitted ?. Note: you must account for all the electrons in your mass totals on both sides of the equation. ____MeV

c)Three isotopes of uranium have mass numbers of 234, 235, and 238 respectively. The atomic number of uranium is 92. How many neutrons are in the nuclei of each of these isotopes?
____ neutrons (U-234)
____ neutrons (U-235)
____ neutrons (U-238)

Answer 1

a) ²²₁₁Na is a emitter

The reason is that the reaction is energetically favourable.

  ²²₁₁ Na²²₁₀ Ne + +

b) The kinetic energy of the will be maximum if no neutrino is emitted. If we ignore the recoil of the neutron, the maximum kinetic energy is

KE = [m(²²₁₁Na)-m(²²₁₀ Ne) - m(e)]

         =[(21.994434u)?(21.991383u)?(0.00054858u)](931.5MeV/1u) = 2.33 MeV

c) The number of neutron is the difference of atomic mass and the number of protons.

234-92 = 142 neutrons (U-234)
235-92 = 143 neutrons (U-235)
236-92 = 144 neutrons (U-238)