1. The problem statement, all variables and given/known data A particular isotope of dysprosium has atomic number 66 and atomic mass 159.952202 u. Identify the nucleus with a radius that is one half that of this isotope. A. Ne (A=20, Z=10) <<<Correct Answer B. O (A=16, Z=8) C. Mn (A=50, Z=25) D. Ni (A=60, Z=28) 2. Relevant equations The only relevant equation I can think of is the equation of a nucleus's radius in terms of its atomic number: r = (1.2X10^-15)(A^[1/3]) 3. The attempt at a solution My attempt has gone as follows: 1. Find the radius of the given dysprosium isotope by plugging it's atomic number into the given formula: r1 = (1.2X10^-15)(66^[1/3]) r1 = 4.849488E-15 m 2. Now I find the radius of the unknown nucleus: r2 = (1/2)r1 r2 = 2.424744E-15 m 3. Finally, by plugging the r2 value into the original equation, I should be able to solve for the atomic number of the unknown nucleus: r2 = 2.424744E-15 m = (1.2X10^-15)(A2^[1/3]) A2 = 8.25 This is obviously not correct, it seems I'm missing a step; possibly one involving the atomic mass, since it is mentioned in the problem. Any help would be appreciated. Thanks!