QUESTION 1

Following are some Parent – Daughter isotope pairs with their half life:

• U-238 going to Pb-206 (T1/2 = 4.5 x 109 years)
• U-235 going to Pb-207 (T1/2 = 0.7 x 109 years)
• C-14 going to N-14 (T1/2 = 5700 years)

Q-1: If the C-14 : N-14 ratio in a shell in a sandstone was found to be 1 : 3, how old is the shell?

Answer-1: _____________ years

Q-2: If the U-235:Pb-207 ratio in a rock from Massachussets was determined to be 1 : 15, how old is the rock?

Answer-2: __________years

Q-3: (a) If the U-238:Pb-206 ratio in a crystal of zircon found in a sandstone was determined to be 1 : 7, what radiometric age will this give for the zircon?

Answer-3: ___________years.

  (b) Does the determined age realistic? If no why not? If yes, how? (Explain briefly).

Answer-4: ________________________.

QUESTION 2

When a radioactive isotopes (parent – P) decay, they produce daughter products ( D) at a constant rate, called the half-life (T 1/2).

Example: if we start with 100 atoms of the parent, after one half-life, there will be 50 parent atoms remaining and 50 daughter atoms newly made. After another half-life (two half-lives), there will be 25 parent atoms remaining and now 75 daughter atoms. Each parent-d aughter isotope pair has its own half-life.

Complete the following half-life decay ratios between P (Parent isotope) and D (daughter isotope)

• 0 half-life:  P = 1, D = 0. P:D ratio = 1:0.
• 1 half life: P = 1/2, D = 1/2. P:D ratio = 1/2: 1/2 = 1:1.
• 2 half life: P = 1/4, D = 3/4. P:D ratio = __1:3___.
• 3 half life: P = ____1/8___, D = ______. P:D ratio = _______.
• 5 half life: P = ___ D = ________. P:D ratio = _______.

QUESTION 3

Each element of the period table is defined by the number of protons in the nucleus of the atom, which assigns the atomic number of the element. The mass number (amu = atomic mass units) of an atom is the sum of the protons (each proton = 1 amu) and the number of neutrons (each neutron = 1 amu).

Based on the above information, Th-232 (Thorium with mass = 232 amu, atomic number 90) would have _____ ___protons and ______ neutrons.