Aim: What is the half-life of a radioisotope Do Now:

Stable and Unstable Nuclei Unstable nuclei spontaneously decay giving off rays and particles Stability of nucleus depends on neutron to proton ratio For elements with low atomic number (1-20) – Neutron/proton=1 – Nucleus of isotope is stable For elements with high atomic number (82-83) – Neutron/proton = about 1.5 – Stable isotope

Stable and Unstable Nuclei  Protons in the nucleus repel each other because of like charges. The binding energy holds the nucleus together.  Stable atoms have a strong binding energy  Atoms with unstable nuclei have an imbalance of energy in the nucleus  Unstable atoms are constantly changing to become more stable

Band of Stability

Transmutation

Question

Half-Life Every radioisotope has a rate of decay. Half-life is the time it takes for half of the sample to decay into new elements.

Half-Life

Table N lists half-life, decay mode (particles emitted during decay), nuclide (radioisotope, and name of nuclide. The half-life of Ra-226 is 1600 years; meaning, in 1600 years half of Ra-226 will decay, and in another 1600 years half of what was remaining will decay. After 3200 years, how many half-lives has Ra- 226 gone through?

Half-Life Formula

Fraction Remaining

Half-life 100 grams of a radioisotope decayed to 12 ½ grams after 90.7 years. What was the half-life?

Half-life

Initial Amount (Original Amount) A radioisotope has a half-life of 10 days. 1 gram remains after 40 days. What was the initial amount of the radioisotope?

Initial Amount (Original Amount)

A radioisotope has a half-life of 10 days. 1 gram remains after 40 days. What was the initial amount of the radioisotope? Step 3: Find initial amount. 1/16 of the original amount remains 1 g = amount remaining 1g = (1/16) x, x= initial amount

Questions 1. Which radioisotopes have the same decay mode and have half-lives greater than 1 hour? (1) Au-198 and N-16 (3) I-131 and P-32 (2) Ca-37 and Fe-53 (4) Tc-99 and U-233

Questions 2. After decaying for 48 hours, 1/16 of the original mass of a radioisotope sample remains unchanged. What is the half-life of this radioisotope? (1) 3.0 h (3) 12 h (2) 9.6 h(4) 24 h