Aim What is the halflife of a radioisotope

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

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 •

Fraction Remaining •

Fraction Remaining •

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 •

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) •

Initial Amount (Original Amount) •

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 1 g = (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