Do Now: To Be Collected (10 minutes)

Do Now: To Be Collected (10 minutes) On a separate sheet of paper: • 1) Write the nuclear reaction of P-32. • 2) What is the mode of decay of Pu-239? • 3) What is represented by X in the following: • A. 19K37 X + 18Ar37 • B 87Fr2202He4 + X • 4) Find the number of protons and neutrons in an atom of 87Fr220

What is Nuclear Fallout?

Uranium Decay Series: • U-238 is unstable and decays into more stable nuclei. • It takes 14 decay steps until a stable, non-radioactive nucleus is finally reached. • The daughter nuclide of one step becomes the parent nuclide of the next:

U Decay Series

Someone might ask… • How long does it take for it to lose it’s radioactivity?

Next topic for Nuclear Decay: Half-Life!!

½ Life

Half Life (1/2 Life) • What is half life? • Half Life: The time required for something to fall to ½ its original value

Lets time one! In this example, Green will decompose into red. Time how long it takes for ½ of them to turn to red DONE

Lets time the second half life! Ok, so it took about 8 seconds for half of the green to turn to red. Will it be the same the second time? How long does it take ½ the remaining green to turn red? DONE

Half Life (1/2 Life) • What is half life? • Half Life: The time required for something to fall to ½ its original value • **No Factor (temp, pressure, or other elements combined with it) can affect the length of a half-life of a radioisotope!!! It is a fixed length of time for each radioactive nuclei** (for element green, it was 8 seconds)

Yo Mr. D, SO WHAT?! • Don’t really see why half-life is important and super cool? • Get ready for it…..

C-14 • C-14 is a naturally occurring isotope and will be incorporated into plants during photosynthesis • Comparing how much C-14 is left to how much N-14 is present will tell us how old a sample is!

C-14 • Example: • C-14 has a half life (T) of 5730 years • Lets say I have a sample that has a C-14 : N-14 ratio of 1 : 1 • How old is my sample? • BAM! 5730 years

Twizzlium Example (do 4 Half-lives) Number of Half-lives

Half-life Chart

Different Half Life problems • Take out HW packet and the ‘Atoms’ packet and flip to the graphic organizer for Half-life • The formula to use is: • # H.L. = t / T • t= time that has gone by • T= length of one half life

R. Chemistry Type Problems • Many HALF-LIFE problems seem harder than they really are. • Here are some helpful hints and examples. • GENERALLY, you need to figure out something before proceeding with the problem.

R. Chemistry Type Problems • Table N in the Reference Tables gives the length of the half-life of some Radioisotopes. • You may need to look up this information sometimes to solve the problem.

Start by making a data table: • t (time elapsed-longer time) • T (length of Half-life) • # half-lives (size of chart) • beginning amount (beg. am’t.) • ending amount (end am’t)

The only TRUE unknown will be the one asked for in the question. • The other missing information can be found using the half-life equation or a chart.

Different Half Life problems • How much of a 50 g sample of N-16 will be left after 21.6 seconds • 1) Determine the number of half-lives • 3 • 2)Cut the amount in half as many times as there are half lives • 50  25  12.5  6.25g

Different Half Life problems • HW #3)The half-life of cesium-137 is 30. years. Howmuch Cs-137was present originally if, after 120. years, 6.0 g remained? • 1) Determine the #HL • 2) Double the amount as many times as there are half lives

Different Half Life problems • HW #1) What is the half-life of a radioactive isotope if 25% of the original mass of the isotope remains after 20. days? • 1) Determine #HL by determining the #of time you can cut the original in half till you get the amount you have • 2)Divide the time elapsed (t) by the #HL

Different Half Life problems • HW #8) An ancient scroll made of papyrus is analyzed, and it is found to contain only 25% of the steady-state concentration of C-14 found in living organisms. How old is the material that the scroll is made of? • 1) Determine how many times you can cut the original amt. in half to get your final amt. • 2) Multiply the #HL by the duration of 1 HL

With your neighbor • Work on the HL practice, alternating roles as you do so. • 15 minutes (group quiz)

Back to the focus question • What is nuclear fall out?

U-238 • Used in nuclear bombs • Once detonated, radioactive material is projected into the air • Clouds of radioactive particles being blown across the sky • Rainfall would take them out of the sky and into the ground

U-238 • This would contaminate the ground water, anything left out in the open (including living things) • When would the water/area be safe again? • The half life for U-238 is 4.5 billion years • Pretty much never again.

U-238 • Soil would need to be removed before planting again • Water table would have to be replaced with fresh water before any of it would be safe …Some serious stuff

Use the rest of this time • To make sure you finish the Half Life Homework assignment

Do Now: To Be Collected (10 minutes)