HALF LIFE PRACTICE

YOU HAVE 5G OF SODIUM 25. HOW MUCH WOULD YOU HAVE AFTER 3 HALF LIVES?

Step 1:2512.56.256.25g remain

Now You

C14 HAS A HALF LIFE OF 5730 YEARS. IF YOU HAD 88G, HOW MUCH C14 WOULD REMAIN AFTER 5 HALF LIVES?

Step 1:884422115.52.75g

ACTINIUM 226 HAS A HALF LIFE OF 28 HOURS. 100 G OF ACTINIUM 226 DEGRADES OVER 56 HOURS. HOW MUCH WILL BE LEFT?

Step 1: 56/28=2Step 2: 100g50g25g

25g

Now You

AFTER 11,200 YEARS, A SAMPLE OF RADIUM-226 HAS DECAYED. IT HAS A HALF-LIFE OF 1600 YEARS. THE SAMPLE WAS ORIGINALLY 162 GRAMS. HOW MUCH IS LEFT?

Step 1: 11,200/1600=7Step 2:

1628140.520.2510.1255.0625 2.53125

2.53125g

THE HALF LIFE OF ISOTOPE X IS 2 YEARS. HOW LONG WOULD IT TAKE FOR 4G TO DECAY TO .5G?

Step 1: 421.5(3 Half lives have passed)Step 2:3X2years=6 years

NOW YOU

CARBON HAS A HALF LIFE OF 5730 YEARS. HOW LONG WOULD IT TAKE 100G TO DECAY TO 25 GRAMS?

Step 1:1005025 (2 half lives have passed)Step 2:5730 years X 2=11460 Years

A SAMPLE INITIALLY CONTAINS 60G OF THORIUM 234. AFTER 48 DAYS ONLY 7.5 GRAMS REMAIN. HOW LONG IS ONE HALF LIFE?

Step 1: 6030157.5 (3 half lives have passed)

Step2: 48/3=16

16 days

Now You

WE START WITH 500G OF ISOTOPE X. IN 10,000 YEARS WE END WITH 7.8G. HOW LING IS ONE HALF LIFE FOR ISOTOPE X?

Step 1: 50025012562.531.2515.67.8

(6 half lives have passed)Step 2: 10,000/6 = 1666.66

One half life is 1666.66 years