Chapter 22

which changes the identity of the element
• To change the nucleus to become stable mass (amu) charge
1 Alpha ~4 +2 nature particle
2
4 He
2protons
2 neutrons a material throws out the above helium atom to become stable
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mass(amu) charge nature
2Beta
3Gamma
~.0005
-1 particle neutron proton + electron (e-)
0 gets rid of the electron
0 pure energy

• Fusion –cram two or more nuclei together = lots of energy given off (makes it larger)
• Fission –tear a nucleus apart = lots of energy given off (makes it smaller)
-atomic bomb –force an extra neutron into the nucleus (mass deficit is gone = too much mass in nucleus = binding energy of nucleus is no longer in effect = splits the nucleus) and then tremendous energy is released plus more neutrons which slam into more nuclei to create a chain reaction.

how long it takes for ½ of the element to decay away
• All radio active elements decay in half lives
• Example
-50 grams of uranium will decay into lead
-when 25 grams of uranium are left in the sample, ½ of the uranium has decayed away. The time it takes for this to happen is called uranium’s half life. (4.5 x 10 9 years)
-when 12.5 grams are left in the sample another half life has passed
(4.5 x 10 9 years + 4.5 x 10 9 years)
-every radio active element has it’s own respective half life
-we can date a sample of an element by knowing how long it takes for ½ of it to decay and measuring the element’s mass in the sample or rock
All radio active elements act this way

used for good things in the medical field could be bad for you if you are exposed to the wrong thing
• Iodine -8.1 days to test thyroid
• Iron -45.1 days to test red blood cells
• Chromium -27.8 days to test red blood cells
• Sodium -14.8 hours to test circulatory systems
• Carbon -5,730 years to date wood (how much carbon is left in the wood after the tree died.

• A chemist wishes to do an experiment using
47 Ca (half life = 4.5 days). He needs 2.5 grams of the element for the experiment. What mass must he order if it takes 48 days for the delivery?

• In 4.5 days half of the element will decay.
• He needs 2.5 grams for the experiment
• So there was
• 5 grams = 4.5 days previous 160 grams = 27 days previous
• 10 grams = 9 days previous 320 grams = 31.5 days previous
• 20 grams = 13.5 days previous 640 grams = 36 days previous
• 40 grams = 18 days previous 1280 grams = 40.5 days previous
• 80 grams = 22.5 days previous 2560 grams = 44.5 days previous
5120 grams = 49 days previous
• He needs to order 5.12 x 10 3 grams in order for 2.5 grams to still be there after the 48 day delivery period.

• If carbon decays with a half life of 5,730 years, could it be used to date a live person.
• If Iodine decays with a half life of 8.1 days and
10 grams of the element was injected into an ear of corn when it first begins to develop, could it be used to date the ear of corn when it is ready to pick?

• 30 days til ready to pick
8.1 days = 5 grams
16.2 days = 2.5 grams
32.4 days = 1.25 grams (1 month)
64.8 days = .625 grams (2 months)
129.6 days = .3125 grams (4 months)