
Grab the three worksheets on the front table

Write the Isotopic Notation for
 Carbon-14
 Iodine-128

A half-life is the time required for one half of
a sample of radioactive material to decay

Unlike chemical reactions, nuclear decay
rates are constant regardless of temperature,
pressure or surface area

So, every X years, the substance will be
reduced to half of its current amount.

If the half-life is 10 years, then every 10 years
we will have ½ of the current amount.

If we have 80g of a substance with a half-life
of 10 years, after 10 years we’ll have 40g. 10
years later, we’d have 20g. 10 years later we’d
have 10g, and so on, and so forth.
Isotope: H-3 (Tritium)
Half-Life: 12y
400g
-
200g
12y
100g
24y
50g
36y
25g
48y
12.5g
60y

C-14 has a half life of 5730 years.
If you have a sample of 50 grams. How much of the
sample will be remaining after 1 half life?
After 2 half lives?
Step 1: Draw a T-Chart
Step 2: Fill in amount and Half-Life
Step 3: Multiply the amount by 2
Step 4: Add 1 Half-Life
Step 5: Continue steps 3-4 until answer is achieved.

After 4 years, only 2g remains of Isotope X,
which has a half-life of 1 year. How much did I
start with?

Step 1: Draw a T-Chart
Step 2: Fill in FINAL amount and Half-Life
Step 3: Multiply the amount up by 2
Step 4: Subtract up 1 Half-Life
Step 5: Continue steps 3-4 until answer is
achieved.

Oh, come on, that’s easy.

9 years ago I put 10g of Isotope Y in a box. Today I
opened it and there was only 2.5g left! What is the
half-life of Isotope Y?

Step 1: Draw a T-Chart
Step 2: Fill in amounts and final half-life value
Step 3: Multiply the final amount by 2 until you get
your original amount
Step 4: How many times did you multiply by 2 to
get your original amount? Divide your half-life by
that #.

I have 100g of element B that has a half-life of
10 years.

I have 50g of element A that has a half-life of
20 years.

Which would reach 12.5g first?

Complete the worksheet labeled Half-life
word problems – Physical Science.
Because many isotopes of atoms decay.
But. . .why nuclides (nucleus of isotopes) decay?
To obtain a stable ratio of neutrons to protons
Stable
Unstable
(radioactive)
They become radioactive!
Radioactivity:
Emission of high-energy
radiation from the nucleus of an
atom
An alpha particle looks like a helium atom
(42He)
mass reduces by 4
atomic # reduces by 2
Essentially, the atom just chucks 2 Neutrons
and 2 Protons away.
✦ Alpha decay (Remember, -4, -2)
224
251
25198
86
Rn →
98
Cf
→
During Alpha radiation an atom's proton
count drops by two, and we know what that
means - a NEW element is formed!

So, Neutrons. We said they’re ALMOST
the same size as Protons?

Neutrons are actually just a Proton with an
Electron inside of it!

That’s why they’re just a LITTLE heavier.
About 1 electron heavier.
✦ A beta particle is written 0-1 e
✦ mass remains the same
✦ atomic # increases by 1
Ok, so this one’s weird. We throw away an
electron, and in doing so, a Neutron
becomes a Proton. Weird, right?
✦ Beta decay (Remember, +0, +1)
120
137

50
Sn
→
56
Ba
→
During Beta radiation an atom's proton
count grows by one. Once again, NEW
element!

Gamma Decay:

Sometimes, elements get tired after
decaying. It’s a lot of work, so they release a
big burst of pure energy.

This is called Gamma Radiation.
(42He)
(0-1 e)
(00 )

Nuclear fusion is the joining of two nuclei to
form a heavier nuclei.

The reaction is followed either by a release or
absorption of energy.

Fusion occurs in stars, such as the sun.
2H
+ 3H → 4He + 1n + energy.

The energy released by fusion is three to four
times greater than the energy released by
fission.

Fission is the splitting of a nucleus that
releases free neutrons and lighter nuclei.

The fission of heavy elements is highly
exothermic which releases about 200 million
eV compared to burning coal which only gives
a few eV.

Fission is used in nuclear power plants.