Warm up

Grab the three worksheets on the front table

Write the Isotopic Notation for

Carbon-14

Iodine-128

Half Life

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

Half-Life

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.

Copy this chart

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-ChartStep 2: Fill in ORIGINAL amount and Half-LifeStep 3: Divide the amount by 2Step 4: Add 1 Half-LifeStep 5: Continue steps 3-4 until answer is achieved.

Know what we start with? 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-ChartStep 2: Fill in amount and Half-LifeStep 3: Multiply the amount by 2Step 4: Add 1 Half-LifeStep 5: Continue steps 3-4 until answer is achieved.

Know what we end with?

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-ChartStep 2: Fill in FINAL amount and Half-LifeStep 3: Multiply the amount up by 2Step 4: Subtract up 1 Half-LifeStep 5: Continue steps 3-4 until answer is achieved.

Ok, ok, but what if I don’t know the half-life?

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-ChartStep 2: Fill in amounts and final half-life valueStep 3: Multiply the final amount by 2 until you get your original amountStep 4: How many times did you multiply by 2 to get your original amount? Divide your half-life by that #.

Practice

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?

Worksheet time!

Complete the worksheet labeled Half-life word problems – Physical Science.

Why are we learning Half-life?

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)

So, what happens when they decay?

They become radioactive!Radioactivity:

Emission of high-energy radiation from the nucleus of an atom

There are 3 types of Decay

An alpha particle looks like a helium atom (4

2He)

mass reduces by 4 atomic # reduces by 2

Essentially, the atom just chucks 2 Neutrons and 2 Protons away.

Alpha Decay

Practice

✦ Alpha decay (Remember, -4, -2)

22486 Rn→

25198 Cf →

25198 During Alpha radiation an atom's proton count drops by two, and we know what that means - a NEW element is formed!

Wanna hear something cool?

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.

There are 3 types of Decay

✦ 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?

Practice

✦ Beta decay (Remember, +0, +1)

12050 Sn →

13756 Ba →

During Beta radiation an atom's proton count grows by one. Once again, NEW element!

There are 3 types of Decay

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.

There are 3 types of radiation

(4

2He)

(0-1

e)

( 0

0 )

Fusion

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.

HERE COMES THE SUN

 2H   + 3H → 4He + 1n + energy.

Fusion

The energy released by fusion is three to four times greater than the energy released by fission.

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.

This chain reaction is the basis of nuclear weapons

Fission

Fission is used in nuclear power plants.

Know the difference