Balancing Decay Reactions

Learning Goal: Students will be able to write balanced decay reactions for alpha and beta

decay.

Isotope Review1. Determine the number of protons and neutrons

in each of the following isotopes.

H31

Neon-22

2. Determine the name and symbol for an isotope whose atoms contain 3 protons and 4 neutrons.

Isotope Review1. Determine the number of protons and neutrons

in each of the following isotopes.

H31

Neon-22

2. Determine the name and symbol for an isotope whose atoms contain 3 protons and 4 neutrons.

1 Proton2 Neutrons

10 Protons12 Neutrons

Lithium-7 Li 73

Decay ReactionsWhen a radioactive isotope decays…- matter is conserved.- total # of particles in the nucleus is conserved.- total (neutral) charge of atom is conserved.

Decay ReactionsWe can use those conservation ideas to predict decay products. For example, when Uranium-238 decays by alpha decay…

U23892 → + ______

alpha particle

daughter nucleus

Decay ReactionsWe can use those conservation ideas to predict decay products. For example, when Uranium-238 decays by alpha decay…

U23892 → He4

2 + ___alpha

particledaughter nucleus

Decay ReactionsWe can use those conservation ideas to predict decay products. For example, when Uranium-238 decays by alpha decay…

U23892 → He4

2 +alpha

particledaughter nucleus

Th23490

Another ExampleWrite the decay reaction formula for the alpha decay of Bismuth-211.

Bi21183 → + ______

alpha particle

daughter nucleus

Another ExampleWrite the decay reaction formula for the alpha decay of Bismuth-211.

→alpha

particledaughter nucleus

He42 + Tl207

81Bi21183

One More Alpha-Decay ExampleA certain radioactive isotope decays by alpha decay, producing Silicon-31 as the daughter nucleus. What was the original isotope?

Si3114→ +___

alpha particle

___original nucleus

One More Alpha-Decay ExampleA certain radioactive isotope decays by alpha decay, producing Silicon-31 as the daughter nucleus. What was the original isotope?

Si3114→ +He4

2S3516

Beta DecayBeta decay still obeys the same general conservation rules as alpha decay, but it works a little differently because of what beta particles are. A beta particle is basically just…

an electron emitted from the nucleus!

Beta DecaySo what would the symbol for a beta particle look like, in a decay reaction formula?

e-1

Remember, this bottom number is the # of protons, which could also be

thought of as the charge of the particle.

0This top number counts how

many total protons and neutrons are present in this particle.

Beta Decay ExampleNow that you know the symbol, predicting decay products should be easy enough. What are the products when Carbon-14 decays by beta decay?

C146 → + ______

betaparticle

daughter nucleus

Now that you know the symbol, predicting decay products should be easy enough. What are the products when Carbon-14 decays by beta decay?

C146 → + ___

betaparticle

daughter nucleus

e0-1

Beta Decay Example

Now that you know the symbol, predicting decay products should be easy enough. What are the products when Carbon-14 decays by beta decay?

C146 → +

betaparticle

daughter nucleus

e0-1 N14

7

Beta Decay Example

What’s occurring in the nucleus during beta decay, for the total #of particles in the nucleus to remain constant, but for proton # to increase?

C146 → +

One of the neutrons is ‘breaking’ into a proton and an electron.

e0-1 N14

7

Beta Decay Example

One More Beta-Decay ExampleWrite the decay reaction formula for the beta decay of Phosphorous-32.

P3215 → + ______

betaparticle

daughter nucleus

Write the decay reaction formula for the beta decay of Phosphorous-32.

P3215 →

betaparticle

daughter nucleus

+ S3216e0

-1

One More Beta-Decay Example

Decay Reaction PracticeDetermine the daughter nucleus produced when each of the following radioactive isotopes decay in the manner stated.

1. (beta)

2. (alpha)

Ca4520

Pu23494

3. (alpha)

4. (beta)

Po21084

Na2411

Decay Reaction Answers

1.

2.

Sc4521

U23092

3.

4.

Pb20682

Mg2412