Band of Stability

The Valley or Band of Stability represents the area where stable, non-radioactive isotopes exist based on their ratio of neutrons to protons. 

Valley of Stability 

Whenever the difference between neutrons to protons within a nucleus is significant enough an isotope is radioactive. 

Concept: The central idea of nuclear chemistry is that unstable nuclei will give off radiation. 

4m

Neutrons act like the glue that keeps the nucleus together. The more neutrons present then the greater the attractive strong force, while the more protons then the greater the repulsive Coulombic force

Concept: Non-radioactive isotopes with the optimum number of neutrons to protons will lie within the Valley of Stability, while radioactive isotopes will lie outside of it. 

11m

Example: Determine if the following nuclide will undergo alpha decay, beta decay or positron emission.

Hydrogen-3                                                                              

 

4m

Example: Determine if the following nuclides will undergo alpha decay, beta decay or positron emission.

Radon-222

2m

Example: Determine if the following nuclides will undergo alpha decay, beta decay or positron emission.

Magnesium-50

3m

Band of Stability Additional Practice Problems

Using general trends, predict the stability of the following nuclei as RADIOACTIVE or STABLE.

1. arsenic-82

2. potassium- 44

3. radium- 233

4. calcium- 40

5. zinc- 64

Watch Solution

Which type of nuclear decay is the following radioactive isotope likely to undergo?

All known stable isotopes are shown on the graph. The points form what is known as the "belt of stability". If a radioactive isotope is above the belt of stability, think about what type of decay would decrease its N/Z ratio. If an unstable isotope is below the belt of stability, think about what type of decay would increase its N/Z ratio. If a radioactive isotope is off the chart (Z > 83), think about what type of decay would decrease Z the most.


a. beta decay
b. alpha decay
c. positron emission or electron capture

Watch Solution

Which of the following isotopes would you expect to be stable?

a. 208Pb

b. Carbon-12

c. Uranium 235

d. 4He

e. 208Po

Watch Solution

Which of the following isotopes would you expect to be stable?

i. carbon-12

ii. 4He

iii. uranium-238

iv. 58Ni

v. 208Po

Watch Solution

Which of the following isotopes would you expect to be stable?

a. uranium-238

b. 4He

c. oxygen-16

d. 208Po

e. 58Ni

Watch Solution

Why does the band of stability curve upward at high atomic numbers?

A. Excess neutrons are required due to the repulsion between the protons.

B. If we have too many protons, not enough electrons will be orbiting the atom to keep it electrically neutral overall.

C. Excess protons are required to help keep the neutrons from sticking together as neutrons have no charge.

D. Atoms with high atomic numbers have a large number of electrons orbiting the nucleus. This increased number of electrons requires a lot of extra mass in the nucleus to keep the electrons in their orbit.

Watch Solution

Which of the following nuclides is likely to lie above the band of stability?

(a) 15O

(b) 39C

(c) 3He

(d) 9Li

(e) 13N

Watch Solution