Types of Radioactive Decay
There are two main categories of radioactive decay:
1. Those that DO involve a change in the mass number (A) of the decaying nucleus, and...
➞ ex: Alpha-Particle Production
➞ ex: Spontaneous Fission
2. Those that DO NOT.
➞ ex: Beta-Particle Production
➞ ex: Gamma Ray Production
➞ ex: Electron Capture
➞ ex: Positron Production
First, we'll examine the 1st category -- those nuclear decay reactions that DO involve a change in the mass number (A).
An alpha-particle (α-particle) is just a helium nucleus, containing 2 protons and 2 neutrons. No electrons!
Here are two example alpha-particle decay reactions:
Fission = the splitting of a heavy nuclide into two lighter nuclides with similar (but smaller) mass numbers. See Californium-254 here...
Now, let's examine the 2nd category -- those nuclear decay reactions that DO NOT involve a change in the mass number (A).
A beta-particle (β-particle) is just an electron and is often represented as either "e-" or "β-"
In a β-decay reaction, an electron is produced and the mass number of the decaying nucleus remains unchanged. See the beta-decays of Thorium-234 and Iodine-131 below...
Gamma-rays are produced when a high-energy (excited) nucleus loses energy in the form of electromagnetic radiation (EMR) called γ-rays.
In the gamma-decay reaction below, an excited Thorium-230* relaxes back down to its ground state by discarding or "giving off" a photon (γ-ray)...
Electron capture is the opposite of beta-particle production.
Instead of producing an electron, the nuclide (ex: mercury-201) adds or "captures" an electron to form new products:
Positron = a beta+ particle, written as shown below (sometimes "e+" is replaced with "β+")
Positron emission is commonly encountered with artificially produced radioactive nucleii of lighter elements. Phosphorus-30 shows how this decay reaction proceeds...
NOTE - Sometimes nuclear decays and particle reactions, such as alpha-particle decay, are accompanied by gamma-ray production.
As first-year general chemistry students, we usually must be told when/if gamma rays are produced.
Why? Because with both A = 0 and Z = 0, it's too difficult to just "know" if a gamma ray is "present" as a product or not. See here...
Writing and Balancing Nuclear Reactions
Balance the following nuclear decay reactions:
ex: Bismuth-214 produces (emits) a beta-particle. Assume only two products.
ex: Neptunium-237 produces (emits) an alpha-particle. Assume only two products.
ex: Fill In. Gold-195 + [ ? ] ➞ Platinum-195.
The key to doing the above electron capture problem, is to remember that A (top) and Z (bottom) values must be conserved.
Radioactive Decay Series
A radioactive decay series occurs when an unstable nucleus cannot reach a stable state through a single decay.
More on this later, but for now let's just show the decay series like this:
In my next post on this topic, SECTION 19 - The Nucleus and Nuclear Chemistry,
We'll have fun discussing half-life and the detection of radioactivity. 👍