Nuclear+Decay


 * What is Radioactive Decay?**

Radioactive decay occurs when incredibly large and/or unstable atoms break down to more stable atoms. There are three kinds of decays, alpha, beta, and gamma.


 * Alpha Decay** occurs when an alpha particle ( 4 2 He )is emitted from the unstable nucleus of the atom. For Example:

( 238 92 U ) → ( 234 90 Th) + ( 4 2 He); This translates as Uranium-238 went through alpha decay and transformed into Thorium-234

The Key example that you should remember is that:

A Z X → A-4 Z-2 Y + 4 2 He ; Where X is the parent nucleus and Y is the daughter nucleus, A is the isotope of the atom and Z is the atomic number. (In case you forgot, when the atomic number changes, the element changes its name as well.)

Whenever, a problem asks you to complete the table for an alpha decay, just remember the formula above and you can solve any problem.

Example #1: Write a table that shows the alpha decay of Americium-243.

**Beta Decay** occurs when a beta particle (e -  or e +  ) is released from an atom. ( these are electrons and positrons, respectively) However, there is one more accompanying particle called the neutrino and anti-neutrino (v and ν̅, respectively) during beta decay. There are two combinations of a beta emission, a electron and an anti-neutrino, or a positron and a neutrino.

 Since the both the neutrino and anti-neutrino are massless and chargeless, when writing a table for a beta decay, the only portion of the atom that changes is the atomic number and the name.

Example #2: Write the table that shows the beta decay of Sulfur-32.

The Key formula to remember is: A Z X → A Z+1 Y + e - + ν̅ or

A Z X → A Z-1 Y + e + + ν

By using the formulas above, you can solve either kind of beta decay. Example #3: Write a table that shows the positron beta decay of Iron.


 * Gamma Decay** occurs when an excited atom that has recently gone through either alpha or beta decay. The atom is in an excited state and needs to balance its extra energy, so it releases photons as a form of extra energy, but not changing the weight or transforming it in any way.

Example #4: Write a table for a Cesium atom that has already gone through beta (electron) decay and settle to ground state by gamma decay.

The Key formula to remember is: <span style="font-family: Arial,sans-serif;">(Take atom from previous decay) → (keep the same atom) + γ

Since this is the simplest form of radioactive decay to write, there is almost no need for a formula. Example #5: Write a table for a positron-beta decay of Cobalt and the gamma decay that shortly follows the positron-beta decay.

1.) 243 95 <span style="font-family: Calibri,sans-serif; font-size: 11pt;">Am → 239 93 <span style="font-family: Calibri,sans-serif; font-size: 11pt;">Np + 4 2 <span style="font-family: Calibri,sans-serif; font-size: 11pt;">He <span style="font-family: Calibri,sans-serif; font-size: 11pt;">2.) 32 16 S → 32 17 Cl + e- + ν̅ 3.) 56 26 Fe → 56 25 Mn + e + + ν 4.) 133 55 Cs → 133 56 Ba* + e - + ν̅ 133 56 Ba* → 133 56 Ba + γ Where the asterisk (*) represents an excited atom from a recent decay, and where γ represents gamma radiation (usually in the form of photons given off from electrons releasing energy when falling to their ground state). 5.) 59 27 <span style="font-family: Arial,sans-serif;">Co → 59 26 <span style="font-family: Arial,sans-serif;">Fe* + e + <span style="font-family: Arial,sans-serif;"> + ν 59 26 Fe* <span style="font-family: Arial,sans-serif;">→ 59 26 <span style="font-family: Arial,sans-serif;">Fe + γ
 * Answers:**

All material was adapted from Serway, Raymond A (2006), // College Physics // (7th ed.): Brookscole ISBN 978-0-534-99723-6 including the definitions and equations.
 * References:**

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