Radioactive Decay – Tutorial   Chapter 4.4

       Std 11c,d

 

The goal of this tutorial is to give you a solid understanding of the process of radioactive decay and to allow you to be able to identify the four major types.

 

First let’s make sure you understand the terms we will be using.  Some things are the same in nuclear equations and some are different.

 

nucleons – these are the particles in the nucleus we call protons and neutrons

atomic number – called the Z number.     Z  = # of protons = # of electrons .  This is the same as normal chemical equations.

mass number – called the A number.       A = # of protons + # neutrons

isotopes – atoms with identical atomic numbers (Z) but different mass numbers (A)

 

 

 mass number ------>    A

                                       X   <-----  symbol for element

 atomic number ----->  Z

 

 

In all types of radioactive decay, atomic particles or energy are given off.  However, in all types of decay, the total mass number (A) and atomic number (Z)  must be in balance on each side of the nuclear equation.

 

 

Major types of radioactive decay with their atomic equations:

 

1.      beta particle emission  ( β particle)  -  Here are two examples of  β particle emission, one with a negative β particle (electron) and one with a positive β particle (positron):

 

a.      Negative β particle emission – is an electron with essentially no mass, and a ( - ) charge.  The negatively charged β particle is the more common β particle.

 

 

234                              234                   0

      Th   ------->                   Pa    +          e     <------  β particle (negative)

  90                                  91                 1-

 

        

Now, you fill in the chart below based on what you see in the atomic formula above for the result of negative β particle emission from Th 234 (thorium):

 

 

LEFT

Th

RIGHT

Pa

RIGHT

e (1-)

# protons

 

 

XXXXX

# neutrons

 

 

XXXXX

Atomic #

 

 

 

 

 

What was the net result of  an electron emission?_______________________

                     (hint:  what changed to what?)

 

b.      Positive β particle emission – is a positron with no mass, but a ( + ) charge.  It is like an electron but with the opposite charge.

 

 

22                          22                   0

    Na   ------>           Ne      +          e    <------  β particle (positive)

11                          10                  1+

 

                 

Now, you fill in the chart below based on what you see in the atomic formula above for the result of the positive β particle emission from Na 22 (sodium):

 

 

LEFT

Na

RIGHT

Ne

RIGHT

e (1+)

# protons

 

 

XXXXX 

# neutrons

 

 

XXXXX

Atomic #

 

 

 

 

What was the net result of positron emission?_______________________

                     (hint:  what changed to what?)

 

2.      alpha particle (α particle) emission

 

 

222                         218               4

     Ra   ------->           Rn     +      He   <--------- α particle  (He nucleus)

  88                           86               2

 

 

Now, you fill in the chart below based on what you see in the atomic formula above for the result of the  α particle  emission from Ra 222 (radium):

 

 

LEFT

Ra

RIGHT

Rn

RIGHT

He

# protons

 

 

 

# neutrons

 

 

 

Atomic #

 

 

 




 

Notice that the net result of the α particle emission did not change any protons to neutrons or vice versa.

        

3.      gamma ray emission  ( γ ray )  - this is a photon of light, has not mass and no atomic number (both are zero):

 

 

 238                      234               4                    0

       U  -------->          Th    +      He    +   2      γ   <------ gamma ray

   92                        90               2                    0                  (photon of light)

 

        

         Now, you fill in the chart below based on what you see in the atomic formula above for the result of both  α particle and  γ  ray emissions from U  238 (uranium). 

 

 

LEFT

U

RIGHT

Th

RIGHT

He

RIGHT

γ

# protons

 

 

 

XXXXX

# neutrons

 

 

 

XXXXX

Atomic #

 

 

 

 

 

Notice again, that the net result of the α particle emission plus a  γ ray did not change any protons to neutrons or vice versa.

 

 4.     electron capture  -  literally, an electron is captured from the area surrounding the atom, called an interorbital electron

 

           

201           0                     201              0

    Hg  +      e   ------->         Au   +        γ  <------- gamma ray

80            1-                       79              0                   (photon of light)

 

 

Now, you fill in the chart below based on what you see in the atomic formula above for the result of the electron capture and the γ  ray emission from Hg 201 (mercury).

 

 

 

LEFT

Hg

LEFT

e  (1-)

Au

γ

# protons

 

XXXXX 

 

XXXXX 

# neutrons

 

XXXXX 

 

XXXXX

Atomic #

 

 

 

 

 

What was the net result of positron emission?_______________________

                     (hint:  what changed to what?)