Radioactive Decay Lab report
Experiment Name: Radioactive decay law
Aim: To draw radioactivity graph
Theory:
A nucleus of a radioactive element that emits an α-particle must transform into a nucleus of another element. The nucleus of the so-called ‘parent’ element loses two neutrons and two protons. Therefore the nucleon number (A) changes by 4 and the proton number (Z) changes by 2. The nucleus formed by this decay is called the ‘daughter nucleus’. We may express such a nuclear decay by the nuclear reaction equation
X!! → Y!!!!!! + He!! (parent) (daughter) (α-particle)
The radioactive decay law enables us to determine a relation between the half-life of a radioactive element and the decay constant. If a sample of a radioactive element initially contains N0 atoms, after an interval of one half-life the sample will contain N atoms. If the half-life of the element is T½ from the decay law, we can write that
𝑁 = 𝑁!𝑒!!"
Procedure: 1. Go to http://phet.colorado.edu/en/simulation/alpha-‐decay, and click on the “Run Now!” button. The below window should appear.
2. Click to “Custom” from the column on the right of the screen and get the below diagram.
3. Adjust the half life to any value you want between 0.5-‐1sec. using double-‐sided green arrow.
4. Add atoms to the bucket by clicking “Add 10” icon below the bucket at the bottom ad get the
below diagram.
5. By clicking “ ” button, get how many undecayed atom remains in each time interval of 0.5s.
Repeat your measurement 10 times, write your data to the below table and calculate the average.
Time (s) 0 0.5 1.0 1.5 2.0 2.5 3.0
N um
be r o
f u nd
ec ay ed
a to m ,N
99
99
99
99
99
99
99
99
99
99
Average 99
6. Draw number of undecayed atom vs time graph.
7. Calculate values of ln N (average) and write them in the table below.
Time (s) 0 0.5 1.0 1.5 2.0 2.5 3.0 Number of undecayed atom, N 99
ln N
8. Draw ln N vs time graph and calculate its slope which is known as decay constant, 𝜆 .
𝜆 = ln𝑁 𝑇!
!
9. Using the below relation, calculate half life of parent nucleus.
𝑇! ! = ln𝑁 𝜆
Use the Nuclear Fission Inquiry Lab Nuclear Fission PhET simulation at http://phet.colorado.edu/en/simulation/nuclear-fission
to answer the questions on this page
1. Use the tab called “Fission – One Nucleus” to answer these questions:
a. Try to figure out how you can make U-‐235 unstable b. How do you know it’s unstable? c. Describe what you would do to make U-‐235 unstable, both in terms
of what you see and do in the simulation and what this represents, physically.
d. In your own words, what does “unstable” mean when used to describe Uranium?
2. Imagine that you have many U-‐235 atoms and you fire a neutron at one of them. What do you think will happen? Explain your prediction using words and drawings.
3. Explore the features of the “Chain Reaction” tab. If you wanted to explain nuclear chain reactions to someone, what would you tell them? Briefly, explain your ideas using appropriate vocabulary and drawings. Make certain that your answer explains why the reaction occurs AND what affects the speed of the reaction.
4. Why is U-‐235 a good isotope of Uranium for creating chain reactions?
5. Now, you want to make an atom bomb. Use an Internet search to determine which materials are used for nuclear bombs, and use these materials to try to make your bomb. (Remember, a bomb must be transportable – what do you need to do so that it is transportable?) What can you do to make the bomb explode?
6. While using the simulation, what observations have you made that makes nuclear reactions good for bombs?
7. What are at least three things that you need in order to make an effective bomb, and why?
8. Explore the features of the “Nuclear Reactor” tab. What is the purpose of the control rods within a nuclear reactor?