Download Artificial Transmutation Notes

Induced Nuclear Reactions – Artificial Transmutation
So far, we have talked about spontaneously occurring nuclear reactions –
when a nucleus is unstable it can naturally emit radiation to become more
stable.
 Why would a nucleus be unstable?
When it has too many
protons.
 The neutrons are there to help the protons repel each other less.
 What is the optimum ration of neutrons to protons?
1:1
 Do you remember what number of protons is the most that an atom
can have not be considered radioactive?
83
So, when an atom is unstable it can emit a few different types of radiation,
and you can look up those types on Table O in your reference tables.
What would the equation look like if an atom of 22688Ra spontaneously
emits an alpha particle?
226
88Ra
→ 22286Ra + 42He
How about it an atom of 21482Pb spontaneously emits a beta particle?
214
82Pb
→ 21483Bi + 0-1e
 What do these two equations have in common?
 Do we end up with the same element that we started with? No
 This is called transmutation – when the atomic nucleus of one
element is changed in to the nucleus of a different element.
 How about the location of the particle in the equation?
They’re
both on the right side.
 That’s how you can tell that the transmutation happened
spontaneously – nothing had to be added to the original atom for it to
transmutate and the only particles present are the ones that are
emitted.
 How would the equation change if we wanted to create artificial
transmutation by bombarding the nucleus with particles to bring
about a change on purpose?
The particle would be on the left
side of the arrow.
 And that’s how you can tell the difference just by looking at the
equation. Here’s an example of artificial transmutation:
14
7N
+ 42He → 178O + 11H
In this case we’ve bombarded an N-14 atom with an alpha particle, turned
the N in to O-17 and emitted a proton. You can predict the outcome of an
artificial bombardment reaction the same way that we did with
spontaneous decay – the atomic masses and numbers on the left of the
arrow has to equal its counterparts on the right. Try this example:
What would we have to bombard an atom of 2713Al with to result in the
formation of an atom of 3015P and the emition of a neutron?
27
13Al
27
13Al
+ ? → 3015P + 10n
+ 42He → 3015P + 10n
 What’s the charge on an alpha particle?
 What’s the charge of a nucleus?
+2
Positive
 What does that tell you about how easy it is to cause transmutation by
bombarding a nucleus with an alpha particle?
It’s not easy
because + repels +
It is possible though because this repulsive force can be overcome if the
particle has sufficient energy. Scientists can supply this energy by
accelerating the particle in a device called – can you guess? – a particle
accelerator. There are different types of particle accelerators with names
like “cyclotron” and “synchrotron”, but they all work on the same basic
principle. There is a long series of tubes that contain electric or magnetic
fields that the particle passes through by attractive and repulsive forces.
Finally, when the particle passes through the last tube it is accelerated in to
the target nuclei at close to the speed of light (3 x 108 m/s.)
 Can all particles be accelerated this way?
No, only the charged
ones.
 Which ones can’t?
Neutrons
 Would you need to accelerate a neutron to bombard a nucleus with it?
No, since it neutrons don’t have a charge, they aren’t repelled
by the target nucleus.
Scientists use neutron bombardment reactions to make stable nuclei
radioactive. Tc-99 can be prepared this way.
What is Tc-99 used for?
To detect brain tumors.
Take a minute to figure out what type of atom would have to be
bombarded with a neutron in order to create an atom of 9943Tc. I’ll tell you
also that an electron is emitted.
1
0n
1
0n
+ ? → 9943Tc + 0-1e
+ 9842Mo → 9943Tc + 0-1e
ARTIFICIAL TRANSMUTATION Problems
1. In the reaction:
+ 2He4  X + 0n1
the nucleus represented by x is ____94Pu241______
238
92U
2. In the reaction:
X + 1H1  3Li6 + 2He4
the nucleus represented by x is ____4Be9______
3. In the reaction:
4
+ 0n1 
2He + X
the nucleus represented by x is ___1H3______
3Li
6
What is that product called?
tritium