Induced radioactivity facts for kids
Induced radioactivity is when we make something that wasn't radioactive become radioactive. It's also called artificial radioactivity or man-made radioactivity. This happens by using radiation to change a stable material. A husband and wife team, Irène Joliot-Curie and Frédéric Joliot-Curie, found this out in 1934. They even won the 1935 Nobel Prize in Chemistry for their amazing discovery!
Irène Curie started her research with her famous parents, Marie Curie and Pierre Curie. They studied natural radioactivity, which is found in certain radioactive isotopes. Irène then decided to explore something new. She wanted to see if stable materials could be made radioactive.
She did this by hitting stable materials with tiny alpha particles (α). These particles are like tiny bullets. The Joliot-Curies found that when they shot alpha particles at light elements, like boron and aluminium, these elements started giving off radiation. What was surprising was that the radiation continued even after the alpha particle source was taken away! They discovered this radiation was made of particles called positrons. Positrons are like electrons but with a positive charge.
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How Induced Radioactivity Works
There are a few ways to make a material artificially radioactive.
Neutron Activation
The most common way to create induced radioactivity is called Neutron activation. This happens when an atomic nucleus captures one or more free neutrons. Imagine a neutron as a tiny building block of an atom. When an atom's nucleus grabs a neutron, it becomes a new, heavier isotope. This new isotope might be stable or it might be unstable (radioactive). It depends on the chemical element involved.
Free neutrons don't last long outside an atom. They break apart in minutes. So, we get free neutrons from things like nuclear decay, nuclear reactions, or high-energy events. These events include cosmic radiation or beams from particle accelerators. Neutrons that are slowed down by a neutron moderator (called thermal neutrons) are more likely to be captured by atomic nuclei.
Photodisintegration
A less common way to make something radioactive is through photodisintegration. In this process, a very powerful photon (a gamma ray) hits an atom's nucleus. This photon has to have more energy than the nucleus's binding energy. When it hits, it can knock a neutron out of the nucleus. This reaction needs a lot of energy. For most heavy atoms, the gamma ray needs about 10 MeV of energy. Many radioactive materials don't produce gamma rays strong enough to cause this reaction.
For example, the isotopes used to treat food (cobalt-60, caesium-137) do not produce gamma rays with enough energy. This means they cannot make the food radioactive.
Induced Radioactivity in Nuclear Reactors
Inside certain types of nuclear reactors, there's a very high flow of neutrons. These conditions can cause induced radioactivity. The parts of these reactors can become very radioactive from all the radiation they are exposed to. This induced radioactivity adds to the amount of nuclear waste that needs to be safely stored. However, it's not called radioactive contamination unless it gets out of control.
Medical Uses
The research started by Irène and Frédéric Joliot-Curie has been very important. It led to modern ways of treating different types of cancers. Doctors can now use controlled radiation to help patients.
Ștefania Mărăcineanu's Contributions
After World War I, a scientist named Ștefania Mărăcineanu received a scholarship. This allowed her to travel to Paris to study more. In 1919, she took a course on radioactivity at the Sorbonne with Marie Curie. She then worked with Marie Curie at the Radium Institute until 1926. She earned her Ph.D. there.
At the Institute, Mărăcineanu studied how long polonium stays radioactive (its half-life). She also found ways to measure alpha decay. Her work made her think that radioactive isotopes could be made from atoms. She believed this happened when atoms were exposed to polonium's alpha rays. This idea was very similar to what the Joliot-Curies later discovered, which won them the 1935 Nobel Prize.
In 1935, Frederic and Irene Joliot-Curie (Marie Curie's daughter) won the Nobel Prize. They won it for discovering artificial radioactivity. However, many facts suggest that Mărăcineanu was the first to make this discovery. Ștefania Mărăcineanu was upset that Irene Joliot-Curie used much of her work without giving her credit. Mărăcineanu publicly stated that she discovered artificial radioactivity during her research years in Paris. Her doctoral paper, presented over 10 years earlier, supported her claim. A book called A devotion to their science: Pioneer women of radioactivity mentions this. It says Mărăcineanu wrote to Lise Meitner in 1936. She expressed her disappointment that Irene Joliot Curie used her work, especially about artificial radioactivity, without her knowing.
See also
- Neutron activation
- Radioactive decay
- Radioactivity
- Slow neutron
- Radiocarbon dating
