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Welcome to our Physics lesson on What are Nuclear Reactions?, this is the first lesson of our suite of physics lessons covering the topic of Nuclear Reactions, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
The term "nuclear reactions" refers to a special category of matter-energy interaction that includes all processes in which two or more objects interact with each other through nuclear forces.
The particles involved in nuclear reactions include atomic nuclei and other particles either involved in the process or produced during them, as well as the corresponding radiation emitted. Nuclear reactions are apparently similar to chemical reactions (where we have to consider the amount of reactants and product based on the law of mass and energy conservation). Thus, in a nuclear reaction, a target (parent) nucleus is hit by another nuclear particle. As a result, a new (daughter) nucleus is obtained, where some energy (and nuclear particles) is/are released or absorbed, depending on the type of nuclear reaction. The hitting particle may be a proton, neutron, gamma ray or an entire atomic nucleus.
Schematically, a nuclear reaction is written as:
where X is the target nucleus, a is the hitting particle, Y is the daughter (hit) nucleus and b is the particle/s produced during the reaction.
Another important quantity to be considered during a nuclear reaction is the energy of reaction, Q. It represents the energy released or absorbed during a nuclear reaction. Thus, based on mass-energy equivalence, when Q > 0, then the total mass of reaction products is smaller than the mass of target nuclei plus that of hitting particle. Likewise, when the total mass of system increases after the reaction, the energy is absorbed by the system (Q < 0).
Do not confuse nuclear reactions with radioactive decay processes. If we use an analogy with linear momentum, nuclear reactions are analogue to collisions (both elastic and inelastic) while decay processes are analogue to explosions, as the energy stored in atomic nuclei is activated when a radioactive decay takes place, similar to energy stored in chemical form that is activated during explosions.
Beryllium-9 absorbs an alpha particle during a nuclear reaction, producing an unknown nucleus and a neutron. What is the unknown nucleus?
In the periodic table, we can see that Beryllium has Z = 4. Thus, giving that an alpha particle (42He) is absorbed by the Beryllium nucleus (energy is added to the system), and a neutron has Z = 0 and A = 1, this nuclear reaction is written schematically as follows.
Hence, we obtain two linear equations in one variable, one for protons Z and the other for nucleons A:
and
Solving these two equations we obtain Z = 6 and A = 12. These values correspond to Carbon-12 element (126Ca). Therefore, the unknown atomic nucleus X is a Ca-12 nucleus.
You have reached the end of Physics lesson 20.4.1 What are Nuclear Reactions?. There are 11 lessons in this physics tutorial covering Nuclear Reactions, you can access all the lessons from this tutorial below.
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