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Nuclear Reactions
In the previous section we discussed how a single atomic nucleus can spontaneously transform into a different nucleus through the process of radioactive decay. As it turns out, it is also possible for a stable nucleus to transform into another nucleus during a process known as a nuclear reaction. During a nuclear reaction, two nuclei collide to form entirely different nuclei.
In the previous section we discussed how a single atomic nucleus can spontaneously transform into a different nucleus through the process of radioactive decay. As it turns out, it is also possible for a stable nucleus to transform into another nucleus during a process known as a nuclear reaction. During a nuclear reaction, two nuclei collide to form entirely different nuclei.
Ernest Rutherford induced one of the earliest recorded nuclear reactions during his discovery of the proton in 1917. As we discussed previously, Rutherford discovered the proton by scattering alpha particles from nitrogen gas. In doing so, he inadvertently induced the following nuclear reaction:
However not enough was known about nuclear structure at the time for Rutherford and others to fully understand the nuclear reconfiguration that had taken place. In 1932, Ernest Walton and John Cockcroft succeeded in inducing a nuclear reaction by firing protons at a lithium-7 nucleus, thus producing two alpha particles. Walton and Cockcroft’s achievement popularly became known as “splitting the atom.”
Since Rutherford’s time, technological advances have substantially increased our ability to induce nuclear reactions, which has allowed us to better understand the atomic nucleus and also discover new particles. The development of particle accelerators in the 1930s permitted reactions at higher energies to be explored. Today’s most advanced particle accelerators, including the Large Hadron Collider at CERN, have allowed physicists to accelerate particles faster than 99.9999% the speed of light.
Energy
While discussing radioactive decay, we learned that the decomposition of a nucleus could be accompanied by a net output of energy because of the release of nuclear binding energy. Likewise, nuclear reactions can convert nuclear binding energy into kinetic energy or gamma radiation. The energy released by one reaction event is corresponds to the difference in mass between the products and reactants. (Reactants are particles present at the start of a reaction, and products are particles that are produced by a reaction.) As an example, consider the reaction of deuterium with lithium-6 to form two atoms of helium-4:
While discussing radioactive decay, we learned that the decomposition of a nucleus could be accompanied by a net output of energy because of the release of nuclear binding energy. Likewise, nuclear reactions can convert nuclear binding energy into kinetic energy or gamma radiation. The energy released by one reaction event is corresponds to the difference in mass between the products and reactants. (Reactants are particles present at the start of a reaction, and products are particles that are produced by a reaction.) As an example, consider the reaction of deuterium with lithium-6 to form two atoms of helium-4:
Since the products are less massive than the reactants, this reaction releases energy according to Einstein’s relation E = mc2. Nuclear reactions such as this one that release energy are called exothermic reactions.
Some nuclear reactions, known as endothermic reactions, require an input of energy in order to take place. As a result, the nuclei resulting from endothermic reactions are more massive than the original nuclei. Rutherford’s nuclear reaction that led to the discovery of the proton is an example of an endothermic reaction.
We can see by this comparing the total masses of the reactants and the products. The helium-4 atom and nitrogen atom sum to:
In this case we see that the products are more massive than the reactants, indicating that this reaction takes in more energy than it produces.
Two important categories of nuclear reactions are known as nuclear fission and nuclear fusion, which we will discuss in much greater detail.
Two important categories of nuclear reactions are known as nuclear fission and nuclear fusion, which we will discuss in much greater detail.