What is the difference between radioactivity and nuclear fission

The energy and mass aspects of the fission process can be explained mathematically as follows. Let the total binding energy of the heavy nucleus and the two fission products be B h , B f1 , and B f2 , respectively. This energy appears in various forms: the kinetic energy of the neutrons, the vibrational energy of the fission fragments, and gamma radiation.

All of these forms of energy are converted to heat by absorption in with the surrounding media in the reactor, mainly the coolant and the moderator for thermal reactors. The most basic fission reaction in nuclear reactors involves the splitting of the nucleus of uranium when it is struck by a neutron. The uranium first absorbs the neutron to yield uranium, and most of these U nuclei split into two fission fragments. Fission reactions typically also release two to four neutrons depending on the speed on the neutrons inducing the fission and probabilistic factors.

One of these neutrons must trigger another fission for a sustained chain reaction. The fission reactions in a nuclear reactor can be written generically as follows:. The uranium nucleus does not split evenly into equal fission fragments. Rather, the tendency, especially with fission induced by thermal neutrons, is for one fragment to be considerably lighter than the other.

Figure 9 not available in on-line version of report shows the distribution of fission products due to fission with the slow neutrons and fast neutrons. It can be seen that the fission product atomic numbers are concentrated in the ranges from about 80 to and from about to in thermal reactors. An example of a fission reaction is:. It turns out that, with some exceptions, like plutonium, only nuclei that can be fissioned with slow neutrons can be used for sustaining chain reactions.

Generally these are the odd-numbered isotopes, such as uranium, uranium, plutonium, and plutonium Other heavy nuclei, like uranium, can be fissioned with fast neutrons, and so are fissionable , but not fissile. There are only three fissile isotopes of practical importance: uranium, uranium, and plutonium Of these, only uranium occurs naturally in significant quantities. The other two occur in trace quantities only. To obtain plutonium and uranium in amounts useful for nuclear energy production, they must be manufactured from materials that occur in relative abundance.

Plutonium is produced from reactions following the absorption of a neutron by uranium; uranium is produced by neutron absorption in thorium Uranium and thorium are called fertile materials, and the production of fissile materials from them is called breeding. The reactions for plutonium are. Subject: Factsheets. Posted on December, Last modified May, Download this page as a PDF. Structure of the Atom The atoms of which every element of matter is composed have a nucleus at the center and electrons whirling about this nucleus that can be visualized as planets circling around a sun, though it is impossible to locate them precisely within the atom.

Radioactive Decay The nuclei of some elements are not stable. There are several ways in which unstable nuclei undergo radioactive decay: Alpha decay, which the emission of a helium-4 nucleus containing two protons and two neutrons. This is the least penetrating form of radiation. It is stopped by the dead layer of skin and so does no harm when outside the body. But it is the most damaging form of radiation when deposited inside the body. Beta decay, which the emission of an electron or a positron a particle identical to an electron except that it has a positive electrical charge.

Electron capture, which is the capture by the nucleus of an electron from among the ones whirling around it. In effect, the electron combines with a proton to yield a neutron. Spontaneous fission, which is the fission of a heavy element without input of any external particle or energy. This is like balancing a chemical equation, in which the number of atoms of each element on both sides of the reaction must be equal In beta decay, the atomic number increases by one if an electron is emitted or decreases by one if a positron is emitted.

Damaged tissues in the heart, liver, and lungs absorb certain compounds of technetium preferentially. Thallium Figure 3. Iodine concentrates in the thyroid gland, the liver, and some parts of the brain. Salt solutions containing compounds of sodium are injected into the bloodstream to help locate obstructions to the flow of blood.

Administering thallium to a patient and subsequently performing a stress test offer medical professionals an opportunity to visually analyze heart function and blood flow. Radioisotopes used in medicine typically have short half-lives—for example, Tc has a half-life of 6.

This makes Tc essentially impossible to store and prohibitively expensive to transport, so it is made on-site instead. Hospitals and other medical facilities use Mo which is primarily extracted from U fission products to generate Tc The parent nuclide Mo is part of a molybdate ion, ; when it decays, it forms the pertechnetate ion,.

These two water-soluble ions are separated by column chromatography, with the higher charge molybdate ion adsorbing onto the alumina in the column, and the lower charge pertechnetate ion passing through the column in the solution. A few micrograms of Mo can produce enough Tc to perform as many as 10, tests. The MoO 4 2- is retained by the matrix in the column, whereas the TcO 4 —. The scan shows the location of high concentrations of Tc To perform a PET scan, a positron-emitting radioisotope is produced in a cyclotron and then attached to a substance that is used by the part of the body being investigated.

For example, F is produced by proton bombardment of 18 O and incorporated into a glucose analog called fludeoxyglucose FDG. How FDG is used by the body provides critical diagnostic information; for example, since cancers use glucose differently than normal tissues, FDG can reveal cancers. The 18 F emits positrons that interact with nearby electrons, producing a burst of gamma radiation. Different levels of gamma radiation produce different amounts of brightness and colors in the image, which can then be interpreted by a radiologist to reveal what is going on.

Unlike magnetic resonance imaging and X-rays, which only show how something looks, the big advantage of PET scans is that they show how something functions.

PET scans are now usually performed in conjunction with a computed tomography scan. Radioisotopes can also be used, typically in higher doses than as a tracer, as treatment.

Radiation therapy is the use of high-energy radiation to damage the DNA of cancer cells, which kills them or keeps them from dividing Figure 3. A cancer patient may receive external beam radiation therapy delivered by a machine outside the body, or internal radiation therapy brachytherapy from a radioactive substance that has been introduced into the body. Note that chemotherapy is similar to internal radiation therapy in that the cancer treatment is injected into the body, but differs in that chemotherapy uses chemical rather than radioactive substances to kill the cancer cells.

The cartoon in a shows a cobalt machine used in the treatment of cancer. The diagram in b shows how the gantry of the Co machine swings through an arc, focusing radiation on the targeted region tumor and minimizing the amount of radiation that passes through nearby regions. The overall process is:. The overall decay scheme for this is shown graphically in Figure 3.

Co undergoes a series of radioactive decays. Radioisotopes are used in diverse ways to study the mechanisms of chemical reactions in plants and animals. These include labeling fertilizers in studies of nutrient uptake by plants and crop growth, investigations of digestive and milk-producing processes in cows, and studies on the growth and metabolism of animals and plants.

For example, the radioisotope C was used to elucidate the details of how photosynthesis occurs. The overall reaction is:. In studies of the pathway of this reaction, plants were exposed to CO 2 containing a high concentration of.

At regular intervals, the plants were analyzed to determine which organic compounds contained carbon and how much of each compound was present.

From the time sequence in which the compounds appeared and the amount of each present at given time intervals, scientists learned more about the pathway of the reaction.

Commercial applications of radioactive materials are equally diverse Figure 3. They include determining the thickness of films and thin metal sheets by exploiting the penetration power of various types of radiation. Flaws in metals used for structural purposes can be detected using high-energy gamma rays from cobalt in a fashion similar to the way X-rays are used to examine the human body. Many foods are preserved by radiation that kills microorganisms that cause the foods to spoil.

Common commercial uses of radiation include a X-ray examination of luggage at an airport and b preservation of food. A battery supplies a potential that causes movement of the ions, thus creating a small electric current. When smoke enters the chamber, the movement of the ions is impeded, reducing the conductivity of the air. This causes a marked drop in the current, triggering an alarm. During a fire, smoke particles impede the flow of ions, reducing the current and triggering an alarm.

Radioactivity is defined as the emission of particles and electromagnetic rays from the nucleus of an unstable atom. Six types of radiation produced during nuclear decay were presented within this chapter and include:. The equation below can be used to determine how much isotope will remain after the passage of a given number of half-lives. Radioactive emissions can cause damage to biological systems by causing the breakdown of proteins and DNA. However, when used is small quantities and in controlled settings, radioactive tracers and treatments have proven to be revolutionary for the medical field.

For example, Radiation therapy is the use of high-energy radiation to damage the DNA of cancer cells, which kills them or keeps them from dividing.

Radioactive tracers have also been very useful in evaluating heart disease, thyroid dysfunction, and other blood disorders. Unless otherwise noted, resources for this chapter have been modified from the following creative commons resources:. Radioactivity and Nuclear Chemistry 3. Practice Problem: Question: The half-life of Zn is 2. Solution: Step 1. Back to the Top 3. Much more common is the fission induced by the capture of a neutron, a nuclear reaction which can be considered as a disintegration into two fragments of the nucleus, triggered by this capture.

The neutron is the ideal projectile to use in this sort of reaction, as its absence of charge allows it to be easily absorbed by the heavy nucleus. The heavy nuclei in which such a splitting occurs are known as ' fissile ', and only a handful of these unstable elements exist.

The only fissile nucleus still present in nature is uranium , a rare isotope of uranium with a half-life of million years. EN FR.