Radioactive decay is the process by which the unstable nucleus tries to change into a more stable form. As, it is the process in which the transformation will take place depending on the composition of the nucleus.
Beta decay is also the decay of one of the neutrons to a proton via the weak interaction:. It does not virtually undergo interactions with matter and therefore is essentially undetectable. This sharing of energy is more or less random from one decay to the next. It is also noticed that beta particles are not monoenergetic for a particular radionuclide, but they are released at varying energy levels over a continuous range spectrum. It is a mechanism for an excited nucleus to release energy.
Emanation could be a sort of radioactivity in which a few unsteady nuclear nuclei disseminate excess energy by an unconstrained electromagnetic radiation. Within the most common form of gamma decay, which is called gamma emission, gamma rays photons or bundles of electromagnetic vitality, of highly short wavelength are radiated.
Gamma rays are electromagnetic radiation high-energy photons with an extreme frequency and a high energy. Gamma decay also includes two other electromagnetic processes: internal conversion and pair production. Internal conversion IC is a process in which the excess energy of the nucleus is directly transferred to one of its own orbital electrons which is ejected instead of the ray.
In this case, the ejected electron is called a conversion electron as shown in Figure 7. Schematic representation of internal conversion involving a K shell electron. Unstable nucleus transfers its energy to an orbital electron to release a converted electron. In internal pair production , the excess energy is converted within the electromagnetic field of a nucleus into an electron and a positron that are released together. Internal conversion always accompanies the predominant process of gamma emission.
Internal pair production needs the excess energy of the unstable nucleus to be at least equivalent to the combined masses of an electron and a positron as shown in Figure 8. A pair of 0. The daughter of radioactive parent may be formed in a long-lived metastable isomeric state as opposed to an excited state.
Isomeric transition : a nuclear process in which a nucleus has abundant energy following the emanation of an alpha molecule or a beta molecule and in turn discharges energy without a change in its number of protons or neutrons. In many nuclides, isomeric transitions produce gamma photons and internal conversion electrons. When an electron is removed from the atom by internal conversion, a vacancy is created.
All transitions are usually followed by either gamma or internal conversion electron emission. The energized atomic state taking after the emission of a beta particle may be nearly steady, and the nucleus may be able to remain in this state for minutes, hours, or even days, sometimes recently discharging a gamma ray.
The isomer no change of the number of proton or neutron works as a separate radioactive material, which is decaying exponentially with the emission of a gamma ray only [ 5 ]. In other words, we can say that the electron capture is a process, in which a parent nucleus captures one of its orbital electrons and releases a neutrino. This neutrino is emitted from the nucleus and carries away some of the transitions energy. The remaining energy appears in the form of characteristic X-rays and Auger electrons, which are emitted by daughter product, whereas the resulting orbital electron vacancy is filled as shown in Figure 9.
The nucleus captures one of its orbital electrons and X-ray. A positron is an antiparticle of an ordinary electron:. After ejection from the nucleus, it loses its kinetic energy in collision with atoms of the surrounding matter and comes to rest; this usually happens within a few millimeters from the site of its origin in body tissue [ 6 ].
Radionuclide that decayed by a particle emission or by nuclear fission has relatively little importance for direct usage as tracers in nuclear medicine. Both of these decay modes occur primarily among very heavy elements that are of a little interest as physiological tracers [ 7 ]. The particles, which are released with kinetic energy, are usually found between 4 and 8 MeV. Decay by alpha particle emission results in transmission of elements, but it is not isobaric.
Activity : It is the total number of nuclei that are decaying per second. It is the probability that any individual atom will undergo decay during the same period:.
This type of compound is called a radioactive tracer or radioactive label. Radioisotopes are used to follow the paths of biochemical reactions or to determine how a substance is distributed within an organism. Radioactive tracers are also used in many medical applications, including both diagnosis and treatment.
They are also used in many other industries to measure engine wear, analyze the geological formation around oil wells, and much more. Radioisotopes have revolutionized medical practice , where they are used extensively. Over 10 million nuclear medicine procedures and more than million nuclear medicine tests are performed annually in the United States. Four typical examples of radioactive tracers used in medicine are technetium , thallium , iodine , and sodium 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. Each radioactive element decays at a unique rate.
This rate is known as a half-life; the amount of time it takes for approximately half of the radioactive atoms in a sample to decay into a more stable form.
The image above indicates that radium has a half-life of 1, years. So every 1, years approximately half of the radium atoms in a sample decay and change to radon the next element in the decay chain. Note that uranium, radium and lead are metals, while radon is an inert gas under normal conditions. It is possible that as radioactive elements decay, their form metal, gas, liquid, etc.
The half-life of slow decaying elements like uranium and carbon can be used to determine the age of organic matter. Radiographers also use half-life information to adjust film exposure times for x-rays and scans using other forms of ionizing radiation.
Image of an alpha particle being emitted from a nucleus. When the ratio of neutrons to protons in the nucleus is too low, certain atoms restore the balance by emitting alpha particles. They are relatively heavy, high-energy particles that cannot penetrate most matter. A piece of paper or the dead outer layers of skin is sufficient to stop alpha particles.
Radioactive material that emits alpha particles alpha emitters can be very harmful when inhaled, swallowed or absorbed into the blood stream because internal organs are more directly exposed without a protective layer of skin cells.
Image of a beta particle. Beta particle emission occurs when the ratio of neutrons to protons in the nucleus is too high. In this case, an excess neutron transforms into a proton and an electron.
The proton stays in the nucleus and the electron -1 is ejected energetically. This process decreases the number of neutrons by one and increases the number of protons by one. Since the number of protons in the nucleus of an atom determines the element, the conversion of a neutron to a proton actually changes the radioactive element radionuclide to a different element.
The speed of individual beta particles depends on how much energy they have, and varies widely. Beta particles can be stopped by a layer or two of clothing or by a few millimeters of a substance such as aluminum. They are capable of penetrating the skin and causing radiation damage, such as skin burns. As with alpha emitters, beta emitters are most hazardous when they are inhaled or ingested. Nuclear reactions produce a great deal more energy than chemical reactions. Nuclear reactions release some of the binding energy and may convert tiny amounts of matter into energy.
That means that nuclear changes involve almost one million times more energy per atom than chemical changes! Figure Confirm that this equation is correctly balanced by adding up the reactants' and products' atomic and mass numbers.
The mass numbers of the original nucleus and the new nucleus are the same because a neutron has been lost, but a proton has been gained, and so the sum of protons plus neutrons remains the same. The atomic number in the process has been increased by one since the new nucleus has one more proton than the original nucleus. In this beta decay, a thorium nucleus has one more proton than the original nucleus.
In this beta decay, a thorium nucleus has become a protactinium nucleus. Protactinium is also a beta emitter and produces uranium Once again, the atomic number increases by one and the mass number remains the same; this confirms that the equation is correctly balanced.
When studying nuclear reactions in general, there is typically little information or concern about the chemical state of the radioactive isotopes, because the electrons from the electron cloud are not directly involved in the nuclear reaction in contrast to chemical reactions. So it is acceptable to ignore charge in balancing nuclear reactions, and concentrate on balancing mass and atomic numbers only.
This reaction is an alpha decay. We can solve this problem one of two ways:. Solution 2: Remember that the mass numbers on each side must total up to the same amount. The same is true of the atomic numbers. Emitting a beta particle causes the atomic number to increase by 1 and the mass number to not change. We get atomic numbers and symbols for elements using our periodic table.
We are left with the following reaction:. Emitting an alpha particle causes the atomic number to decrease by 2 and the mass number to decrease by 4.
We are left with:. The decay of a radioactive nucleus is a move toward becoming stable. Often, a radioactive nucleus cannot reach a stable state through a single decay. In such cases, a series of decays will occur until a stable nucleus is formed. Several of the radioactive nuclei that are found in nature are present there because they are produced in one of the radioactive decay series.
For example, there may have been radon on the earth at the time of its formation, but that original radon would have all decayed by this time.
The radon that is present now is present because it was formed in a decay series mostly by U A nuclear reaction is one that changes the structure of the nucleus of an atom. The atomic numbers and mass numbers in a nuclear equation must be balanced.
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