Nuclear reactions artificial radioactivity

Scientists have learned how to make some isotopes undergo nuclear reactions. Artificial radioactivity is induced by bombardment of certain nuclei with subatomic particles (or atoms), which are produced either by other nuclear reactions or in machines called particle accelerators. For example, the first artificially induced nuclear reaction was produced by Ernest Rutherford (1871-1937) in 1919 ... 

ISOTOPES There are 50 Isotopes of Yttrium. Only one Is stable (Y-89), and It constitutes 100% of the element s natural existence on Earth. The other Isotopes range from Y-77 to Y-108 and are all produced artificially In nuclear reactions. The radioactive Isotopes have half-lives ranging from 105 nanoseconds to 106.65 days. 

One may rightfully raise the question as to why some products of nuclear reactions are radioactive while others are not. The answer concerns the stability of atomic nuclei. Essentially, any radioactive element, whether artificial or natural, can be considered abnormal. A nucleus that undergoes radioactive decay is in an unstable condition, and the process of decay always leads to stable isotopes. This tendency toward the achievement of stability is illustrated by the stepwise decay of naturally radioactive uranium to form a stable isotope of lead and the formation of stable carbon by the decay of artificial radioactive nitrogen. Although the conditions resulting in the instability of atomic nuclei are fairly well understood, further consideration of these factors is beyond the scope of this discussion. 

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. In many analytical applications, the ratio of occurrence of the isotopes is important. For example, it may be important to know the exact ratio of the abundances (relative amounts) of the isotopes 1, 2, and 3 in hydrogen. Such knowledge can be obtained through a mass spectrometric measurement of the isotope abundance ratio. 

Radioactivity, Induced—Radioactivity produced in a substance after bombardment with neutrons or other particles. The resulting activity is "natural radioactivity" if formed by nuclear reactions occurring in nature and "artificial radioactivity" if the reactions are caused by man. 

Californium is a synthetic radioactive transuranic element of the actinide series. The pure metal form is not found in nature and has not been artificially produced in particle accelerators. However, a few compounds consisting of cahfornium and nonmetals have been formed by nuclear reactions. The most important isotope of cahfornium is Cf-252, which fissions spontaneously while emitting free neutrons. This makes it of some use as a portable neutron source since there are few elements that produce neutrons all by themselves. Most transuranic elements must be placed in a nuclear reactor, must go through a series of decay processes, or must be mixed with other elements in order to give off neutrons. Cf-252 has a half-life of 2.65 years, and just one microgram (0.000001 grams) of the element produces over 170 mhhon neutrons per minute. 

Neither californium nor its compounds are found in nature. All of its isotopes are produced artificially in extremely small amounts, and all of them are extremely radioactive. All of its isotopes are produced by the transmutation from other elements such as berkelium and americium. Following is the nuclear reaction that transmutates californium-250 into cahfornium-252 Cf + (neutron and A, gamma rays) — Cf + (neutron and A, gamma rays) —> Cf. 

TRANSMUTATION. The natural or artificial transformation of atoms of one element into atoms of a different element as the result of a nuclear reaction. The reaction may be one in which two nuclei interact, as in the formation of oxygen from nitrogen and helium nuclei (/3-particles), or one in which a nucleus reacts widi an elementary particle such as a neutron or proton. Thus, a sodium atom and a proton form a magnesium atom. Radioactive decay, e.g., of uranium, can be regarded as a type of transmutation. The first transmutation was performed bv the English physicist Rutherford in 1919. 

Following this theory, the transformation of one element into another one was realized. The nuclear equation of this artificial radioactive reaction is illustrated below ... 

After 1933 Fermi turned increasingly to experimental physics. Inspired by recent work in which artificial radioactive substances were produced by a-particle bombardment, Fermi and several collaborators used neutron bombardment to create several transuranic elements heavier than uranium, including plutonium. This work, and his finding that slow neutrons produce nuclear reactions more efficiently than fast ones, earned Fermi wide acclaim and the 1938 Nobel Prize in physics. After accepting the prize in Sweden, Fermi and his Jewish wife immigrated to the United States to escape the Nazis. 

Radiopharmaceuticals are labeled with artificial radionuclides that are obtained by bombardment of stable nuclei with subatomic particles or photons. Nuclear reactions produced in such a way convert stable in unstable (radioactive nuclei). Several kind of devices are used for such purposes, including nuclear reactors, particle accelerators, and generators. 

None of the reactions or processes stndied in previous chapters affected the nucleus of an atom. No atom changed from one element to another. This chapter considers the effects of nuclear change. In most cases, such changes cause a transformation from one element to another. They include the natural radioactivity of certain isotopes (Section 3.3), as well as the artificial nuclear reactions discovered during the twentieth century. Nuclear reactions differ from ordinary chemical reactions in the following ways ... 

These reactions are examples of artificial transmutation—the change of one element into another. Several small particles, in addition to those involved in natural radioactivity, are involved in artificial nuclear reactions. Some of these additional particles are listed in Table 21.4. They are used as projectiles to bombard nuclei or are produced along with other products of such reactions, or both. 

The actinides are all radioactive elements. Actinium, thorium, protactinium, and uranium are the only four actinides that have been found in the environment the others are artificial, being produced through various nuclear reactions. It should be noted that at the creation of the universe some amount of Pu could have been formed however, with an 80 million year half-life, it would have fully decayed during the past 10 billion years. 

The nucleus is stable, so that this nuclear reaction does not lead to the production of artificial radioactivity. Many other eleuicnts, hotsever, undergo similar reactions with the production of unstable nuclei, which then undergo radioactive decomposition. 

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. 

The study of electron transfer reactions began in earnest when radioactive isotopes, produced for nuclear research and the atom bomb program during World War II, became accessible. Glen Seaborg, in a 1940 review of artificial radioactivity, noted the first attempt to measure the self-exchange reaction between aqueous iron(III) and iron(II), equation (1.9).1"... 

Fermi, Enrico. (1901-1954). An Italian physicist who later became a U.S. citizen. He developed a statistical approach to fundamental problems of physical chemistry based on Pauli s exclusion principle. He discovered induced or artificial radioactivity resulting from neutron impingement, as well as slow or thermal neutrons. He was professor of physics at Columbia (1939) and awarded the Nobel Prize in physics in 1938. He was the first to achieve a controlled nuclear chain reaction, directed the construction of the first nuclear reactor at the University of Chicago (1942), and worked on the atomic bomb at Los Alamos. He also carried on fundamental research on subatomic particles using sophisticated statistical techniques. Element 100 (fermium) is named after him. 

Natural radioactivity is a spontaneous process artificial radioactivity is nonspontaneous and results from a nuclear reaction that produces an unstable nucleus. 

Tritium is formed continuously in the upper atmosphere in nuclear reactions induced by cosmic rays. For example, fast neutrons arising from cosmic-ray reactions can produce tritium by the reaction 14N( , 3H)12C. Tritium is radioactive (/ ", 12.4 years) and is believed to be the main source of the minute traces of 3He found in the atmosphere. It can be made artificially in nuclear reactors, for example, by the thermal neutron reaction, 6Li(/ ,a)3H, and is available for use as a tracer in studies of reaction mechanism. 

The artificial radioactivity of waters is caused particularly by radionuclides formed by nuclear fission reactions (nuclear explosions, nuclear reactors). The contribution of artificial radioactivity from scientific and medical institutions is small. The foUowing radionuclides in particular can be considered in this case Sr, I, Cs, Ce, Ce, etc. Other... 

Isotopes of many lighter elements with lower mass numbers are radioactive, too. At least one radioisotope is known for every element. Most of these do not occur in nature but can be generated in reactors by nuclear reactions. Tritium (jH) is a naturally occurring radioisotope of hydrogen. Artificial radioactive isotopes are known for a number of elements. 

The radioactivity of naturally occurring and artificially produced isotopes, nuclear fission (the reactions involved in commercial nuclear reactors) and nuclear fusion (the source of the sun s power) are all examples of nuclear reactions (Fig. 21.1). Radioactivity started as a scientific curiosity. From these humble beginnings developed nuclear power (the main provider of power for the generation of electricity in some countries) and the awesome power of nuclear warheads. 

The law of conservation of matter Matter is neither lost nor gained in chemical reactions (Section 3.1). The only known exception to this law is in nuclear reactions, which occur only with radioactive isotopes or under the special conditions of artificial nuclear reactions (Section 13.5). The conservation law (so far) has always been reliable for chemical changes other than nuclear reactions. 

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