Nitrogen transmutation

Unstable isotopes decompose (decay) by a process referred to as radioactivity. Ordinarily the result is the transmutation of elements the atomic number of the product nucleus differs from that of the reactant. For example, radioactive decay of produces a stable isotope of nitrogen, N. The radiation given off (Figure 2.6) may be in the form of—... 

The half-lives of the elements vary widely, as shown in Table 3.2. Some isotopes, nitrogen-14 for example, are stable and experience no natural radioactive decay. However, bombarding even a stable element with energetic alpha rays can cause transmutation. Rutherford discovered the proton when he created hydrogen from a stable isotope of nitrogen. 

Since all Rutherford could know from his scintillation experiments was that alpha particles infrequently caused nitrogen nuclei to emit protons—he could not see the actual interaction—he had assumed it was a disintegration process. Only the cloud chamber could provide a visual representation of the transmutation process itself and give physicists the chance to discover the intricacies of the exchange. 

New Zealand-born physicist, successfully transmuted nitrogen into oxygen by changing the number of its protons. (World History/Topham/The Image Works)... 

Transmutation is the process where one element is artificially changed into another element. Rutherford conducted the first transmutation experiment in 1919 when he bombarded nitrogen atoms with alpha particles. The nitrogen was transmuted into oxygen and hydrogen according to the reaction ... 

This was just the start. In 1919 Rutherford found that alpha particles emitted from radium could chip protons from the nuclei of nitrogen atoms. This was something new. Radioactive elements decayed spontaneously into other elements because they were fundamentally unstable. But there was nothing unstable about nitrogen. Yet Rutherford had nevertheless managed to transmute it artificially. The newspapers found a catchy phrase for this feat splitting the atom . 

By this time, Rutherford had evidence that hydrogen nuclei could come from more complex nuclei (56). In 1919, he reported an anomalous effect when he subjected diy air to a particles H atoms seemed to be produced even when there was no hydrogen in the system Rutherford correctly interpreted the presence of H nuclei as a sign that the a particles caused some sort of transmutation, and that the H nuclei were fragments of that reaction. I infer from Rutherford s use of the term disintegration that he pictured the reaction as an induced fission of nitrogen. In fact, the reaction was + He — + H. Rutherford and his associates... 

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. 

Rutherford gave an estimate of the dimensions of the nucleus and then discussed the passage of (3 and a particles through matter, the transmutation of nitrogen into oxygen he had observed 2 years before,22 the existence of isotopes of both radioactive and stable elements, their separation, and finally the structure of nuclei for which a reduction of the mass had been established with respect to the sum of the masses of their constituents, which were assumed to be protons and electrons, in appropriate number. 

Note that the transmutation of nitrogen leads to a kind of oxygen which is different from ordinary oxygen to the extent of having an additional neutron in the nucleus, hence a mass of 17 rather than the more usual 16. 

Fifteen years after Rutherford s transmutation of nitrogen, an equally if not more significant experiment was conducted successfully by Frederic and Irene Curie Joliot. They bombarded boron with alpha particles and produced nitrogen in a manner shown by the following reaction ... 

The remarkable feature of this transmutation was the fact that the nitrogen isotope produced was radioactive. These nitrogen atoms of mass 13 (rather than 14) underwent radioactive decay by emission of positive electrons, or positrons, to form stable carbon atoms of mass 13,... 

The 14N atom is the fourth mostabundantnucleus that is produced by nucleosynthesis in the stars (after l60,12C and 20Ne). Its nucleosynthesis occurs primarily in stars of insufficient mass to become supernovae, especially in AGB stars (see Glossary). It is the natural byproduct of the fusion of hydrogen into helium in the carbon-nitrogen cycle. The 14N is created by proton-capture reactions transmuting the initial C and O within the star to 14N during the CN cycle. Production from intial C and O makes 14N a secondary nucleus, since it can be made only in proportion to the amount of C... 

In almost all of the previous examples, we have looked at nuclear reactions that occur by spontaneous decay. There are other types of nuclear reactions that can occur, known as transmutation reactions. These reactions can be induced by forcing a reaction between the nucleus of an element and nuclear particles (such as neutrons), or nuclei. Ernest Rutherford carried out the first transmutation by bombarding nitrogen-14 nuclei with alpha particles. This resulted in the production of oxygen-17 and a proton, as shown below ... 

Note that in equation (10), as in the other nuclear equations listed, atomic numbers and mass numbers are both conserved. This reaction was the first artificial transmutation, carried out (as contrasted to spontaneous transmutations or natural radioactivity in which one nucleus is transformed to another, irrespective of the influence of man). The a particle in equation (10) is the projectile and the nitrogen nucleus the target. 

The New Zealand-born Father of Nuclear Physics held a lifelong interest in alchemy, and included ffermes Trismegistus on his coat of arms. His conversion of nitrogen into oxygen is seen by some as the world s first scientifically verifiable transmutation. 

Two chemists, an American named W. D. Harkins and an Englishman named P.M.S. Blackett, studied this strange phenomenon further. Blackett took photos of 400 000 alpha particle tracks that formed in cloud chambers. He found that 8 of these tracks forked to form a Y, as shown in Figure 29. Harkins and Blackett concluded that the Y formed when an alpha particle collided with a nitrogen atom in air to produce an oxygen atom and a proton, and that a transmutation had thereby occurred. 

The discovery that a transmutation had happened started a flood of research. Soon after Harkins and Blackett had observed a nitrogen atom forming oxygen, other transmutation reactions were discovered by bombarding various elements with alpha particles. As a result, chemists have synthesized, or created, more elements than the 93 that occur naturally. These are synthetic elements. All of the transuranium elements, or those with more than 92 protons in their nuclei, are synthetic elements. To make them, one must use special equipment, called particle accelerators, described below. 

---