Protons transmutation

The stmcture of the particles inside the nucleus was the next question to be addressed. One step in this direction was the discovery of the neutron in 1932 by Chadwick, and the deterrnination that the nucleus was made up of positively charged protons and uncharged neutrons. The number of protons in the nucleus is known as the atomic number, Z. The number of neutrons is denoted by A/, and the atomic mass is thus A = Z - - N. Another step toward describing the particles inside the nucleus was the introduction of two forces, namely the strong force that holds the protons and neutrons together in spite of the repulsion between the positive charges of the protons, and the weak force that produces the transmutation by P decay. 

Electron Capture and /5" "-Decay. These processes are essentially the inverse of the j3 -decay in that the parent atom of Z andM transmutes into one of Z — 1 andM. This mode of decay can occur by the capture of an atomic electron by the nucleus, thereby converting a proton into a neutron. The loss of one lepton (the electron) requires the creation of another lepton (a neutrino) that carries off the excess energy, namely Q — — Z(e ), where the last term is the energy by which the electron was bound to the atom before it was captured. So the process is equivalent to... 

A neutron can get close to a target nucleus more easily than a proton can. Because a neutron has no charge and hence is not repelled by the nuclear charge, it need not be accelerated to such high speeds. An example of neutron-induced transmutation is the formation of cobalt-60, which is used in the radiation treatment of cancer. The three-step process starts from iron-58. First, iron-59 is produced ... 

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. 

Here the effect of the (3 emission is to increase the atomic number by 1 (i.e., to transmute X into the next heaviest element in the periodic table, Y), to leave the atomic weight unchanged (a so-called isobaric transmutation), and to emit the (3 particle, which is conventionally given a mass of 0 and a charge of —1. Although it does not actually happen like this, it is often useful to think of the (3 process as being the conversion of a neutron into two equal but oppositely charged particles, the proton and the electron, as follows ... 

The nuclear reaction involving the bombardment of curium with calcium that directly produced element 116 occurred on December 6, 2000, at the Joint Institute for Nuclear Research in Dubna, Russia, in cooperation with personnel of the Lawrence-Livermore Berkeley Group. This nuclear reaction resulted in the production of a few atoms of the isotope ununhexium-292, which has a half-life of 0.6 milliseconds and emits four neutrons. Uuh-292 is also the most stable isotope of element 116 as it continues to decay into elements with Z numbers of 114, 112, 110, 108, and 106, plus emitting four alpha particles for each transmutation. (Z numbers are the number of protons in the nuclei of atoms.)... 

The synthesis of helium follows a somewhat indirectpath. The longest part is the first, because it involves the transformation of a proton into a neutron, and such transmutations proceed via the weak interaction (slow at these temperatures). The leisurely pace of these reactions confers long life upon main-sequence stars. 

Beyond iron, nucleosynthesis proceeds via neutron capture by iron and its neighbours. Two types of neutron capture, slow denoted by s and rapid denoted by r, come into play depending on the intensity and duration of neutron irradiation. Once the neutron has been absorbed, the resulting product depends on whether the neutron has time to convert into a proton inside the nucleus before a further neutron is absorbed. If the transmutation occurs before further capture, we have an s process, otherwise an r process. 

Theoretically, nuclear strength is enhanced by internal transmutations of protons into neutrons, under the mandate of the weak interaction, either by positron emission (p — n + e+ + v) or by electron capture (p + e n + v). However, the weak interaction is much slower than the strong interaction. The question remains as to whether it will happen inside the star, or outside, once the matter has been expelled, i.e. after the explosion. This is not just an academic question. The answer we give will determine whether or not we can corroborate explosive nucleosynthesis by observation. 

The other chemically important mode of radioactive transmutation is provided by negative beta particles (fi), which are electrons emitted by atomic nuclei, not from the surrounding electronic orbitals. The beta particle arises from the decay of a neutron to a proton ... 

The creation of the proton causes the atomic number to increase by one. An example of beta transmutation is the decay of lead-212 ... 

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

Yhde generation by this method involves a 1,2-prototropic shift of the proton a to the imine, furnishing, in this instance, a mixture of yhdes 124 and 125, which undergo subsequent ent o-cycloaddition. Due to the highly reactive nature of the dipolarophile, it is unlikely that a single ylide is initially formed, followed by dipole transmutation (Scheme 3.36). 

In 1899 he identified two forms of radioactivity, which he called alpha and beta particles. As we saw earlier, he deduced that alpha particles are helium nuclei. Beta particles are electrons - but, strangely, they come from the atomic nucleus, which is supposed to be composed only of protons and neutrons. Before the discovery of the neutron this led Rutherford and others to believe that the nucleus contained some protons intimately bound to electrons, which neutralized their charge. This idea became redundant when Chadwick first detected the neutron in 1932 but in fact it contains a deeper truth, because beta-particle emission is caused by the transmutation ( decay ) of a neutron into a proton and an electron. 

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 . 

III hen a radioactive nucleus emits an alpha or beta particle, the identity UU of the nucleus is changed because there is a change in atomic number. The changing of one element to another is called transmutation. Consider a uranium-238 nucleus, which contains 92 protons and 146 neutrons. When an alpha particle is ejected, the nucleus loses 2 protons and 2 neutrons. Because an element is defined by the number of protons in its nucleus, the 90 protons and 144 neutrons left behind are no longer identified as being uranium. What we have now is a nucleus of a different element—thorium. 

Transmutation The conversion of an atomic nucleus of one element to an atomic nucleus of another element through a loss or gain of protons. 

Bombardment reactions are often summarized in a terse form, such as Be(a,n). This means that the target (9Be) is bombarded by a particles ( He), and that neutrons (in) are produced. By the rules for balancing nuclear equations, we know that j=C also is produced. Give the complete balanced nuclear equation for each of the following transmutation bombardments (p stands for proton, and d stands for deuteron in this notation). 

JOLIOT-CURIE. IRENE 11897-195ft. A French nuclear scientist who won the Nohel prize for chemistry with her husband Frederick Joliet-Curie. Their joint work involved production of artiliciul radioactive elements by using t/-rays to bombard boron. They discovered that hydrogen-containing material when exposed to what they considered p rays would emit protons. Tliev were involved in many firsts they gave Ihe first chemical proof of aitillcial transmutation and of capture of alpha particles, and were the firsi to prepare positron emitter. Her career started with a Sc.D. at the Univ ersity of Paris, and included scores of honors and awards. 

Another kind of particle and another kind of interaction were discovered from a detailed study of beta radioactivity in which electrons with a continuous spectrum of energies are emitted by an unstable nucleus. The corresponding interactions could be viewed as being due to the virtual transmutation of a neutron into a proton, an electron, and a new neutral particle of vanishing mass called the neutrino. The theory provided such a successful systematization of beta decay rate data for several nuclei that the existence of the neutrino was well established more than 20 years before its experimental discovery. The beta decay interaction was very weak even compared to the electron-photon interaction. 

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. 

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