Beta decay reaction

When neodymiun-146 is bombarded with and captures neutrons, it becomes Nd-147 with a half-life of 11 days. Through beta decay, Nd-l47 then becomes Pm-147 with a half-life of 2.64 years. Other comphcated neutron and beta decay reactions from these radioactive elements are possible. 

This beta decay reaction has a half-life of 5730 years. Because the amount of stable carbon in the dead organism remains constant while the carbon-14 continues to decay, the ratio of unstable carbon-14 to stable carbon-12 and carbon-13 decreases. By measuring this ratio and comparing it to the nearly constant ratio present in the atmosphere, the age of an object can be estimated. For example, if an object s C-14 to (C-12 + C-13) ratio is one-quarter the ratio measured in the atmosphere, the object is approximately two half-lives, or 11 460 years, old. Carbon-14 dating is limited to accurately dating objects up to approximately 24 000 years of age. 

The principal nuclear reactions that take place when mixtures of U and U are used as fuel in a reactor are illustrated in Fig. 3.1. Fissile materials are double underlined, and their fission cross sections for 2200 m/s neutrons are given on upward-slanting arrows. Fertile materials are sin e underlined, and their capture cross sections for 2200 m/s neutrons are given on horizontal arrows. Beta-decay reactions with short enough half-lives to be important are shown by vertical arrows. 

Each of the uranium isotopes is a member of one of the four possible radioactive decay series involving successive alpha and beta decay reactions. is the longest-lived member and the parent of the 4n -t- 2 series, which includes as a member. is the longest-lived member and the natural parent of the 4n + 3 series, decays by alpha emission to Th, the longest-lived member and natural parent of the 4n series, to be described in Chaps. 6 and 8. decays by alpha emission to Th, also a member of the 4n series. Problems arising from the radioactivity of and its daughters are discussed in Chap. 8. U decays by beta emission to Np, the longest-lived member of the 4n -I- 1 series, the only one not of natural occurrence. is an intermediate member of this series. 

Beta particles are charged particles emitted from the nucleus of an atom with a mass and charge equal in magnitude to that of an electron. In beta decay reactions, as the electron is ejected, the number of protons in the resulting atom increases, changing the atomic number of the atom but not the mass. For example, plutonium-241 undergoes beta decay to form americium-241. 

The uranium-239 then undergoes two beta decays, first to Np, and then to Pu, which is a fissionable material and the desired product. Write balanced nuclear equations for the bombardment reaction and the two beta-decay reactions. 

The second kind of ray also turns out to be a beam of particles, but these particles are negatively charged and therefore attracted to the positively charged plate (see Fig. 20.1). Called beta rays, or /8-rays, they have been identified as electrons. The nuclear symbol for a beta particle, or /8-particle, is iC, indicating zero mass number and a -1 charge. /3-particles have considerably more penetrating power than a-particles, but they can be stopped by a sheet of lead or aluminum about 5 mm thick (see Fig. 20.2). The emission of a beta particle is a beta decay reaction, or beta decay. 

The Th nucleus resulting from the disintegration of uranium-238 is also radioactive. In a beta-decay reaction, it emits a beta particle, ] e, and produces an isotope of protactinium, 2 Pa ... 

What happens to the nucleus of an atom that experiences a beta-decay reaction Compare the final nuclide with the original nuclide. Does the element undergo transmutation ... 

Because the path of the s process is blocked by isotopes that undergo rapid beta decay, it cannot produce neutron-rich isotopes or elements beyond Bi, the heaviest stable element. These elements can be created by the r process, which is believed to occur in cataclysmic stellar explosions such as supemovae. In the r process the neutron flux is so high that the interaction hme between nuclei and neutrons is shorter that the beta decay lifetime of the isotopes of interest. The s process chain stops at the first unstable isotope of an element because there is time for the isotope to decay, forming a new element. In the r process, the reaction rate with neutrons is shorter than beta decay times and very neutron-rich and highly unstable isotopes are created that ultimately beta decay to form stable elements. The paths of the r process are shown in Fig. 2-3. The r process can produce neutron-rich isotopes such as Xe and Xe that cannot be reached in the s process chain (Fig. 2-3). 

The study of the radiochemical reactions of arsenic atoms in benzene solution was carried further by comparing the product spectra of neutron irradiated ASCI3 solutions and GeC solutions which have undergone beta decay. The product spectra were found to be remarkably similar, especially when considered only as to the number of As-0... 

Dr. Hafemeister Most isotopes really can be studied just as well or better by beta decay. I can think of only one that can t—Le, potassium-40. This is a strange case because it is an odd-odd nucleus, and there are only about four odd-odd nuclei that are stable. An odd-odd nucleus means that it decays to the neighboring even-even nuclei, and in this case one cannot populate it by beta decay. However, in most cases one does just as well with beta decay, particularly since using a nuclear reaction for direct population is so expensive. It can be done, so there should be a good reason to spend the money. Radiation damage studies by these techniques are feasible and may well be useful. 

Polonium is found only in trace amounts in the Earths crust. In nature it is found in pitchblende (uranium ore) as a decay product of uranium. Because it is so scarce, it is usually artificially produced by bombarding bismuth-209 with neutrons in a nuclear (atomic) reactor, resulting in bismuth-210, which has a half-hfe of five days. Bi-210 subsequently decays into Po-210 through beta decay The reaction for this process is Bi( ) Bi — °Po + (3-. Only small commercial milligram amounts are produced by this procedure. 

Americium does not exist in nature. All of its isotopes are man-made and radioactive. Americium-241 is produced by bombarding plutonium-239 with high-energy neutrons, resulting in the isotope plutonium-240 that again is bombarded with neutrons and results in the formation of plutonium-241, which in turn finally decays into americium-241 by the process of beta decay. Both americium-241 and americium-243 are produced within nuclear reactors. The reaction is as follows Pu + (neutron and X gamma rays) —> " Pu + (neutron and X gamma rays) —> Pu—> Am + beta minus ([ -) followed by " Am—> jNp-237 + Hej (helium nuclei). 

Only a small fraction of Bk-249 is obtained by the above reaction because neutrons also induce fission. Alternatively, uranium—238 may be converted to Bk-249 by very short but intense neutron bombardment followed by five successive beta decays. 

Seventeen radioisotopes have been synthesized in nuclear reactions. Among them Kr-85 and Kr-87 have the longest half-lives of 10 and 6 % years, respectively, both undergoing beta decay. 

Protactinium-233 is produced by the beta decay of the short-lived thorium-233. Thorium-233 is obtained by neutron capture of natural thorium-232. The nuclear reactions are as follows ... 

Again, both mass and charge are conserved. Gamma emission often accompanies both alpha and beta decay, but because gamma emission does not change the parent element it is often emitted when writing nuclear reactions. 

Classify the following reactions as alpha, beta, or gamma decay (specify the subtype if it s beta decay), and supply the missing particles. 

The disadvantages of this reaction place some real constraints on its use 1) The (t,p) cross section is only about 5 percent of the total cross section 2) The dominant reaction, usually (t,2n), produces abundant prompt Y rays 3) Reactions such as (t,n) and (t,d) [as well as (t,p)] often result in short-lived beta decaying products 4) The usual in-beam techniques such as angular distributions are complicated by the necessity to use the outgoing proton to identify the reaction As a result of the first three disadvantages, much of the Y ay and electron count rates are not from the (t,p) reaction and thus experiments of reasonable duration have limited statistics ... 

Beta-decay half-lives were measured for eight neutron rich isotopes produced by fragmentation of E/A-30MeV 180 ions.The first measurements of the half-lives of Be(4.2 0.7 ms.)and 17C(202 17 ms.) have been made along with the half-lives of 9Li, 1 Li, 1 2Be, 1 -B, 15B. The lifetime of -Be is the shortest known beta lifetime.This is the first experiment to use the MSU Reaction Product Mass Separator... 

The prompt neutrons emitted in fission are available for fission in other nuclei - hence the chain reaction. The fission fragments formed initially are rich in neutrons. For example the heaviest stable isotopes of krypton and barium are 86Kr and 138Ba. Excess neutrons are emitted from the fission fragments as delayed neutrons or converted to protons by beta decays. For example... 

Plutonium is a man-made element, and only infinitesimal traces occur naturally. It melts at 641°C and boils at 3330°C. 239Pu is formed in nuclear reactors by neutron capture in 238U, followed by two successive beta decays (Fig. 5.1). Further neutron captures lead to 240Pu and 241 Pu. 238Pu is formed from 239Pu by (n,2n) reactions, or from 235U by three successive neutron captures and two beta decays. Table 5.1 shows the half-lives, alpha and X-ray energies of the principal Pu isotopes. 

In the previous problem, notice how much higher the fission product s mass number, A, is when compared to the stable element s average atomic mass. All will decay by beta (e ) emission to achieve a more normal A to Z ratio. Write the decay reactions for the four fission products above. 

Taken together, these conclusions created serious problems in physical interpretation. How could neutron capture by a single isotope initiate three such different reaction processes How could the capture of just one neutron create such great instability that multiple beta decays were needed to alleviate it Nuclear isomerism was known, but how to explain the triple isomerism of 239U Worst of all, how could one account for the inherited isomerism - for several generations - in the... 

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