Neptunium-237, radioactive decay

Neptunium-237 undergoes an a, p, a, a, p, a, a, a, p, a, p sequence of radioactive decays. Determine the daughter nuclide after each decay and write a balanced nuclear equation for each step. 

Actinides in the environment can be classified into two groups (i) the uranium and thorium series of radionuclides in the natural environment and (ii) neptunium, plutonium, americium and curium which are formed in a nuclear reactor during the neutron bombardment of uranium through a series of neutron capture and radioactive decay reactions. Transuranics thus produced have been spread widely in the atmosphere, geosphere and aquatic environment on the earth, as a result of nuclear bomb tests in the atmosphere, and accidental release from nuclear facilities (Sakanoue, 1987). Most of these radionuclide inventories have deposited in the northern hemisphere following the tests conducted by the United States and the Soviet Union. 

You might ask, why should there be another element present The answer is very simple the neptunium nucleus undergoes radioactive decay by emitting an electron, and this is always accompanied by the changing of a neutron into a proton, thus increasing the positive charge on the nucleus. 

After the discovery of uranium radioactivity by Henri Becquerel in 1896, uranium ores were used primarily as a source of radioactive decay products such as Ra. With the discovery of nuclear fission by Otto Hahn and Fritz Strassman in 1938, uranium became extremely important as a source of nuclear energy. Hahn and Strassman made the experimental discovery Lise Meitner and Otto Frisch provided the theoretical explanation. Enrichment of the spontaneous fissioning isotope U in uranium targets led to the development of the atomic bomb, and subsequently to the production of nuclear-generated electrical power. There are considerable amounts of uranium in nuclear waste throughout the world, see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendelevium Neptunium Nobelium Plutonium Protactinium Rutherfordium Thorium. 

So, it seems that of these 92 natural elements, only 88 can be considered naturally occurring since the above four are transient species, newly formed by radioactive decay. Neptunium and plutonium can similarly be found in ultratrace quantities due to de novo synthesis coupled to rapid decay. We could stretch a point by noting that all helium on our planet is also formed de novo. However, although these fresh helium atoms are lost into space, the nuclei are totally stable. 

The absorbs a thermal neutron and by radioactive decay yields neptunium and plutonium. The sequence is... 

FlC- 1-2, The three naturally occurring radioactive decay series and the man-made neptunium series. Although (which is the parent to the actinium series) and (which is the parent to the thorium series) have been discovered in nature, die decay series shown here begin with the most abundant Icmg-Uved nuclides. 

A fourth long radioactive decay series, the neptunium series (Fig. 1.2), is conqxrsed of nuclides having mass numbers which divided by 4 have a remainder of 1 (the 4n + 1 series). The name comes from the longest lived A = 4n + I nuclide heavier than Bi, Np, which is considered as the parmt species it has a half-life of 2.14 X 10° y. Inasmuch as this half-life is considerably shorter than the age of the earth, primordial Np no longer exists on earth, and, therefore, the neptunium series is not found as a natural... 

Plutonium does not undergo transformation processes in the air beyond those related to radioactive decay. Radioactive decay will be important for the short-lived isotopes with half-lives less than the average residence time in the troposphere of approximately 60 days. For example, plutonium-237 has a half-life of 46 days and undergoes electron capture to form neptunium-237 which has a half-life of 2.1x10 years (Nero 1979). Therefore, neptunium-237 may form in the stratosphere prior to deposition of plutonium-237 on the earth s surface as fallout. 

The only nonnaturaUy occurring radioactive decay series, the neptunium series, has a formula ... 

The other more short-lived actinides must be made synthetically by using high-energy collisions in a particle accelerator. These machines collide a particle such as a gamma ray with an atom of the naturally formed actinide elements. They split after collision the other elements are formed in the process of radioactive decay. The first of these new elements were named after the planets in a similar fashion to uranium (planet Uranus) — neptunium (Neptune) and plutonium (Pluto). The rest have been named for historical themes or places in which they were first created. 

FIGURE 1.6 The artificial radioactive decay chain of the 4n -t 1 series, beginning with neptunium-237, deeaying through uranium-233 and ending with thallium-205. 

In 1940 E. McMillan and P. H. Abelson at the University of California, Berkeley, irradiated U with neutrons this led to the formation of element number 93, which they called neptunium [52.18]. What they did can be described by the first formulas in Table 52.3. Their successful result was the start of intensive work that led to the discovery of all the actinide elements. In fact neptunium and also plutonium occur in nature. Minute amounts of these elements are produced in the radioactive decay of uranium. 

Neptunium. Np is in a class with Pa no efforts have been made to use it as a fuel solute, but consideration has been given to its formation in and removal from blanket solutions of [30a]. The chemistry of neptunium has been reviewed by Hindman et al. [30b], and the hydrolytic behavior has been reviewed by Kraus [30c]. Continuous separation of Np239 would provide a Pu product of high purity by radioactive decay, whereas plutonium recovered from long-term irradiation of usually contains appreciable amounts of Pu °. Spectrophotometric cells for use at elevated temperatures and pre.ssures in the study of the chemistry of neptunium (and other materials) have recently been developed by Wag-gener [30d] and have been used to measure the absorption spectra of dilute neptunium perchlorate in its six-, five-, four-, and three-valence states, using heavy w ater as the solvent. Dilute solutions of neptunyl nitrate in nitric acid have been so studied at temperatures up to 250°C the pentavalent state was found to be stable under the test conditions [30e]. 

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

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