- Uranium Atomic Number Most Common Isotope
- Uranium Atomic Number Periodic Table
- Uranium Atomic Number 23
- U Element
Since the German chemist Martin Heinrich Klaproth identified uranium in 1789, atomic number 92 has become one of the most troubling substances on the planet. It’s naturally radioactive, but its isotope uranium-235 also happens to be fissile, as Nazi nuclear chemists learned in 1938, when they did the impossible and split a uranium nucleus in two. American physicists at U.C. Berkeley were soon to discover they could force uranium-238 to decay into plutonium-239; the substance has since been used in weapons and power plants around the world. Today, the element continues to stoke international tensions as Iran stockpiles uranium in defiance of an earlier treaty, and North Korea’s “Rocket Man” leader Kim Jong-un continues to resist denuclearization.
Since the German chemist Martin Heinrich Klaproth identified uranium in 1789, atomic number 92 has become one of the most troubling substances on the planet. Uranium (U), radioactive chemical element of the actinoid series of the periodic table, atomic number 92. It is an important nuclear fuel. Atomic Number of Uranium Uranium is a chemical element with atomic number 92 which means there are 92 protons and 92 electrons in the atomic structure.
But what is uranium, exactly? And what do you need to know about it beyond the red-hot headlines? Here we answer your most pressing nuclear questions:
Where does uranium come from?
Uranium is a common metal. “It can be found in minute quantities in most rocks, soils, and waters,” geologist Dana Ulmer-Scholle writes in an explainer from the New Mexico Bureau of Geology and Mineral Resources. But finding richer deposits—the ones with concentrated uranium actually worth mining—is more difficult.
When engineers find a promising seam, they mine the uranium ore. “It’s not people with pickaxes anymore,” says Jerry Peterson, a physicist at the University of Colorado, Boulder. These days, it comes from leaching, which Peterson describes as pouring “basically PepsiCola—slightly acidic” down into the ground and pumping the liquid up from adjacent holes. As the fluid percolates through the deposit, it separates out the uranium for harvesting.
What are the different types of uranium?
Uranium has several important isotopes—different flavors of the same substance that vary only in their neutron count (also called atomic mass). The most common is uranium-238, which accounts for 99 percent of the element’s presence on Earth. The least common isotope is uranium-234, which forms as uranium-238 decays. Neither of these products are fissile, meaning their atoms don’t easily split, so they can’t sustain a nuclear chain reaction.
That’s what makes the isotope uranium-235 so special—it’s fissile, so with a bit of finessing, it can support a nuclear chain reaction, making it ideal for nuclear power plants and weapons manufacturing. But more on that later.
There’s also uranium-233. It’s another fissile product, but its origins are totally different. It’s a product of thorium, a metallic chemical much more abundant than uranium. If nuclear physicists expose thorium-232 to neutrons, the thorium is liable to absorb a neutron, causing the material to decay into uranium-233.
Just as you can turn thorium into uranium, you can turn uranium into plutonium. Even the process is similar: Expose abundant uranium-238 to neutrons, and it will absorb one, eventually causing it to decay to plutonium-239, another fissile substance that’s been used to create nuclear energy and weapons. Whereas uranium is abundant in nature, plutonium is really only seen in the lab, though it can occur naturally alongside uranium.
How do you go from a rock to a nuclear fuel source?
People don’t exactly lay out step-by-step guides to refining nuclear materials. But Peterson got pretty close. After you’ve extracted uranium from the earth, he says chemical engineers separate the uranium-rich liquid from other minerals in the sample. When the resulting uranium oxide dries, it’s the color of semolina flour, hence the nickname “yellowcake” for this intermediate product.
From there, a plant can purchase a pound of yellowcake for $20 or $30. They mix the powder with hydrofluoric acid. The resulting gas is spun in a centrifuge to separate from uranium-238 and uranium-235. This process is called “enrichment.” Instead of the natural concentration of 0.7 percent, nuclear power plants want a product that’s enriched to between 3 and 5 percent uranium-235. For a weapon, you need much more: These days, upwards of 90 percent is the goal.
Once that uranium is enriched, power plant operators pair it with a moderator, like water, that slows down the neutrons in the uranium. This increases the probability of a consistent chain reaction. When your reaction is finally underway, each individual neutron will transform into 2.4 neutrons, and so on, creating energy all the while.
Any fun facts I should take with me to my next dinner party?
Try this: In PopSci‘s “Danger” issue earlier this year, David Meier, a research scientist at Pacific Northwest National Lab, talked about his work to create a database of plutonium sources. Turns out, every plutonium product has a visible origin story, because “there’s not one way of processing it,” Meier says. The United States had two plutonium production sites. While the intermediate product from Hanford, Washington (the Manhattan Project site from which PNNL grew) was brown and yellow, the Savannah River site in Akon, South Carolina, produced “a nice blue material,” Meier says. Law enforcement officials hope these subtle differences—which may also correspond to changes in the chemical signature, particle size, or shape of the material—will one day help them track down illicit nuclear development.
Or, dazzle your guests with a short history of radioactive dinnerware. The manufacture of uranium glass, also called canary glass or Vaseline glass began in the 1830s. Before William Henry Perkin created the first synthetic color in 1856, dyes were terribly expensive and even then they didn’t last. Uranium became a popular way to give plates, vases, and glasses a deep yellow or minty green tinge. But put these household objects under a UV light and they all fluoresce a shocking neon chartreuse. Fortunately for the avid collectors who actively trade in uranium glass, most of these objects aren’t so radioactive as to pose a risk to human health.
Last one: In 2002, the medical journal The Lancet published an article on the concerning potential for depleted uranium—the waste leftover after uranium-235 extraction—to end up on the battlefield. The concern is that its high density would make it an incredible projectile, capable of piercing even the most well-enforced battle tank. Worse yet, it could then contaminate the surrounding landscape and anyone it.
MORE TO READ
- Nuclear properties
- Processes of nuclear decay
- Nuclear structure and shape
- Extension of the periodic table
- Transactinoid elements and their predicted properties
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University Professor of Chemistry; Associate Director-at-Large, Lawrence Berkeley Laboratory, University of California, Berkeley; Chancellor, 1958–61. Chairman, Atomic Energy Commission, 1961–71. Cowinner,...
Alternative Title: transuranic element
Transuranium element, any of the chemical elements that lie beyond uranium in the periodic table—i.e., those with atomic numbers greater than 92. Twenty-six of these elements have been discovered and named or are awaiting confirmation of their discovery. Eleven of them, from neptunium through lawrencium, belong to the actinoid series. The others, which have atomic numbers higher than 103, are referred to as the transactinoids. All the transuranium elements are unstable, decaying radioactively, with half-lives that range from tens of millions of years to mere fractions of a second.
Since only two of the transuranium elements have been found in nature (neptunium and plutonium) and those only in trace amounts, the synthesis of these elements through nuclear reactions has been an important source of knowledge about them. That knowledge has expanded scientific understanding of the fundamental structure of matter and makes it possible to predict the existence and basic properties of elements much heavier than any currently known. Present theory suggests that the maximum atomic number could be found to lie somewhere between 170 and 210, if nuclear instability would not preclude the existence of such elements. All these still-unknown elements are included in the transuranium group.
Discovery of the first transuranium elements
The first attempt to prepare a transuranium element was made in 1934 in Rome, where a team of Italian physicists headed by Enrico Fermi and Emilio Segrè bombarded uranium nuclei with free neutrons. Although transuranium species may have been produced, the experiment resulted in the discovery of nuclear fission rather than new elements. (The German scientists Otto Hahn, Fritz Strassman, and Lise Meitner showed that the products Fermi found were lighter, known elements formed by the splitting, or fission, of uranium.) Not until 1940 was a transuranium element first positively produced and identified, when two American physicists, Edwin Mattison McMillan and Philip Hauge Abelson, working at the University of California at Berkeley, exposed uranium oxide to neutrons from a cyclotron target. One of the resulting products was an element found to have an atomic number of 93. It was named neptunium.
Transformations in atomic nuclei are represented by equations that balance all the particles of matter and the energy involved before and after the reaction. The above transformation of uranium into neptunium may be written as follows:
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In the first equation the atomic symbol of the particular isotope reacted upon, in this case U for uranium, is given with its mass number at upper left and its atomic number at lower left: 23892U. The uranium-238 isotope reacts with a neutron (symbolized n, with its mass number 1 at upper left and its neutral electrical charge shown as 0 at lower left) to produce uranium-239 (23992U) and the quantum of energy called a gamma ray (γ). In the next equation the arrow represents a spontaneous loss of a negative beta particle (symbolized β−), an electron with very high velocity, from the nucleus of uranium-239. What has happened is that a neutron within the nucleus has been transformed into a proton, with the emission of a beta particle that carries off a single negative charge; the resulting nucleus now has one more positive charge than it had before the event and thus has an atomic number of 93. Because the beta particle has negligible mass, the mass number of the nucleus has not changed, however, and is still 239. The nucleus resulting from these events is an isotope of the element neptunium, atomic number 93 and mass number 239. The above process is called negative beta-particle decay. A nucleus may also emit a positron, or positive electron, thus changing a proton into a neutron and reducing the positive charge by one (but without changing the mass number); this process is called positive beta-particle decay. In another type of beta decay a nuclear proton is transformed into a neutron when the nucleus, instead of emitting a beta particle, “captures,” or absorbs, one of the electrons orbiting the nucleus; this process of electron capture (EC decay) is preferred over positron emission in transuranium nuclei.
The discovery of the next element after neptunium followed rapidly. In 1941 three American chemists, Glenn T. Seaborg, Joseph W. Kennedy, and Arthur C. Wahl, produced and chemically identified element 94, named plutonium (Pu). In 1944, after further discoveries, Seaborg hypothesized that a new series of elements called the actinoid series, akin to the lanthanoid series (elements 58–71), was being produced, and that this new series began with thorium (Th), atomic number 90. Thereafter, discoveries were sought, and made, in accordance with this hypothesis.
Synthesis of transuranium elements
The most abundant isotope of neptunium is neptunium-237. Neptunium-237 has a half-life of 2.1 × 106 years and decays by the emission of alpha particles. (Alpha particles are composed of two neutrons and two protons and are actually the very stable nucleus of helium.) Neptunium-237 is formed in kilogram quantities as a by-product of the large-scale production of plutonium in nuclear reactors. This isotope is synthesized from the reactor fuel uranium-235 by the reaction
and from uranium-238 by
Plutonium, as the isotope plutonium-239, is produced in ton quantities in nuclear reactors by the sequence
Because of its ability to undergo fission with neutrons of all energies, plutonium-239 has considerable practical applications as an energy source in nuclear weapons and as fuel in nuclear power reactors.
The method of element production discussed thus far has been that of successive neutron capture resulting from the continuous intensive irradiation with slow (low-energy) neutrons of an actinoid target. The sequence of nuclides that can be synthesized in nuclear reactors by this process is shown in the figure, in which the light line indicates the principal path of neutron capture (horizontal arrows) and negative beta-particle decay (up arrows) that results in successively heavier elements and higher atomic numbers. (Down arrows represent electron-capture decay.) The heavier lines show subsidiary paths that augment the major path. The major path terminates at fermium-257, because the short half-life of the next fermium isotope (fermium-258)—for radioactive decay by spontaneous fission (370 microseconds)—precludes its production and the production of isotopes of elements beyond fermium by this means.
Heavy isotopes of some transuranium elements are also produced in nuclear explosions. Typically, in such events, a uranium target is bombarded by a high number of fast (high-energy) neutrons for a small fraction of a second, a process known as rapid-neutron capture, or the r-process (in contrast to the slow-neutron capture, or s-process, described above). Underground detonations of nuclear explosive devices during the late 1960s resulted in the production of significant quantities of einsteinium and fermium isotopes, which were separated from rock debris by mining techniques and chemical processing. Again, the heaviest isotope found was that of fermium-257.
Uranium Atomic Number Most Common Isotope
An important method of synthesizing transuranium isotopes is by bombarding heavy element targets not with neutrons but with light charged particles (such as the helium nuclei mentioned above as alpha particles) from accelerators. For the synthesis of elements heavier than mendelevium, so-called heavy ions (with atomic number greater than 2 and mass number greater than 5) have been used for the projectile nuclei. Targets and projectiles relatively rich in neutrons are required so that the resulting nuclei will have sufficiently high neutron numbers; too low a neutron number renders the nucleus extremely unstable and unobservable because of its resultantly short half-life.
Uranium Atomic Number Periodic Table
The elements from seaborgium to copernicium have been synthesized and identified (i.e., discovered) by the use of “cold,” or “soft,” fusion reactions. In this type of reaction, medium-weight projectiles are fused to target nuclei with protons numbering close to 82 and neutrons numbering about 126—i.e., near the doubly “magic” lead-208—resulting in a relatively “cold” compound system. The elements from 113 to 118 were made using “hot” fusion reactions, similar to those described above using alpha particles, in which a relatively light projectile collides with a heavier actinoid. Because the compound nuclei formed in cold fusion have lower excitation energies than those produced in hot fusion, they may emit only one or two neutrons and thus have a much higher probability of remaining intact instead of undergoing the competing prompt fission reaction. (Nuclei formed in hot fusion have higher excitation energy and emit three to five neutrons.) Cold fusion reactions were first recognized as a method for the synthesis of heavy elements by Yuri Oganessian of the Joint Institute for Nuclear Research at Dubna in the U.S.S.R. (now in Russia).
Uranium Atomic Number 23
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U Element
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