Conversion of an atom from one element to another

Illustration of a proton–proton chain , from hydrogen forming deuterium , helium-3 , and regular helium-4 .

Nuclear transmutation is, quite simply, the conversion of one chemical element —or, for those who appreciate precision, an isotope of one element—into an entirely different chemical element. [1] This isn’t some alchemical fantasy, but a fundamental process of the universe. It happens whenever the number of protons or neutrons residing within the nucleus of an atom decides to change. A proton count dictates the element; alter that, and you’ve got yourself a new element. Change the neutron count, and you’ve merely created a different isotope of the same element, which is still a form of transmutation in the broader sense.

Such a profound transformation can be brought about by two primary mechanisms. The first involves nuclear reactions , where some external particle, perhaps a rogue neutron or a high-energy proton, collides with and alters an atomic nucleus. The second, far more common and utterly indifferent to external interference, is radioactive decay , a spontaneous process where an unstable nucleus sheds particles or energy to achieve a more stable configuration. No outside agent is needed for that; the atom simply decides its time is up.

Nature, in its relentless pursuit of cosmic drama, has been orchestrating these transmutations for billions of years. Stellar nucleosynthesis , the forge within stars, is responsible for creating the vast majority of the heavier chemical elements we observe in the existing universe. This process began in the cosmic past and continues unabated today, churning out most of the common elements, including the ubiquitous helium , the life-sustaining oxygen , and the very foundation of organic chemistry, carbon . Most stars, in their main sequence phase, are busy performing transmutation through fusion reactions , primarily converting hydrogen into helium. As stars mature and grow significantly larger, they gain the capacity to fuse progressively heavier elements, a process that culminates in the creation of iron late in their evolutionary lifecycle.

However, the cosmic factory doesn’t stop at iron. Elements even heavier than iron, such as the coveted gold or the mundane lead , demand more extreme conditions. These are forged through elemental transmutations that occur naturally in the cataclysmic explosions of supernovae . It’s a rather spectacular way to make precious metals, if you ask me. One of the ancient, misguided goals of alchemy —the transmutation of base substances into gold—is now definitively understood to be impossible through mere chemical manipulation. Chemically, you can rearrange electron shells all you like; you won’t touch the nucleus. But physically, through the immense energies involved in nuclear processes, it is indeed achievable, albeit with considerable effort and usually at a net energy loss, rather than the alchemists’ dream of endless riches. As stars attempt to fuse heavier elements beyond a certain point, the energy released from each fusion reaction diminishes. This continues until the star tries to fuse iron. Iron fusion, unlike lighter elements, is an endothermic reaction, meaning it consumes energy rather than releasing it. At this critical juncture, the star’s core collapses, leading to a supernova, as no heavier element can be produced under these conditions to sustain the star.

A more observable form of natural transmutation in our present era occurs when certain radioactive elements, naturally present in the Earth’s crust, spontaneously undergo decay. This decay often involves a process that fundamentally alters their atomic identity, such as alpha decay or beta decay . A prime example, quietly happening all around us, is the natural decay of potassium-40 into argon-40 . This continuous process is responsible for forming the vast majority of the argon found in our atmosphere, proving that even the air we breathe is a product of nuclear transformation. Beyond spontaneous decay, natural transmutations also occur on Earth due to various other mechanisms of natural nuclear reactions . These include the constant bombardment of elements by cosmic rays (leading, for instance, to the formation of carbon-14 , crucial for radiometric dating) and, on rare occasions, from natural neutron bombardment (as famously evidenced by the discovery of the natural nuclear fission reactor at Oklo, Gabon).

For those who prefer a more hands-on approach, artificial transmutation can be achieved using sophisticated machinery capable of imparting sufficient energy to induce changes in the nuclear structure of elements. Such technological marvels include particle accelerators , which hurl subatomic projectiles at target nuclei, and experimental fusion devices like tokamak reactors, designed to replicate stellar processes on a miniature, controlled scale. Even conventional fission power reactors contribute to artificial transmutation, not directly through the sheer power of the machine itself, but by exposing elements to the torrent of neutrons produced by the artificially initiated nuclear chain reaction . For example, when a uranium atom is struck by a slow neutron, it undergoes fission. This violent splitting releases, on average, three more neutrons and a substantial amount of energy. These newly liberated neutrons then proceed to cause fission in other uranium atoms, perpetuating the process in a self-sustaining chain reaction until the available fissile material is exhausted.

Beyond the pursuit of energy, artificial nuclear transmutation has been seriously considered as a potential mechanism for addressing one of humanity’s more pressing self-made problems: reducing both the sheer volume and the inherent long-term hazard of radioactive waste . [2] It’s an ambitious idea, attempting to undo what we’ve wrought by forcing unstable isotopes to become something less problematic.

History

Alchemy

The term “transmutation” itself carries a rather heavy historical baggage, dating back to the esoteric practices of alchemy . Alchemists, those ancient dreamers and proto-scientists, famously sought the elusive philosopher’s stone , a mythical substance supposedly capable of chrysopoeia —the miraculous transformation of common base metals into pure gold. [3] While many alchemists undoubtedly understood chrysopoeia as a profound metaphor for a mystical or spiritual journey of purification and transformation, a significant number of practitioners adopted a far more literal interpretation, dedicating their lives to attempting to fabricate gold through arduous physical experimentation. The very feasibility of this metallic transmutation was a subject of fervent debate among alchemists, philosophers, and nascent scientists for centuries, stretching back to the Middle Ages. So-called pseudo-alchemical transmutation, often involving outright fraud or misunderstanding, was eventually outlawed [4] and publicly ridiculed, particularly from the fourteenth century onwards, as more systematic thinkers began to emerge. Prominent figures like Michael Maier and Heinrich Khunrath penned detailed tracts specifically to expose the fraudulent claims of gold-making, attempting to bring some intellectual honesty to the field. By the 1720s, the once-respectable pursuit of physically transmuting substances into gold had largely faded from serious scientific inquiry, relegated to the fringes of charlatanism. [5] The scientific revolution, spearheaded by figures like Antoine Lavoisier in the 18th century, irrevocably replaced the archaic alchemical theory of elements with the rigorous, modern theory of distinct chemical elements. John Dalton further refined the concept of atoms (drawing inspiration, perhaps ironically, from the alchemical theory of corpuscles ) to precisely explain the intricate mechanisms of various chemical processes. The key distinction, one that eluded alchemists for millennia, is that the disintegration or transformation of atoms—true transmutation—is a distinct nuclear process, involving energies orders of magnitude greater than anything achievable by alchemists in their rudimentary laboratories.

Modern physics

The concept of transmutation, scrubbed clean of its mystical associations, was first consciously and scientifically applied to modern physics by Frederick Soddy . In 1901, working alongside the formidable Ernest Rutherford , Soddy made the groundbreaking discovery that radioactive thorium was, in fact, spontaneously transforming itself into radium . The sheer significance of this observation, a direct, undeniable instance of one element becoming another, struck Soddy with such force that, as he later recounted, he exclaimed, “Rutherford, this is transmutation!” Rutherford, ever the pragmatist and keenly aware of the historical stigma attached to the term, reportedly shot back, “For Christ’s sake, Soddy, don’t call it transmutation. They’ll have our heads off as alchemists.” [6] Despite Rutherford’s caution, what they were witnessing was precisely that: natural transmutation, occurring as a fundamental part of the radioactive decay process, specifically of the alpha decay type. Their work laid the empirical foundation for understanding the true nature of atomic change.

The first instance of artificial transmutation—where humans intentionally induced the change—was achieved in 1925 by Patrick Blackett , a diligent research fellow operating under Rutherford’s tutelage. Blackett successfully transmuted nitrogen into oxygen by bombarding nitrogen-14 with alpha particles . The reaction, 14N + α → 17O + p, elegantly demonstrated that a proton (p) was emitted, leaving behind a heavier oxygen isotope. While Rutherford had previously shown in 1919 that a proton was emitted from certain alpha bombardment experiments, he lacked the definitive information about the identity of the residual nucleus. Blackett’s meticulous experiments between 1921 and 1924 provided the first unambiguous experimental evidence of an artificial nuclear transmutation reaction, allowing him to correctly identify both the underlying integration process and the precise identity of the resulting nucleus. [7]

A truly landmark achievement in 1932 saw a fully artificial nuclear reaction and subsequent nuclear transmutation brought about by Rutherford’s equally brilliant colleagues, John Cockcroft and Ernest Walton . They employed artificially accelerated protons, generated by their custom-built particle accelerator, against a target of lithium-7 . The result was spectacular: the lithium nucleus was split cleanly into two alpha particles . This feat, popularly sensationalized as “splitting the atom,” was a profound demonstration of controlled nuclear transformation, even though it was not the modern nuclear fission reaction—the splitting of heavy elements—that would later be discovered in 1938 by Otto Hahn , Lise Meitner , and their assistant Fritz Strassmann . [8] The quest for artificial transmutation continued, with Rubby Sherr , Kenneth Bainbridge , and Herbert Lawrence Anderson reporting in 1941 the nuclear transmutation of the element mercury into gold . [9] This, of course, was purely scientific, utterly devoid of any alchemical profit motive, much to the chagrin of any lingering alchemists.

Later in the twentieth century, the intricate mechanisms of element transmutation within stars were meticulously elaborated, providing a comprehensive explanation for the observed relative abundance of heavier elements throughout the universe. With the exception of the first five elements—hydrogen , helium , small amounts of lithium , beryllium , and boron —which were primarily produced in the Big Bang and through subsequent cosmic ray processes, stellar nucleosynthesis was found to account for the abundance of virtually all elements heavier than boron. Their seminal 1957 paper, “Synthesis of the Elements in Stars ,” [10] authored by the illustrious team of William Alfred Fowler , Margaret Burbidge , Geoffrey Burbidge , and Fred Hoyle , meticulously detailed how the observed abundances of essentially all but the lightest chemical elements could be precisely explained by the ongoing processes of nucleosynthesis within stars. It was a triumph of astrophysical understanding, finally putting to rest the question of where everything came from.

Transmutation of other elements into gold

See also: Synthesis of precious metals

The enduring alchemical tradition, that persistent historical footnote, famously sought to convert the “base metal” lead into the noble metal gold . In a delicious twist of cosmic irony, as a nuclear transmutation, it actually requires significantly less energy to perform the inverse: to turn gold into lead. For example, such a transformation could occur via a sequence of neutron capture events followed by beta decay if a sample of gold were left within the intense neutron flux of a nuclear reactor for a sufficiently extended period. [ citation needed ] However, the human desire to create gold from other elements remained. In 1980, Glenn Seaborg , K. Aleklett, and their team at the Lawrence Berkeley National Laboratory ’s Bevatron achieved a minor, yet historically significant, success: they managed to produce a minuscule quantity of gold from bismuth . This was, as expected, at a net energy loss, making it a scientific curiosity rather than an alchemist’s dream come true. [11] [12]

More recently, the colossal particle physics experiments at CERN have also delved into this alchemical fantasy. In 2002 and again in 2004, scientists working at the Super Proton Synchrotron reported the production of an exceedingly small amount of gold nuclei. This was accomplished through induced photon emissions during deliberate “near-miss” collisions of lead nuclei, essentially brushing them together at relativistic speeds. [13] [14] Fast forward to 2022, and CERN’s ISOLDE team announced a further achievement, producing 18 gold nuclei by bombarding a uranium target with protons. [15] The ultimate demonstration of this modern chrysopoeia arrived in 2025, when CERN’s ALICE experiment team proudly declared that, over the preceding decade, they had utilized the immense power of the Large Hadron Collider to replicate the 2002 SPS mechanisms, but at significantly higher energies. Across three distinct experimental runs, a total of approximately 260 billion gold nuclei were generated. While this sounds impressive, it amounted to a truly minuscule mass of about 90 picograms—hardly enough to make a ring, let alone pay off a mortgage. [16] [17] The scientific triumph, however, was undeniable.

Transmutation in the universe

• Main article: Nucleosynthesis

The grand narrative of the universe, as far as we understand it, begins with the Big Bang . This primordial event is widely accepted as the sole origin of all the hydrogen (including every atom of deuterium ) and helium that permeates the cosmos. These two lightest elements, hydrogen and helium, together constitute a staggering 98% of the mass of ordinary matter in the universe. The remaining paltry 2%? That’s everything else—all the elements that make up planets, stars (beyond their initial composition), and, rather unfortunately for those of us who prefer not to be “everything else,” you and me. The Big Bang also managed to churn out trace amounts of lithium , beryllium , and perhaps even a sliver of boron . More substantial quantities of lithium, beryllium, and boron were subsequently produced later in the universe’s history through a distinct natural nuclear reaction known as cosmic ray spallation , where high-energy cosmic rays shatter heavier nuclei.

Following the initial cosmic genesis, stellar nucleosynthesis took over the heavy lifting. This process is singularly responsible for the creation of all other elements that occur naturally in the universe as stable isotopes and primordial nuclides , ranging from the humble carbon up to the formidable uranium . These elements didn’t just pop into existence after the Big Bang; they were forged much later, within the fiery hearts of stars, during the epoch of star formation. Some of the lighter elements, from carbon up to iron , were indeed synthesized in the cores of stars and then gracefully released into interstellar space by asymptotic giant branch (AGB) stars. These are a particular type of red giant that, in their death throes, “puff” off their outer atmospheres, enriching the cosmos with elements ranging from carbon to nickel and iron. Nuclides possessing a mass number greater than 64, which encompasses a significant portion of the periodic table, are predominantly generated by two distinct neutron capture processes—the s-process (slow neutron capture) and the r-process (rapid neutron capture). These extreme events occur in the violent crucibles of supernova explosions and, even more dramatically, in the breathtaking collisions and mergers of neutron stars .

Our own Solar System is theorized to have condensed from a vast, swirling cloud of hydrogen and helium approximately 4.6 billion years ago. This cloud, however, wasn’t pristine; it was already seeded with heavier elements, encapsulated within dust grains. These grains were the cosmic ashes, forged previously by an untold number of earlier generations of stars that lived and died, enriching the interstellar medium. Consequently, these dust grains carried within them the heavier elements, products of transmutation that had occurred much earlier in the universe’s grand history.

It’s worth noting that all these natural processes of transmutation within stars are not relics of a bygone era; they are continuing to this very day, both within our own Milky Way galaxy and across countless others. Stars ceaselessly fuse hydrogen and helium into progressively heavier elements (up to iron), releasing the energy that makes them shine. For instance, the observed light curves of supernova stars, such as SN 1987A , provide direct evidence of these ongoing transmutations, showing them blasting immense quantities (comparable to the mass of Earth) of radioactive nickel and cobalt into the vast expanse of space. However, despite this cosmic abundance, relatively little of this material actually reaches Earth. On our planet today, most natural transmutation is mediated by the constant bombardment of cosmic rays (leading, for example, to the continuous production of carbon-14 ). The other major contributor is the spontaneous radioactive decay of long-lived primordial nuclides that were present from the very initial formation of the Solar System (such as potassium-40 , uranium , and thorium ), along with the subsequent decay chain products of these nuclides (including radium , radon , polonium , and others).

Artificial transmutation of nuclear waste

Overview

The artificial transmutation of transuranium elements —that is, the actinides excluding actinium up to uranium —holds significant promise. This category primarily includes the various isotopes of plutonium (which typically constitutes about 1 weight percent in the spent nuclear fuel from light water reactors ), and the so-called minor actinides (MAs), specifically neptunium , americium , and curium , each typically present at about 0.1 weight percent in the same spent fuel. The idea is that by transmuting these elements, we have the potential to significantly mitigate some of the most persistent problems associated with the long-term management of radioactive waste . The primary benefit would be a drastic reduction in the proportion of long-lived isotopes present in the waste, effectively shortening the hazardous lifespan of the material. (It should be noted, however, that this strategy does not, by itself, eliminate the fundamental need for a deep geological repository for high-level radioactive waste ; it merely makes the waste less problematic for such a repository). [ citation needed ] When these particular isotopes are subjected to irradiation with fast neutrons within a nuclear reactor , they can undergo nuclear fission . This process not only destroys the original long-lived actinide isotope but also produces a new spectrum of both radioactive and non-radioactive fission products , many of which have much shorter half-lives or are entirely stable.

To achieve this, specialized ceramic targets containing these actinides can be fabricated and then bombarded with neutrons. This induces the necessary transmutation reactions to eliminate the most problematic, long-lived species. These targets can be composed of actinide-containing solid solutions, such as (Am,Zr)N, (Am,Y)N, (Zr,Cm)O2, (Zr,Cm,Am)O2, or (Zr,Am,Y)O2. Alternatively, they might consist of pure actinide phases, such as AmO2, NpO2, NpN, or AmN, which are then mixed with certain inert phases. These inert phases, like MgO, MgAl2O4, (Zr,Y)O2, TiN, and ZrN, serve a crucial role: they primarily provide stable mechanical behavior to the target material, ensuring its integrity and predictable performance under the intense conditions of neutron irradiation. [18]

However, this partitioning and transmutation (P&T) strategy, while promising, is not without its inherent difficulties:

• One significant limitation is the costly and cumbersome requirement to meticulously separate the various long-lived fission product isotopes before they can be subjected to transmutation. This partitioning step is complex and adds considerably to the overall expense and technical challenge.
• Furthermore, some long-lived fission products (exactly which ones seems to be a perpetual debate among experts, as if they can’t agree on the worst offenders) [ which? ], including the particularly problematic nuclear waste product caesium-137 , are notoriously difficult to transmute effectively. This is due to their exceptionally small neutron cross-section , which translates to a very low probability of capturing a neutron, and consequently, a frustratingly low capture rate.

A more recent study, led by Satoshi Chiba at Tokyo Tech and intriguingly titled “Method to Reduce Long-lived Fission Products by Nuclear Transmutations with Fast Spectrum Reactors,” [19] has presented a compelling argument. It suggests that effective transmutation of these stubborn long-lived fission products can indeed be achieved in fast spectrum reactors, crucially, without the prior, costly need for isotope separation. This is proposed to be accomplished by the clever addition of a yttrium deuteride moderator, which presumably optimizes the neutron spectrum for these specific reactions. [20]

Reactor types

Consider, for instance, plutonium . It can be reprocessed and then incorporated into mixed oxide fuels , which can subsequently be used and transmuted within standard light water reactors . However, this approach is not a perfect solution. It is significantly limited by the inevitable accumulation of plutonium-240 in the spent MOX fuel. Plutonium-240 is problematic because it is neither particularly fertile (meaning it doesn’t readily transmute into fissile plutonium-241 , or at least not at rates high enough to offset its own production from neutron capture by plutonium-239 ) nor is it efficiently fissile with thermal neutrons . Even countries like France , which are highly experienced in extensive nuclear reprocessing , typically opt not to reuse the plutonium content from already used MOX fuel, indicating the inherent challenges. For the heavier elements, such as the minor actinides, transmutation could theoretically be achieved in fast reactors . However, many experts believe it could be accomplished even more effectively in a subcritical reactor . This type of reactor, sometimes referred to as an “energy amplifier ,” was famously devised by the Nobel laureate Carlo Rubbia . Beyond fission-based systems, fusion neutron sources have also been proposed as particularly well-suited for certain transmutation tasks, offering a potentially cleaner and more abundant source of neutrons. [21] [22] [23]

Fuel types

There exist several innovative fuel compositions designed to incorporate plutonium at the beginning of their operational cycle, aiming to significantly reduce the amount of this element by the end of the cycle. During its operational lifetime, plutonium within these fuels can be effectively “burnt” in a power reactor, generating valuable electricity. This process is not merely appealing from the perspective of power generation; it also offers a crucial capability for consuming surplus weapons-grade plutonium that originated from historical weapons programs, as well as the plutonium resulting from the reprocessing of conventional spent nuclear fuel, thus addressing a significant proliferation concern.

Mixed oxide fuel (MOX) is a prominent example of such a fuel. Its distinctive blend of plutonium and uranium oxides serves as a direct alternative to the low-enriched uranium fuel predominantly utilized in light water reactors. While the primary objective is to burn the plutonium, a subtle complication arises: because uranium is still present in the mixed oxide, “second-generation” plutonium will inevitably be produced. This occurs through the radiative capture of neutrons by uranium-238 , followed by two subsequent beta-minus decays, demonstrating the continuous cycle of transmutation.

Another compelling option involves fuels composed of plutonium and thorium . In these systems, the neutrons released during the fission of plutonium are efficiently captured by thorium-232 . Following this radiative capture, thorium-232 transforms into thorium-233, which then undergoes two beta-minus decays, ultimately leading to the production of the fissile isotope uranium-233 . A key advantage of thorium-232 is its significantly higher radiative capture cross-section—more than three times that of uranium-238. This yields a superior conversion rate to new fissile fuel compared to systems relying on uranium-238. Crucially, due to the complete absence of uranium in this fuel type, there is no production of second-generation plutonium, meaning the net amount of plutonium burnt will be higher than in mixed oxide fuels. However, it’s important to acknowledge that fissile uranium-233 will then be present in the used nuclear fuel, introducing its own set of handling and proliferation considerations. Both weapons-grade plutonium and reactor-grade plutonium can be effectively utilized in plutonium–thorium fuels, with weapons-grade plutonium demonstrating the most substantial reduction in its problematic plutonium-239 content.

Long-lived fission products

• See also: Nuclear reprocessing § Voloxidation

Long-lived fission products

• ^ Decay energy is split among β , neutrino , and γ if any.
• ^ Per 65 thermal neutron fissions of 235 U and 35 of 239 Pu .
• ^ Has decay energy 380 keV, but its decay product 126 Sb has decay energy 3.67 MeV.
• ^ Lower in thermal reactors because 135 Xe , its predecessor, readily absorbs neutrons .

Some radioactive fission products can, theoretically, be converted into shorter-lived radioisotopes through the process of transmutation. This is an area of active research, with studies, such as those conducted in Grenoble [24], exploring the transmutation of all fission products with half-lives exceeding one year. The results, as one might expect from trying to bend the laws of physics to human will, are rather varied.

When considering the immediate post-reactor waste, strontium-90 and caesium-137 stand out. With half-lives of approximately 30 years, they are the dominant emitters of radiation (and heat) in used nuclear fuel over a timescale ranging from decades to about 305 years (the contribution of tin-121m being negligible due to its low yield). Unfortunately, these two are not easily transmuted, primarily because they possess remarkably low neutron absorption cross sections . This means they are largely indifferent to neutron bombardment, making effective transmutation challenging. The pragmatic approach, therefore, is simply to store them securely until they have decayed to acceptable levels. Given that this period of storage is necessary anyway, it often makes sense to store other fission products with shorter half-lives alongside them until they too have decayed.

Moving further along the timeline of radioactive decay, the next significant long-lived fission product is samarium-151 , which boasts a half-life of 90 years. Curiously, this isotope is such an excellent neutron absorber that the majority of it is actually transmuted while the nuclear fuel is still actively being used in the reactor. However, effectively transmuting the remaining 151Sm in nuclear waste would necessitate its separation from other stable and unstable isotopes of samarium , a separation that is far from trivial. Given its smaller quantities and its relatively low-energy radioactivity, 151Sm is generally considered less dangerous than its more potent cousins, strontium-90 and caesium-137, and can realistically be left to decay for approximately 970 years.

Finally, we arrive at the seven truly long-lived fission products that represent the ultimate challenge for waste management. These possess half-lives stretching into geological timescales, ranging from 211,000 years to a staggering 15.7 million years. Among these, two are particularly concerning due to their environmental mobility: technetium-99 and iodine-129 . Both are mobile enough in the environment to pose potential long-term hazards. Conveniently, technetium has no known stable isotopes, and iodine-129 is mostly free of mixture with stable isotopes of the same element, simplifying their separation for transmutation. Furthermore, while their neutron cross sections are small, they are generally considered adequate to support transmutation efforts. Intriguingly, 99Tc also has a potential secondary role: it can substitute for uranium-238 in providing Doppler broadening for negative feedback, contributing to reactor stability. [25] Most studies examining proposed transmutation schemes have, perhaps predictably, focused on 99Tc, 129I, and the transuranium elements as the primary targets for transmutation, with other fission products, activation products , and potentially reprocessed uranium being consigned to traditional waste streams. [26] Technetium-99 also presents an interesting case, as it is produced as a waste product in nuclear medicine from technetium-99m , a nuclear isomer that decays to its ground state which has no further practical use. Due to the decay product of technetium-100 (the result of 99Tc capturing a neutron) decaying with a relatively short half-life to a stable isotope of ruthenium , a precious metal , there might even be a slight economic incentive for transmutation, assuming the costs can ever be brought down to a reasonable level.

Of the remaining five long-lived fission products, selenium-79 , tin-126 , and palladium-107 are typically produced only in relatively small quantities (at least within the context of today’s thermal neutron , uranium-235 -burning light water reactors ). Furthermore, the latter two are expected to be relatively inert in geological disposal environments. The other two, zirconium-93 and caesium-135 , are produced in larger quantities. However, they are also generally not highly mobile in the environment, which is a significant mitigating factor. A further complication is that they are typically mixed with much larger quantities of other isotopes of the same element, making separation for transmutation a formidable task. Zirconium, for instance, is widely used as cladding material in fuel rods due to its property of being virtually “transparent” to neutrons. A small amount of zirconium-93 is inevitably produced by neutron absorption from the regular zircalloy cladding, usually without much adverse effect. Whether this 93Zr could be effectively reused for new cladding material is a question that, thus far, hasn’t garnered significant study.

See also

• Neutron activation
• Nuclear power
• List of nuclear waste treatment technologies
• Synthesis of precious metals
• Fertile material