物理学家们使用了一束钛-50 轰击钸-244靶，成功合成了超重元素钅𫓧。这是首次使用比钙-48 重的原子核来合成超重元素。该研究团队由加利福尼亚州劳伦斯伯克利国家实验室的杰克琳·盖茨领导，他们希望这项研究能为发现全新元素铺平道路。超重元素位于元素周期表的右下方，原子序数大于 103。合成和研究这些巨大的元素，挑战了我们实验和理论能力的极限，并为我们提供了关于原子核内部力的新见解。合成这些元素的技术在过去几十年中得到了极大的改进，通常涉及用过渡金属离子束照射锕系元素靶（原子序数在 89-102 之间）。本世纪初，超重元素是通过用钙-48 离子束轰击锕系元素靶来合成的。盖茨说："使用这种技术，科学家们成功合成了原子序数为 118 的钅𫓨。钙-48 特别适合这项任务，因为它具有非常稳定的质子和中子构型，这使得它能够有效地与靶原子核融合。"

📡 使用钛-50 轰击钸-244靶，成功合成了超重元素钅𫓧，这是首次使用比钙-48 重的原子核来合成超重元素。 该研究团队由加利福尼亚州劳伦斯伯克利国家实验室的杰克琳·盖茨领导，他们希望这项研究能为发现全新元素铺平道路。 超重元素位于元素周期表的右下方，原子序数大于 103。合成和研究这些巨大的元素，挑战了我们实验和理论能力的极限，并为我们提供了关于原子核内部力的新见解。 合成这些元素的技术在过去几十年中得到了极大的改进，通常涉及用过渡金属离子束照射锕系元素靶（原子序数在 89-102 之间）。 本世纪初，超重元素是通过用钙-48 离子束轰击锕系元素靶来合成的。盖茨说："使用这种技术，科学家们成功合成了原子序数为 118 的钅𫓨。钙-48 特别适合这项任务，因为它具有非常稳定的质子和中子构型，这使得它能够有效地与靶原子核融合。

📢 由于钅𫓧是通过钛-50 轰击钸-244靶产生的，因此它被认为位于核素图中“稳定岛”的附近。 “稳定岛”是指一群超重原子核，物理学家预测它们对自发裂变具有很强的抵抗力。与相同元素的较轻同位素相比，这些原子核的半衰期长得多。 如果能到达这个“稳定岛”，它将成为合成钅𫓨以外的新元素的关键踏脚石。 目前，盖茨的团队希望他们的研究结果能够为新一轮实验铺平道路，并计划使用他们的钛-50 离子束轰击更重的锎-249 靶。如果这些实验取得类似的成功，它们将成为发现更重超重元素的关键一步。

📣 该研究团队使用劳伦斯伯克利国家实验室的 VENUS 离子源来产生钛-50 离子束。 该离子源使用超导磁体来约束高度电离的钛-50 等离子体。 然后，他们使用劳伦斯伯克利国家实验室的 88 英寸回旋加速器设施来加速这些离子。 反应结束后，伯克利气体填充分离器将钅𫓧原子核与其他反应产物分离。 这使得研究小组能够测量原子核衰变时产生的产物链。 总的来说，研究小组检测到两条可以归因于钅𫓧-290 的衰变路径。 这尤其重要，因为这种同位素被认为位于核素图中“稳定岛”的附近。 “稳定岛”是指一群超重原子核，物理学家预测它们对自发裂变具有很强的抵抗力。与相同元素的较轻同位素相比，这些原子核的半衰期长得多。 如果能到达这个“稳定岛”，它将成为合成钅𫓨以外的新元素的关键踏脚石。 目前，盖茨的团队希望他们的研究结果能够为新一轮实验铺平道路，并计划使用他们的钛-50 离子束轰击更重的锎-249 靶。如果这些实验取得类似的成功，它们将成为发现更重超重元素的关键一步。

Physicists have used a beam of titanium-50 to create the element livermorium. This is the first time that nuclei heavier than calcium-48 have been used to synthesize a superheavy element. The international team, led by Jacklyn Gates at Lawrence Berkeley National Laboratory (LBNL) in California, hopes that their approach could pave the way for the discovery of entirely new elements.

Superheavy elements are found at the bottom right of the periodic table and have atomic numbers greater than 103. Creating and studying these huge elements pushes our experimental and theoretical capabilities and provides new insights into the forces that hold nuclei together.

Techniques for synthesizing these elements have vastly improved over the decades, and usually involve the irradiation of actinide targets (elements with atomic numbers between 89–102) with beams of transition metal ions.

Earlier in this century, superheavy elements were created by bombarding actinides with beams of calcium-48. “Using this technique, scientists managed to create elements up to oganesson, with an atomic number of 118,” says Gates. Calcium-48 is especially suited for this task because of its highly stable configuration of protons and neutrons, which allows it to fuse effectively with target nuclei.

Short-lived and difficult

Despite these achievements, the discovery of new superheavy elements has stalled. “To create elements beyond oganesson, we would need to use targets made from einsteinium or fermium,” Gates explains. “Unfortunately, these elements are short-lived and difficult to produce in large enough quantities for experiments.”

To try to move forward, physicists have explored alternative approaches. Instead of using heavier and less stable actinide targets, researchers considered how lighter, more stable actinide targets such as plutonium (atomic number 94) would interact with beams of heavier transition metal isotopes.

Several theoretical studies have proposed that new superheavy elements could be produced using specific isotopes of transition metals, such as titanium, vanadium, and chromium. These studies largely agreed that titanium-50 has the highest reaction cross-section with actinide elements, giving it the best chance of producing elements heavier than oganesson.

However, there is significant uncertainty surrounding the nuclear mechanisms involved in these reactions, which have hindered experimental efforts so far.

Theoretical decrease

“Based on theoretical predictions, we expected the production rate of superheavy elements to decrease when beams beyond calcium-48 were used to bombard actinide targets,” Gates explains. “However, we were unsure about the extent of this decrease and what it would mean for producing elements beyond oganesson.”

To address this uncertainty, Gates’ team implemented a reaction that has been explored in several theoretical studies – by firing a titanium-50 beam at a target of plutonium-244. Based on the nuclear mechanisms involved, this reaction has been predicted to produce the superheavy element livermorium, which has an atomic number of 116.

To create the titanium-50 beam, the researchers used LBNL’s VENUS ion source. This uses a superconducting magnet to contain a plasma of highly ionized titanium-50. They then accelerated the ions using LBNL’s 88-Inch Cyclotron facility. After the reaction, the Berkeley Gas-filled Separator isolated livermorium nuclei from other reaction products. This allowed the team to measure the chain of products created as the nuclei decayed.

Altogether, the team detected two decay paths that could be attributed to livermorium-290. This is especially significant because the isotope is thought to lie tantalizingly close to and “island of stability” in the chart of the nuclides. This comprises a group of superheavy nuclei that physicists predict are highly resistant to decay through spontaneous fission. This gives these nuclei vastly longer half-lives compared with lighter isotopes of the same elements.

If the island is reached, it could be a crucial stepping stone for synthesizing new elements beyond oganesson. For now, Gates’ team is hopeful its result could pave the way for a new wave of experiments and plan to use their titanium-50 beam to bombard a heavier target of californium-249. If these experiments see similar levels of success, they could be a crucial next step toward discovering even heavier superheavy elements.

The research is described in a preprint on arXiv.

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