Page 7 of 8
Imagine a cyclotron as a record with a skip in it. Researchers deposit charged krypton particles in the center of the record and use magnets to move it in a circle. There is a continuous field of radio waves bisecting the cyclotron at a fixed position -- the skip -- and every time the particle passes through the field, it gets a jolt of energy, moves a little faster, and edges farther from the center, out toward the periphery of the cyclotron. It passes through the scratch again, gets more energy, and picks up speed, until it is moving at the velocity you need to collide it into your target. Once again using magnets, researchers then steer it out of the cyclotron and aim it at the target.
"You've got a positively charged krypton ion injected axially, which means down the center, and every time it goes past a gap where there's a radio frequency field, it gets a voltage kick," Schroeder says. "So when it crosses that gap, an electric field appears and gives it a higher energy, it gets a little voltage increase, and as it does it moves to a higher orbit. So it starts in the center and spirals out, until there's a little hole where it comes out. In the cyclotron, this isn't just a little blurp of stuff. You have a continuous beam of particles extracted from the machine, and with magnets, they are delivered to your target area."
In the experiment to produce element 118, the target was a thin strip of lead. But it wasn't merely an inert piece -- the lead was deposited on a thin foil that was constantly spinning. Researchers tried to collide a krypton nucleus into a lead nucleus, but with such infinitesimal particles, the odds of smacking them exactly together are remarkably slim. Typically, the krypton interacts instead with the electron cloud surrounding the nucleus, and this generates heat -- enough heat, over time, to ruin the experiment. "This is a lot of what's called beam power, and as the krypton goes through the lead foil, it's constantly knocking electrons off until it finally collides with the nucleus," Schroeder says. "There's the core nucleus, but there's also this electron cloud around it, and there's a very high probability of knocking electrons off, which causes it to loses energy. That amount of energy is not very much, when you take into account the fact that it's being lost in this lead multiplied by so many particles, that's a lot of heat being generated. So they have to have a target that's spinning, so you're not hitting one isolated piece constantly. The lifetime of the target is a big consideration in this."
For eleven days, Gregorich's team stripped electrons from krypton gas, spun it around the cyclotron, and fired it at a spinning foil of lead. Then on April 19, Gregorich called Hoffman into his office and showed her some startling results. Victor Ninov had been going over the energy levels recorded by the collision and found three alpha decay chains. (Lab researchers never actually detect such heavy elements, merely the alpha particles that spin off when heavy elements decay into more stable matter.) According to the data, they had produced exactly three atoms of element 118. Berkeley researchers appeared to have cracked the mystery of the superheavy elements and, after a drought of more than twenty years, planted their flag on the firm soil of the magic island. The experiment worked so perfectly, the results were so accurately predicted by Smolanczuk's model, that Ninov exclaimed, "Does Robert talk to God or what?"
When Gregorich's team published the results of its experiment in Physical Review Letters, it caused an immediate sensation. Secretary of Energy Bill Richardson called it a "stunning discovery, which opens the door to further insights into the structure of the atomic nucleus," while others suggested that the Berkeley researchers could be on the "road to the Stockholm." Scientists at Germany's GSI lab began the process of confirming the lab's work, meticulously replicating the experiment and searching for alpha chains. Soon, troubling news was leaking back to the Lawrence lab: GSI couldn't find element 118 despite weeks of work. Scientists at the GANIL heavy-ion research lab in France and at Japan's Institute of Physical and Chemical Research also came up with nothing. At first, LBNL researchers thought that because of the rarity of the element, even the slightest change in the equipment could ruin the results; their discovery might still stand if they could repeat the experiment. The second time the experiment was run, however, element 118 never showed up.
Gregorich's team dug up its old data and reanalyzed the results of the first experiment. Soon the awful truth began to emerge: No one could find the original chain of alpha decay. It had just vanished. Had someone misread the data? Had the instruments failed? The Lawrence Lab convened a technical committee to find out what had gone wrong, and the results of the investigation are still pending. Meanwhile, Gregorich's team had to bite the bullet. On July 27, they retracted their announcement. Element 118 was gone. "I'm glad Glenn didn't live to see this," Ghiorso says. "Because if he had lived, he probably would have become a coauthor, just because we're sentimental and we would have included him. It would've killed him to find out he was wrong. None of us are happy about it; we don't like to make mistakes. But if you do make mistakes, you have to admit them as soon as you find out."
The retraction was an international embarrassment, a deeply disappointing moment for the Berkeley researchers, some of whom had been with Seaborg's original team in the lab's glory years. Now, when their life's work is written, an awkward coda will haunt them at the end of their careers.