Elements that do not exist in nature--that have been created in a laboratory--are unstable. After
hours or days of one element bombarding another with enough energy for both to fuse, the resulting new
element typically is born and begins to decay instantly.
Neptunium and plutonium (elements 93 and 94) were the first elements created in a
laboratory, at the University of California at Berkeley in 1940. Scientists have since fabricated many
more elements, each one heavier and with a shorter half-life than the one before it.
In the 1960s, a few physicists predicted that some elements around element 114 would
survive longer than any of their synthesized predecessors. Early estimates for the half-lives of these
more stable elements were as high as billions of years. Later computer modeling reduced the
anticipated half-lives to seconds or minutes before the element began to decay.
Half-lives of seconds or minutes may seem brief. But consider that various atoms of element
110 created in the laboratory have had half-lives ranging from 100 microseconds to 1.1 milliseconds.
The only atom of element 112 that had been created before 1998 had a lifetime of 480 microseconds.
As described further in the box below, the long-lived nuclei of elements around element 114 would
comprise an "island of stability" in a "sea" of highly unstable elements.
When a collaboration of Russian and Livermore scientists at the Joint Institute for Nuclear
Research in Dubna, Russia, created element 114 in 1998, the first atom survived for 30 seconds before
it began to decay, a spontaneous process that leads to the creation of another element with a lower
number on the periodic table. (See the box below for more information on stability and instability.) A
total of 34 minutes elapsed before the final decay product fissioned, splitting in two the surviving
nucleus. These lifetimes may seem brief, but they are millions of times longer than those of other
recently synthesized heavy elements.
Since that groundbreaking effort in 1998, the team has created another atom of element 114.
This one has a different number of neutrons and thus a different mass, thereby making it a different
isotope of element 114. The team has also created several previously undiscovered isotopes of
elements 112, 110, and 108 to which element 114 decayed. More recently, the team added element
116 to the periodic table with the creation of three atoms of the element in a series of experiments.
Nuclear chemist Ken Moody leads the Livermore portion of the international collaboration. "In
1998, we proved that there really was an island of stability," he said. "We proved that years of nuclear
theory actually worked."
The collaboration began in 1989. with heavy element chemist Ken Hulet representing
Livermore and Yuri Oganessian, scientific director of the Flerov Laboratory of Nuclear Reactions at the
Joint Institute, leading the Russians. In the early 1990s, the U.S.-Russian team discovered two
isotopes of element 106, one isotope of 108, and one of 110 at the Dubna institute.
"In 1990, when Ron Lougheed, who has since retired, and I went to Dubna, we were the first
U.S. scientists to perform experiments at that institute," adds Moody. "Remember what was happening
then. The Berlin Wall had just fallen, and Eastern Europe was in turmoil. The early days of the
collaboration were definitely interesting."
Forty days and nights
Noah's flood could have come and gone in the time it took the collaboration to create the first
atom of element 114. For 40 days of virtually continuous operation, calcium ions bombarded a spinning
target of plutonium in Dubna's U400 cyclotron. While the first atom of element 114 was actually created
on November 22, 1998, Russian researchers discovered it in data analysis and communicated the news
to Livermore on December 25, 1998--quite the Christmas present.
The box below shows the "recipe" for the early Dubna experiments that created isotopes of
element 114. Plutonium, with an atomic number, or Z, of 94, and calcium, Z = 20, add up to the
necessary Z = 114. By fusing plutonium-244, an isotope of plutonium with 150 neutrons, and
calcium-48, a neutron-rich isotope with 28 neutrons, a compound nucleus with 114 protons and 178
neutrons (150 + 28) would in theory be possible. In fact, however, when the plutonium-244 and
calcium-48 nuclei collide with enough energy to overcome their mutual electrostatic repulsion, the
compound nucleus has excess energy. A few neutrons evaporate to de-excite the nucleus and produce
an isotope with 175 neutrons.
To discover whether new elements were created by the bombardment of plutonium, the team
was interested in finding "events" comprising a series of alpha decays ending with spontaneous fission.
In alpha decay, an isotope loses an alpha particle, which is two protons and two neutrons (or a helium
nucleus). For example, an atom of element 114 with 175 neutrons (described as isotope 114-289) would
emit an alpha particle, thereby becoming isotope 112-285, having lost 2 protons and 2 neutrons. The
atom of 112-285 would become 110-281, which would become 108-277. At some point, fission would
occur, ending the process. At the same time, however, unwanted nuclei generated by the experiment
also undergo alpha decay and fission, mimicking the decay sequence of element 114. Trillions of these
unwanted nuclei are produced every day, whereas the expected production rate for an element 114
isotope was much less than one atom per day. To deal with the problem of unwanted nuclei in earlier
experiments, Dubna scientists had developed a gas-filled mass separator to separate unwanted nuclei
from the desired ones. "It worked marvelously," says Moody.
Heavy-element reaction products recoil from the spinning plutonium target wheel and enter the
mass separator, a chamber filled with low-pressure hydrogen gas confined between the pole faces of a
dipole magnet. The magnetic field is adjusted so that, for the most part, only the nuclei of interest pass
through to the detector array.
The desired nuclei are focused with a set of magnetic quadrupoles, pass through a
time-of-flight counter, and are captured by a position-sensitive detector. A signal from the time-of-flight
counter allows the team to distinguish between the effect of products passing through the separator and
the radioactive decay of products that are already implanted in the detector. The flight time through the
counter is also used to discriminate between low- and high-Z products, because heavier elements travel
more slowly. The position-sensitive detector lowers the rate of background interference, allowing
scientists to identify and ignore unwanted products.
During 40 days in November and December 1998, with ten-thousand trillion ions per hour of
calcium-48 bombarding the plutonium target, the team observed the signals of just three spontaneous
fission decays. Three synthesized compound nuclei had been created and passed through the
separator before fissioning. Two of them lasted about 1 millisecond each and proved to be products from
the decay of the nuclear isomer of americium-244.
Only one of the events involved an implant in the detector followed by three alpha decays in
the detector array. This isotope of element 114 (114-289) had a lifetime of 30.4 seconds. It decayed to
element 112, which, with a lifetime of 15.4 minutes, decayed to element 110. Element 110, with a
lifetime of 1.6 minutes, then decayed to element 108, which decayed by spontaneous fission.
In 2000 and 2001, the collaboration performed three experiments in which a curium-284 target
was bombarded with calcium-48 ions to create element 116. The team chose this combination of
isotopes because they would produce isotopes of element 116 that should decay to the previously
observed isotopes of element 114.
Researchers produced the super-heavy isotope 116-292 once in each of these experiments.
They also created some other isotopes repeatedly. Isotopes 114-288, 112-284, and 110-280 have been
found five times, lending credibility to several experimental results. However, the first atom of 114-289
with the 30.4-second lifetime has yet to be replicated.
In the final analysis
The recipe for element 114 in the box below refers to the analysis of 7 gigabytes of data from
the first experiments. The team has since accumulated another 23 gigabytes of data, all requiring
extensive analysis to verify the times and energies of the alpha decays. Valid decay sequences must
fall within the alpha decay time and energy parameters of what is known as the Geiger-Nuttall
Scientists at Livermore and Dubna analyzed the data in parallel. Livermore gave the Dubna
institute a computer workstation for the Russian scientists to use on that mountain of information.
Nuclear chemists John Wild and Nancy Stoyer analyzed the data at Livermore. "These duel analyses
were independent but were calibrated. In the end, our results agreed," says Wild.
The team must also confirm that the sequences they saw were not composed of random
events. "The problem of randomness is real, especially for long-lived elements," adds Wild. "The longer
the lifetime of a member of a decay sequence, the greater the probability that the decay could be
A novel Monte Carlo method to estimate the probability of whether a decay chain was random
or the real thing was the brainchild of nuclear chemist Mark Stoyer. It is a pseudo-random number
generator that places random fission events into the real data throughout the duration of the experiment.
Nancy Stoyer developed the search code that sifted the data, including Monte Carlo-generated random
fissions, for decay sequences similar to the 114-289 decay sequence that had been observed
Because the actual decay chains end with a spontaneous-fission event, Nancy Stoyer's
search algorithm looks backward from the planted fission event for candidate alpha-decay chains that
match actual decay chains and end with a fission event. The number of returned "accidental" decay
chains defines the probability that a decay sequence is random. For the first atom of element 114, the
random probability was 0.6 percent. "If we eliminate decay chains in which all alpha events do not meet
the Geiger-Nuttall relationship," says Moody, "the random probability falls to 0.06 percent. That's
New elements still to come
The Livermore researchers are continuing its work to explore the southwest shores of the
island of stability. With funding from the Laboratory Directed Research and Development program, they
have begun efforts to add elements 115 and 113 to the periodic table. They are in the process of
sending 22 milligrams of pure americium-243 to Dubna for the work on element 115.
Current exploration of the island of stability, or its beaches, is limited to stable targets and
projectile beams. There exists no suitable combination of projectile and target to produce 114-298, the
long-predicted highly stable isotope. The isotopes 114-289 and 114-288 require the most neutron-rich
isotopes of plutonium and calcium. In the future, when radioactive beam accelerators are capable of
producing intense beams of even more neutron-rich isotopes, researchers may venture farther toward
the center of the island. For example, calcium-50 has a half-life of 14 seconds, far too short to gather
material together to put into a conventional ion source. However, plans are for a radioactive beam facility
to produce calcium-50 and accelerate it to energies required for the experiments well before it can
decay. Thus, an isotope of element 114 with a mass of 290 or 291, two neutrons closer to the center of
the island, may well be possible.
As scientists continue to explore for new elements, they expect that more spherical and
longer-lived isotopes will be produced, which will most certainly require more sensitive detection
schemes. Challenges abound.
Livermore researchers also want to study the chemical properties of elements 112 and 114.
The combination of chemical and nuclear properties defines the usefulness of any nuclide. Most heavy
elements exist in such small amounts, or for such short times, that no one has pursued practical
applications for them. However, several heavy elements do have uses--americium is used in smoke
detectors, curium and californium are used for neutron radiography and neutron interrogation, and
plutonium is elemental in nuclear weapons. Although elements 114 and 116 have no immediate use,
they do exist, and more of them can be manufactured when uses for them are found. Adds Moody,
"Showing that the isotopes of element 114 produced by the collaboration have unique chemical
properties will also provide proof that they are indeed a new element."
A primer on stability and instability
Why should element 114 be so
much more stable and long-lived than so
many of its synthesized predecessors?
The answer lies in basic chemistry.
The nucleus of an atom is
surrounded by one or more orbital shells
of electrons. The electron configurations of
atoms of the many elements vary
periodically with their atomic number,
hence "the periodic table of the
Elements with unfilled shells
seek out electrons in other elements to fill
them. These include carbon, oxygen, and
all of the "reactive" elements that want to
react with other elements. This is the
basis of covalent bonding. The noble
gases (on the far right column of the
periodic table) have a completely filled
outer electron shell and hence are highly
stable. They are termed noble because
they are "aloof," with no desire to react
with other elements.
Protons and neutrons are in
analogous shells within the nucleus. The
proton shells of helium, oxygen, calcium,
nickel, tin, and lead are completely filled
and arranged such that the nucleus has
achieved extra stability. The atomic
numbers of these elements--2, 8, 20, 28,
50, and 82--are known as "magic
numbers." These same numbers plus 126
are magic numbers for neutrons. Notice
that the magic numbers are all even. No
truly stable element heavier than nitrogen
has an odd number of both protons and
neutrons. Elements with even numbers of
protons and neutrons make up about 90
percent of Earth's crust.
A nucleus is "doubly magic"
when the shells of both the protons and
neutrons are filled. Lead-208 has 82
protons and 126 neutrons, both of which
are magic numbers. Lead-208 is thus
doubly magic and seems to be virtually
A long-lived, stable element
such as lead does not decay. However, all
elements with an atomic number greater
than 83 (bismuth) exhibit radioactive
decay. Decay may happen in several
ways. For heavy elements, an unstable or
radioactive isotope usually decays by
emitting helium nuclei (alpha particles) or
electrons (beta particles), leaving a
daughter nucleus of an element with a
different number of protons. This process
typically continues until a stable nucleus
is reached. Plutonium, for example,
decays ultimately to lead.
The heavy elements that have
been created in the laboratory are so
unstable that they decay almost
immediately and have extremely short
half-lives and thus lifetimes. How quickly a
particular isotope decays is measured by
its half-life. Plutonium-239, which decays
very slowly, has a half-life of about 24,000
years, while plutonium-238's half-life is
just 88 years. Half-lives are a result of a
statistical process. If an experiment
produces only one atom, then a half-life
cannot be determined. Thus, with one or a
few atoms, scientists talk instead about
In the mid-1960s, a physicist in the
U.S. predicted that the next magic proton
number above 82 would be 114, not 126, and
that an atom with a doubly magic nucleus of
114 protons and 184 neutrons should be the
peak of an island of stability. Russian
scientists had come to the same conclusion at
about the same time.
In the years since, increasingly
sophisticated computer models have indicated
that element 114 would exhibit significant
nuclear stability even with neutron numbers as
low as 175. Note that element 114 is expected
to lie in the same column (or group) of the
periodic table as lead. The two elements are
expected to share many properties.
One kilogram of deuterium-tritium
fusion fuel would produce the same energy as
30 million kilograms of coal. Other major
advantages include no chemical combustion
products and therefore no contribution to acid
rain or global warming, radiological hazards
that are thousands of times less than those
from fission, and an estimated cost of
electricity comparable to that of other
long-term energy options.
A stormy voyage to the island of stability
As of November 2001,
scientists throughout the world had
synthesized 20 elements that do not
exist in nature. The ones up to
meitnerium (109) have been given
official names. Elements 110, 111,
112, 114, and 116 will not be named
until their existence has been
corroborated with several experiments
or by several different groups. Recall
that one of the fundamental tenets of
science is reproducibility.
In 1940, Ed McMillan and
his team at Berkeley bombarded
uranium with neutrons to create
neptunium (element 93). Then Glenn
Seaborg and his colleagues created
plutonium-238, the first isotope of
plutonium (element 94), through the
decay of neptunium-238, which they
produced by bombarding uranium with
deuterium (heavy hydrogen).
Elements 99 and 100 were discovered
in the debris of the first hydrogen
bomb test in 1952 from the
simultaneous capture of many
neutrons by uranium. The heavy,
highly radioactive uranium isotopes
decayed quickly by beta emission
down to more stable isotopes of
elements 99 (einsteinium) and 100
(fermium). Elements 95, 96, 97, 98,
and 101 were created by irradiating
heavy nuclei with beams of alpha
particles to boost the atomic numbers
two steps at a time.
Beginning in the late 1950s,
the new particle accelerators were
capable of accelerating ions heavier
than helium. First, ions of the lightest
elements were directed at the
heaviest elements. But it took excess
energy to cause them to fuse,
producing a very hot nucleus that
tended to fission almost immediately.
Known as "hot fusion," this method
yielded elements 102 through 106 by
1974. Many of these experiments
included Livermore scientists.
In 1974, Yuri Oganessian at
the Joint Institute at Dubna found that
if heavier ions are directed at lead and
bismuth, less energy was needed to
create new elements. These two
elements are extra-stable, and thus
the resulting compound nucleus has
less energy and is more likely to
remain intact. This process is known
as "cold fusion," not to be confused
with the discredited fusion energy
process of the same name. Even with
cold fusion, so few nuclei of the new
element are produced during an
experiment that existing detection
techniques were not sensitive enough
to find them.
The field of synthesizing ever heavier
elements went on hiatus for several years until
sophisticated new separation and detection methods
were developed in the early 1980s in Germany. German
researchers were then able to create and detect
elements 107, 108, and 109 in experiments that have
since been corroborated such that these synthetic
elements now have names. They also created isotopes
of 110, 111, and 112, but these results have not yet
been fully corroborated.
The German group, the Consortium for Heavy
Ion Research at Darmstadt, Germany, has produced an
isotope of element 112 that decayed into the same
isotope of 110 that the Dubna-Livermore team found in
1994. This isotope had the same energy and lifetime,
which is encouraging validation.
The voyage to the island of stability has been
a stormy one. It took until 1998 to even reach the
beach. As shown in the figure below, the island's peak
is still tantalizingly just out of reach.
The Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.