Group members include (left to right): Philip Wilk, Jackie Kenneally, Ken Moody, Dawn Shaughnessy, Mark Stoyer, Nancy Stoyer, and John Wild (retired). Two retirees not pictured are Jerry Landrum and Ron Lougheed.
Two superheavy elements, elements 113 and 115, were recently
synthesized through a collaborative effort between scientists from
the Physical and Life Sciences Directorate at the Lawrence Livermore
National Laboratory and researchers from the Joint Institute for Nuclear
Research at the Flerov Laboratory for Nuclear Reactions in Dubna, Russia.
Two isotopes of element 115 survived 30-80 milliseconds before decaying
into isotopes of element 113 that survived approximately ten times
longer prior to decaying themselves. Following a series of alpha-decays,
the element 115 atoms decayed into long-lived isotopes (multiple hours)
of element 105 (Db). The great-great-great granddaughter Db isotopes
were also chemically identified in subsequent experiments.
A heavy element is an element with an atomic number greater than 92.
The first heavy element is neptunium (Np), which has an atomic number of
93. Some heavy elements are produced in reactors, and some are produced
artificially in cyclotron experiments.
2. What is a superheavy element?
The definition of superheavy elements (SHE) varies among different
groups of people. We use the term term SHE to refer to those elements with
an atomic number greater than or equal to 112. The first superheavy element
is element 113, which has been recently discovered by a collaboration of
scientists from the Lawrence Livermore National Laboratory and the Joint
Institute of Nuclear Research in Russia. Like some of the heavy elements,
superheavy elements are produced artificially in cyclotron experiments.
3. What is an atomic number?
The atomic number refers to the number of protons in an elements nucleus.
Each element has a unique atomic number and is known by that number until
it receives an official name. For example, the two new superheavy elements
113 and 115 have 113 and 115 protons, respectively, in their nuclei.
4. What are isotopes?
Elements are defined by their atomic numbers or number of protons in the
nucleus. Elements, however, have more than one isotope. An isotope contains
varying numbers of neutrons in the nucleus. Gold, for example, has one stable
isotope often denoted as .
It has an atomic number of 79 (meaning 79 protons in the nucleus) and a mass
number of 197, or the total number of neutrons and protons in the nucleus.
Thus, there are 197 – 79 = 118 neutrons in this isotope. However, more
than 30 isotopes of gold are known. Each isotope has its own decay characteristics
and half-life. For example, ,
an isotope with one more neutron (119) that the stable isotope ,
has a half-life of 2.7 days and decays by beta-decay. A very different gold
has a half-life of 5 ms and decays by alpha-decay.
5. How are new elements discovered?
Several experimental techniques have been used to make new chemical elements.
Some of these include heavy ion transfer reactions, cold or hot fusion evaporation
reactions, neutron capture reactions, light-ion charged particle induced
reactions, and even nuclear explosions. These techniques each have advantages
and disadvantages making them suitable for studying nuclei in certain regions.
The types of nuclear reactions that have been successfully used to produce
new elements in the last decade are cold fusion reactions and hot fusion
reactions. Cold fusion reactions use beam and target nuclei that are
closer to each other in mass in order to produce a compound nucleus
(the complete fusion of one target nucleus with one beam nucleus) with
generally lower excitation energy that typically requires evaporation
of one or no neutrons. This generates fewer neutron-rich isotopes of
an element that have higher survival probabilities with respect to
fission, but have lower fusion probabilities. An example of this type
of reaction is 70Zn
+ 208Pb → 277112
+ 1n with a cross-section of ~1 picobarn.
Because the 112 isotope ultimately decays by a emission to known nuclei
[namely isotopes of elements 102 (No) and 104 (Rf)], identification of this
element is straightforward. Hot fusion reactions use more asymmetric beam
and target nuclei, produce a compound nucleus with generally higher excitation
energy that typically requires evaporation of three to five neutrons, generate
more neutron-rich isotopes of an element, have lower survival probabilities
with respect to fission, but have higher fusion probabilities. An example
of this type of reaction is 48Ca + 244Pu → 288114
+ 4n with a cross-section of ~1 pb. Because of the neutron-richness
of this isotope of element 114, it never subsequently decays to any known
isotope, and thus its identification is more problematic. Cold fusion
reactions have been successful in producing elements 104—112 and hot
fusion reactions have recently provided evidence for elements 113—116
6. What is a cyclotron?
A cyclotron is a particle accelerator that boosts ions to very
high velocities through a series of small kicks as the ions travel
in a circular motion (or spiral). The cyclotron was invented at the
University of California, Berkeley, by Ernest O. Lawrence, the namesake
of the Lawrence Livermore National Laboratory.
U400 cyclotron in Dubna, Russia
7. What are some properties
of artificially made isotopes?
Isotopes of various elements that are created artificially in
accelerator experiments are unstable and radioactive. Once produced,
these new isotopes begin to decay; that is, change into another isotope.
The time required for half of an isotopes atoms to decay is called
the isotopes half-life. As the atomic number of each new heavy
element increases, the half-life typically decreases, meaning that
new elements tend to decay more quickly. However, physicists in the
1960s predicted that this trend toward shorter half-lives would change
around element 114. They thought that some elements around element
114 would have longer half-lives, forming an island of stability in
the midst of a sea of highly unstable elements.
8. What is the island
The "island of stability" refers to a predicted region
of superheavy elements on the chart of nuclides with half-lives that
are longer by several orders of magnitude than the half-lives of other
superheavy elements. Half-lives for elements in the island of stability
may range from seconds to minutes, while half-lives for other superheavy
elements may be measured in micro- or nanoseconds. The existence of
the island of stability was shown in 1998 with the discovery of the
superheavy element 114. The island of stability is a specific subset
of the superheavy elements, which is characterized by nuclei that
have a spherical shape.
9. What is the sea of instability?
The "sea of instability" refers to a region of elements
on the periodic table that are highly unstable. These elements have
extremely short half-lives that may be measured in micro- or nanoseconds.
(A nanosecond is the time it takes for light to travel one foot.) This
region of unstable elements surrounds the island of stability.
Select the image to see a larger version.
10. Why is discovering
new superheavy elements important?
Discovering new superheavy elements proves long-held nuclear
theories regarding the existence of the island of stability and
the ultimate limits of the periodic table of the elements. These discoveries
also help scientists to better understand how nuclei are held together
and how they resist the fission process. The skills that are acquired
by conducting these heavy-element experiments can then be applied to
solving national needs like stockpile stewardship and homeland security.
For example, an improved understanding of the fission process will
enable scientists to enhance the safety and reliability of the nations
nuclear stockpile and nuclear reactors.
11. How can superheavy
elements be used?
Like most scientific discoveries, researchers do not yet know
the immediate practical applications of the discovery of elements 113
and 115. Previously discovered heavy elements are used in smoke detectors
(americium), neutron radiography and neutron interrogation (curium
and californium), and nuclear weapons (plutonium). Scientists expect
that practical applications of elements 113 and 115 also exist and
will be discovered in the future.
12. How long did it
take to discover elements 113, 114, 115, 116, and 118?
Elements 113 and 115—The experiment began
on July 14, 2003, and ended on August 10, 2003. In that time, four
atoms of element 115 were produced that decayed after a given time,
thereby producing element 113, which also decayed and so on. However,
years of successful experiments, previous to the 115 and 113 discovery,
were needed to show that the experiment could be successful. More
than a year was then spent to clean the target material, ship it
to Russia, make the target, and run the experiment.
Element 114—The first element 114 experiment
lasted about one year, and two atoms were discovered during that
Element 116—The element 116 experiment also
lasted about one year, and three atoms were discovered during that
Element 118—Element 118 was produced during
two separate experiments, each one lasting for several months. A
total of three atoms were discovered in both experiements combined.
13. Why are the superheavy-element
experiments conducted in Russia?
We collaborate with our Russian colleagues because we share
a similar passion for the study of heavy elements, and we bring complementary
skills and resources to the solution of magnificent problems such as
the confirmation of the existence of the "Island of Stability" and
the characterization of the chemical properties of exotic elements.
This collaboration has been very fruitful and stimulating—enabling
each group to achieve more in a shorter period of time. This equipment
is operated by the highly trained scientific staff at the Dubna laboratory.
14. What special equipment
is needed to discover superheavy elements?
There are three pieces of special equipment: (1) a cyclotron,
which produces the intense beams of calcium-48 ions used to produce
the superheavy elements; (2) a separator that separates the atoms of
interest from everything else produced in these reactions; and (3)
a detection system that can observe and record all of the events that
take place during the experiment.
15. When will elements
113 and 115 be named?
We don't know when the elements will be named. The naming of
new elements is a long process governed by the International Union
of Pure and Applied Chemistry (IUPAC). Any discovery of new elements
must first be confirmed by an independent laboratory and established
beyond a reasonable doubt. Afterwards, the research team that discovered
the element is asked to propose a name and symbol for the element.
The proposed name is then reviewed by a panel of experts and, if all
goes well, finally approved by the IUPAC. This naming process can take
many years. For example, element 110 was discovered in 1995 and received
its name, darmstadtium (Ds), in 2003, while element 106 was discovered
in 1974 but was not officially named as seaborgium (Sg) until 1997.
Until elements 113 and 115 receive their official names, they will
be known by their temporary IUPAC names: ununtrium (Uut) for element
113 and ununpentium (Uup) for element 115.