Criteria that must be satisfied
Discovery of a New Chemical Element to be Recognized
IV. RADIOACTIVE PROPERTIES
The following list mentions properties connected to the radioactive
decay of the produced nuclides.
||Kind of decay (a, b,
g, SF=spontaneous fission)
||Energy of a-particles
||Maximum energy of b-particles
||Energy of g-radiations
||X-ray spectrum (K or L)
Genetic relation between ancestor and nth generation
descendant (there may be more than one)
Ki (Kind of decay). This property need not necessarily
refer to the kind of decay of the new isotope itself, but to that of
a descendant. In the latter case, though, proof is necessary that
the hypothetical ancestor really occurred.
Above, b stands for all weak interaction
processes (b-, b+,
e), g for all
electromagnetic ones (e.g. also for conversion electrons and emitted
electron-positron pairs) and X also for Auger electrons. For SF see
also under Fc.
Br (Branching ratio). A nuclide might show more
than one decay mode. Their intensity ratios, if determined with reasonable
accuracy, are rather characteristic properties.
T (Half-life). The information on T is
sometimes very imprecise, e.g. in the case of poor statistics, or if
it is only known that the descendant has been seen after a specified
time which may then be much longer than the half-life of the hypothetical
parent. Some information of this kind is inevitably available. Evidently,
T is a more distinctive property the more precisely it is known.
With few exceptions, a half-life cannot be used as an assignment property.
Theoretical understanding of half-lives is insufficient for this purpose.
Combination of a very high a-particle energy
with a relatively long half-life is a strong indication for Z>100.
Cases are known, however, where high spin isomers with Z around
84 combine the same characteristics. Similarly, fast SF occurs not only
for transfermium elements but also for SF isomers with Z around
The hindrance factor in a-decay is known
to be nearly equal to 1 in ground state transitions between nuclei with
even A and even Z. In other cases, it may (but not necessarily
must) be much larger. Thus, observation of a relatively long half-life
(high hindrance) in a-decay excludes assignment
to a transition between ground states of even-even nuclides. Such
a hindrance can be considered to be an assignment property. Also in
other cases, half-lives can sometimes be used to exclude specific
Ea (Energy of a-particles).
The energy of an a-particle can often be
determined very accurately and can then be a very distinctive characterization
property. For nuclide, with a complex a-spectrum,
good counting statistics may be necessary. Rare cases do exist where
different nuclides have quite similar combinations of Ea's
Eb (Minimum energy
of a b-spectrum). The maximum
energy of a continuous b-spectrum, if present,
can be determined with moderate precision and is then a rather characteristic
Eg (Energy of a
g-radiation). The energy of a
g-radiation, if present, can be determined
accurately and is then a good characterization property.
X (X-ray spectrum). The energy of X-rays can be determined
in the same way as those of g-rays. They
can be distinguished from g-rays if observed
with reasonable statistics, since X-rays (both K and L) show very characteristic
patterns. Similarly, Auger electrons might be distinguished from conversion
electrons. The presence of X-radiations of the correct energy is an
unambiguous assignment property yielding the atomic number of the atom
emitting those X-rays.
Fc (Fission characteristics). SF allows use of a sensitive
technique for the detection of the presence of several actinide
and trans-actinide nuclides. But most fission characteristics (such
as total kinetic energy (TKE) and fission fragment mass distribution),
even if measured with reasonable statistics, are not good assignment
properties. If the nuclear charges of coincident fission fragments could
be measured, this would determine the Z-value for the fissioning nuclide.
Gn (Genetic relations). (with nth descendant.)
This can yield an excellent assignment criterion, but only in the case
that the descendant has a well assigned value of Z and, preferably,
also of A. The reality of the proposed genetic relation, which
must be well established, can be demonstrated (even in the case of poor
statistics) by the observation of one or, preferably, all of the following
||time correlations between the decays of a parent and
||a correct ratio of parent and daughter decay intensities,
||a position correlation (e.g. observation of two a
particles -assigned to an ancestor and a descendant-starting from
the same place).
V. CONCLUDING REMARKS
In this Phase (i) Report we have enumerated various characterization
properties and assignment properties that relevant to the discovery
of new elements having atomic numbers greater than 100. We have not
referred specifically to earlier publications in this field. In Phase
(ii) we will apply these ideas so as to develop discovery profiles for
each of the individual transfermium elements. In the Phase (ii) Report*,
we will refer in detail to all relevant publications on those elements
and also mention earlier reviews dealing with the discovery of the transfermium
Part ii. Introduction to Discovery Profiles, Part iii. Discovery Profiles
of the Transfermium Elements, Responses from the concerned laboratories
in Berkeley, Dubna and Damstadt, and Reply to responses by Transfermium
Working Group, Pure Appl. Chem. 1993, 65, 1757-1814.