PERIODIC LAW OF ATOMIC NUCLEI. ISOTOPES AT END OF THE PERIODIC SYSTEM

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• Document Creation Date: December 22, 2016
• Document Release Date: August 18, 2011
• Sequence Number: 962
• Publication Date: July 20, 1950
• Content Type: REPORT

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COUNTRY USSR
CLASSIFICATION SECRET SECRET
CENTRAL INTELLIGENCE AGENCY REPORT
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
DATE OF
INFORMATION 1949
SUBJECT Scientific - Nuclear physics
HOW
PUBLISHED Thrice-monthly periodical
WHERE
PUBLISHED Moscow
DATE
PUBLISHED 11 Nov 1949
LANGUAGE Russian
TRH DOCDNSNT CONTAINS INFORMATION AFFECTING THE NATIONAL DEFENSE
or THE DSITDD STATES WITHIN THE MEANING Al ERFIOMASS ACT SO
N. S. C.. SI AND SS. AS AMSROS1. ITS TRANSMISSION OR THE NSTSLATION
Or ITS CORTERTR IN ANY MANNER TO AN NNADTNDNUSD PERSON IS FRW
015100 ST LAW. REPRODUCTION OF THIS FORM IS PEONINITSD.
DATE DIST.) Jul 1950
NO. OF PAGES 4
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION
SOURCE Dokla Akademii Nauk SSSR, Vol LXIX, No 2, 1949.
PERIODIC LAW OF ATOMIC NUCLEI.
ISOTOPES AT END OT,MIEE:. PERIODIC. SYSTEM
A. P. Znoyko
Submitted 3 Sep 1949
STATE
ANY
The discovery of the periodic system of atomic nuclei (1) has enabled us
not only to predict isotopes which have not yet been found and to define their
properties, but also to predict elements following after the known No 96, Cm.
It became possible to indicate the mass of nuclei which have been pre?-'-
dibtec),to characterize them with respect to their decay period, energy, type
of emitted radiation, and other nuclear properties, and to select, tentatively,
reactions for their isolation.
The present communication aims to show that the regularly changing proper-
ties of nuclei in the periodic system demonstrate that elements No 97, 98, 99,
and 100 must have nuclei, the half-life of which can be measured in years. Con-
sequently, the elements in question ought to be susceptible to synthesis and in-
vestigation within a not too distant time. It also appears that more stable un-
known nuclei of the known elements At (aatatin), Rn (radon), Fr (francium), Pit
(plutonium), .and others must exist and be the principal isotopes of these ele-
ments.
Many isotopes at the end of the periodic system of atomic nuclei appar-
ently remain undiscovered. They definitely must have existed under the condi-
tions of the genesis of elements and consequently can be discovered and synthe-
sized. In the appended graph, we have indicated by triangles 142 nuclei of iso-
topes which, without any doubt, exist or must have existed.
Isotopes of elements at the end of the fourth period up to Ra and elements
of1the fifth period continued after Cm up to Z = 100 have been plotted in the
coordinate system Z/A - A, as shown in the graph.
The properties of atomic nuclei change in a?regular manner along each iso-
tope curve (from left to right) separately for even and odd values of Z. With-
in the limits of the isotope period of each element, (from top-to bottom) a sim-
ilar regular change of nuclear properties takes place, separately for even and
Z
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odd masses, corresponding to a certain value of Z. Regular changes of nu-
clear properties also occur along diagonals of the graph. For example, it
is known that nuclei situated along a diagonal even Zs, even masses - odd
Zs, odd masses will be more stable than those disposed along a diagonal even
Zs, odd masses - odd Zs even masses.
Thus, the periodic system of atomic nuclei enables one not only to pre-
dict the existence and to forecast the properties of istopes which have not
yet been discovered, but also to verify these assumptions by comparing the
results obtained for a certain isotope in tracing the changes of nuclear
properties, e.g., first along the isotope curve and then along the isotopes
of the element in question, the isobar upright, etc. We have shown in the
graph all points corresponding to known isotopes (2), indicating the type of
emitted radiation and the half-life in the case of radioactive nuclei.
Stable isotopes of the greatest relative occurrence are indicated by
circles, while the most stable radioactive isotopes are indicated by squares.
Triangles indicate predicted isotopes, and triangles containing a square
the most stable predicted isotopes.
A study of the isotope curves in the graph shows that the period of nu-
clear decay (stability of nuclei), in the fifth period after Ra, first in-
creases from the left to the right for even Zs along each isotope curve un-
til a maximum is reached, and then drops in a regular manner. The same oc-
curs with reference to the odd Zs of each curve.
In passing to a higher number of the isotope curve (from top to bottom),
it can be observed that the maximum of nuclear stability gradually moves from
left to right. This indicates the existence of the most stable nuclei of the
last elements in the lower right-hand corner of the graph.
Let us show on the examples of the unknown nuclei U236 and pu242 that
these nuclei have a very slow period of decay. U236 is shown in the graph
on the isotope curve j = 52, which depicts nuclei having an even mass. In
view of the fact that U236 has an even Z, let us trace the variation of t
along J ^ 52 for nuclei9 awing an even Z. It follows from the graph that the
T,s corresponding to even Zs of the isotope curve J - 52, and the Zs corres-
ponding to even masses of the uranium isotope period have the following values:
Z
6.7 yr 1.39X1010 ? 4000 yr
For Z - 92
A
228
230 1232 234 236
238
Z
9.3 min
20.8 da 70! yr.- 2.35x1:05yr 7
4.5x109 yr
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Conse9uently, the half-life of a U236 nucleus must be shorter than
1.39 x 101- years and longer than 6,000 years, and, on the basis of data
on uranium isotopes, at the same time fall into the interval between
2.35 x 105 years and 4.51 x 109 years. Even this semiquantitative treat-
ment indicates that the hypothetic nucleus u236 must have a half-life of
at least 106 years.
Similarly, a conclusion can be reached to the effect that the most
stable nuclei of Pu are the still unknown nuclei Pu242 and Pu244, and that
one of the latter is the principal isotope of plutonium.
We can see that the most stable nuclei of the isotopes Ra226, Th232,
and U238, the masses of which differ by six units, follow the law
iz+2 = iz+2
similarly to the principal isotopes in the region In, Sb, I. Cs, which we
have described (il)~rilr :') .
If the stability of isotopes of elements No 97, 98, 99, and 100 is
estimated by extrapolating according to isotope curves and isotope periods,
the conclusion is reached that the isotopes of these elements which lie on
the curve J = 53 have a half-life of the order of many years. For instance,
a high stability must be ascribed to the nuclei 97247, 98250, 99251, and
100274
The type of emitted radiation and other properties can be predicted
for isotopes of elements No 97-100. In accordance with the rule that K-
capture in the case of nuclei with an even j always occurs when Z is odd,
and that in the case of nuclei with an odd j it always occurs no matter
whether Z is even gr odd, one may expect that the isotopes 9741, 97242,
98243, 99245, 99246, and 100247 will exhibit K-capture. One must also as-
sume that the nucleus 98250, to give an example, will exhibit o< -decay with-
out K-capture.
The absence of elements At-Fr in nature becomes understandable, because
the isotopes of these elements complete the fourth nuclear period (before Ra)
and must have a half-life measured in hours and minutes.
It is obvious that the most stable isotopes of At, Rn, and Fr are not
At210, Rn222, and Fr223, which are known at present, but the normal nuclei
At209, Rn212, and Fr213 lying in their own (fourth) structural period. The
latter are the principal isotopes of the elements in question. The fact that
Fr223 emits /9-radiation definitely indicates that the principal isotope is
Fr213.
We have indicated some of the conclusions resulting from a consideration
of the isotopes appearing at the end of the periodic system of atomic nuclei.
The importance of the periodic system in research on this subject is obvious.
The aid extended by N. A. Novosel'skaya in treating the material and
writing this paper is appreciated.
1. A. P. Znoyko, Doklady Akademii Nauk, SSSR, Vol LXVIII, No 6 (1949)?
r00-W-7111497
2. G. T. Seaborg and I. Perlman, Reviews of Modern Pysics, Vol XX, No 4,
585 (1948)
fraph follows:7
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