Island of stability


Island of stability

The island of stability is a term from nuclear physics that describes the possibility of elements with particularly stable "magic numbers" of protons and neutrons. This would allow certain isotopes of some transuranic elements to be far more stable than others; that is, decay much more slowly.

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The idea of the island of stability was first proposed by Glenn T. Seaborg. The hypothesis is that the atomic nucleus is built up in "shells" in a manner similar to the electron shells in atoms. In both cases shells are just groups of quantum energy levels that are relatively close to each other. Energy levels from quantum states in two different shells will be separated by a relatively large energy gap. So when the number of neutrons and protons completely fill the energy levels of a given shell in the nucleus, the binding energy per nucleon will reach a local minimum and thus that particular configuration will have a longer lifetime than nearby isotopes that do not have filled shells. [cite web | title = Shell Model of Nucleus | work = HyperPhysics | publisher = Department of Physics and Astronomy, Georgia State University | url = http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/shell.html | accessdate = 2007-01-22 ]

A filled shell would have "magic numbers" of neutrons and protons. One possible magic number of neutrons is 184, and some possible matching proton numbers are 114, 120 and 126 — which would mean that the most stable possible isotopes would be ununquadium-298, unbinilium-304 and unbihexium-310. Of particular note is Ubh-310, which would be "doubly magic" (both its proton number of 126 and neutron number of 184 are thought to be magic) and thus the most likely to have a very long half-life. (The next lighter doubly-magic nucleus is Lead-208, the heaviest stable nucleus and most stable heavy metal.) None of these transuranic isotopes has yet been produced, but isotopes of elements in the range between 110 through 114 are slower to decay than isotopes of nearby nuclei on the periodic table.

Half-lives of large isotopes

[

(1) stable elements.
(2) radioactive elements with half-lives of over a million years. Their long half-lives give them very small, if not negligible, radioactivities. They may be handled without any precautions.
(3) radioactive elements with half-lives of over 500 years. They may present low health hazards due to the fact that their radiation levels are near the background radiation level. Their half-lives allow them to have commercial applications.
(4) radioactive elements with half-lives of over a day. Their short half-lives pose high safety risks. They are dangerous to health. They have little potential for any commercial use.
(5) radioactive elements with half-lives of over a minute. These are highly radioactive elements. They pose severe health risks. They have no potential for commercial use.
(6) radioactive elements with half-lives of "under" a minute. These elements are extremely radioactive. Very little is known about these elements. Their short life times makes it impossible for them to exist outside research laboratories.]

Fermium is the largest element that can be produced in a nuclear reactor. The stability (half-life of the longest-lived isotope) of elements generally decreases from element 101 to element 109 and then approaches an island of stability with longer-lived isotopes in the range of elements 111 and 114 cite book | last = Emsley | first = John | title = Nature's Building Blocks | edition = (Hardcover, First Edition) | publisher = Oxford University Press | date = 2001 | pages = (pages 143,144,458) | id = ISBN 0198503407 ] . The longest-lived observed isotopes are shown in the following table.

The half lives of elements in the island are uncertain. Many physicists think they are relatively short, on the order of minutes, hours, or perhaps days. However, some theoretical calculations indicate that their half lives may be long (some calculations put it on the order of 109 years) [ [http://ie.lbl.gov/toipdf/theory.pdf Moller Theoretical Nuclear Chart 1997] ] . It is possible that these elements could have unusual chemical properties, and, if long lived enough, various applications (such as targets in nuclear physics and neutron sources). However, the isotopes of several of these elements still have too few neutrons to be stable. The island of stability still hasn't been reached, since the island's "shores" have neutron richer nuclides than those produced.

The alpha-decay half-lives of 1700 nuclei with 100 ≤ Z ≤ 130 have been calculated in a quantum tunneling model with both experimental and theoretical alpha-decay Q-values. citejournal|journal=Phys. Rev. C|volume=73|pages=014612|year=2006|title=α decay half-lives of new superheavy elements|author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|month=January|day=26|url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000073000001014612000001&idtype=cvips&gifs=yes|doi=10.1103/PhysRevC.73.014612] [citejournal| journal=Nucl. Phys. A|volume=789|pages=142–154|year=2007| title=Predictions of alpha decay half lives of heavy and superheavy elements|author=C. Samanta, P. Roy Chowdhury and D.N. Basu|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVB-4NF4F0Y-2&_user=2806701&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=3f680654b5659191d67f31681a4cfc83| doi=10.1016/j.nuclphysa.2007.04.001] [citejournal|journal=Phys. Rev. C|volume=77|pages=044603|year=2008|title=Search for long lived heaviest nuclei beyond the valley of stability|author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000077000004044603000001&idtype=cvips&gifs=yes|doi=10.1103/PhysRevC.77.044603] [citejournal|journal=At. Data & Nucl. Data Tables|year=2008|title=Nuclear half-lives for α -radioactivity of elements with 100 < Z < 130 |author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WBB-4S26JRX-1&_user=2806701&_coverDate=03%2F14%2F2008&_alid=740505626&_rdoc=6&_fmt=high&_orig=search&_cdi=6706&_sort=d&_docanchor=&view=c&_ct=211&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=dc85a3a8a2ac1faa38c3804f16f86c13] [citejournal|journal=Phys. Rev. C|volume=75|pages= 047306|year=2007|title=α decay chains from element 113|author=P. Roy Chowdhury, D. N. Basu and C. Samanta |month=January|day=26|url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000075000004047306000001&idtype=cvips&gifs=yes|doi=10.1103/PhysRevC.75.047306] [cite journal | doi = 10.1143/JPSJ.76.124201 | title = Quantum tunneling in 277112 and its alpha-decay chain | author = Chhanda Samanta, Devasish Narayan Basu, and Partha Roy Chowdhury | journal = Journal of the Physical Society of Japan | year = 2007 | volume = 76 | pages = 124201–124204] The theoretical calculations are in good agreement with the available experimental data.

Island of relative stability

232Th (thorium), 235U and 238U (uranium) are the only naturally occurring isotopes beyond bismuth that are relatively stable over the current lifespan of the universe. Bismuth was found to be unstable in 2003, with an α-emission half-life of 1.9 × 1019 years for Bi-209. All other isotopes beyond bismuth are relatively or very unstable. So the main periodic table ends at bismuth, with an island at thorium and uranium. Between bismuth and thorium there is a sea trough of severe instability, which renders such elements as astatine, radon, and francium extremely short-lived relative to all but the heaviest elements found so far.

Current theoretical investigation indicates that in the region Z =106-108 and N~160-164 a small ‘island/peninsula’ might survive fission and beta-decay, and superheavy nuclei in this region might predominantly undergo alpha decay. citejournal| journal=Nucl. Phys. A|volume=789|pages=142–154|year=2007| title=Predictions of alpha decay half lives of heavy and superheavy elements|author=C. Samanta, P. Roy Chowdhury and D.N. Basu|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVB-4NF4F0Y-2&_user=2806701&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=3f680654b5659191d67f31681a4cfc83| doi=10.1016/j.nuclphysa.2007.04.001] [citejournal|journal=Phys. Rev. C|volume=77|pages=044603|year=2008|title=Search for long lived heaviest nuclei beyond the valley of stability|author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000077000004044603000001&idtype=cvips&gifs=yes|doi=10.1103/PhysRevC.77.044603] [citejournal|journal=At. Data & Nucl. Data Tables|year=2008|title=Nuclear half-lives for α -radioactivity of elements with 100 ≤ Z ≤ 130 |author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WBB-4S26JRX-1&_user=2806701&_coverDate=03%2F14%2F2008&_alid=740505626&_rdoc=6&_fmt=high&_orig=search&_cdi=6706&_sort=d&_docanchor=&view=c&_ct=211&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=dc85a3a8a2ac1faa38c3804f16f86c13] . Also, 298114 is not the center of the magic island as predicted earlier. citejournal|journal=Nucl. Phys. A Tables|year=1969|title=On the nuclear structure and stability of heavy and superheavy elements |author=Sven Gösta Nilsson, Chin Fu Tsang, Adam Sobiczewski, Zdzislaw Szymaski and, Slawomir Wycech, Christer Gustafson, Inger-Lena Lamm, Peter Möller and, Björn Nilsson|url= http://www.sciencedirect.com/science?_ob=ArticleListURL&_method=list&_ArticleListID=745546610&_sort=d&view=c&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=325c9fc8ab851444ddd2450f32585b97] On the contrary, the nucleus with Z=110, N=183 appears to be near the center of a possible 'magic island' (Z=104 -116, N~176 -186). In the N~162 region the beta-stable, fission survived 268106 is predicted to have alpha-decay half life ~3.2hrs that is greater than that (~28s) of the deformed doubly-magic 270108.citejournal|journal=Phys. Rev. Lett. |volume=97|pages= 242501|year=2006|title=Doubly Magic Nucleus 270108 Hs-162|author= J. Dvorak, W. Brüchle, M. Chelnokov, R. Dressler, Ch. E. Düllmann, K. Eberhardt, V. Gorshkov, E. Jäger, R. Krücken, A. Kuznetsov, Y. Nagame, F. Nebel,1 Z. Novackova, Z. Qin, M. Schädel, B. Schausten, E. Schimpf, A. Semchenkov, P. Thörle, A. Türler, M. Wegrzecki, B. Wierczinski, A. Yakushev, and A. Yeremin|url= http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000097000024242501000001&idtype=cvips&gifs=yes|doi=10.1103/PhysRevLett.97.242501] The superheavy nuclei 268106 has not been produced in the laboratory as yet (2008). For superheavy nuclei with Z >116 and N ~184 the alpha-decay half-lives are predicted to be less than one second. The Z=120, 124, 126 with N=184 are predicted to form spherical doubly-magic nuclei and survive fission.citejournal|journal=Nature |volume=433|pages= 705|year=2005|title= Shape coexistence and triaxiality in the superheavy nuclei|author= S. Cwiok, P.-H. Heenen and W. Nazarewicz |url=http://www.phys.utk.edu/witek/fission/utk/Papers/natureSHE.pdf|doi= 10.1038/nature03336 ] Calculations in a quantum tunneling model show that such superheavy nuclei would undergo alpha-decay within microseconds or, less. citejournal| journal=Nucl. Phys. A|volume=789|pages=142–154|year=2007| title=Predictions of alpha decay half lives of heavy and superheavy elements|author=C. Samanta, P. Roy Chowdhury and D.N. Basu|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVB-4NF4F0Y-2&_user=2806701&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=3f680654b5659191d67f31681a4cfc83| doi=10.1016/j.nuclphysa.2007.04.001] [citejournal|journal=Phys. Rev. C|volume=77|pages=044603|year=2008|title=Search for long lived heaviest nuclei beyond the valley of stability|author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000077000004044603000001&idtype=cvips&gifs=yes|doi=10.1103/PhysRevC.77.044603] [citejournal|journal=At. Data & Nucl. Data Tables|year=2008|title=Nuclear half-lives for α -radioactivity of elements with 100 ≤ Z ≤ 130 |author=P. Roy Chowdhury, C. Samanta, and D. N. Basu|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WBB-4S26JRX-1&_user=2806701&_coverDate=03%2F14%2F2008&_alid=740505626&_rdoc=6&_fmt=high&_orig=search&_cdi=6706&_sort=d&_docanchor=&view=c&_ct=211&_acct=C000058844&_version=1&_urlVersion=0&_userid=2806701&md5=dc85a3a8a2ac1faa38c3804f16f86c13] .

ynthesis problems

Manufacturing nuclei in the island of stability may be very difficult, because the nuclei available would not deliver the necessary sum of neutrons. So for the synthesis of isotope 298 of element 114 by using plutonium and calcium, one would require an isotope of plutonium and one of calcium, which have together a sum of at least 298 nucleons (more is better, because at the nuclei reaction some neutrons are emitted). This would require for example in the case of synthesis of element 114 the usage of calcium-50 and plutonium-248. However these isotopes (and heavier calcium and plutonium isotopes) are not available in weighable quantities. This is also the case for other target/projectile-combinations.

However it may be possible to generate the isotope 298 of element 114, if nuclear transfer reactions would work.One of these reactions may be::204Hg + 136Xe → 298Uuq + 40Ca + 2n

References

ee also

* Island of stability: UnunquadiumUnbiniliumUnbihexium
* Table of nuclides — a visualization of the island of stability
* Periodic table and Periodic table (extended)
* Douglas Preston and Lincoln Child featured the island of stability in their 2000 novel "The Ice Limit".

External links

* [http://arxivblog.com/?p=350 The hunt for superheavy elements] (April 7, 2008)
* [http://159.93.28.88/popeko/e114_287.html The synthesis of spherical superheavy nuclei in 48Ca induced reactions] (needs login so can not access !)
* [http://www.radiochemistry.org/periodictable/elements/115.html Uut and Uup Add Their Atomic Mass to Periodic Table] (Feb 2004)
* [http://www.ias.ac.in/currsci/aug10/articles9.htm New elements discovered and the island of stability sighted] (Aug 1999 - includes report on article later retracted)
* [http://www.cerncourier.com/main/article/39/7/18 First postcard from the island of nuclear stability] (1999)
* [http://www.cerncourier.com/main/article/41/8/17 Second postcard from the island of stability] (Oct 2001)
* [http://imglib.lbl.gov/ImgLib/COLLECTIONS/BERKELEY-LAB/SEABORG-ARCHIVE/index/96B05658.html Superheavy Elements "Island of Stability"] (single text slide - undated)
* [http://physicsweb.org/articles/world/17/7/7 Superheavy elements] (Jul 2004 Yuri Oganessian of JINR )
* [http://curious.astro.cornell.edu/question.php?number=599 Can superheavy elements (such as Z=116 or 118) be formed in a supernova? Can we observe them?]
* [http://www.pbs.org/wgbh/nova/sciencenow/3313/02.html NOVA - Island of Stability]
* [http://www.nytimes.com/2004/02/08/opinion/08SACK.html?ex=1391576400&en=68476e9da837f91f&ei=5007&partner=USERLAND New York Times Editorial by Oliver Sacks regarding the Island of Stability theory] (Feb 2004 re 113 and 115)
* [http://www.ptep-online.com/index_files/2007/PP-09-20.PDF Upper Limit of the Periodic Table and Synthesis of Superheavy Elements]


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