Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes

Abstract

Evidence for the existence of long-lived neutron-deficient isotopes has been found in a study of naturally-occurring Th using inductively coupled plasma-sector field mass spectrometry. They are interpreted as belonging to the recently discovered class of long-lived high spin super-and hyperdeformed isomers.In recent years, long-lived high spin super-and hyperdeformed isomeric states with unusual radioactive decay properties have been discovered in heavy and very heavy nuclei [1][2][3][4] . This discovery motivated us to perform a search for naturally-occurring long-lived isomeric states. (Up to now there is only one such isomeric state known, namely the 75.3 keV excited state in 180 Ta with a half-life of >1.2x10 15 y (ref. 5 )). Madagascan monazite and commercially available Th and U standard solutions were studied using different mass spectrometers, including an accelerator mass spectrometer. In the present paper we present the results obtained with pure Th standard solutions and also in one case with a monazite digest solution, using inductively coupled plasma-sector field mass spectrometer (ICP-SFMS).The instrument was an Element2 (Thermo-Electron, Bremen, Germany). The predefined medium resolution mode of m/∆m = 4000 (10% valley definition) was used throughout the experiments so as to separate atomic ions from interfering molecular ions with the same mass number. The sensitivityenhanced setup of the instrument was similar to that described in Ref.6 where a capacitive decoupling system and high-performance "X" skimmer were used, providing sensitivity for 232 16 O + peaks. Two 1000 mg l -1 Th stock solutions "A" and "B" from two manufacturers, Inorganic Venture and Customer Grade, were obtained from LGC Promochem AB (Borås, Sweden). Complete elemental screening was performed on both solutions to assess the impurity concentration levels PDF created with pdfFactory trial version www.pdffactory.com 2 The solutions were analyzed during three separate sessions: May 25, October 5, and November 6, 2005. A range of about 0.2 mass unit was scanned in each measured spectrum. This range was divided into approximately 60 channels. During the first session, masses from 210 to 269 were analyzed with an integration time per channel of 0.6 sec. During the second and third sessions, selected mass regions (where some indication of unidentified signals had been detected) were measured using an integration time per channel of 3 and 12 sec, respectively. Instrumental sensitivity varied significantly among runs as a result of matrix effects caused by the introduction of highly concentrated solutions into the ICP source. During the first session, the monazite digest (1000 mg monazite l -1 ) and Th solution A (diluted to 20 mg Th l -1 ) were scanned once. (The Th content in the monazite was approximately 2%. The contents of typical rare earth elements in it, like Ce, Dy and Er, were about 5%, 0.05% and 0.02%, respectively.) During the second session, 20 mg l -1 of Th A and B solutions spiked with 2 µg l -1 Bi were studied and eac...

EVIDENCE FOR THE POSSIBLE EXISTENCE OF A LONG-LIVED SUPERHEAVY NUCLEUS WITH ATOMIC MASS NUMBER A = 292 AND ATOMIC NUMBER Z ≅ 122 IN NATURAL Th

“…Statistical analysis, done in the same way as described earlier, 10 shows that the probability that the observed 292.262 u peak is due to an accidental concentration of events is about 3x10 -5 , for each of the three measurements separately.…”

“…However, background was the main obstacle when looking for isotopes with relative abundance of (1-10)x10 -11 in natural materials. 10 Therefore, purified natural Th was used in our measurements.…”

“…10 Inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) was used for the experiments. The ICP-SFMS is an Element2 (Finnigan, Thermo-Electron, Bremen, Germany).…”

Accelerator mass spectrometry – from DNA to astrophysics

“…However, the group of A. Marinov et al from Jerusalem recently reported positive evidence from highresolution inductively coupled plasma -sector field mass spectrometry (ICP-SF-MS) for long-lived neutrondeficient Th isotopes [29], neutron deficient Rg isotopes in gold [30], and a SHE nuclide with A = 292 and Z ~ 122 in thorium [31]. This triggered extensive AMS experiments at the 14-MV tandem accelerator in Munich [32,33], and at the 3-MV VERA facility in Vienna [34][35][36].…”

Discovery of the Element with Atomic Number 112 (IUPAC Technical Report)

“…The Marinov collaboration also recently claimed discovery [24,26,27] of several long-lived, naturally occurring, very neutron-deficient thorium isomeric states, e.g., 210 Th and long-lived isotopes (allegedly Rg) with mass numbers 261 and 265 in natural Au at the sub-ppb level of abundance. These claims are based on mass spectroscopic data where an inductively coupled plasma ion source is used and very low background count rates are observed.…”