Search for a superheavy nuclide with A = 292 and neutron-deficient thorium isotopes in natural thorianite

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• 作者：F. Dellinger ; O. Forstner ; R. Golser ; W. Kutschera ; A. Priller ; P. Steier ; A. Wallner ; G. Winkler
• 关键词：Superheavy element ; Thorianite ; Thoria ; Neutron-deficient thorium isotopes ; AMS
• 刊名：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
• 出版年：2010
• 出版时间：April 2010
• 年：2010
• 卷：268
• 期：7-8
• 页码：1287-1290
• 全文大小：440 K

文摘

In the search for long-lived superheavy elements (SHEs) in nature the claim for the detection of a SHE species with A = 292 in a commercially available thorium solution at an abundance of (1–10) × 10⁻¹² relative to ²³²Th using ICP-SFMS has been raised very recently by Marinov et al. The same group also claimed the finding of four long-lived isomeric states in neutron-deficient thorium isotopes at an abundance of (1–10) × 10⁻¹¹ relative to ²³²Th using the same experimental method. The aim of our study was to examine, whether the ratios mentioned above could also be found in a natural thorium mineral, using AMS as a much more sensitive technique assuring the complete suppression of molecular background. Chemically untreated thorianite (ThO₂) was used for both measurements. In addition, commercial thorium(IV) oxide (thoria) powder was also analyzed in the SHE measurements.

No events were observed in the A = 292 SHE search, resulting in an upper limit of 4 × 10⁻¹⁵ for the abundance of such a species relative to ²³²Th. For two neutron-deficient thorium isotopes, ²¹¹Th and ²¹⁸Th, we find upper limits of 5 × 10⁻¹⁵. For ²¹³Th and ²¹⁷Th we observed a few events – albeit uncertain – which would put their abundance also into the 10⁻¹⁵ range.