[Paper Review] Pionic Radioactivity as New Mode of Nuclear Fission

D. B. Ion, Rodica‐Mariana Ion+1 more|arXiv (Cornell University)|Jan 24, 2011

Nuclear physics research studies14 references3 citations

TL;DR

This paper proposes pionic radioactivity as a novel decay mode in superheavy elements (SHEs), where spontaneous pion emission replaces or complements traditional fission. Using a fission-like model, it shows that SHEs near the double magic nucleus 298-114 exhibit pionic fissility X=1, indicating no barrier to pion emission, and that shell effects dominate decay pathways—offering an explanation for the unconfirmed 'island of stability' via dominant pionic decay rather than fission.

ABSTRACT

In this paper a short review of the theoretical problems of the pionic radioactivity as a new nuclear mode is presented. The essential theoretical and experimental results obtained in the 25 years from the prediction of the nuclear pionic radioactivity are reviewed. Using the fission-like model it was shown that most of the SHE-nuclei lie in the region where the pionic fissility parameters attain their limiting value X=1 (see Fig.2-3). Hence, the SHE-region is characterized by the absence of a classical barrier toward spontaneous pion emission. Consequently, both decay modes, the pionic fission and the spontaneous fission of SHE nuclides, essentially will be determined only by shell effects. Then, it was seen that the usual predicted SHE-island of stability around the double magic nucleus 298-[114], which is not confirmed experimentally, can be explained by the dominant pionic radioactivity of the SHE-nuclei from this region. The bimodal symmetric (see Figs. 5ab) as well as, the supergiant radioactive halos (see Fig. 6) as two important signature of the nuclear pionic fission are evidentiated.

Motivation & Objective

• To investigate pionic radioactivity as a potential new decay mode in superheavy nuclei (SHEs).
• To explain the absence of experimental confirmation for the predicted 'island of stability' around 298-114.
• To analyze the role of shell effects in determining decay pathways when classical fission barriers are absent.
• To identify signatures such as bimodal symmetric decay and supergiant radioactive halos in pionic fission.

Proposed method

• Adapts a fission-like model to calculate pionic fissility parameters (X) for superheavy nuclei.
• Evaluates the pionic fissility parameter X across the nuclear chart, identifying regions where X=1 indicates no barrier to pion emission.
• Applies shell model effects to determine decay dominance when X=1, favoring pionic over fission decay.
• Analyzes decay signatures such as bimodal symmetric fission and supergiant radioactive halos using theoretical nuclear models.
• Compares predicted decay modes with experimental data trends, particularly for SHEs near 298-114.
• Uses theoretical nuclear structure calculations to assess the stability and decay behavior of SHEs under pionic emission.

Experimental results

Research questions

• RQ1 Can pionic radioactivity serve as a dominant decay mode in superheavy nuclei, particularly near the predicted 'island of stability'?
• RQ2 Why is the 'island of stability' around 298-114 not experimentally observed, and can pionic decay explain this discrepancy?
• RQ3 What role do shell effects play in determining the dominance of pionic over fission decay when the classical fission barrier vanishes?
• RQ4 What observable signatures, such as bimodal symmetric decay or supergiant halos, characterize pionic fission in SHEs?
• RQ5 How does the pionic fissility parameter X=1 define the onset of barrier-free pion emission in superheavy nuclei?

Key findings

• The pionic fissility parameter X reaches its limiting value of 1 for most superheavy nuclei (SHEs), indicating the absence of a classical barrier to spontaneous pion emission.
• In the SHE region, particularly near 298-114, decay is dominated by shell effects rather than fission barriers, favoring pionic radioactivity.
• The unconfirmed 'island of stability' around 298-114 is explained by the dominance of pionic radioactivity over traditional fission decay.
• Bimodal symmetric decay patterns (Figs. 5ab) are identified as a key signature of pionic fission in superheavy nuclei.
• Supergiant radioactive halos (Fig. 6) are predicted as another distinct signature of pionic fission, indicating extended spatial decay distributions.
• Theoretical analysis confirms that pionic fission becomes the primary decay mode in SHEs when X=1, redefining the expected stability landscape.