Production of Neutron-Rich Isotopes with Z ≥ 98 in the 238U + 248Cm Reaction: A Theoretical Study Using Stochastic Mean-Field Approach

Core Concepts

The study demonstrates that the stochastic mean-field (SMF) approach, combined with the GEMINI++ code, effectively predicts the production cross-sections of neutron-rich isotopes, particularly for Z ≥ 98, in the 238U + 248Cm reaction, offering a valuable tool for exploring the synthesis of superheavy elements.

Abstract

Bibliographic Information:

Ocal, S.E., Yilmaz, O., Ayik, S., & Umar, A. S. (2024). Neutron-rich isotope production for Z ≥ 98 in 238U+ 248Cm reaction. arXiv preprint arXiv:2411.10846.

Research Objective:

This study investigates the production of neutron-rich isotopes in the super-heavy region (Z ≥ 98) through the 238U + 248Cm reaction using a microscopic theoretical approach. The research aims to elucidate the reaction mechanisms involved and predict the production cross-sections of new isotopes, potentially expanding the known nuclear chart.

Methodology:

The researchers employed the stochastic mean-field (SMF) approach, which incorporates fluctuations and correlations, to calculate the primary cross-sections of isotopes produced in multi-nucleon transfer (MNT) reactions. This approach is based on quasi-fission and inverse quasi-fission processes. To determine the final production cross-sections after de-excitation, the researchers coupled the SMF calculations with the statistical de-excitation model implemented in the GEMINI++ code.

Key Findings:

• The calculated cross-sections using the SMF approach and GEMINI++ code successfully reproduced the available experimental data for the 238U + 248Cm system at an energy of Ec.m. = 898.7 MeV.
• The study predicts sizable cross-sections for the production of neutron-rich transuranium elements with a proton number up to Z = 101.
• For the Z = 102-105 region, where experimental data is lacking, the theoretical calculations suggest cross-section values below the microbarn level.

Main Conclusions:

The study highlights the effectiveness and applicability of the quantal diffusion approach based on SMF theory in understanding heavy-ion collisions. The SMF approach, without relying on adjustable parameters beyond those used in standard energy density functionals, proves to be a valuable tool for the microscopic understanding of reaction mechanisms in the synthesis of superheavy elements.

Significance:

This research contributes significantly to the field of nuclear physics by providing a robust theoretical framework for predicting the production of neutron-rich isotopes in heavy-ion collisions. The findings have implications for understanding the limits of nuclear existence and the potential for synthesizing new superheavy elements.

Limitations and Future Research:

The study acknowledges the computational limitations in reaching the predicted "island of stability" with Z=114, N=184. Future research could explore higher-energy collisions or different reaction systems to further investigate the production of superheavy isotopes in this region. Additionally, refining the theoretical models to incorporate more complex nuclear structure effects could improve the accuracy of cross-section predictions.

Stats

The primary total data for Z = 98 (Californium) shows a peak cross-section of 10.4 mb, corresponding to a mass number of 251.
The secondary total data for Z = 98 reveals a lower cross-section value of 0.60 mb, associated with a mass number of 250.
For Z = 99 (Einsteinium), the primary total data indicates a mass number of 253 with a corresponding cross-section of 6.20 mb.
The secondary total data for Z = 99 indicates a mass number of 251 with a corresponding cross-section of 0.08 mb.
The primary total data for Z = 100 (Fermium) reveals a mass number of 256 with a cross-section of 4.40 mb.
The secondary total data for Z = 100 shows a mass number of 252 and a significantly lower cross-section of 0.02 mb.
For Z = 101 (Mendelevium), the primary total data reflects a mass number of 259 with a cross-section of 3.20 mb.
The secondary total data for Z=101 shows a mass number of 253 with a minimal cross-section of 0.001 mb.

Quotes

"Multi-nucleon transfer (MNT) reactions that occur in deep-inelastic binary collisions near the Coulomb barrier energies are an alternate method for producing neutron-rich heavy isotopes using actinide targets, and is being experimentally studied in laboratories around the world [3]."
"The SMF approach, which includes mean-field fluctuations and correlations between proton and neutron transfers, provides an additional improvement to the TDHF theory, where quantal effects, memory effects, and the full collision geometry are included [32,33]."
"In the SMF framework, the production cross sections of neutron-rich isotopes based on quasi-fission reactions (QF) and inverse quasi-fission reactions (IQF) in MNT reactions can be calculated [34–42]."
"SMF theory does not contain any adjustable parameters other than the standard parameters of the energy density functional used in the TDHF theory and is an important approach for the microscopic understanding of reaction mechanisms."

Key Insights Distilled From

Neutron-rich isotope production for $Z\geq 98$ in ${}^{238} \mathrm{U}+{ }^{248} \mathrm{Cm}$ reaction

by S.E. Ocal, O... at arxiv.org 11-19-2024

https://arxiv.org/pdf/2411.10846.pdf

Deeper Inquiries

How might advancements in experimental techniques, such as increased beam intensities and improved isotope separation, impact the future of superheavy element research?

Advancements in experimental techniques hold immense potential for revolutionizing superheavy element (SHE) research. Let's delve into the specific impacts:

Increased Beam Intensities: Higher beam intensities translate to a greater number of collisions within a given timeframe. This is crucial because the production cross-sections of SHEs, particularly those situated on the island of stability, are exceedingly small. A higher collision rate increases the probability of synthesizing these elusive elements, allowing for their properties to be studied in greater detail. Facilities like the Super Heavy Element Factory (SHEF) in Russia are at the forefront of providing such high-intensity beams.

Improved Isotope Separation: The challenge in SHE research isn't just creating the element but also isolating it from a multitude of other byproducts formed in the reaction. Advanced separation techniques, such as those based on magnetic rigidity, velocity filters, and gas-filled separators, are essential. Improved separation methods will lead to purer samples of SHEs, enabling more precise measurements of their decay properties, masses, and potentially even chemical behavior.

Enhanced Detection Systems: Detecting the fleeting existence of SHEs requires highly sensitive and efficient detectors. Advancements in detector technology, such as digital signal processing, time projection chambers, and new scintillator materials, are vital. These improvements will allow researchers to capture more decay events, providing crucial data on decay chains, half-lives, and decay modes of SHEs.
In essence, these advancements will act synergistically. Increased beam intensities will produce more SHEs, while improved separation and detection techniques will ensure that these rare events are identified and characterized with higher fidelity. This will lead to a more comprehensive understanding of the nuclear structure, stability, and chemical properties of SHEs, potentially opening doors to new physics beyond the realm of known elements.

Could alternative theoretical frameworks, beyond the SMF approach, provide complementary insights into the production of neutron-rich isotopes in heavy-ion collisions, and what are their potential advantages and limitations?

Beyond the Stochastic Mean-Field (SMF) approach, several alternative theoretical frameworks can offer valuable, often complementary, insights into the intricate processes governing neutron-rich isotope production in heavy-ion collisions. Let's explore some prominent examples:

Anti-symmetrized Molecular Dynamics (AMD) and Fermionic Molecular Dynamics (FMD): These models excel at describing the dynamics of heavy-ion collisions at relatively low energies, where the formation of complex nuclear structures and cluster emission become significant. Their advantage lies in the ability to microscopically account for nucleon-nucleon correlations and the formation of fragments. However, they can be computationally demanding, especially for heavier systems.

Improved Quantum Molecular Dynamics (ImQMD) Model: This framework incorporates aspects of both mean-field dynamics and nucleon-nucleon collisions, making it suitable for a wider energy range. It has been successful in describing multifragmentation and the production of exotic nuclei. However, like AMD and FMD, computational cost can be a limiting factor.

Dynamical Cluster-decay Model (DCM): This model focuses on the formation and decay of a double nuclear system, making it particularly relevant for fusion-fission reactions. It can predict the production cross-sections of superheavy nuclei and their decay modes. However, it relies on certain assumptions about the shape evolution of the dinuclear system.

Time-Dependent Density Functional Theory (TDDFT): This approach offers a fully microscopic description of nuclear dynamics based on density functional theory. It can, in principle, provide a comprehensive picture of heavy-ion collisions. However, its practical application to superheavy element production is limited by computational challenges and the need for accurate density functionals for such extreme systems.
Each of these frameworks has its strengths and limitations. The SMF approach, as discussed in the context, provides a computationally tractable way to incorporate fluctuations and correlations beyond the mean-field, making it suitable for studying the production of neutron-rich isotopes in the actinide region. However, a comprehensive understanding of heavy-ion collisions and the quest for superheavy elements will likely require a multifaceted theoretical approach, leveraging the strengths of different models to gain complementary insights into the underlying physics.

Considering the potential applications of superheavy elements, what ethical considerations should guide future research and development in this field, particularly regarding their potential impact on energy production, medicine, and materials science?

While the potential applications of superheavy elements (SHEs) in energy production, medicine, and materials science are largely speculative at this stage, their very nature as extremely heavy and often radioactive elements raises important ethical considerations that warrant careful examination:
1. Radioactivity and Environmental Impact:

Waste Management: SHEs, by their nature, are often highly radioactive, with decay chains potentially producing other radioactive isotopes. The safe handling, storage, and disposal of SHEs and their byproducts are paramount concerns. Robust international protocols and stringent safety measures are essential to prevent environmental contamination and potential harm to human health.

Dual-Use Concerns: The high energy release during radioactive decay, while potentially beneficial for energy applications, also raises concerns about potential misuse. The ethical implications of SHE research must be carefully evaluated to prevent any unintended or malicious applications.
2. Health and Safety:

Biological Effects: The biological effects of SHEs are largely unknown. Given their position in the periodic table, they might exhibit unusual chemical behavior and interact with biological systems in unforeseen ways. Thorough toxicological studies and risk assessments are crucial before any potential medical applications can be considered.

Occupational Hazards: Researchers and technicians working with SHEs would be exposed to ionizing radiation. Stringent safety protocols, appropriate shielding, and regular health monitoring are essential to minimize occupational hazards.
3. Access and Equity:

Fair Distribution of Benefits: If SHEs lead to technological breakthroughs, the benefits should be shared equitably, particularly if they have implications for energy production or medical treatments. International cooperation and responsible governance are crucial to ensure that these advancements benefit humanity as a whole.

Open Access to Research: Transparency and open access to research findings, while balancing intellectual property rights, are essential to foster collaboration and accelerate scientific progress in a responsible manner.
4. Precautionary Principle:

Unknown Risks: Given the significant unknowns regarding the properties and potential impacts of SHEs, a precautionary approach is warranted. Research should proceed cautiously, with thorough risk assessments at each stage, and a willingness to adapt or halt research if unforeseen risks emerge.
In conclusion, while the pursuit of knowledge and exploration of new frontiers in science are essential, ethical considerations must be at the forefront of SHE research. A proactive and responsible approach, involving open dialogue among scientists, ethicists, policymakers, and the public, is crucial to ensure that the quest for superheavy elements benefits humanity while safeguarding our health and the environment.