Nuclear systematics of the heavy elements—II Lifetimes for alpha, beta and spontaneous fission decay

The application of random-matrix theory (RMT) to compound-nucleus (CN) reactions is reviewed. An introduction into the basic concepts of nuclear scattering theory is followed by a survey of phenomenological approaches to CN scattering. The implementation of a random-matrix approach into scattering theory leads to a statistical theory of CN reactions. Since RMT applies generically to chaotic quantum systems, that theory is, at the same time, a generic theory of quantum chaotic scattering. It uses a minimum of input parameters (average $S$ matrix and mean level spacing of the CN). Predictions of the theory are derived with the help of field-theoretical methods adapted from condensed-matter physics and compared with those of phenomenological approaches. Thorough tests of the theory are reviewed, as are applications in nuclear physics, with special attention given to violation of symmetries (isospin and parity) and time-reversal invariance.

/pdf/random-matrices-and-chaos-in-nuclear-physics-nuclear-3x6ykem47p.pdf

Random matrices and chaos in nuclear physics: Nuclear reactions

We measured the mass and kinetic-energy partitioning in the spontaneous fission of $^{258}\mathrm{Fm}$, $^{259}\mathrm{Md}$, $^{260}\mathrm{Md}$, $^{258}\mathrm{No}$, and $^{260}]$. All fissioned with mass distributions that were symmetric. Total-kinetic-energy distributions peaked near either 200 or 235 MeV. Surprisingly, these energy distributions were skewed upward or downward from the peak in each case, except for $^{260}]$, indicating a composite of two energy distributions. We interpret this as a mixture of liquid-drop-like and fragment-shell directed symmetric fission, although theory had not anticipated this phenomenon.

Bimodal symmetric fission observed in the heaviest elements

We have measured the mass and kinetic-energy distributions from the spontaneous fission of {sup 258}Fm, {sup 258}No, {sup 259}Md, {sup 260}Md, and {sup 260}(104). All are observed to fission with a symmetrical division of mass. The total-kinetic-energy distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the total-kinetic-energy distributions are resolved into two Gaussians, the constituent peaks lie near 200 and 233 MeV. We conclude that both low- and high-energy fission modes occur in four of the five nuclides studied. We call this property bimodal fission.'' Even though both modes are possible in the same nuclide, one generally predominates. We offer an explanation for each mode based on shell structures of the fissioning nucleus and of its fragments. The appearance of both modes of fission in this region of the nuclide chart seems to be a coincidence in that the opportunity to divide into near doubly magic Sn fragments occurs in the same region where the second fission barrier is expected to drop in energy below the ground state of the fissioning nucleus. Appropriate paths on the potential-energy surface of deformation have been found by theorists, but no physical grounds have beenmore » advanced that would allow the near equal populations we observe traveling each path. We suggest that this failure to find a reason for somewhat equal branching may be a fundamental flaw of current fission models. Assuming the proposed origins of these modes are correct, we conclude the low-energy, but also mass-symmetrical mode is likely to extend to far heavier nuclei. The high-energy mode will be restricted to a smaller region, a realm of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in {sup 132}Sn.« less

Spontaneous fission properties of 258Fm, 259Md, 260Md, 258No, and 260

Interactions between autoionising resonances are described. The authors begin from the simplest cases, namely isolated autoionising resonances and shape resonances, and build up to more complicated situations, through the case of two interacting resonances to an infinite Rydberg manifold of autoionising resonances. Next, cases in which the background phase shift of the continuum can vary are considered, and this situation is shown to be equivalent to the presence of an intruder state. The q reversal and vanishing width effects are described, treated both theoretically and through some real examples. They summarise the general treatment of a Rydberg manifold perturbed by an intruder state, and the influence of the intruder on the shape parameters is discussed in detail. They present a formula for the profiles of two interacting Rydberg series of autoionising resonance. Lastly, symmetry reversal effects in resonantly enhanced multiphoton ionisation spectroscopy are considered and an example is given.

https://iopscience.iop.org/article/10.1088/0034-4885/51/11/002/pdf

Interacting resonances in atomic spectroscopy

SPONTANEOUS-FISSION HALF-LIFE OF $sup 258$Fm AND NUCLEAR INSTABILITY.

79-day fermium isotope of mass 257

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

J. E. Evans

Author Tools

Chat about Author

Papers

SPONTANEOUS-FISSION HALF-LIFE OF $sup 258$Fm AND NUCLEAR INSTABILITY.

79-day fermium isotope of mass 257