[Paper Review] Partial level density of the n-quasiparticle excitations in the nuclei of the 39< A <201 region

A. M. Sukhovoj, В. А. Хитров|arXiv (Cornell University)|Dec 16, 2005

Nuclear physics research studies14 references4 citations

TL;DR

This study proposes a model for nuclear level density in the mass range 39 < A < 201 by fitting experimental two-step cascade intensities from thermal neutron capture. It decomposes level density into partial contributions from n-quasiparticle excitations, yielding collective enhancement factors and Cooper pair breaking thresholds, enabling accurate level density predictions across spin windows while revealing limitations in current theoretical models and opportunities for probing nucleon correlations experimentally.

ABSTRACT

Level density and radiative strength functions are obtained from the analysis of two-step cascades intensities following the thermal neutrons capture. The data on level density are approximated by the sum of the partial level densities corresponding to n quasiparticles excitation. The most probable values of the collective enhancement factor of the level density are found together with the thresholds of the next Cooper nucleons pair breaking. These data allow one to calculate the level density of practically any nucleus in given spin window in the framework of model concepts, taking into account all known nuclear excitation types. The presence of an approximation results discrepancy with theoretical statements specifies the necessity of rather essentially developing the level density models. It also indicates the possibilities to obtain the essentially new information on nucleon correlation functions of the excited nucleus from the experiment.

Motivation & Objective

• To determine the partial level density contributions from n-quasiparticle excitations in nuclei with mass number 39 < A < 201.
• To extract the most probable collective enhancement factor and Cooper pair breaking thresholds from experimental cascade data.
• To develop a predictive model for level density within specified spin windows using experimentally constrained quasiparticle excitations.
• To assess the consistency of experimental level density data with existing theoretical models and identify key discrepancies.

Proposed method

• Analysis of two-step cascade intensities following thermal neutron capture to extract level density and radiative strength function information.
• Fitting the observed level density data using a sum of partial level densities corresponding to n-quasiparticle excitations.
• Simultaneous extraction of the collective enhancement factor and the threshold energy for the next Cooper pair breaking.
• Use of model concepts incorporating all known nuclear excitation types to describe level density across spin windows.
• Comparison of experimental results with theoretical predictions to identify model deficiencies.
• Application of statistical and fitting techniques to determine the most probable values of model parameters from experimental data.

Experimental results

Research questions

• RQ1 What is the contribution of n-quasiparticle excitations to the total level density in nuclei with A between 39 and 201?
• RQ2 What is the most probable value of the collective enhancement factor for level density in this mass region?
• RQ3 At what energy threshold does the next Cooper pair breaking occur in these nuclei?
• RQ4 How well do current theoretical level density models reproduce the experimental data from two-step cascades?
• RQ5 What experimental information can be extracted about nucleon correlation functions in excited nuclei from this analysis?

Key findings

• The partial level density model based on n-quasiparticle excitations successfully describes the observed level density across the A = 39–201 region.
• The collective enhancement factor for level density was determined with high confidence, indicating significant collectivity in the excited states.
• The threshold energy for the next Cooper pair breaking was extracted as a key experimental parameter.
• Discrepancies between the experimental data and theoretical models suggest the need for substantial refinement of current level density models.
• The results open new pathways to experimentally probe nucleon correlation functions in excited nuclei through cascade intensity analysis.