Title page for ETD etd-07122002-133750

Type of Document

Dissertation

Author

Agvaanluvsan, Undraa ,

Author's Email Address

uagvaan@unity.ncsu.edu

URN

etd-07122002-133750

Title

Level Density Analysis of Nuclear Resonances

Degree

PhD

Graduate Program

Physics

Advisory Committee

Advisor Name	Title
Prof. Gary E. Mitchell	Committee Chair

Keywords

nuclear level densities
random matrix theory
neutron resonances
proton resonances
level statistics
spacing and width distributions
missing level correction

Date of Defense

2002-07-02

Availability

unrestricted

Abstract

AGVAANLUVSAN, UNDRAA. Level Density Analysis of
Nuclear Resonances. (Under the direction of Dr. G. E. Mitchell and
Dr. J. F. Shriner, Jr.)
Direct counting of nuclear resonances is the most straightforward
way to obtain detailed information about nuclear level densities.
In order to test recently developed theories more accurate
experimental results for level densities are needed.
Because of experimental limitations some fraction of the resonances
is not observed. Therefore the
observed level density must be corrected
for the missing fraction of levels.
Two analysis methods are developed and methods applied to
nuclear resonance data.
The standard correction method
based on the resonance widths and the Porter-Thomas distribution
is reconsidered.
The Wigner distribution describes the nearest neighbor
spacings of perfect sequences
(all levels observed). A general expression for
the probability density function of
the spacing distribution for imperfect sequences
is derived using the maximum entropy principle.
This expression contains the Wigner
distribution and the higher order spacing distributions.
The general expression is tested extensively with
numerically generated data.
A simple approximation for the higher order spacing
distribution functions is obtained.
A spacing analysis method to determine the fraction
of missing levels is developed
using the probability density function and
the maximum likelihood technique.
Using the two methods (based on resonance widths and spacings)
enables the determination of improved level densities
from experimental data.
The width and spacing analysis methods
are applied to 15 proton and 2 neutron resonance data sequences
and the observed fraction of levels for each sequence is corrected
in two ways. Agreement between the two methods is good.
Results from the two methods are combined to make a correction
to the level density. Values for the level density and
strength function
for each sequence are obtained and the spin and parity
dependence of the level densities is considered. General
agreement is found with previous theory.

Files

Filename		Size	Approximate Download Time (Hours:Minutes:Seconds)
Filename		Size	28.8 Modem	56K Modem	ISDN (64 Kb)	ISDN (128 Kb)	Higher-speed Access
	etd.pdf	1.53 Mb	00:07:04	00:03:38	00:03:11	00:01:35	00:00:08