skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Photon Strength and the Low-Energy Enhancement

Abstract

The ability of atomic nuclei to emit and absorb photons with energy E{sub {gamma}} is known as the photon strength function f(E{sub {gamma}}). It has direct relevance to astrophysical element formation via neutron capture processes due to its central role in nuclear reactions. Studies of f(E{sub {gamma}}) have benefited from a wealth of data collected in neutron capture and direct reactions but also from newly commissioned inelastic photon scattering facilities. The majority of these experimental methods, however, rely on the use of models because measured {gamma}-ray spectra are simultaneously sensitive to both the nuclear level density and f(E{sub {gamma}}). As excitation energy increases towards the particle separation energies, the level density increases rapidly, creating the quasi-continuum. Nuclear properties in this excitation energy region are best characterized using statistical quantities, such as f(E{sub {gamma}}). A point of contention in studies of the quasi-continuum has been an unexpected and unexplained increase in f(E{sub {gamma}}) at low {gamma}-ray energies (i.e. below E{sub {gamma}} {approx}3 MeV) in a subset of light-to-medium mass nuclei. Ideally, a new model-independent experimental technique is required to address questions regarding the existence and origin of this low-energy enhancement in f(E{sub {gamma}}). Here such a model-independent approach is presented formore » determining the shape of f(E{sub {gamma}}) over a wide range of energies. The method involves the use of coupled high-resolution particle and {gamma}-ray spectroscopy to determine the emission of {gamma} rays from the quasi-continuum in a nucleus with defined excitation energy to individual discrete levels of known spins and parities. This method shares characteristics of two neutron capture-based techniques: the Average Resonance Capture (ARC) and the Two-Step Cascade analysis (TSC). The power of the new technique lies in the additional ability to positively identify primary {gamma}-ray decay from defined excitation energy regions to low-lying discrete states. This approach was used to study the shape of f(E{sub {gamma}}) in {sup 95}Mo populated in the (d,p) direct reaction.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1037852
Report Number(s):
LLNL-PROC-531854
TRN: US1201707
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: Frontiers in Gamma-Ray Spectroscopy 2012 - FIG12, New Delhi, Iceland, Mar 05 - Mar 07, 2012
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CAPTURE; DECAY; DIRECT REACTIONS; ENERGY-LEVEL DENSITY; EXCITATION; NEUTRON REACTIONS; NEUTRONS; NUCLEAR PROPERTIES; NUCLEAR REACTIONS; NUCLEI; ORIGIN; PHOTONS; RESONANCE; SCATTERING; SHAPE; SPECTRA; SPECTROSCOPY; STRENGTH FUNCTIONS

Citation Formats

Wiedeking, M, Bernstein, L A, Krticka, M, Bleuel, D L, Allmond, J M, Basunia, M S, Burke, J T, Fallon, P, Firestone, R B, Goldblum, B L, Hatarik, R, Lake, P T, Lee, I Y, Lesher, S R, Paschalis, S, Petri, M, Phair, L, and Scielzo, N D. Photon Strength and the Low-Energy Enhancement. United States: N. p., 2012. Web.
Wiedeking, M, Bernstein, L A, Krticka, M, Bleuel, D L, Allmond, J M, Basunia, M S, Burke, J T, Fallon, P, Firestone, R B, Goldblum, B L, Hatarik, R, Lake, P T, Lee, I Y, Lesher, S R, Paschalis, S, Petri, M, Phair, L, & Scielzo, N D. Photon Strength and the Low-Energy Enhancement. United States.
Wiedeking, M, Bernstein, L A, Krticka, M, Bleuel, D L, Allmond, J M, Basunia, M S, Burke, J T, Fallon, P, Firestone, R B, Goldblum, B L, Hatarik, R, Lake, P T, Lee, I Y, Lesher, S R, Paschalis, S, Petri, M, Phair, L, and Scielzo, N D. Wed . "Photon Strength and the Low-Energy Enhancement". United States. https://www.osti.gov/servlets/purl/1037852.
@article{osti_1037852,
title = {Photon Strength and the Low-Energy Enhancement},
author = {Wiedeking, M and Bernstein, L A and Krticka, M and Bleuel, D L and Allmond, J M and Basunia, M S and Burke, J T and Fallon, P and Firestone, R B and Goldblum, B L and Hatarik, R and Lake, P T and Lee, I Y and Lesher, S R and Paschalis, S and Petri, M and Phair, L and Scielzo, N D},
abstractNote = {The ability of atomic nuclei to emit and absorb photons with energy E{sub {gamma}} is known as the photon strength function f(E{sub {gamma}}). It has direct relevance to astrophysical element formation via neutron capture processes due to its central role in nuclear reactions. Studies of f(E{sub {gamma}}) have benefited from a wealth of data collected in neutron capture and direct reactions but also from newly commissioned inelastic photon scattering facilities. The majority of these experimental methods, however, rely on the use of models because measured {gamma}-ray spectra are simultaneously sensitive to both the nuclear level density and f(E{sub {gamma}}). As excitation energy increases towards the particle separation energies, the level density increases rapidly, creating the quasi-continuum. Nuclear properties in this excitation energy region are best characterized using statistical quantities, such as f(E{sub {gamma}}). A point of contention in studies of the quasi-continuum has been an unexpected and unexplained increase in f(E{sub {gamma}}) at low {gamma}-ray energies (i.e. below E{sub {gamma}} {approx}3 MeV) in a subset of light-to-medium mass nuclei. Ideally, a new model-independent experimental technique is required to address questions regarding the existence and origin of this low-energy enhancement in f(E{sub {gamma}}). Here such a model-independent approach is presented for determining the shape of f(E{sub {gamma}}) over a wide range of energies. The method involves the use of coupled high-resolution particle and {gamma}-ray spectroscopy to determine the emission of {gamma} rays from the quasi-continuum in a nucleus with defined excitation energy to individual discrete levels of known spins and parities. This method shares characteristics of two neutron capture-based techniques: the Average Resonance Capture (ARC) and the Two-Step Cascade analysis (TSC). The power of the new technique lies in the additional ability to positively identify primary {gamma}-ray decay from defined excitation energy regions to low-lying discrete states. This approach was used to study the shape of f(E{sub {gamma}}) in {sup 95}Mo populated in the (d,p) direct reaction.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2012},
month = {2}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share: