Photon Strength and the Low-Energy Enhancement
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.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 1037852
- Report Number(s):
- LLNL-PROC-531854; TRN: US1201707
- 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
Similar Records
Photon strength and the low-energy enhancement
Spin dependence of the giant-dipole-resonance strength function in highly excited nuclei in the mass region A =39--45
Related Subjects
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