Figure 1. Schematic diagram of the HIGS - the DFELL-TUNL g-ray facility.
There are a number of distinct advantages of this system as compared
to presently available ones. The first is the high-intensity beams
which will allow us to measure nuclear processes having low cross sections
with high precision in realistic times. The second advantage is the
fact that tagging is not needed. The high quality of the electron beam
permits energy definition by the use of collimation alone. This means that,
unlike many tagged sources, there will be NO untagged high-energy g rays
in the vicinity of the target and detectors. In addition, the energy
of these beams can be continuously tuned from 2 to 225 MeV. The energy
resolution of these beams will be exceptional. For example, a 1 mm
radius collimator located 30 meters from the collision point should allow
us to produce 100 MeV g rays having a FWHM energy spread of less than 400
keV. These g-ray beams will be 100% polarized, and the beam environment
will be exceptionally clean; backgrounds will be negligibly small.
The Research Program at HIGS
TUNL researchers, in collaboration with outside theoretical and experimental colleagues, have proposed a broad based research program in nuclear physics which is designed to exploit the unique flux, energy resolution and polarization of the HIGS beams. Included in this program are proposals for experiments relevant to nuclear astrophysics. Key experiments include:
1. d(g,n)p Preliminary results have been obtained in the case
of d(g,n)p in the threshold region. This is an important region , relevant
to Big-Bang nucleosynthesis. The HIGS 100% linearly polarized beam
allows for a separation of the M1 and the E1 parts of the cross section.
2. A study of 12C (a,g)16O by means of the inverse reaction 16O(g,a)12C.
3. 9Be(g,n)aa to study the inverse reaction.
4. 26Mg (g,n) 25Mg / 26Mg (g,a)22Ne as a means to study the n/a branching ratio in the 22Ne + a reaction.
5. 28Si + g to study the process of Silicon burning.
6. 180Ta (g,g’)—Study the details of the de-excitation of the isomeric state of 180Ta.
7. Nuclear Resonance Fluorescence: the HIGS beams have the intensity and energy resolution to allow for a new level of NRF spectroscopy. Preliminary results on 138Ba are very exciting and indicate the power of this facility.
A description of the presently available facility and the anticipated
facility following the present upgrade will be given, along with a summary
of that part of the research program relevant to nuclear astrophysics.