FISSION CROSS SECTION
AND FISSION FRAGMENT DISTRIBUTIONS
INTRODUCTION
The RPI lead slowing down spectrometer (LSDS) is
a unique tool that can be used to study the fission
process of a sample of small quantities or a sample
with small cross section. The spectrometer utilizes
a LINAC driven pulsed neutron source in the center
of a lead cube 1.8m on a side. The neutrons emitted
in the center of the cube are slowed down by successive
scattering collision with the lead. This process
results in a high neutron flux in the lead cube.
A sample placed inside the lead cube can be interrogated
by this neutron flux. This increase in the neutron
flux come with a cost of degradation in the energy
resolution. The energy resolution of our LSDS is
about 30% in the energy range from 1 eV to 50 keV.
For comparison, the neutron flux inside the LSDS
is about 10000 times larger than the flux incident
on a sample in a conventional time-of-flight experiment
with a flight path distance of 5 meters.
The RPI LSDS was previously used for fission cross
section measurements on variety of actinides with
the heaviest being Es-254. Typically these isotopes
are hard to obtain and are limited to small quantities
due to high activity or limited inventory.
In this research we are adding another dimension
to these measurements. We are designing a double
girded fission chamber that will allow in addition
to the cross section measurements to also measure
the fission fragments mass and energy distributions.
This type of measurements will give a very detailed
picture of the fission process as a function of the
neutron energy.
EXPERIMENTS
The experimental setup includes the RPI LSDS shown
in the figure 1
Figure 1 – The RPI lead slowing
down spectrometer
The fission detector currently under development
is shown in figure 2. The detector is a double gridded
fission chamber. The sample located in the center
of the chamber is deposited on thin gold coated Mylar
films. The chamber is designed such that when a fission
event occurs the fission fragments will be emitted
to both sides of the fission chamber. Information
about the mass and energy of the fission fragments
is obtained by from the signals of the grids and
anodes.
Figure 2 – The RPI double gridded fission chamber.
This
research is supported by DOE-SSAA grant number DE-FG03-03NA00079.
