Resonance Measurements at Rensselaer Polytechnic Institute
311
almost a total 4π detection coverage with a capture sample located in the center
of the detector. A liner of B 4 C with enriched 10 B is used to absorb scattered
neutrons which could cause capture in the detector crystals and be mistaken for
a capture event. The detector is located at a flight path of ∼25.6 m which provides
excellent resolution up to a neutron energy of several keV. A recent measurement
was performed measuring the capture yield of several separated Gd isotopes. This
new measurement identified several new resonances in the measured Gd isotopes;
particularly 169 new resonances in 155 Gd and 96 new resonances in 157 Gd. This
showcases the ability of the RPI low energy capture detector to provide high quality
capture data on separated isotopes which can extend the resolved resonance region
of isotopes. A full analysis of the Gd results can be found in reference [3].
Using this detector the total energy deposited in the detector can be measured as a
function of the ToF. This is of particular value when measuring isotopes which have
both capture and fission. A recent measurement was performed at RPI using this
detector which measured the capture and fission from a sample of 235 U. By only
looking at events which deposited a greater energy than the binding energy from
capture, a selection of events only from fission could be obtained. This allowed
for the separation of the fission signal from the capture signal at all energies. The
results were typically in agreement with previous evaluations; however, the new
measurement suggested a lower cross section in the range from 0.6 to 2.25 keV
compared to the ENDF 7.1 evaluation. The measurement was used in the new
evaluation of 235 U for ENDF 8.0, and the new evaluation agrees much better with
this measurement. A full analysis of the measurement and techniques used can be
found in reference [4].
3.2 Mid-Energy Capture
A detector array was recently built at RPI at a 45 m flight path in order to perform
capture measurements in the mid-energy region. This region extends from the end
of the resolved resonance region into the unresolved resonance region. The array
consists of four C 6 D 6 detectors mounted in a low mass system centered around
a capture sample. C 6 D 6 was chosen for the detector material due to its very low
capture cross section limiting the probability for false capture detection. A B 4 C
sample is used in order to obtain the neutron flux shape at low energies in order
to calculate the capture yields. To measure the flux shape at higher energies, a thin
plastic beam monitor was created and placed behind the detection system [5]. The
array utilizes the combination of the total detection method with a pulse weighting
criteria in order to obtain the capture yields.
A recent measurement was done on a sample of isotopic 56 Fe in order to measure
the capture yield at higher energies. The measured yield was higher than the ENDF
7.1 evaluation but lower than the JEFF 3.3 evaluation. These results were sent to
the International Atomic Energy Agency (IAEA) for their new evaluation of 56 Fe.
Figure 1 shows the comparison of the data with the previous ENDF 7.1 and JEFF 3.3
311
almost a total 4π detection coverage with a capture sample located in the center
of the detector. A liner of B 4 C with enriched 10 B is used to absorb scattered
neutrons which could cause capture in the detector crystals and be mistaken for
a capture event. The detector is located at a flight path of ∼25.6 m which provides
excellent resolution up to a neutron energy of several keV. A recent measurement
was performed measuring the capture yield of several separated Gd isotopes. This
new measurement identified several new resonances in the measured Gd isotopes;
particularly 169 new resonances in 155 Gd and 96 new resonances in 157 Gd. This
showcases the ability of the RPI low energy capture detector to provide high quality
capture data on separated isotopes which can extend the resolved resonance region
of isotopes. A full analysis of the Gd results can be found in reference [3].
Using this detector the total energy deposited in the detector can be measured as a
function of the ToF. This is of particular value when measuring isotopes which have
both capture and fission. A recent measurement was performed at RPI using this
detector which measured the capture and fission from a sample of 235 U. By only
looking at events which deposited a greater energy than the binding energy from
capture, a selection of events only from fission could be obtained. This allowed
for the separation of the fission signal from the capture signal at all energies. The
results were typically in agreement with previous evaluations; however, the new
measurement suggested a lower cross section in the range from 0.6 to 2.25 keV
compared to the ENDF 7.1 evaluation. The measurement was used in the new
evaluation of 235 U for ENDF 8.0, and the new evaluation agrees much better with
this measurement. A full analysis of the measurement and techniques used can be
found in reference [4].
3.2 Mid-Energy Capture
A detector array was recently built at RPI at a 45 m flight path in order to perform
capture measurements in the mid-energy region. This region extends from the end
of the resolved resonance region into the unresolved resonance region. The array
consists of four C 6 D 6 detectors mounted in a low mass system centered around
a capture sample. C 6 D 6 was chosen for the detector material due to its very low
capture cross section limiting the probability for false capture detection. A B 4 C
sample is used in order to obtain the neutron flux shape at low energies in order
to calculate the capture yields. To measure the flux shape at higher energies, a thin
plastic beam monitor was created and placed behind the detection system [5]. The
array utilizes the combination of the total detection method with a pulse weighting
criteria in order to obtain the capture yields.
A recent measurement was done on a sample of isotopic 56 Fe in order to measure
the capture yield at higher energies. The measured yield was higher than the ENDF
7.1 evaluation but lower than the JEFF 3.3 evaluation. These results were sent to
the International Atomic Energy Agency (IAEA) for their new evaluation of 56 Fe.
Figure 1 shows the comparison of the data with the previous ENDF 7.1 and JEFF 3.3