Program - Brookhaven National Laboratory

system without isotope separation. Therefore, their capture cross sections as well as those of 107 Pd are
important for the R & D of nuclear transmutation systems. Additionally, capture gamma-ray spectra
contain much information on important physical quantities such as gamma-ray strength function, and the
information is quite useful for theoretical calculation of neutron capture cross sections of Pd isotopes, especially
107 Pd. From the viewpoint mentioned above, we started a systematic study on keV-neutron capture
cross sections and capture gamma-ray spectra of Pd isotopes ( 104,105,106,108,110 Pd and 107 Pd), using a timeof-flight
method with a pulsed 7 Li(p,n) 7 Be neutron source and a large anti-Compton NaI(Tl) gamma-ray
spectrometer. We have completed the measurements for 104,105,106,108,110 Pd in the neutron energy region
from 15 to 100 keV and measurements 104,105,106 Pd at around 550 keV. This contribution presents the
results of those measurements. This work was supported by JSPS KAKENHI Grant Number(22226016).
NA 4 11:40 AM
Isotopic Mo Neutron Total Cross Section Measurements in the Energy Range 1 to 620 keV
R. Bahran, Y. Danon, A. Daskalakis, B. McDermott and E. Blain
Gaerttner LINAC Center, Rensselaer Polytechnic Institute, Troy, NY 12180
D. Barry, G. Leinweber, M. Rapp and R. Block
Bechtel Corp., Knolls Atomic Power Laboratory, P.O. Box 1072, Schenectady, NY12301
The Gaerttner LINAC Center is home to a 60 MeV electron linear accelerator (LINAC) that is used
as a pulsed neutron source for neutron time-of-flight (TOF) measurements. High resolution cross section
measurements of isotopically enriched molybdenum samples were performed at the RPI LINAC Center with
a newly developed Mid-Energy 6 Li-glass Neutron Detector Array (MELINDA) positioned at the 100-meter
experimental flight station. The neutron transmission detector system employs four identical cube-shaped
modules. Each module consists of a 1.27 cm thick 6 Li-glass scintillator, two out-of-beam photomultiplier
tubes, and a low-mass, light-tight aluminum casing with inner reflective surfaces. The modular design of the
system allows operational reliability, relatively easy maintainability, and lower overall life-cycle costs than a
single all-in-one detector system. Fast electronics were employed to take full advantage of the fast 6 Li-glass
scintillator response time and narrow LINAC neutron burst width (10-15 ns). Transmission measurements
were performed by placing a sample in a collimated neutron beam and measuring the number of neutrons
passing through the sample with the neutron detector and comparing with the number detected with no
sample in the beam. The measurements provide transmission data that cover the energy range between 1
keV - 620 keV performed on highly enriched metallic samples of four stable molybdenum isotopes, 95 Mo,
96 Mo, 98 Mo and 100 Mo. New methods were developed to accurately determine important data reduction
parameters from these transmission measurements including the detector resolution, dead time, and a
precise characterization of the observed background in each measured sample. A unique method to measure
the different background components (neutron and γ-ray) was performed by cycling different materials with
saturated resonances into the beam. The dominant time-dependent γ-ray background component, which
is mainly a result of thermal neutron capture in the water moderator of the neutron producing target,
was determined by placing several thicknesses of polyethylene in the beam and extrapolating the γ-ray
background to zero-thickness polyethylene. Saturated notch filters of Na, Al, Mg, S, Li, and Be were
used to determine the time-dependent neutron background at specific energies across the energy range of
interest. In the resolved resonance region (RRR), new high-accuracy resonance parameters were extracted
from fitting experimental data using the multilevel R-matrix Bayesian code SAMMY. In the unresolved
resonance region (URR), fits to the total cross sections were obtained using the Bayesian Hauser-Feshbach
statistical model code FITACS, which is currently incorporated into the SAMMY code.
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