Neutron transmission measurements at nELBE

Abstract

Neutron total cross sections are an important source of experimental data in the evaluation of neutron-induced cross sections. The sum of all neutron-induced reaction cross sections can be determined with a precision of a few per cent in a relative measurement. The neutron spectrum of the photoneutron source nELBE extends in the fast region from about 100 keV to 10 MeV and has favourable conditions for transmission measurements due to the low instantaneous flux of neutrons and low gamma-flash background. Several materials of interest (in part included in the CIELO evaluation or on the HPRL of OECD/NEA) have been investigated: 197Au [1, 2], natFe [2], natW [2], 238U, natPt, 4He, natO, natNe, natXe. For gaseous targets high pressure gas cells with flat end-caps have been built that hold up to 200 bar pressure. The experimental setup will be presented including results from several transmission experiments and the data analysis leading to the total cross sections will be discussed.

Characterization of organic glass scintillator bars and their potential for a hybrid neutron/gamma ray imaging system for proton radiotherapy range verification

“…An example of a measured WACC spectrum for the 10 cm OGS bar is shown in the top panel of figure 3. The three diagonal features that can be seen correspond to Compton scattering events where the total gamma ray energy is shared by the target and reference detectors: 0.662 MeV from 137 Cs, 1.173 MeV and 1.332 MeV from 60 Co. The bottom panel of figure 3 shows the projected spectrum for 0.395 MeV ≤ 𝐸 ref ≤ 0.405 MeV where the three Compton peaks and their fits with Equation 2.2 can be seen.…”

“…The parameters 𝑎, 𝑏, and 𝑐 define the background. We set 𝑘 = 1 in all cases aside from the 60 Co gamma ray lines where 𝑘 = 2, i.e. the two Compton peaks overlap and must be fit together.…”

“…For the WACC measurements, which were made after the BSG measurements, it was observed that the detector gain varied noticeably with the different source activities. For this reason, the WACC measurements used a combination of the 137 Cs and 60 Co sources measured simultaneously to ensure gain stability in the detector over the course of the measurement.…”

“…The gamma ray TOF gate was taken from events within 3𝜎 of the centroid of a Gaussian fit to the Bremsstrahlung peak; the neutron TOF gate was selected by eye. The small peak around 25 ns (just before the main Bremsstrahlung peak) was identified as double hits in the OGS detector [60]. The peak around 50 to 60 ns was identified as backscattered gamma rays off the beam dump, located 3.44 m downstream of the primary OGS detector.…”

Resonance region evaluation of 16O for criticality safety and reactor applications

“…After the study presented in Reference [3], there had been attempt to unveil the normalization (n,α) cross section issue. As a result, measurements of (n,α) cross section were done at the time-of-flight (TOF) GELINA facility at the JRC from the energy threshold 2.354 MeV to 9 MeV [4]. In addition, transmission measurements at the nELBE TOF facility at HZDR were also done in the energy range 100 keV to 10 MeV.…”