For thermal neutron detectors, effective shielding is a crucial aspect of signal-to-background optimization. This is especially important for cold to thermal neutrons, as the detectors are most ...sensitive in this energy range. In this work, a few common shielding materials, such as cadmium, B
4
C and epoxy-Gd
2
O
3
mixtures, are analytically evaluated based on interaction cross sections extracted from Geant4. For these materials, the neutron absorption and scattering dependence on material thickness and incident neutron energy are examined. It is also considered how the absorption and scattering change with different material compositions, such as
10
B-content in B
4
C, and component ratio in epoxy-Gd
2
O
3
mixtures. In addition, a framework is introduced to quantify the effectiveness of the neutron shielding, comparing the relationship between absorption and scattering of different shielding materials. The aim is to provide a general tool kit, which can be used to quickly identify an appropriate shielding material, with the required thickness, to reach a desired thermal neutron shielding performance. Finally, as an example, the developed tool kit is applied to the specific shielding application for the Multi-Grid CSPEC detector, currently in development for the European Spallation Source.
We present a survey of the radiation background at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, TN, USA during routine daily operation. A broad range of detectors was used to ...characterize primarily the neutron and photon fields throughout the facility. These include a WENDI-2 extended range dosimeter, a thermoscientific NRD, an Arktis 4He detector, and a standard NaI photon detector. The information gathered from the detectors was used to map out the neutron dose rates throughout the facility and also the neutron dose rate and flux profiles of several different beamlines. The survey provides detailed information useful for developing future shielding concepts at spallation neutron sources, such as the European Spallation Source (ESS), currently under construction in Lund, Sweden.
The Lund Broad-band Neutron Facility provides access to a variety of neutron sources together with a well-established user infrastructure. Neutrons from radioactive sources have been successfully ...employed for the research and development of both detectors and materials for the European Spallation Source. A recently procured d-t neutron generator delivers higher neutron fluxes than those provided by the radioactive sources, and further allows for pulsed operation. With the currently on-going construction of a dedicated neutron beam-line at our 3 MeV Pelletron accelerator, the facility is anticipated to produce approximately 10
10
n/s. Cost-effective access to neutrons as well as a platform for educational purposes are the ultimate goals of the project.
A multi-cell He gas scintillator active target, designed for the measurement of photoreaction cross sections, is described. The target has four main chambers, giving an overall thickness of 0.103 ...g/cm
3
at an operating pressure of 2 MPa. Scintillations are read out by photomultiplier tubes and the addition of small amounts of N
2
to the He, to shift the scintillation emission from UV to visible, is discussed. First results of measurements at the MAX IV Laboratory tagged-photon facility show that the target has a timing resolution of around 1 ns and can cope well with a high-flux photon beam. The determination of reaction cross sections from target yields relies on a Monte Carlo simulation, which considers scintillation light transport, photodisintegration processes in
4
He, background photon interactions in target windows and interactions of the reaction-product particles in the gas and target container. The predictions of this simulation are compared to the measured target response.
The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering ...data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical Δ(1232) degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as αn=11.55±1.25(stat)±0.2(BSR)±0.8(th)×10(-4) fm(3) and βn=3.65∓1.25(stat)±0.2(BSR)∓0.8(th)×10(-4) fm(3), with χ(2)=45.2 for 44 degrees of freedom.
Shielding, coincidence, and time-of-flight measurement techniques are employed to tag fast neutrons emitted from an (241)Am/(9)Be source resulting in a continuous polychromatic energy-tagged beam of ...neutrons with energies up to 7MeV. The measured energy structure of the beam agrees qualitatively with both previous measurements and theoretical calculations.
The Applied Nuclear Physics Group at Lund University is constructing a prototype CANS (Compact Accelerator-driven Neutron Source). The CANS is based around a 3 MV, single-ended, Pelletron ...accelerator, which is used to impinge a 2.8 MeV deuterium beam into a beryllium target. The anticipated neutron production will be on the order of 1010 n/s in 4π sr. A further upgrade to the ion source of the Pelletron is expected to increase neutron production to 1011 n/s. Neutron energies will be up to 9 MeV with peak emission at ∼5 MeV. Shielding and moderation will be provided by a large water tank surrounding the target, with three exit ports to allow neutrons of different energies to be directed to experiments. The design is supported by simulation results which predict fast-neutron fluxes of 9×104 to 5×106 n/cm2/s, and thermal-neutron fluxes of 1×104 to 5×104 n/cm2/s to be readily obtainable with a 10 µA deuteron beam.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory have been investigated using the novel approach of Monte Carlo simulation. Results are ...compared to analytical calculations as well as experimental data for both specialized testing and production running to demonstrate a thorough understanding of the behavior of the detector system.
Untagged gamma-ray and tagged-neutron yields from 241AmBe and 238PuBe mixed-field sources have been measured. Gamma-ray spectroscopy measurements from 1 to 5MeV were performed in an open environment ...using a CeBr3 detector and the same experimental conditions for both sources. The shapes of the distributions are very similar and agree well with previous data. Tagged-neutron measurements from 2 to 6MeV were performed in a shielded environment using a NE-213 liquid-scintillator detector for the neutrons and a YAP(Ce) detector to tag the 4.44MeVgamma-rays associated with the de-excitation of the first-excited state of 12C. Again, the same experimental conditions were used for both sources. The shapes of these distributions are also very similar and agree well with previous data, each other, and the ISO recommendation. Our 238PuBe source provides approximately 2.6 times more 4.44MeVgamma-rays and 2.4 times more neutrons over the tagged-neutron energy range, the latter in reasonable agreement with the original full-spectrum source-calibration measurements performed at the time of their acquisition.
•Untagged gamma-ray (1–5MeV) and tagged-neutron (2–6MeV) yields from Be compound sources are measured.•Shapes of gamma-ray distributions are similar and agree well with previous data and each other.•Shapes of neutron distributions are similar and agree well with previous data, each other, and the ISO 8529-2 recommendation.
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