22 research outputs found
Performance evaluation of the Boron Coated Straws detector with Geant4
The last decade has witnessed the development of several alternative neutron
detector technologies, as a consequence of upcoming neutron sources and
upgrades, as well the world-wide shortage of He. One branch of development
is the family of B-based gaseous detectors. This work focuses on the
boron coated straws (BCS) by Proportional Technologies Inc., a commercial
solution designed for use in homeland security and neutron science. A detailed
Geant4 simulation study of the BCS is presented, which investigates various
aspects of the detector performance, e.g. efficiency, activation, absorption
and the impact of scattering on the measured signal. The suitability of the BCS
detector for Small Angle Neutron Scattering (SANS), direct chopper spectrometry
and imaging is discussed.Comment: 50 pages, 37 figures, minor changes after review, results unchange
Suppression of intrinsic neutron background in the Multi-Grid detector
One of the key requirements for neutron scattering instruments is the
Signal-to-Background ratio (SBR). This is as well a design driving requirement
for many instruments at the European Spallation Source (ESS), which aspires to
be the brightest neutron source of the world. The SBR can be effectively
improved with background reduction. The Multi-Grid, a large-area thermal
neutron detector with a solid boron carbide converter, is a novel solution for
chopper spectrometers. This detector will be installed for the three
prospective chopper spectrometers at the ESS. As the Multi-Grid detector is a
large area detector with a complex structure, its intrinsic background and its
suppression via advanced shielding design should be investigated in its
complexity, as it cannot be naively calculated. The intrinsic scattered neutron
background and its effect on the SBR is determined via a detailed Monte Carlo
simulation for the Multi-Grid detector module, designed for the CSPEC
instrument at the ESS. The impact of the detector vessel and the neutron
entrance window on scattering is determined, revealing the importance of an
optimised internal detector shielding. The background-reducing capacity of
common shielding geometries, like side-shielding and end-shielding is
determined by using perfect absorber as shielding material, and common
shielding materials, like BC and Cd are also tested. On the basis of the
comparison of the effectiveness of the different shielding topologies and
materials, recommendations are given for a combined shielding of the Multi-Grid
detector module, optimised for increased SBR.Comment: 26 pages, 18 figures, revise
ANCILLARY PROGRAMS OF A NUCLEAR SPECTROMETRIC PROGRAM PACKAGE CLOSELY RELATED TO EXPERIMENTAL ANALYSIS
EXPERIENCES IN THE RADIOCHEMICAL ANALYSIS OF THE PRIMARY COOLANT OF WWER TYPE NPPs USING INORGANIC ION EXCHANGERS
A simulational study of the indirect geometry neutron spectrometer, BIFROST at the European Spallation Source, from neutron source position to detector position
The European Spallation Source (ESS) is intended to become the most powerful
spallation neutron source in the world and the flagship of neutron science in
the upcoming decades. The exceptionally high neutron flux will provide unique
opportunities for scientific experiments, but also set high requirements for
the detectors. One of the most challenging aspects is the rate capability and
in particular the peak instantaneous rate capability, i.e. the number of
neutrons hitting the detector per channel or cm at the peak of the neutron
pulse. The primary purpose of this paper is to estimate the incident rates that
are anticipated for the BIFROST instrument planned for ESS, and also to
demonstrate the use of powerful simulation tools for the correct interpretation
of neutron transport in crystalline materials. A full simulation model of the
instrument from source to detector position, implemented with the use of
multiple simulation software packages is presented. For a single detector tube
instantaneous incident rates with a maximum of 1.7 GHz for a Bragg peak from a
single crystal, and 0.3 MHz for a vanadium sample are found. This paper also
includes the first application of a new pyrolytic graphite model, and a
comparison of different simulation tools to highlight their strengths and
weaknesses.Comment: 45 pages, 20 figure
Experimental study of concrete activation compared to MCNP simulations for safety of neutron sources
The neutron activation of shielding materials and the generated decay gamma
radiation are well-known issues in terms of occupational exposure. Though the
trace elements of shielding concretes can be dominant sources of the produced
activity in such cases, their concentrations are often missing from the input
data of shielding-related Monte Carlo simulations. For this reason, three
concrete types were studied, that were considered in the European Spallation
Source (ESS) ERIC. Their composition - including the trace elements - were
determined via XRF, PGAA and NAA techniques. Realistic input data were
developed for these materials, containing the parent elements of all the
dominant radioisotopes, and were validated against measured data of neutron
irradiation experiments.Comment: 29 pages, 9 figure