Design and verification of a multi-layer single-sphere neutron spectrometer with water as the moderator

Measuring the neutron energy spectrum is important in nuclear radiation detection and protection. Common neutron spectrometers include the Bonner sphere spectrometer (BSS), time-of-flight neutron spectrometer, and plastic scintillation detector. Among them, the BSS is the most widely used for its wide measurement range and simple operation. A BSS usually occupies a large space because it contains several independent spheres working at the same time, leading to poor consistency. This paper proposes a multi-layer single-sphere spectrometer using water as the moderator. The spectrometer includes a multi-layered sphere that can be filled with water or air and a ^3He proportional counter placed in the center of the sphere. To verify the feasibility of this design, we use Geant4 to calculate the moderating ability of water and the response functions of the multi-layer single-sphere spectrometer. Additionally, several standard neutron energy spectra (from IAEA) are used to test the response characteristics of this spectrometer through simulation. The simulation results prove the feasibility of the design. This research provides a theoretical basis for a multi-layer single-sphere neutron spectrometer with water as the moderator.

A Novel Method to Detect Cement through Direct Measurement – Case Histories

Cement quality is typically determined through the use of sonic logging tools, more commonly known as cement bond logs (CBLs), or more recently ultrasonic imaging tools (USITs). In general, these tools have served the industry well over time, but with the advent of new and exotic cement blends, as well as multistage cement jobs in today's unconventional horizontal wells, the quality and even location of the cement has become more problematic for basic CBL/USIT tools to detect. In addition, these tools are ineffective through multiple uncemented casing strings. A novel method to detect cement was developed as an offshoot of a technology used for detecting proppant in hydraulically fractured wells. This technique uses a non-radioactive tracer which exhibits a high thermal neutron capture cross section that is then incorporated into the proppant grains during manufacture. The proppant can then be detected using standard neutron-logging tools, at any time during the well's life. By incorporating small volumes of this detectible proppant into the cement slurry, the cement can then be detected using the same logging tools. This leads to identification of the top of cement, as well as the cement quality. If desired, the taggant can be staged such that the top and bottom of a cement stage can be detected. This paper will first review the industry concerns with cement detection. It will then discuss the principles and theory behind how the taggant works, both for basic proppant detection, as well as the novel application as a vehicle for cement detection. This will also include lab testing showing no impact of the tagged proppant on cement performance. The authors will conclude by presenting several case histories of cement detection, including two horizontal well applications, one each in the Permian and Canada. A third case history will also be presented in which the cement was detected through multiple strings of uncemented casing, to verify success of a cement squeeze in a surface casing remediation. This new technique allows for cement detection in wells in which conventional CBL/USITs are difficult to interpret, including detection of exotic cement blends, and through multiple strings of casing. This allows for more confidence in cement isolation, particularly in today's unconventional wells, where isolation of uphole formations is critical. This paper will be useful for drilling and completion engineers who are concerned with their ability to confirm cement quality, as well as production engineers who must perform remedial cementing operations.

Characterization of NIS neutron irradiation facility for calibration and metrological application

In this study, the Neutron Irradiation Facility (NIF) of the National Institute of Standards (NIS) was characterized for metrological applications to improve the accuracy of the calibration process. The NIS neutron irradiation facility consists of a 5 Ci Am-Be and 0.1 μg Cf-252 sources. The flux and dose rate of the Am-Be source was calculated by using MCNP5 code simulation at different distances from the source. The dose rate delivered by the source was determined using NM2-neutron monitor at different source-to-detector distances. A comparison between the measured and the calculated dose rate was performed and the deviation between them was explained in the skeletal arrangement of room scattering contribution. A shadow cone was designed and constructed to determine the scattering contribution at different source-to-detector distances. The optimum source-distance used for calibration was specified. It was found that the Am-Be calculated flux vary with distances from about 107–104 (n/cm2.S−1). The measured and the calculated dose rates were in agreement up to 150 cm distance from the source center after which the measured dose was greater than that calculated. The determined neutron scattering calculated from the measured-to-calculate dose ratio increased from 7% to 25% with increased distances from 150 to 300 cm. Moreover, the standard dose used in the calibration should be measured by a standard neutron monitor at each distance due to the higher value of the room scattering contribution where the optimum distance for calibration was 150 cm. The combined uncertainty of the measured neutron dose was 4.04%.

Calibration of CFUL01 fission chambers in the standard neutron fields of the BR1 reactor at SCK CEN

Recent subcritical VENUS-F experiments showed that fission chambers with a threshold deposit like U-238 can essentially improve the on-line sub-criticality measurments with the beam interruption method, which is currently supposed to be the main method for the ADS MYRRHA. To suppress the uncertainty caused by fissions in the U-235 impurities, the fraction of U-235 in the U deposit should be accurately known. Three PHOTONIS CFUL01 type fission chambers with U-238 deposit were purchased for sub-critical experiments in the VENUS-F reactor. To verify the purity of their deposits, the effective U-235 masses were measured in the empty cavity of the BR1 reactor with a well-known thermal neutron spectrum. It turned out that the measured effective U-235 mass in two fission chambers is lower than the declared mass (as it should be), but this is not the case for the third fission chamber. Then, the effective U-238 mass in these FCs was measured in the well-known fast spectrum of the MARK-III convertor in the BR1 reactor. Finally, the isotopic composition was obtained and it was found that the purity of two CFUL01 FCs is in agreement with the values declared in the certificates but it is not the case for the third fission chamber. As the length of the deposit is bigger than the length of the MARK-III convertor, necessary corrections were calculated with MCNP. The developed procedure using the BR1 standard irradiation fields can be applied for calibration and impurity determination of large fission chambers.

Methodology of 63Cu(n,2n)62Cu Reaction Rate Measurement

This paper presents the measurement of the spectrum-averaged cross section (SACS) of 63Cu(n,2n)62Cu reaction in 252Cf spontaneous fission neutron spectrum. The SACS in the 252Cf spectrum was chosen as a validation tool since 252Cf is the only standard neutron field and 62Cu isotope is not easy to measure by gamma spectroscopy since the gamma line of interest is an annihilation peak, which is also produced by 64Cu isotope. Fortunately, contributions to the annihilation peak from these isotopes can be distinguished due to the very different half-lives. SACS was inferred from the experimental reaction rate. The SACS in the 252Cf spontaneous fission neutron field for the 63Cu(n,2n)62Cu reaction was determined as equal to (0.1763 ± 0.0077 mb). This value agrees with value (0.183 ± 0.007) × 10−3 b within uncertainty presented by W. Mannhart. However, it differs by 12.7% from IRDFF-II value, which is equal to (0.19874 ± 8.954 10−3) × 10−3 b. Furthermore, reasonable agreement is not achieved with ENDF/B-VIII.0, JEFF-3.3, CENDL-3.1, ROSFOND-2010, nor JENDL-4.0 nuclear data libraries.

Design of Neutron Microscopes Equipped with Wolter Mirror Condenser and Objective Optics for High-Fidelity Imaging and Beam Transport

We present and compare the designs of three types of neutron microscopes for high-resolution neutron imaging. Like optical microscopes, and unlike standard neutron imaging instruments, these microscopes have both condenser and image-forming objective optics. The optics are glancing-incidence axisymmetric mirrors and therefore suitable for polychromatic neutron beams. The mirrors are designed to provide a magnification of 10 to achieve a spatial resolution of better than 10 μm. The resolution of the microscopes is determined by the mirrors rather than by the L/Dratio as in conventional pinhole imaging, leading to possible dramatic improvements in the signal rate. We predict the increase in the signal rate by at least two orders of magnitude for very high-resolution imaging, which is always flux limited. Furthermore, in contrast to pinhole imaging, in the microscope, the samples are placed far from the detector to allow for a bulky sample environment without sacrificing spatial resolution.

Neutron beam line for TOF measurements at the Spanish National Accelerator Lab (CNA)

A few years ago, the Spanish National Accelerator Lab (CNA) developed the first accelerator-based neutron facility in Spain called HiSPANoS (HiSPAlis Neutron Source). The first applications of the line were related to integral measurements applied to nuclear astrophysics, dosimetry and single event effects produced by neutrons in electronic devices. The successful of HiSPANoS pushed the enhancement of the facility. In collaboration with the NEC® Company, two devices were designed for pulsing ion beams (Chopper) and for compressing in time (Buncher) the pulsed beams. The Chopper-Buncher system has been already installed and commissioned. Proton and deuteron beams are delivered with repetition rates from 62.5 kHz to 2 MHz and 1 ns pulse width. In addition, a new line of the 3 MV Tandem Pelletron accelerator was designed for neutron time-of-flight (TOF) experiments. Conventional devices and a dedicated Pick-Up for timing measurements form the new line. In order to check the performance of the whole TOF system, we have carried out the measurement of the neutron spectrum produced by 7Li(p,n)7Be reaction at Ep = 1912 keV. Such spectrum has been measured by the TOF technique few times and it can be considered a standard neutron field, in particular in nuclear astrophysics. The first result of such experiment performed at CNA is shown in some detail. The excellent performance of the accelerator, the Chopper-Buncher system and the acquisition system allow us to offer the TOF line at HiSPANoS-CNA to the neutron community.