Design and performance evaluation of a large field-of-view dual-particle time-encoded imager based on a depth-of-interaction detector

Time-encoded imaging is useful for identifying potential special nuclear materials and other radioactive sources at a distance.In this study,a large field-of-view time-encoded imager was developed for gamma-ray and neutron source hotspot imaging based on a depth-of-interaction(DOI)detector.The imager primarily consists of a DOI detector system and a rotary dual-layer cylindrical coded mask.An EJ276 plastic scintillator coupled with two SiPMs was designed as the DOI detector to increase the field of view and improve the imager performance.The difference in signal time at both ends and the log of the signal amplitude ratio were used to calculate the interaction position resolution.The position resolution of the DOI detector was calibrated using a collimated Cs-137 source,and the full width at half maximum of the reconstruction position of the Gaussian fitting curve was approximately 4.4 cm.The DOI detector can be arbitrarily divided into several units to independently reconstruct the source distribution images.The unit length was optimized via Am-Be source-location experiments.A multidetector filtering method is proposed for image denoising.This method can effectively reduce image noise caused by poor DOI detector position resolution.The vertical field of view of the imager was(-55°,55°)when the detector was placed in the center of the coded mask.A DT neutron source at 20 m standoff could be located within 2400 s with an angular resolution of 3.5°.

Determination of thickness of wax deposition in oil pipelines using gamma-ray transmission method

Wax deposition in pipelines is a crucial problem in the oil industry.An approach that combines the gammaray transmission method with scanning technology is proposed to detect the thickness of wax deposition.The performance of the method is validated through simulations with MCNP code.An experiment is also carried out with a 300 mCi ^(137)Cs source and a LaBr_3 detector.A good correspondence is observed between the simulation and experimental results.The results indicate that the approach is efficient for detecting the thickness of wax deposition in oil pipelines.

Improved formation density measurement using controllable D-D neutron source and its lithological correction for porosity prediction

Controllable D-D neutron sources have a long service life,low cost,and non-radioactivity.There are favorable prospects for its application in geophysical well logging,since traditional chemical radioactive sources used for well logging pose potential threats to the safety of the human body and environment.This paper presents an improved method to measure formation density that employs a D-D neutron source.In addition,the lithological effect on the measured density was removed to better estimate the formation porosity.First,we investigated the spatial distribution of capture gamma rays through Monte Carlo simulations as well as the relationship between the ratio of capture gamma ray counts and formation density to establish theoretical support for the design of density logging tools and their corresponding data processing methods.Second,we obtained the far to near detector counts of captured gamma rays for an optimized tool structure and then established its correlation with the density and porosity of three typical formations with pure quartz,calcite,and dolomite minerals.Third,we determined the values for correcting the densities of sandstone and dolomite with the same porosity using limestone data as the reference and established the equations for calculating the correction values,which lays a solid foundation for accurately calculating formation porosity.We observed that the capture gamma ray counts first increased then decreased and varied in different formations;this was especially observed in high-porosity formations.Under the same lithologic conditions(rock matrix),as the porosity increases,the peak value of gamma ray counts moves toward the neutron source.At different detector-source distances,the ratio of the capture gamma ray counts was well correlated with the formation density.An equation of the formation density conversion was established based on the ratio of capture gamma ray counts at the detector-source distances of 30 cm and 65 cm,and the calculated values were consistent with the true values.After correction,the formation density was highly consistent with the true value of the limestone density,and the mean absolute error was 0.013 g/cm3.The calculated porosity values were very close to the true values,and the mean relative error was 2.33%,highlighting the accuracy of the proposed method.These findings provide a new method for developing D-D neutron source logging tools and their well-log data processing methods.

Detection of heavy metals in aqueous solution using PGNAA technique

A prompt gamma neutron activation analysis setup was developed for heavy metal detection in aqueous solutions with a 300 m Ci241Am-Be neutron source and a4 4 inch(diameter height) BGO detector. In the present work, heavy metals, including Mn, Cu, Ni, Cr and Zn, were measured by the setup. The minimum detectable concentrations of Mn, Cu, Ni, Cr and Zn were 246.6, 391.2, 218.1,301.5 and 2804.1 ppm, respectively. The minimum detectable concentration of each element and the linearity response between the characteristic peak counts and elements concentrations have been studied. And the results showed that all heavy metals had a good linear relationship between characteristic peak counts and concentrations.