Energy deposition and radiation dose distribution by the use of gold, a high-Z biocompatible element in water solution, is estimated as a function of source energy typical of brachytherapy sources (15 keV, 20 keV, 30 keV, 40 keV, 80 keV, 90 keV, 150 keV, 300 keV, 1 MeV), solution concentration (5-25 mg Au/g H 2 O), and solution placement (1-2 cm concentric shells). Monte Carlo (MC) simulations are carried out with the MCNP5 code, compared with other widely used MC codes such as PENELOPE and GEANT, to validate the dose estimates, which may vary considerably due to artifacts and data libraries, and extended to a sensitivity analysis using perturbation estimates. The energy deposition and radiation dose are estimated as a function of monoenergetic source radiation energy, and concentration of gold in solution. MC simulation is carried out in the coupled photon-electron radiation mode for x-rays emanating from a radiation source implanted in a water cell, for which results are valid for a cancer cell modelled by a spherical water phantom. For carrying out sensitivity studies, the Monte Carlo perturbation feature with material perturbations was used to sample derivatives in a single run which were used in a Taylor series to estimate both dose and Dose Enhancement Factor (DEF) from single MC runs. Close agreement was found between dose estimates from MCNP5, PENELOPE and GEANT, in spite of artifacts such as cut-offs in electron transport. It was also found that dose increases with energy of a source, and that dose enhancement, for a given concentration, decreases with source energy. The perturbation estimates result in enhanced computational efficiency.

Summary The Arabian American Oil Co. (ARAMCO) recently installed a nuclear salt-in-crude monitor (SICM) that continuously measures the salt content of a flowing stream of crude oil. This device was developed by Texaco Inc.'s Bellaire (TX) Research Laboratory. The monitor consists of two parts: a counting chamber and an instrument console. The counting chamber is a length of 24-in.-diameter pipe containing a long-life neutron source and a gamma ray detector, both mounted in cross pipes so that there is no direct contact with the flowing crude. Neutrons from the source are absorbed by chloride ions in the stream, which in turn emit gamma rays. The intensity of the gamma rays is proportional to the amount of chlorine in the crude. The gamma ray detector is electrically connected to the instrument console, which is located in a control room. The console contains the necessary instrumentation to process the data from the detector, to compute the salt concentration, and to provide a continuous printed record of the salt per thousand barrels (PTB). Introduction and Background Chlorine, usually in the form of salt, is a troublesome contaminant in crude oil production pipelines and plants, and it must be maintained within certain limits to minimize crude oil handling and processing problems. ARAMCO has recognized the need for an improved method to monitor salt content in crude oil at gas/oil separation plants, shipping stations, and refineries to ensure that crude being transported meets salt contents specification of 10 lbm PTB (20 ppm chlorine). The Texaco laboratory has developed and built an SICM to meet our needs. The SICM is an instrument designed to monitor the salt content continuously and automatically in a flowing stream of crude oil. The salt content determination is accomplished by measuring the chlorine levels present in the crude using a nuclear technique that was verified several years ago during the development of the Texaco chlorine log. The measurement technique also provides simultaneous readings of the sulfur levels in the crude. Because the nuclear reactions occur essentially instantaneously, the measurement of salt (chlorine) and sulfur are unaffected by the velocity of the flow stream. The instrument is capable of measuring less than 10 lbm of salt PTB with an accuracy of +2 lbm PTB or better. Sulfur content can be measured down to 0.25% with an accuracy of +0.05% sulfur as long as the salt concentration remains below several hundred pounds PTB. These specifications are applicable only to flowlines containing no free gas. The SICM consists of two major subsystems: a counting chamber and an instrument console (Fig. 1). The standard counting chamber is a 48-in. section of 24-in.-diameter, 1/2-in.-wall pipe that can be installed in any size flowline to monitor the total crude stream. The counting chamber contains a long-lived radioactive source and a gamma ray detector system, each housed in a cross pipe and protected from direct contact with the flowing crude oil. The counting chamber is electrically connected to the instrument console, which can be located several hundred feet away. The console, a microprocessor-based system. is a self-contained unit that requires only 115-V AC line power. It contains the instrumentation necessary to power the detector assembly and to process the data from the counting chamber. JPT P. 1009^

Explosive detection systems (EDS) based on thermal neutron activation can be used for detection and identification of concealed explosives such as trinitrotoluene, cyclonite, and ammonium nitrate (NH 4 NO 3 ). Activation results in emission of characteristic gamma rays of constituents whose relative intensities yield atomic fractions of the explosives and instant identification. Applications of EDS can also be at airports and seaports as well as in vehicles. Such systems have been studied, developed and tested and are being refined in their design and functionality as several issues still need to be resolved, such as the associated high radiation dose and development of fast algorithms for their identification. This paper considers a portable EDS, incorporating a neutron source and radiation detection systems, which can fit into a portable briefcase of dimensions 40 cm × 30 cm × 8 cm. The detection efficiency and radiation dose are computed by carrying out simulations, to estimate the strengths of characteristic photon yields, using the Monte Carlo code MCNP5 to present a useful and efficient engineering design. Two factors of concern were found to be the excessive photons from material of least interest ( 10 B, Ca, Pb) and the excessive radiation dose in the immediate vicinity of a portable system. However, an accurate estimate of the H/N ratio was obtained with simulation carried out for ~1kg concealed TNT explosive. The ratio was found to be ~1.61 which is very close to the actual ratio (1.67). Thus, the accurate identification of TNT explosives can be efficiently carried out by such a portable system.