Gamma-spectrometry measurements of filtration media from an Advanced Gas-cooled Reactor.

Filtration media used to quantify particulate and gaseous releases have been collected from Hartlepool Power Station in the United Kingdom and measured using high-sensitivity gamma-spectrometry systems. Radionuclides that are relevant to the monitoring regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) have been detected. Results are reported and compared to detections recorded on the International Monitoring System (IMS). Time series activity plots have been produced and results interpreted with respect to known plant activities. The reported results improve the understanding of trace-level radionuclide emissions from Advanced Gas-cooled Reactors (AGRs) and aid interpretation of IMS measurements. This work is being performed as part of the Xenon Environmental Nuclide Analysis at Hartlepool (XENAH) collaboration between the Atomic Weapons Establishment (AWE, UK), EDF Energy (UK), Pacific Northwest National Laboratory (PNNL, US) and the Swedish Defence Agency (FOI, Sweden).

Evaluation of radioactivity levels and radiological hazards of some endemic plants used as medicine in Ankara, Turkey.

In this study, natural radioactivity levels (226Ra, 232Th, and 4 K) of some medicinal plant samples with known anti-oxidative properties, which are frequently consumed by animals and humans, were obtained from Ankara province and its surroundings (Mamak, Kizilcahamam, Beypazari, Kahramankazan, and Polatli districts) were determined using a thallium-doped sodium iodide NaI(Tl) gamma spectrometry. By using the determined natural radioactivity concentrations in the collected plant samples, the number of radiological doses that people could be exposed by consuming these plants was calculated. As a result of the study, 226Ra, 232Th, and 4 K radioactivity concentration ranges of the plant samples were found be 14.69 ± 1.27-59.08 ± 3.12 Bq kg-1, 1.78 ± 0.04-50.05 ± 2.76 Bq kg-1 and 207.24 ± 34.09-826.13 ± 25.40 Bq kg-1, respectively. The highest 226Ra, 232Th, and 4 K activity concentrations were measured in Astragalus densifolius subsp. ayashensis (Kahramankazan), Astragalus kochakii (Kahramankazan) and Rumex patientia (Patience Dock) (Kahramankazan) plants, respectively. The lowest 226Ra, 232Th and,4 K activity concentration plants were determined respectively as Rumex patientia (Mamak), Lavandula angustifolia (Kizilcahamam), and Astragalus acikirensis (Polatli). The establishment and routine repetition of environmental radioactivity monitoring programs in each region are important for human and animal health, and the results of this study gain importance for Ankara and its surroundings in terms of environmental health.

226Ra measurement via gamma-ray spectrometry of 222Rn progeny - quantification of radon losses from sample capsules.

Radium-226 detection in sediment samples is generally executed by means of gamma-ray spectrometry. Data evaluation relies (besides the 186.2 keV 226Ra gamma peak) on the combined analysis of major gamma peaks that are produced by the short-lived radon (222Rn) daughters 214Pb and 214Bi. Precondition for this detection approach is equilibrium decay of all members of the decay chain between 226Ra and 214Bi. In closed systems, this equilibrium is reached after about five half-lives of 222Rn (19 days). However, a closed system can only be guaranteed if the capsule which contains the sample prevents diffusive escape of radon. Such radon-tightness cannot be guaranteed for a wide range of plastic materials. Due to its polymer structure, plastic material generally tends to allow radon diffusion and hence radon loss from the sample resulting in a disturbance of the required decay equilibrium. The paper introduces an approach that allows quantifying radon loss from sample capsules by direct radon measurements using mobile radon detection equipment. The experimental findings are supported by theoretical considerations. An examined alternative approach based on the offset of the 186.2 keV data point from an efficiency function that is calculated exclusively from short-lived radon progeny peaks in the gamma-ray spectrum did not prove to be applicable due to a lack of supporting peaks in the low-energy section of the spectrum.

Distribution of natural radionuclides in NORM samples from North Abu Rusheid area, Egypt.

The North Abu Rusheid area in Egypt is a well-known high background natural radiation area (HBNRA) due to the existence of naturally occurring radioactive materials (NORMs) in mylonitic rocks. In this study, 27 rock samples were selected for dose estimation studies. 238U and 232Th were measured using inductively coupled plasma mass spectrometry (ICP-MS) and 40K was measured using sodium iodide (thallium) gamma-ray spectroscopy. The ranges of activity concentrations (Bq/kg) of 238U, 232Th and 40K in the samples varied from 270 ± 2 to 2120 ± 29, 350 ± 2 to 1840 ± 27 and 20 ± 2 to 1390 ± 35 with mean values of 980 ± 349, 770 ± 351, and 640 ± 402 Bq/kg, respectively. The radiological hazard parameters were estimated from activity concentrations of 238U, 232Th and 40K and compared to United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) values. The present study revealed that the hazard parameters were several times higher than the worldwide averages. The U/Th concentration ratio ranged from 0.7 to 3 and could be attributed to the presence of kasolite, uranothorite, zircon, and columbite in mylonitic rocks. From the radiological protection viewpoint, it is necessary to monitor natural radionuclides in these rocks prior to their use in residential and commercial construction materials.

Natural and artificial radioactive pollution in sediment and soil samples of the Bosphorus, Istanbul.

This study focused on the determination of natural (238U, 232Th, and 40K) and artificial (137Cs) radionuclide concentrations both in 55 sediment samples collected from various depths in the Bosphorus and 5 soil samples from the coastline of the Bosphorus, Istanbul, using gamma-ray spectrometry with an HPGe detector. The mean activity concentrations of natural 238U, 232Th, and 40K and anthropogenic 137Cs were determined to be 11.41 ± 0.21 Bq kg-1, 6.87 ± 0.16 Bq kg-1, 369.61 ± 3.41 Bq kg-1, and 6.54 ± 0.11 Bq kg-1, respectively, in the sediment samples. The average activity concentrations of 238U, 232Th, 40K, and 137Cs radionuclides in the soil samples were also measured to be 11.65 ± 0.18 Bq kg-1, 9.55 ± 0.15 Bq kg-1, 369.43 ± 3.09 Bq kg-1, and 4.57 ± 0.09 Bq kg-1, respectively. Radiological contour maps based on the activity concentrations of natural and artificial radionuclides in the sediment samples for the Bosphorus, Istanbul, were created. The total annual effective doses due to soil samples were calculated to be 34.58 µSv y-1.

Study on reconstruction and analytical method of seawater radioactive gamma spectrum.

Gamma detector detection technology based on NaI(Tl) scintillation crystal has become a popular research topic and has been applied in the field of marine radioactive environment automatic monitoring because of its advantages of low power consumption, low cost and strong environmental adaptability. However, insufficient energy resolution of the NaI(Tl) detector and great Compton scattering in the low-energy region caused by the abundance of natural radionuclides in seawater hinder the automatic analysis of radionuclides in seawater. This study adopts the combination of theoretical derivation, simulation experiment, water tank test and seawater field test, establishing an effective and feasible spectrum reconstruction method. The measured spectrum in seawater is regarded as the output signal formed by the convolution of the incident spectrum and the detector response function. The acceleration factor p is introduced to construct the Boosted-WNNLS deconvolution algorithm, which is used to iteratively reconstruct the spectrum. The analysis results of the simulation test, water tank test and field test meet the radionuclide analysis speed and accuracy requirements for the in-situ automatic monitoring of seawater radioactivity. The spectrum reconstruction method in this study converts the physical problem of insufficient detection accuracy of spectrometer in the practical application into a mathematical problem of deconvolution solution, restores the original radiation information in seawater, and improves the resolution of the seawater gamma spectrum.

Characterization of a 4παß(LS)-γ(HPGe) prototype system for low-background measurements.

A ground-level prototype system for low-background measurements was developed and tested. The system consists of a high-purity germanium (HPGe) detector used for detecting γ rays and coupled to a liquid scintillator (LS) used for detecting α and ß particles. Both detectors are surrounded by shielding materials and anti-cosmic detectors ("veto") used to suppress background events. The energy and timestamp of detected α, ß and γ emissions are recorded event-by-event and analyzed offline. By requiring timing coincidence between the HPGe and LS detectors, background events originating from outside the volume of the measured sample can be effectively rejected. The system performance was evaluated using liquid samples containing known activities of an α emitter (241Am) or a ß emitter (60Co) whose decays are accompanied by γ rays. The LS detector was found to provide a solid angle of almost 4π for α and ß particles. Compared to the traditional γ-singles mode, operating the system in coincidence mode (i.e., α-γ or ß-γ) reduced the background counts by a factor of ∼100. Consequently, the minimal detectable activity for 241Am and 60Co was improved by a factor of 9, being 4 mBq and 1 mBq for an 11-d measurement, respectively. Furthermore, by applying a spectrometric cut in the LS spectrum that corresponds to α emission from 241Am, a background reduction factor of ∼2400 (compared to γ-singles mode) was achieved. Beyond low-background measurements, this prototype exhibits additional compelling features, such as the ability to focus on certain decay channels and study their properties. This concept for a measurement system may be of interest to laboratories that monitor environmental radioactivity, studies involving environmental measurements and/or trace-level radioactivity.

IDENTIFICATION OF AREAS OF HIGH POTENTIAL-BEARING MINERALIZATIONS, EASTERN DESERT OF EGYPT: INSIGHTS FROM AIRBORNE GAMMA-RAY SPECTROMETRIC DATA.

A major number of mineral deposits are related to hydrothermal processes. Therefore, the mapping of the hydrothermally alteration areas, connected with mineralization, is crucial in the search for metal deposits. To achieve this purpose, areas of hydrothermal alterations are targeted by processing the airborne gamma-ray spectrometric data to detect areas enriched in potassium that may indicate the existence of potassic alteration zones, which are often associated with hydrothermal alterations accompanied by mineral deposits. Data processing and analysis were performed using the K/eTh ratio, deviation of ideal potassium (Kd) and F-parameter. Besides, determining the environmental radiation risk due to the fact that the study area contains many excavation sites for various mining materials and quarries. Hydrothermal alteration indicator maps show five known mineralizations of gold, copper, molybdenum, fluorite and wolframite, which are associated with hydrothermal processes that took place in the study area. It is possible to note the intimate correlation of mineral deposits present in areas with high potassium content. Positive correlation between the computed hydrothermal alteration indicators (K/eTh, Kd and F-parameter), shown on the ternary image map, revealed favorable high and intermediate targets for the detection of various mineral deposits in the study area. On the other hand, the estimated mean values of absorbed dose rate for all rock units were within the permissible range (28-120 nGy h-1), and the mean annual effective dose rate was below the permissible limit of 1.0 mSv y-1 for these rocks.

Seasonal variations of terrestrial gamma dose, natural radionuclides and human health.

The aim of the research was to study seasonal variations in gamma radiation and the statistical significance of these variations. Moreover, we compared in-situ and laboratory analyses of uranium, thorium, radium and potassium K-40 contents. Exposure to a low level of radiation is a minor (but still is) contributor to overall cancer risk therefore we compared doses generated by gamma radiation with overall cancer risk. The research was performed in SW Poland in two granitoid massifs -Strzelin and Karkonosze. The in-situ measurements were performed seasonally using gamma-ray spectrometer Exploranium with BGO detector and Radiometer RK-100. The laboratory measurements were performed using spectrometer with HPGe detector Canberra-Packard and alpha spectrometry technique. The general trend of seasonal variations of natural radionuclides, terrestrial ambient gamma dose (TGDR) and ambient gamma dose rate (AGDR) was difficult to identify. We noticed slightly increased values of all analysed parameters in warmer seasons, and lower in colder, although there were some exceptions. These exceptions were induced by precipitation and varied soil water content, but variations were mostly not statistically significant. The statistically important deviation from the trend was registered only in equivalent uranium data when the survey was carried out during or just after intensive precipitation. We observed a good positive correlation between in-situ and laboratory results (TGDR in situ/Lab r = 0.696), therefore, we recommend using in-situ measurements in a dense measuring grid before collecting selected soil samples to better evaluate the level of natural radiation in the environment. The average ambient gamma dose in the Karkonosze Massif was 0.52 mSv y-1 whereas in the Strzelin Massif was 0.39 mSv y-1. The overall cancer risk in Karkonoski county is higher than in Strzelin county. A connection between increased gamma radiation and higher overall cancer risk is possible but should be examined during more elaborated research.

Estimation of soil radioactivity-depth profiles using Bayesian inversion of borehole gamma spectrometry data.

Inversion of in situ borehole gamma spectrometry data is a faster and relatively less laborious method for calculating the vertical distribution of radioactivity in soil than conventional soil sampling method. However, the efficiency calculation of a detector for such measurements is a challenging task due to spatial and temporal variation of the soil properties and other measurement parameters. In this study, the sensitivity of different soil characteristics and measurement parameters on simulated efficiencies for a 662 keV photon peak were investigated. In addition, a Bayesian data inversion with a Gaussian process model was used to calculate the activity concentration of 137Cs and its uncertainty considering the sources of uncertainty identified during the sensitivity analysis, including soil density, borehole radius, and the uncertainty in detector position in the borehole. Several soil samples were also collected from the borehole and surrounding area, and 137Cs activity concentration was measured to compare with the inversion results. The calculated 137Cs activity concentrations agree well with those obtained from soil samples. Therefore, it can be concluded that the vertical radioactivity distribution can be calculated using the probabilistic method using in situ gamma spectrometric measurements.

Unmanned stationary online monitoring system based on buoy for marine gamma radioactivity.

Research on unmanned online monitoring equipment for marine radioactivity surrounding nuclear power plants is of great significance. In this work, a small radioactivity monitoring system based on buoy was designed and manufactured for the emergency situation of nuclear accidents. The core of the radioactivity monitoring system is the underwater gamma spectrometer. The spectrometer can respond to gamma rays from 60 keV to 3 MeV, and can identify the nuclides whose characteristic rays belong to this energy range. The detection efficiency curve was calculated through Monte Carlo simulation and verified in a standard liquid source. A data acquisition processor was also designed to coordinate the detectors in the system and wirelessly transmit online monitoring data. Three experiments were carried out in the seawater around the Tianwan Nuclear Power Plant in Lianyungang, China using this online marine radioactivity monitoring system based on buoys. The stability and radioactivity monitoring capabilities of the system have been verified.

Gamma spectrometric measurement of uranium isotopic composition and mass in sintered UO2 pellets using the efficiency transfer method.

Gamma spectrometric measurements to determine the isotopic composition and total uranium mass in UO2 pellets (D = 7.5 mm; H = 3.5 mm, ρ = 10 g/cm3) were carried out. The required efficiency curve was obtained by applying the efficiency transfer method from a calibration standard (D = 65 mm; H = 20 mm) of a slightly acidified water solution. The average isotopic composition of ten UO2 pellets was consistent with values of natural uranium given by IUPAC. The average relative bias for the 235U/238U amount ratio was -0.73% using the 1001 keV gamma line for 238U and 0.50% using the 63 keV gamma line (186 keV was always used for 235U). For the total uranium mass, the mean deviation as compared to mass determinations using a balance was 5.5% using the 1001 keV gamma line for 238U and 4.3% using the 63 keV gamma line.

2D inversion of in situ gamma-ray spectrometric measurements of 137Cs for site characterization.

Environmental contamination by radioactive materials can be characterized by in situ gamma surface measurements. During such measurements, the field of view of a gamma detector can be tens of meters wide, resulting in a count rate that integrates the signal over a large measurement support volume/area. The contribution of a specific point to the signal depends on various parameters, such as the height of the detector above the ground surface, the gamma energy and the detector properties, etc. To improve the spatial resolution of the activity concentration, contributions of a radionuclide from nearby areas to the count rate of a single measurement should be disentangled. The experiments described in this paper, deployed 2D inversion of in situ gamma spectrometric measurements using a non-negative least squares-based Tikhonov regularization method. Data were acquired using a portable LaBr3 gamma detector. The detector response as a function of the distance of the radioactive source, required for the inversion process, was simulated using the Monte Carlo N-Particle (MCNP) transport code. The uncertainty on activity concentration was calculated using the Monte Carlo error propagation method. The 2D inversion methodology was first satisfactorily assessed for 133Ba and 137Cs source activity distributions using reference pads. Secondly, this method was applied on a 137Cs contaminated site, making use of above-ground in-situ gamma spectrometry measurements, conducted on a regular grid. The inversion process results were compared with the results from in-situ borehole measurements and laboratory analyses of soil samples. The calculated 137Cs activity concentration levels were compared against the activity concentration value for exemption or clearance of materials which can be applied by default to any amount and any type of solid material. Using the 2D inversion and the Monte Carlo error propagation method, a high spatial resolution classification of the site, in terms of exceeding the exemption limit, could be made. The 137Cs activity concentrations obtained using the inversion process agreed well with the results from the in-situ borehole measurements and those from the soil samples, showing that the 2D inversion is a convenient approach to deconvolute the contribution of radioactive sources from nearby areas within a detector's field of view, and increases the resolution of spatial contamination mapping.

Sedimentary and environmental conditions of Al-Rassafeh Badyieh (Area-2), Syria through aerial gamma ray spectrometry and multifractal techniques.

The interpretation of aerial gamma ray spectrometry in term of geological and environmental analysis is undertaken herein through applying a specific methodology including different radioactive and statistical techniques for characterizing the sedimentary and environmental conditions of the Al-Rassafeh Badyieh (Area-2), Syria. The radioactive technique uses the uranium favorability index (UI) and alteration(F) parameters, that are evaluated through analyzing the relationships between eU, eTh, K and their ratios (eTh/eU, eU/eK, and eTh/eK) for the nine scored lithological units already determined in the study area. The statistical technique applies the non linear multifractal approach with the concentration-number model (C-N) and log-log graphs to differentiate between different radioactive ranges of UI and F parameters. The radioactive element re-distribution, the favorability as regards uranium potentiality, and the degree of uranium remobilization are separately estimated and documented for the nine scored lithological units. Those units show a limited uranium remobilization and redistribution. The sedimentary and environmental conditions of the Area-2 are clarified through analyzing the eTh/eU ratio, where marine and continental environments are indicated in the study region.

Comparative analysis of gamma ray spectrometers applied to Irati Formation, Paraná basin, São Paulo State, Brazil.

This paper describes the use of gamma ray spectrometry in the study of rock samples from the Irati Formation, Paraná sedimentary basin, São Paulo State, Brazil. This technique allowed to measure the natural radiation emitted by 40K, as well the radionuclides belonging to the decay series of 238U (eU = 226Ra = 214Bi) and 232Th (eTh = 228Th = 208Tl) which occur in the analyzed samples. Four gamma ray spectrometers have been utilized for comparing the results obtained: a portable sodium iodide [NaI(Tl)] scintillation detector (Digidart), a handheld bismuth germanate oxide (BGO) detector and two bench NaI(Tl) crystals, differing in their geometry (Planar and Well types). This study involved the calibration of the spectrometers, except in the case of the BGO that is factory calibrated. Afterwards, gamma ray analysis was done for 122 rock samples colleted at Partecal Quarry located at Assistência District, Rio Claro city, which have been of interest for the oil and gas sector. For comparison purposes, the obtained datasets were subjected to different statistical tests, including the analysis of variance (ANOVA) that proved to be of great value for checking the differences of the mean concentration values of eU, eTh and K. The results pointed out several factors that affect the gamma ray analysis for the natural radioelements uranium, thorium, and potassium such as the samples size, shape and geometry, detector type, shielding and counting time. These factors are of difficult control in order to get reliable radiometric measurements by this technique.

Background shielding by dense samples in low-level gamma spectrometry.

In low activity gamma spectrometric measurements of large, dense samples, the bulk sample material shields the HPGe crystal from external background sources. If not accounted for in studies that utilise background-subtraction methods, this effect may result in systematic errors in the sample activity and detection limit estimation. We introduce a Monte Carlo based method to minimise the impact of this effect on sample gamma spectra. It is validated using simulated detector backgrounds and applied to a measurement of low-activity [Formula: see text] . One main prerequisite for the correct application of this method is to know in advance the nuclides which contribute to the detector background spectrum and their spatial distribution. With a thorough understanding of the detector backgrounds, the method improves the accuracy of sensitive low-background measurements of low-activity samples. Even without knowing the background sources and their distribution, conservative results may still be presented that account for the potential systematic errors introduced by this background shielding effect.

Study of radionuclides and heavy metal migration through soil profiles (0-60 cm) at points near the targets of NATO strikes in 1995: environmental monitoring and assessment.

The activity concentrations of natural and artificial radionuclides (40K, 232Th, 226Ra, 238U, 137Cs) and concentrations of six heavy metals of interest (Cd, Cr, Cu, Ni, Pb and Zn) were investigated in 18 soil samples through soil depths (0-10, 10-20, 20-30, 30-40.40-50, 50-60 cm) at the three selected sites in the Hadzici. Since at this area ammunition with depleted uranium had been used during the NATO strikes in 1995, this study was conducted with the aim to assess the radiological and environmental health hazards. Radioactivity was determined by gamma spectrometry using HPGe and LEGE detectors and content of heavy metals by using a flame atomic absorption spectrometry. The correlation with distribution of the radionuclides and their activity concentrations through depths was found only at the site 1 for 40K, 232Th and 226Ra, where minimum/maximum activity concentrations for 40K were 814.42 Bq/kg/1039.48 Bq/kg, for 232Th 53.98 Bq/kg/74.12 Bq/kg and for 226Ra 50.32 Bq/kg/65.73 Bq/kg. Vertical distribution of 137Cs along 3 site profiles was used for distinction of cultivated and uncultivated soil. Using the activity ratio of 238U/226Ra and 235U/238U, the presence of depleted uranium (DU) was established at the site 3. Obtained Igeo values for determined heavy metals showed that all of three sites were unpolluted to moderately polluted. Pb content in all three sites showed correlation with concentration decreasing with increasing soil depth.

Natural radioactivity assessment and geophysical interpretation of parts of Igarra area, Southern Nigeria.

To evaluate the concentration of natural radionuclides and to carry out geophysical interpretation of part of Igarra area, Southern Nigeria, an integrated geophysical approach was adopted involving radiometric, gravity, and magnetic methods. The RS-230 Super-Spec spectrometer, G-512 Lacoste and Romberg gravimeter, and the GSM-19v7.0 Overhauser instrument were used for the radiometric, gravity, and magnetic data acquisitions, respectively, along a specified traverse within the area. The datasets were processed using Oasis Montaj, Grav-Master, and Ms-Excel software. Gravity results show that the mean free air and Bouguer anomalies in the area are - 67.42 and - 84.22 mGal, while magnetic survey indicates that the mean corrected magnetic field intensity in this area is 32218.49 nT. Radiometric survey results show that the mean radioactivity concentrations of thorium ([Formula: see text], uranium ([Formula: see text]), and potassium ([Formula: see text]) are 31.81 Bq/kg, 26.48 Bq/kg, and 167.33 Bq/kg, respectively. Further analysis also revealed that the mean radioactivity equivalent of the area is 84.86 Bq/kg; absorbed dose rate is 72.74nGy/h, while the mean external hazard index is 0.30. A novel model equation for estimating absorbed dose rate from radioactivity equivalent was also obtained and validated. The gravity and magnetic survey results indicate the presence of low-density and high magnetic basement rocks underlying this area, while radiometric results reveal that radiations in this area did not exceed acceptable standards of 370 Bq/kg for radioactivity equivalent, 84 nGy/h for absorbed dose rate, and unity which corresponds to 370 Bq/kg for external hazard index as recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation and the International Atomic Energy Agency.

Minimum detectable activity concentration of radio-cesium by a LaBr3(Ce) detector for in situ measurements on the ground-surface and in boreholes.

A 3.81 × 3.81 cm LaBr3(Ce) detector based portable measurement setup has been developed for in situ gamma spectrometric survey of a contaminated site. This system is suitable for above- and below ground surface gamma spectrometric measurements of 137Cs. However, the minimum detectable activity concentration (MDAC), an important parameter of a measurement system, should be estimated for planning purposes of the gamma spectrometric survey. In this study, the MDAC of 137Cs for the measurement setup was investigated. The efficiency of the measurement setups was calculated from Monte Carlo simulations using MCNP code. The numerical model of the different studied set-ups, used in MCNP, performed well for the known cases. The results show that the MDAC varies with the position of the detector with respect to ground surface. A 5-20 min acquisition time, depending on the detector position, can be sufficient to get a MDAC of about 10% of the exemption limit of 137Cs (100 Bq/kg).

Maximum detection distances for gamma emitting point sources in mobile gamma spectrometry.

In this study an algorithm was developed for calculating maximum detectable distance (MDD) for mobile gamma-ray detection of lost sources in-situ for some common mobile spectrometer systems and gamma sources (137Cs and 60Co). The MDD is a function of detector efficiency, vehicle speed, acquisition time interval, radiation background level and accepted frequency of false alarms. To test its accuracy in predicting the MDD experiments were conducted in-situ. Results indicate agreement with experimental mobile detection distance measurements for 60Co and 137Cs point sources. Both the algorithm and the field test show that at a vehicle speed of 50 km/h, the optimal acquisition time intervals range between 3 and 10 s when searching for unshielded sources with activities of 137Cs and 60Co in the order of 100 MBq. Longer acquisition time intervals (20-30 s) are better to detect higher activity sources at the same speed. However, at higher speeds, shorter time intervals should be selected to increase the MDD. The developed algorithm can help select the optimal combination of detectors, vehicle speed, and instrument settings when using mobile searching in the event of loss of gamma-ray sources.