Comparison of Various Spectra Methods Used in Vehicle-Based Nai(Tl) Spectrometry Survey.

Vehicle-based NaI(Tl) spectrometry is widely used in searching for lost sources. There are several spectra methods can be used to detect abnormal radiation caused by manmade nuclides among a sequence of spectra. In order to test which method has the highest sensitivity, an experiment was done, and three commonly used spectra methods were used to process the acquired spectra. The result indicated that: the noise adjusted singular value decomposition method is more sensitive than other methods. Finally, its drawback was also discussed.

Modeling Study of a Proposed Field Calibration Source Using K-40 and High-Z Targets for Sodium Iodide Detectors.

Calibration sources based on the primordial isotope potassium-40 (K) have reduced controls on the source's activity due to its terrestrial ubiquity and very low specific activity. Potassium-40's beta emissions and 1,460.8 keV gamma ray can be used to induce K-shell fluorescence x rays in high-Z metals between 60 and 80 keV. A gamma ray calibration source that uses potassium chloride salt and a high-Z metal to create a two-point calibration for a sodium iodide field gamma spectroscopy instrument is thus proposed. The calibration source was designed in collaboration with the Sandia National Laboratory using the Monte Carlo N-Particle eXtended (MCNPX) transport code. Two methods of x-ray production were explored. First, a thin high-Z layer (HZL) was interposed between the detector and the potassium chloride-urethane source matrix. Second, bismuth metal powder was homogeneously mixed with a urethane binding agent to form a potassium chloride-bismuth matrix (KBM). The bismuth-based source was selected as the development model because it is inexpensive, nontoxic, and outperforms the high-Z layer method in simulation. Based on the MCNPX studies, sealing a mixture of bismuth powder and potassium chloride into a thin plastic case could provide a light, inexpensive field calibration source.

A simple method for activity determination of ¹³4Cs and ¹³7Cs in foodstuffs using NaI(Tl) scintillation spectrometer.

A simplified peak fitting technique for the analysis of the overlapped pulse-height spectra of (134)Cs and (137)Cs γ-rays obtained with a NaI(Tl) scintillation spectrometer was studied. In this analysis, nearly an upper half of 662 keV (137)Cs peak data was employed for fitting of the Gaussian peak using the least squares algorithm. Consistent results were obtained as compared with the reference value of test samples mixed with (134)Cs and (137)Cs standard solutions.

Monte Carlo calculation of response functions to gamma-ray point sources for a spherical NaI(Tl) detector.

Response functions of a 7.62 cm-diameter spherical NaI(Tl) detector to gamma-ray point sources in the energy range up to 1.5 MeV were calculated by means of the Monte Carlo method using PENELOPE-2006 (Salvat et al., 2006). The detector materials and dimensions were modeled realistically. The calculated response functions agreed well with the experimental spectra.

Feasibility study of activity measurement of positron emitters based on gamma-gamma coincident detection by two NaI(Tl) detectors.

Detection of two and more γ-rays in coincidence by two NaI(Tl) detectors with almost 4π geometry allows absolute characterization of radionuclides emitting coincidence gammas. The method is a generalization of the Eldridge-Crowther method developed originally for x-rays and low energy γ-rays. This method is applied to the case of (94)Nb decay with two coincident gamma-rays emitted in one cascade. The application of this method for the case of coincident positron-gamma emission ((22)Na and (26)Al sources) meets some difficulties. In these decays, two 511 keV gamma quanta produced in positron annihilation are strongly correlated. Despite the fact that the third gamma emitted in (22)Na and (26)Al decays is not correlated with two annihilation quanta, the number of independent observables for (22)Na and (26)Al decays is less than the number of unknowns. The small parameter ω(00), the probability that both annihilation quanta escape detection in both NaI(Tl) detectors, cannot be determined. However, if this parameter is defined from experimental data for one source with known activity ((22)Na), the activity of the other source ((26)Al) can be calculated from experimental data for (26)Al decay.

Application of the Monte Carlo method for the efficiency calibration of CsI and NaI detectors for gamma-ray measurements from terrestrial samples.

Gamma-ray measurements in terrestrial/environmental samples require the use of high efficient detectors because of the low level of the radionuclide activity concentrations in the samples; thus scintillators are suitable for this purpose. Two scintillation detectors were studied in this work; CsI(Tl) and NaI(Tl) with identical size for measurement of terrestrial samples for performance study. This work describes a Monte Carlo method for making the full-energy efficiency calibration curves for both detectors using gamma-ray energies associated with the decay of naturally occurring radionuclides (137)Cs (661keV), (40)K (1460keV), (238)U ((214)Bi, 1764keV) and (232)Th ((208)Tl, 2614keV), which are found in terrestrial samples. The magnitude of the coincidence summing effect occurring for the 2614keV emission of (208)Tl is assessed by simulation. The method provides an efficient tool to make the full-energy efficiency calibration curve for scintillation detectors for any samples geometry and volume in order to determine accurate activity concentrations in terrestrial samples.

Automated quantitative analysis of in-situ NaI measured spectra in the marine environment using a wavelet-based smoothing technique.

An algorithm for automated analysis of in-situ NaI γ-ray spectra in the marine environment is presented. A standard wavelet denoising technique is implemented for obtaining a smoothed spectrum, while the stability of the energy spectrum is achieved by taking advantage of the permanent presence of two energy lines in the marine environment. The automated analysis provides peak detection, net area calculation, energy autocalibration, radionuclide identification and activity calculation. The results of the algorithm performance, presented for two different cases, show that analysis of short-term spectra with poor statistical information is considerably improved and that incorporation of further advancements could allow the use of the algorithm in early-warning marine radioactivity systems.

Irradiation of 4''x4'' NaI(Tl) detector by the 14 MeV neutrons.

Within the EURopean Illicit TRAfficking Countermeasures Kit (EURITRACK) project, a new Tagged Neutron Inspection System (TNIS) has been developed and installed in the Port of Rijeka in Croatia. The system was based on the examination of sea containers with the 14 MeV neutron beam. During the operation the characteristic gamma rays were produced and measured by several 5''x5''x10'' NaI(Tl) detectors. During this procedure some of the detectors were exposed to an intensive neutron beam radiation. It was necessary to check for possible radiation damage of the NaI(Tl) scintillator during the gamma detector selection phase of the project. The 4''x4'' NaI(Tl) detector was exposed to 14 MeV neutrons for 20 h. From the presented results on energy resolution and activation measurements it could be concluded that there are no significant differences in energy resolution before and after the irradiation by 4.7x10(11) of 14 MeV neutrons. The only problem could be the high level of medium and long term induced activity in the energy region below 2 MeV.

Monte Carlo calibration of whole-body counters with NaI(Tl) detectors in stretcher geometry.

A usercode for the EGSnrc Monte Carlo package has been developed for the simulation of whole-body counters with NaI(Tl) detectors in stretcher geometry. The geometry of the whole-body counter and the information about the detectors are specified in a plain text file, which enables users to easily adapt the codes to their installation. Bottle phantoms consisting of 1 and 2 l Cautex bottles filled with the radionuclide dissolved in water have been modelled as phantoms depicting the human body to be measured. These kind of phantoms can be defined by the users in the input file. Sets of efficiency factors for calculating activities from counts in measured spectra have been generated by two methods: 'direct simulation of nuclide decay' uses compiled data on photon energies and yields for all nuclides of interest and simulates a given number of decays of those nuclides for phantom masses from 10 to 100 kg while 'single-energy simulation' uses idealized 'nuclides' with single-energy emissions of 100 % yield to study the response of the systems over the energy range of interest (0-2000 keV in 20-keV steps). At University Hospital of Cologne and Karlsruhe Institute of Technology both methods have been successfully applied for the evaluation of spectra measured within intercomparison exercises.

A new experimental procedure for determination of photoelectric efficiency of a NaI(Tl) detector used for nuclear medicine liquid waste monitoring with traceability to a reference standard radionuclide calibrator.

To determine photopeak efficiency for (99m)Tc of the NaI(Tl) detector used for liquid waste monitoring at the Nuclear Medicine Unit of IRCCS Paediatric Hospital Bambino Gesù in Rome, a specific experimental procedure, with traceability to primary standards, was developed. Working with the Italian National Institute for Occupational Prevention and Safety, two different calibration source geometries were employed and the detector response dependence on geometry was investigated. The large percentage difference (almost 40%) between the two efficiency values obtained showed that geometrical effects cannot be neglected.

Gamma spectrum unfolding for a NaI monitor of radioactivity in aquatic systems.

Spectrum unfolding is a powerful method that can enhance the readability of experimental energy spectra obtained by detectors of poor resolution. It is applied to the NaI-based monitor. The UMG 3.3 package is used for unfolding the experimental spectra with the response matrix obtained by MCNP4c2. The main parameter influencing the quality of the results is the chi(2). The goal of this study is to optimize the choice of this factor. The statistical accuracy of the technique is evaluated.

Deconvolution of gamma-ray spectra obtained with NAI(Tl) detector in a water tank.

Maximum-likelihood fitting by the expectation maximization deconvolution method is presented to analyse gamma-ray spectra recorded using an NaI(Tl) detector for a water monitoring system. The applicability of the method was tested by deconvolving measured spectra taken using an industry standard 3'' x 3'' cylindrical NaI(Tl) detector in a model water tank with several calibration sources. The results show significant removal of the Compton continuum counts and efficient transfer of the counts into the corresponding photo-peaks. The peak-to-total count ratio and the number of counts in the photo-peaks in the deconvolved spectra increased approximately 4.67 and 5.29 times, respectively, compared with those of measured spectra taken using an NaI(Tl) scintillation detector in the case of (137)Cs.

Response function of NaI(Tl) detectors and multiple backscattering of gamma rays in aluminium.

The response function, converting the observed pulse-height distribution of a NaI(Tl) detector to a true photon spectrum, is obtained experimentally with the help of an inverse matrix approach. The energy of gamma-ray photons continuously decreases as the number of scatterings increases in a sample having finite dimensions when one deals with the depth of the sample. The present experiments are undertaken to study the effect of target thickness on intensity distribution of gamma photons multiply backscattered from an aluminium target. A NaI(Tl) gamma-ray detector detects the photons backscattered from the aluminium target. The subtraction of analytically estimated singly scattered distribution from the observed intensity distribution (originating from interactions of primary gamma-ray photons with the target) results in multiply backscattered events. We observe that for each incident gamma photon energy, the number of multiply backscattered photons increases with increase in target thickness and then saturates at a particular target thickness called the saturation thickness (depth). Saturation thickness for multiply backscattering of gamma photons is found to decrease with increase in energy of incident gamma-ray photons.

An approximation for response function to gamma-rays of NaI(Tl) detectors up to 1.5 MeV.

The response functions of a 7.62 x 7.62 cm NaI(Tl) scintillation detector to photons from point gamma-ray sources, 10 cm from the scintillator surface, in the energy up to 1.5 MeV, were calculated using the Monte Carlo method, applying simple approximations based on the peak to total ratio and the detector resolution. The Compton continuum of the detector response function was assumed as an isotropic (rectangular) region for the photon energies up to 1 MeV. In the energies between 1 and 1.5 MeV, the Compton continuum was obtained assuming a single Compton scattering with free electrons. The photopeak of the detector response function was assumed as a line. Each determined channel of the response function was distributed to Gaussian functions. The obtained response functions were compared with the experimental values and a good agreement was found.

Towards the use of small amounts of activated charcoal along with well-type NaI(Tl) detector for indoor radon measurements.

The feasibility of using small quantities of activated charcoal and a 7.6 cm x 7.6 cm NaI(Tl) well-type detector was investigated for indoor radon measurements. Vials, filled with 10 g of charcoal, were exposed for different indoor radon concentration levels typical of Kuwait dwellings. After exposure, the vials were sealed and kept for 3 h to allow radon to come into radioactive equilibrium with its progenies and were then analysed by gamma-ray spectrometry using the well-type NaI(Tl) detector. The variation of radon absorption by the vials filled with charcoal with exposure time was also studied. A comparative study of the present technique with the standard technique of using 70 g charcoal canisters and flat NaI detector was also performed. After establishing the suitability of the technique, the charcoal vials were then used to investigate the effect of air-ventilation on the concentration levels of the indoor radon. Results show that there is a reduction in the radon concentration level (up to 25%) when the air-ventilation system was switched on. The paper presents the results of the study on the feasibility of combining small amounts of activated charcoal with a well-type NaI(Tl) detector in the measurement of indoor radon concentrations.

Performance improvement of small gamma camera using NaI(Tl) plate and position sensitive photo-multiplier tubes.

The purpose of this study was to improve the performance of a small gamma camera, utilizing a NaI(Tl) plate and a 5" position sensitive PMT. We attempted to build a NaI(Tl) plate crystal system which retained all its advantages, while at the same time integrating some of the advantages inherent in an array-type scintillation crystal system. Flood images were obtained with a lead hole mask, and position mapping was performed by detecting hole positions in the flood image. Energy calibration was performed using the energy spectra obtained from each hole position. Flood correction was performed using a uniformity correction table containing the relative efficiency of each image element. The spatial resolution was improved about 16% after correction at the centre field of view. Resolution deterioration at the outer field of view (OFOV) was considerably ameliorated, from 6.7 mm to 3.2 mm after correction. The sensitivity at the OFOV was also increased after correction, from 0.7 cps microCi(-1) to 2.0 cps microCi(-1). The correction also improved uniformity, from 5.2% to 2.1%, and linearity, from 0.5 mm to 0 mm. The results of this study indicate that the revised correction method can be employed to considerably improve the performance of a small gamma camera using a NaI(Tl) plate-type crystal. This method also provides high spatial resolution and linearity, like array-type crystals do, while retaining the specific advantages of plate-type crystals.

Standardization of 67Ga by 4pigamma (NaI) and 4pibeta-gamma coincidence methods.

The nuclide 67Ga is widely used in nuclear medicine for diagnostic purposes. It decays with a half-life of 3.259 days to 67Zn, a stable nuclide. The decay mode is electron capture with several branches followed by gamma-de-excitation. One of the excited levels of 67Zn with energy 93 keV has a half-life of 9.1 micros, which makes its absolute standardization by coincidence methods difficult. Two methods were used to standardize a solution of this nuclide: (a) 4pi-EC(PPC)-gamma(NaI) coincidence counting with efficiency extrapolation to infinite dead time and (b) high-efficiency 4pigamma counting with a well-type NaI detector.

Quality management program and misadministrations--Nuclear Regulatory Commission. Final rule.

The Nuclear Regulatory Commission (NRC) is amending regulations governing therapeutic administrations of byproduct material and certain uses of radioactive sodium iodide to require implementation of a quality management program to provide high confidence that the byproduct material or radiation from byproduct material will be administered as directed by an authorized user physician. The Commission believes this performance-based amendment will result in enhanced patient safety in a cost-effective manner while allowing the flexibility necessary to minimize intrusion into medical judgments. This amendment also modifies the notification, reporting, and recordkeeping requirements related to the quality management program and misadministrations.