Weak Radioactive Sources Research Articles

Experimental investigation of gamma-ray interaction parameters and buildup factors in lanthanide compounds: Insights into penetration depth

This experimental investigation focuses on the gamma-ray interaction parameters and the buildup factor in lanthanide compounds (CeO2, Ce(SO4)2, Dy2(SO4)3, C3O9Sm2, C3Gd2O9, Pr2O3). These compounds were exposed to weak radioactive gamma sources with energies of 356, 511, 662, 1173, 1275, and 1332 keV by adopting narrow and broad beam geometry experimental arrangements. The incident and transmitted radiation intensities were measured using a NaI (Tl) detector. Experimentally measured values of mass attenuation coefficient and effective atomic number of lanthanide compounds were found to be in precise agreement with theoretical values obtained from NIST XCOM and Direct-Zeff database respectively. Additionally, the experimentally determined buildup factor values were compared with energy absorption buildup factor (EABF) and exposure buildup factor (EBF) values obtained from Phy-X/PSD software, providing insights into the gamma-ray penetration depth in terms of mean free path (MFP). At 356 keV, the EABF analysis showed that most compounds had a penetration depth of around 8 mean free paths. In contrast, the EBF analysis indicated penetration depths exceeding 10 mean free paths for all compounds except Ce (SO4)2. This new approach holds immense potential for transformative advancements in medical diagnostics, therapy, and the development of innovative technologies in nuclear sciences.

An experimental approach to determine the gamma radiation interaction mean free path and exposure buildup factor for biomolecules

This experimental approach was designed to understand the gamma interaction parameters for the essential biomolecules, including starch soluble, cholesterol, myristic acid, glucose, oxalic acid, dextrose, salicylic acid, ethyl cellulose and sucrose. The empirical determination of gamma interaction parameters, such as interaction mean-free-path (MFP), buildup factor, and effective atomic number (Zeff) was performed by measuring mass attenuation coefficient (μ/ρ) at energies of 356 keV, 511 keV, 662 keV, 1173 keV, 1275 keV and 1332 keV. This was achieved using weak radioactive sources and a NaI(Tl) scintillation spectrometer with collimated and non-collimated transmission geometry. The experimentally determined values of gamma-ray interaction parameters were obtained non-destructively and precisely agreeing with the expected values from simulations and codes. In addition, the research findings also revealed a novel trend in gamma interaction mean free path as a function of energy and variable buildup factors for the selected biomolecules. These research findings provide valuable insight into the process of gamma radiation interaction. This approach may fulfil the increasing demand of medical, technical and academic research laboratories for a cost-effective and reliable empirical methodology to understand gamma radiation interaction with matter.

Detecting and tracking multiple mobile radioactive sources by data fusion of a surveillance camera and a sodium iodide (NaI) detector.

Nowadays, the use of radioactive materials has increased due to recent progress in nuclear technology, but concerns about the missing or smuggling of radioactive materials have persisted. Nuclear threats such as terrorist attacks or the malicious use of radioactive materials out of regulatory control (MORC) are always severe problems that can result in adverse environmental, health, economic, and security effects. Applying new technologies to monitor and track MORC will prevent radioactive materials from being illegally transported across borders or from one place to another. In this research, we have constructed a detection system to automatically and remotely localize multiple mobile gamma-emitting radiation sources among other objects by combining an IP camera and a sodium iodide detector. An algorithm for the detection system has been developed to identify the objects' paths from camera data and correlate radiation data with the paths to detect contaminated objects. We evaluated the system using two weak radioactive sources (Co-60, Cs-137), which were hidden on moving objects, and succeeded in finding harmful targets. The results have also shown that by increasing the number of contaminated sources from one to two, the detection accuracy decreases by about 2.5 times. However, by doubling the speed of mobile targets, the detection accuracy improved by about 30%. Detecting and tracking MORC with a single detection system is limited to small regions. By equipping many surveillance cameras in a city with relatively inexpensive radioactive detectors, a network sensing system is established to find radioactive hotspots in a smart city.

Data-driven head motion correction for PET using time-of-flight and positron emission particle tracking techniques.

Positron emission tomography (PET) is susceptible to patient movement during a scan. Head motion is a continuing problem for brain PET imaging and diagnostic assessments. Physical head restraints and external motion tracking systems are most commonly used to address to this issue. Data-driven methods offer substantial advantages, such as retroactive processing but typically require manual interaction for robustness. In this work, we introduce a time-of-flight (TOF) weighted positron emission particle tracking (PEPT) algorithm that facilitates fully automated, data-driven head motion detection and subsequent automated correction of the raw listmode data. We used our previously published TOF-PEPT algorithm Dustin Osborne et al. (2017), Tasmia Rahman Tumpa et al., Tasmia Rahman Tumpa et al. (2021) to automatically identify frames where the patient was near-motionless. The first such static frame was used as a reference to which subsequent static frames were registered. The underlying rigid transformations were estimated using weak radioactive point sources placed on radiolucent glasses worn by the patient. Correction of raw event data were achieved by tracking the point sources in the listmode data which was then repositioned to allow reconstruction of a single image. To create a "gold standard" for comparison purposes, frame-by-frame image registration based correction was implemented. The original listmode data was used to reconstruct an image for each static frame detected by our algorithm and then applying manual landmark registration and external software to merge these into a single image. We report on five patient studies. The TOF-PEPT algorithm was configured to detect motion using a 500 ms window. Our event-based correction produced images that were visually free of motion artifacts. Comparison of our algorithm to a frame-based image registration approach produced results that were nearly indistinguishable. Quantitatively, Jaccard similarity indices were found to be in the range of 85-98% for the former and 84-98% for the latter when comparing the static frame images with the reference frame counterparts. We have presented a fully automated data-driven method for motion detection and correction of raw listmode data. Easy to implement, the approach achieved high temporal resolution and reliable performance for head motion correction. Our methodology provides a mechanism by which patient motion incurred during imaging can be assessed and corrected post hoc.

Experimental investigation of ion recombination in a locally made low-voltage ionization chamber

In this study, the weak alpha radiation sources and the beta radiation by the effect of them on the electrical conductivity of air inside the ionization chamber are studied by measuring the produced current. The aim of this study is to make an ionization chamber to measure the ionization caused by weak radioactive sources which produce the electrical current at the order of femto- to pico-amperes and try to estimate the ion recombination coefficient at low ion densities. A parallel-plate ionization chamber with proper shielding and noise reduction circuits are made which measure data and sent them to a personal computer by USB port. The current-voltage characteristics of the ion chamber are measured when different radioactive sources are placed inside the chamber at the different separation of electrodes. The recombination constant obtained is estimated equal to 1.18 × 10−6 cm3/s. It is shown that current-voltage characteristic for ion chamber with different electrode separation lies on a unique curve by a proper normalization in the pico- and femto-ampere current range.

Enhancing the sensitivity for weak radioactive source detection

Considering the difficulties of the low signal-to-noise ratio in weak radioactive source detections, this study proposes an abandon Gaussian tails method based on the analysis of the characteristic information denoted by the full-energy peak of the gamma spectrum of a gamma-emitting radioactive source. Based on the study of the signal-to-background ratio and the statistical fluctuations in the signal of the weak radioactive source, a factor ζ, incorporating the statistical fluctuations of signal and background and the signal-to-background ratio, is suggested to characterize the sensitivity of a radioactive source detection. When ζ reaches its maximum value, the optimal counting window around the centroid of the full-energy peak can be obtained. To evaluate the effectiveness of the proposed approach, comparisons between the proposed abandon Gaussian tails, the conventional full-energy counting, and other experiential methods were performed. The results show that the sensitivity can be significantly improved. Further, experiments with different intensity of radiation sources and duplicated experiments were conducted to examine the stability of the proposed method.

Determination of effective atomic number of multifunctional materials using backscattered beta particles – a novel method

The effective atomic number of multifunctional composite materials has been determined experimentally by adopting backscattering of beta particles technique. A 2.2 MeV beta particles emitted from a weak radioactive beta source were allowed to backscatter at an angle of 150 degrees from the elemental and composite targets. The backscattered beta particles were detected with the end window Geiger–Mueller gas detector. Experimentally, it is observed that the yield of the backscattered beta particle increases with increasing the target thickness for pure elements. Then, the yield of backscattering beta particle saturates after a certain thickness. The linear fit between the saturated thickness and the atomic number of the elemental target has been used to determine the effective atomic number of composite materials. The determined Zeff values of multifunctional composite targets have been compared with the values obtained by Monte Carlo method and computational codes.

Controlled Mobile Radiation Detection Under Stochastic Uncertainty

Building upon recent insights on the effect of sensor mobility on the detection performance of mobile radiation sensors, this letter analyzes the impact of stochastic noise in the motion of the sensors on their decision-making accuracy. A stochastic optimal control law for the sensors is designed to maximize decision-making performance. Numerical simulations indicate that noisy sensor motion significantly reduces decision-making accuracy, and is especially detrimental to the detection of weak radioactive sources.

Experimental special relativity with a meter stick and a clock

We present measurements of the velocity of electrons, performed with an apparatus using the time-of-flight method, to demonstrate that the speed of light c is the limiting speed for electrons. The results obtained show the applicability of relativity in a regime where nonrelativistic physics predicts velocities exceeding c. The main advantages of the apparatus are the simplicity of its operation and the data analysis. By using electrons from weak radioactive sources the experiment is suitable for the undergraduate laboratory. Furthermore, we show that with electrons from a linear accelerator and the same apparatus, excellent agreement between data and the relativistic expression for the speed of electrons in the keV-MeV energy range is observed.

Studies for software optimization for gross counting portal monitors

After investigating several possible source-detection algorithms for gross-counting radiation portal monitors, a program has been developed to locate signals from weak radioactive sources in real time. By using a smoothing method of weighted moving averages and by including corrections for background suppression due to the presence of large vehicles as well as changing background levels, this program was capable of detecting significantly weaker sources than current software during testing. The limitations of this method are discussed.

Efficient strategies for low-statistics nuclear searches

We demonstrate that with statistically accurate strategies the reliability, speed, and sensitivity of nuclear search can be significantly improved. We offer two efficient strategies for the quick localization of a weak radioactive source in a large search area. The comparison of our search strategies with a simple uniform search shows improvement of the average search time by 5-10 times. We show that the proposed search strategies significantly reduce the search time while keeping the number of both false negatives and false alarms under control.

K-shell fluorescence yields of medium and heavy elements using a simple method

K-shell fluorescence yields, ω K , of medium and heavy elements in the atomic number range 62 ≤ Z ≤ 83 at incident photon energies of 123.6 and 320 keV were measured by adopting the simple method proposed earlier, using an NaI(Tl) detector coupled to an active filter amplifier and a 1K multi-channel analyser. The intensities were measured by placing the source and the target right on the face of the detector and by employing very weak radioactive sources ( 57 Co and 51 Cr) of the order of 10 4 Bq. Measured values were compared with the recent standard fitted values of Hubbell et al., and were found to be in close agreement. The ω K values of bismuth, gold, tungsten, gadolinium and samarium were measured for the first time.

K-shell fluorescence yields of medium and heavy elements using a simple method

K-shell fluorescence yields, ωK, of medium and heavy elements in the atomic number range 62⩽Z⩽83 at incident photon energies of 123.6 and 320 keV were measured by adopting the simple method proposed earlier, using an NaI(Tl) detector coupled to an active filter amplifier and a 1K multi-channel analyser. The intensities were measured by placing the source and the target right on the face of the detector and by employing very weak radioactive sources (57Co and 51Cr) of the order of 104 Bq. Measured values were compared with the recent standard fitted values of Hubbell et al., and were found to be in close agreement. The ωK values of bismuth, gold, tungsten, gadolinium and samarium were measured for the first time. © 1998 John Wiley & Sons, Ltd.

Method for the Determination of K Shell Fluorescence Yields

A simple method is proposed for determining the K shell fluorescence yield, ω K , using an NaI(Tl) detector coupled to an active filter amplifier and a 1K multi-channel analyser. By placing the target and the source right on the face of the detector, that is, by forming a 2π geometrical configuration, the intensities are measured by employing weak radioactive sources of strengths of the order of 10 4 Bq. The target criterion is suggested following Bambynek et al.'s prescription for optimization of target thickness. The ω K values were determined using several trials for each target to demonstrate the reliability and reproducibility of the method. The ω K values were obtained for lead, tantalum and gold elemental targets, and also for lead compounds and for some rare earth compounds. These values were compared with the recent standard fitted values of Hubbell et al. and were found to be in close agreement. The method is discussed in detail.

Escaping charged fusion product spectrometer on Alcator C-Mod

A spectrometer for studying escaping charged fusion products has been designed, built, and installed on the Alcator C-Mod tokamak. The ultimate goal of deploying this diagnostic is to evaluate the effectiveness of 3He minority heating through the broadened spectrum of unconfined 14.7 MeV protons from D-3He reactions. Other physics issues that will be addressed with this diagnostic include: first-orbit losses, central ion temperature, 3He burnup, etc. The spectrometer is located 25.8 cm below the midplane and at least 5 cm behind the shadow of the rf limiter. The diagnostic is equipped with a 300 μm thick ion-implanted-silicon detector that is bakeable up to 200 °C. Eighteen apertures of various dimensions and viewing angles, with aluminum foils of various thicknesses, allow for a choice of different charged fusion products and a control of the signal level. In-vessel calibration is provided by two weak radioactive sources of α particles.

Compensation schemes for peak-tailing uncertainties in PIXE spectra, using the GUPIX code

Many specimen types give rise to very intense peaks in the low-energy X-ray region of PIXE spectra. The tailing components of these peaks, arising in part from radiative Auger bands and from detector imperfections, are not perfectly known, and in the second case may exhibit dependence upon time and upon counting rate. A least-squares fit to the spectrum may therefore produce a channel versus energy relationship that is slightly in error; this in turn results in mis-fitting of the weak trace element peaks in the high-energy region of the spectrum. Two schemes are shown to avert this problem in the overall context of our GUPIX fitting code. One involves including X-rays from a weak radioactive source in the spectrum, which assists the code to converge to accurate energy calibration parameters. The other is a weighting scheme incorporated in GUPIX to de-emphasise the contribution of tailing features to the overall goodness-of-fit. Both are tested in some detail.

Gamma ray spectroscopy with high-Z thermal detectors

A massive thermal detector to be used to search for rare decays and to detect high-energy γ-rays has been operated both at sea level and underground. It consists of a 20.9 g monocrystal of TeO 2 whose temperature is measured by means of a neutron transmutation doped thermistor. The detector was first operated in Milano at a base bolometer temperature of 22.5 mK and with a FWHM resolution of 90 keV, rather independent of the γ-ray energy. Much better results have been obtained when the detector was operated underground, under a suitable shielding against local radioactivity and inside a Faraday cage. The base bolometer temperature could be as low as 14.5 mK which, together with the elimination of pile-up, allowed to achieve FWHM resolutions of 1% for γ-rays above 2.0 MeV. The increase in the base temperature of the bolometer when exposed to a weak radioactive source is discussed in view of possible applications in the search for dark matter.

Low-energy positron scattering from atomic hydrogen

The first and so far only experimental results on scattering of positrons from atomic hydrogen are reported. Total ionization cross sections as a function of energy have been measured at the University of Bielefeld [1] with a positron beam from a weak radioactive source. Due to the low beam intensity (< 3 × 10 3 e +/s) no other processes, such as positronium formation or differential elastic scattering, could be investigated yet. In a collaboration with groups from the Brookhaven National Laboratory (USA) and from the City College of the City University of New York these measurements will now be done using the high-intensity (up to 10 9 e +/s) positron beam at BNL [2], the concept of which will also be discussed briefly.

Compaction Monitoring in the Ekofisk Area Chalk Fields

In late Nov. 1984, the subsidence phenomenon was recognized in the Ekofisk field. To determine the magnitude and areal extent of the formation compaction, a program for measuring compaction with electric logging tools was initiated. Initial time-lapse surveys performed with cased-hole neutron tools indicated that reservoir compaction was occurring, but the accuracy of the determination of compaction rate was low. In addition to the cased-hole neutron survey, radioactive markers and a gamma ray (GR) detection tool were used to determine compaction rate in the reservoir more accurately and to determine whether compaction was occurring in the overburden. A program for implanting radioactive-marker bullets and subsequent monitoring with a four-detector GR tool was implemented. There are currently 13 wells equipped with radioactive markers in the compaction monitoring program. Compaction monitoring accuracy using the four-detector GR tool was found to depend on wellbore geometry, completion design, and radioactive-marker placement. This paper gives the results of the program to date and describes the operational procedures and analysis techniques used for compaction monitoring in the greater Ekofisk area chalk fields.

The optimal measurement time for short-lived weak radioactive sources

Abstract It is shown that an optimal measurement time can be simply determined for short-lived weak sources. The calculated values are presented in a widely applicable graphic form.