Gamma-ray Energy Spectra Research Articles

Least-squares fitting algorithm for peak pile-up correction in gamma-ray spectroscopy

In gamma-ray spectroscopy, a pulse pile-up occurs when a gamma-ray hits the detector within a time period shorter than the duration of the pulse induced by a preceding gamma-ray. The resulting pulse is the sum of two overlapping pulses. At a high counting rate, the pulse pile-up can lead to significant loss of data and/or deterioration of the measured gamma-ray energy spectrum. If the temporal separation of consecutive gamma-ray events is small enough, the resulting pile-up pulse exhibits only a single peak. Such events are described as peak pile-ups. It is not trivial to detect and correct peak pile-ups. Consequently, such events are typically wrongly reconstructed as a single pulse or rejected by the pile-up correction algorithms developed to date. We study a least-squares fitting algorithm modified to include detection and correction of peak pile-ups. Performance of the proposed algorithm is studied using data measured with LaBr3:Ce scintillator and a 400 MBq 137Cs source as well as with artificially synthesized pile-up data. The pile-up correction success rate grows rapidly with the temporal separation of piled-up pulses and reaches 50% as soon as the pulses are separated by a time at least of the order of the single pulse rise time. A success rate exceeding 90% is reached for the temporal separation equal to about twice the rise time. The reconstruction efficiency measured as the overall rate of the successful reconstruction of the double-pulse pile-up is about 92%.

Activation analysis for the reference low-activation vanadium alloy NIFS-HEAT-2

• Activation analysis was performed for a NIFS-HEAT2 (V-4Cr-4Ti) sample. • The sample was irradiated in Japan Material Testing Reactor (JMTR) ~15 years before. • Detected impurities were 0.41 wppm Co and 0.71 wppm Nb. • Ag impurity concentration was estimated to be <0.034 wppm. • Results are supporting the superior low activation properties of NIFS-HEAT-2. Activation analysis of impurities was performed on a test specimen of the reference low-activation vanadium alloy NIFS-HEAT-2 (V-4Cr-4Ti) which has been irradiated in Japan Materials Testing Reactor (JMTR) ~16 years before. Since the radioactive nuclides from V, Cr and Ti are produced with short half-lives, intense peaks of 60 Co (T 1/2 = 5.27 years) were dominant in the measured gamma-ray energy spectra and peaks of 94 Nb (2.03 × 10 4 years) were also observed. The concentrations were evaluated to be 0.41 wppm and 0.71 wppm respectively from comparison with results of radioactivity calculation using the FISPACT-2005 code. In the analysis, detection of 108m Ag (418 years), which would have a considerable influence on the material recycling after the usage in a fusion reactor, was intense motivation. Although the peaks of 108m Ag has not been detected, the concentration of Ag was estimated to be <0.034 wppm from analysis of detection limit in gamma-ray peak count. Gamma-ray peaks originated from other impurity elements were not observed in the spectra, and the present analysis are supporting the superior low activation properties of NIFS-HEAT-2.

Search for dark matter signatures in the gamma-ray emission towards the Sun with the Fermi Large Area Telescope

Dark matter particles from the Galactic halo can be gravitationally trapped in the solar core or in external orbits. The enhanced density of dark matter particles either in the solar core or in external orbits can result in the annihilation of these particles producing gamma rays via long-lived intermediate states or directly outside the Sun, respectively. These processes would yield characteristic features in the energy spectrum of the subsequent gamma rays, i.e., a box-like or line-like shaped feature, respectively. We have performed a dedicated analysis using a 10-years sample of gamma-ray events from the Sun collected by the Fermi Large Area Telescope searching for spectral features in the energy spectrum as a signature of dark matter annihilation. In the scenario of gamma-ray production via long-lived mediators we have also evaluated the dark matter-nucleon spin-dependent and spin-independent scattering cross section constraints from the flux limits in a dark matter mass range from 3 GeV/c$^2$ up to about 1.8 TeV/c$^2$. In the mass range up to about 150 GeV/c$^2$ the limits are in the range $10^{-46} - 10^{-45}$ cm$^{2}$ for the spin-dependent scattering and in the range $10^{-48} - 10^{-47}$ cm$^{2}$ for the spin-independent case. The range of variation depends on the decay length of the mediator.

GAMMA DOSE RATES IN THE HIGH BACKGROUND RADIATION AREA OF MANGALORE REGION, INDIA.

Elevated levels of natural background radiation due to scattered patches of monazite sand around the beaches of Mangalore, India, have been reported earlier. A comparative study of gamma dose rates was performed in both normal background and high natural background radiation areas around Mangalore using different types of portable gamma dosimeters. In addition to this, gamma-ray energy spectra were acquired, in situ, using a NaI(Tl) based portable gamma spectrometer. Soil and sand samples were collected for laboratory analysis with HPGe detectors. Measurements were carried out during the years 2016-18 revealed that in majority of the locations the gamma dose rates were similar to the normal background regions, whereas, in certain locations the dose rates were higher with values up to 530 nSv/h.

Investigation of accelerated carbon ions with the presence of QED effect by ultra-intense high-power lasers

In this study, we have investigated carbon ions, fast electrons and gamma-ray energy spectra and the corresponding temperatures when next-generation 10 petawatt (PW) lasers (irradiances of $$5\times 10^{22} \, {\mathrm {W}}\, {\mathrm {cm}}^{-2}$$ ) hit solid targets with a preformed plasma at the front surface. We employed 2D particle-in-cell (PIC) code with the presence of quantum electrodynamics (QED) effects. The maximum energy reached by the accelerated particles, and the corresponding temperature due to nonlinear plasma processes can be affected by varied plasma scale lengths. Here, we show the effects of varied plasma scale lengths on particle acceleration at irradiances on the order of $$10^{22}\,{\mathrm {W}}\,{\mathrm {cm}}^{-2}$$ , which is a new development for laser technology. We have observed that fully ionized carbon ions can reach up to 2.5 GeV energies with an optimum plasma scale length of $$1\, \upmu \hbox {m}$$ and the corresponding temperature of 40 MeV. Accelerated electron energies reach up to 1.5 GeV with the temperatures of 50 MeV for 10 PW laser–plasma interactions with the presence of QED effects. We have demonstrated that by varying plasma scale length, heavy ion energy and temperature can be controlled, which is important for various applications such as hadron therapy and X-ray imaging.

Modern African nuclear detector laboratory

The upcoming detector facility aims at developing new state-of-the-art particle detectors as well as providing hands-on training to postgraduate students using both analog and digital signal processing from nuclear radiation detectors. The project is two-fold and aims at developing: 1) ancillary detectors to be coupled with the new GAMKA array at iThemba LABS. Of particular interest to our group is the determination of nuclear shapes, which depend on the hyperfine splitting of magnetic substates; 2) PET scanners for cancer imaging using a cheaper technology. Performance of NaI(Tl) inorganic scintillator detectors has been evaluated using PIXIE-16 modules from XIA digital electronics. Gamma-ray energy spectra were acquired from 60Co and 137Cs radioactive sources to calculate the detector resolution as well as to optimize the digital parameters. The present study focuses on improving and optimizing the slow and fast filter parameters for NaI(Tl) detectors which can eventually be used in the list mode of data aquisition.

Estimating QCD uncertainties in Monte Carlo event generators for gamma-ray dark matter searches

Motivated by the recent galactic center gamma-ray excess identified in the Fermi-LAT data, we perform a detailed study of QCD fragmentation uncertainties in the modeling of the energy spectra of gamma-rays from Dark-Matter (DM) annihilation. When Dark-Matter particles annihilate to coloured final states, either directly or via decays such as W(*)→ qq̄′, photons are produced from a complex sequence of shower, hadronisation and hadron decays. In phenomenological studies their energy spectra are typically computed using Monte Carlo event generators. These results have however intrinsic uncertainties due to the specific model used and the choice of model parameters, which are difficult to asses and which are typically neglected. We derive a new set of hadronisation parameters (tunes) for the PYTHIA 8.2 Monte Carlo generator from a fit to LEP and SLD data at the Z peak. For the first time we also derive a conservative set of uncertainties on the shower and hadronisation model parameters. Their impact on the gamma-ray energy spectra is evaluated and discussed for a range of DM masses and annihilation channels. The spectra and their uncertainties are also provided in tabulated form for future use. The fragmentation-parameter uncertainties may be useful for collider studies as well.

Structures of the intracloud electric field supporting origin of long-lasting thunderstorm ground enhancements

The problem of thundercloud electrification is one of the most difficult ones in atmospheric physics. The structure of electric fields in clouds escapes from the detailed in situ measurements; few balloon flights reveal these rather complicated structures. To gain insight into the problem of the charge structure of a thundercloud, we use new key evidence---the fluxes of particles from a thundercloud, the so-called thunderstorm ground enhancements---TGEs. TGEs originate from electron acceleration and multiplication processes in the strong electric fields in the thundercloud, and the intensity and energy spectra of electrons and gamma rays as observed on the Earth's surface are directly connected with the atmospheric electric field. Discovery of long-lasing TGEs poses new challenges for revealing structures in the thundercloud responsible for hours-extending gamma ray fluxes. In the presented paper, we demonstrate that experimentally measured intensities and energy spectra of the ``thundercloud particles'' give clues for understanding charge structures embedded in the atmosphere. A rather short ``runaway'' process above the detector site, which is consistent with the tripole structure of the cloud electrification, is changing to a much less energetic emission that lasts for hours. Measurements of enhanced particle fluxes are accompanied by the simulation experiments with corsika and geant4 codes.

In Situ Gamma-ray Spectrometry Using an LaBr3(Ce) Scintillation Detector

Background: A variety of inorganic scintillators have been developed and improved for use in radiation detection and measurement, and in situ gamma-ray spectrometry in the environment remains an important area in nuclear safety. In order to verify the feasibility of promising scintillators in an actual environment, a performance test is necessary to identify gamma-ray peaks and calculate the radioactivity from their net count rates in peaks. Materials and Methods: Among commercially available scintillators, LaBr3(Ce) scintillators have so far shown the highest energy resolution when detecting and identifying gamma-rays. However, the intrinsic background of this scintillator type affects efficient application to the environment with a relatively low count rate. An algorithm to subtract the intrinsic background was consequently developed, and the in situ calibration factor at 1 m above ground level was calculated from Monte Carlo simulation in order to determine the radioactivity from the measured net count rate. Results and Discussion: The radioactivity of six natural radionuclides in the environment was evaluated from in situ gamma-ray spectrometry using an LaBr3(Ce) detector. The results were then compared with those of a portable high purity Ge (HPGe) detector with in situ object counting system (ISOCS) software at the same sites. In addition, the radioactive cesium in the ground of Jeju Island, South Korea, was determined with the same assumption of the source distribution between measurements using two detectors. Conclusion: Good agreement between both detectors was achieved in the in situ gamma-ray spectrometry of natural as well as artificial radionuclides in the ground. This means that an LaBr3(Ce) detector can produce reliable and stable results of radioactivity in the ground from the measured energy spectrum of incident gamma-rays at 1 m above the ground.

Measurement of basic characteristics of scintillation-type radiation survey meters with multi-pixel photon counter

The basic characteristics of three low-cost radiation survey meters using multi-pixel photon counters (MPPC), the C12137, T-GMK2-S, and iMetry, were measured. The linearity of the dose rate was confirmed over the full range of each instrument. All the survey meters could obtain gamma-ray energy spectra, with an accuracy within ± 30% of the theoretical value. These survey meters are therefore applicable for radiation management.

Evaluation of Nuclear Warhead Symmetry Detection by Compton Camera

Compton camera is a promising instrument for nuclear material imaging in arms control scenarios. In planning to build a Compton camera to detect the symmetry of shielded nuclear materials, the energy spectrum of gamma-rays escaping from the Steve Fetter Nuclear Warhead model is obtained using Monte Carlo simulation. Then, a point model is defined for our study. The proposed Compton camera uses a 5-cm × 5-cm × 1-mm double-sided silicon strips detector as the scattering detector and a segmented ϕ5.08 × 5.08-cm NaI(Tl) array as the absorbing detector. How high-energy gamma-rays impact low-energy characteristic gamma-ray imaging is studied. The result shows that high-energy gamma-rays will reduce the imaging accuracy and signal-to-noise ratio. The holistic angle resolution measured can reach 4.15 deg by all characteristic gamma-rays. The symmetry research result shows that the Compton camera can detect the symmetry property of a nuclear warhead with obvious symmetry or asymmetry.

Feasibility of miniature radiation portal monitor for measurement of radioactivity contamination in flowing water in pipe

In this study, a miniature radiation portal monitor and an operation program were developed and tested for monitoring radioactive contamination of water caused by nuclear power plant accidents or unplanned release of radioactive materials. In order to set the optimum voltage of the detector, the voltage was increased by 1 V and the detection efficiency was measured. It was confirmed that the detector had a stable count and a high signal-to-noise ratio at 60 V. The detector response, gamma-ray energy spectrum, and energy linearity were tested using the detector with an applied voltage of 60 V. The R-square value of the detector response based on the intensity was 0.9980 and the R-square value of the channel linearity based on the energy was 0.9851, which indicates the detection characteristics to be very good. In addition, the system showed good resolution characteristics in which the gamma-ray emission energy 122 keV of the 57Co had an energy resolution of 16.02%, 662 keV of the 137Cs spectrum had 4.88%, and 1,332 keV of the 60Co had 2.02%. Based on the results from this study, it is determined that continuous research work may contribute in reducing the radioactive exposure caused by contamination of groundwater and drinking water in radioactive spill accidents.

Energy calibration for plastic scintillation detectors based on Compton scatterings of gamma rays

Plastic scintillation detector should be calibrated before using it. Therefore, this paper provides a practical and simple method to calibrate plastic scintillation detectors based on Monte Carlo simulation. Firstly, the responses of the plastic scintillation detector to gamma rays with different Gaussian Energy Broadening are simulated, and then the relationship between Gaussian Energy Broadening and shape of gamma ray energy spectrum is obtained. Secondly the energy spectrum meeting experiment can be simulated according to the relationship above. Then the information of energy spectrum acquired from experiment is confirmed with simulated energy spectrum, the plastic scintillation detector can be calibrated. Two radiation sources 22Na and 137Cs are applied to calibrate plastic scintillation detector in experiment based on this method.

Multiscale Spatial Density Smoothing: An Application to Large-Scale Radiological Survey and Anomaly Detection

ABSTRACTWe consider the problem of estimating a spatially varying density function, motivated by problems that arise in large-scale radiological survey and anomaly detection. In this context, the density functions to be estimated are the background gamma-ray energy spectra at sites spread across a large geographical area, such as nuclear production and waste-storage sites, military bases, medical facilities, university campuses, or the downtown of a city. Several challenges combine to make this a difficult problem. First, the spectral density at any given spatial location may have both smooth and nonsmooth features. Second, the spatial correlation in these density functions is neither stationary nor locally isotropic. Finally, at some spatial locations, there are very little data. We present a method called multiscale spatial density smoothing that successfully addresses these challenges. The method is based on recursive dyadic partition of the sample space, and therefore shares much in common with other multiscale methods, such as wavelets and Pólya-tree priors. We describe an efficient algorithm for finding a maximum a posteriori (MAP) estimate that leverages recent advances in convex optimization for nonsmooth functions.We apply multiscale spatial density smoothing to real data collected on the background gamma-ray spectra at locations across a large university campus. The method exhibits state-of-the-art performance for spatial smoothing in density estimation, and it leads to substantial improvements in power when used in conjunction with existing methods for detecting the kinds of radiological anomalies that may have important consequences for public health and safety.

Source Correlated Prompt Neutron Activation Analysis for Material Identification and Localization

This paper investigates the energy spectrum of photon signatures from an associated particle imaging deuterium tritium (API-DT) neutron generator interrogating shielded uranium. The goal is to investigate if signatures within the energy spectrum could be used to indirectly characterize shielded uranium when the neutron signature is attenuated. By utilizing the correlated neutron cone associated with each pixel of the API-DT neutron generator, certain materials can be identified and located via source correlated spectrometry of prompt neutron activation gamma rays. An investigation is done to determine if fission neutrons induce a significant enough signature within the prompt neutron-induced gamma-ray energy spectrum in shielding material to be useful for indirect nuclear material characterization. The signature deriving from the induced fission neutrons interacting with the shielding material was slightly elevated in polyethylene-shielding depleted uranium (DU), but was more evident in some characteristic peaks from the aluminum shielding surrounding DU.

Technical Note: Monte Carlo calculations of the AAPM TG-43 brachytherapy dosimetry parameters for a new titanium-encapsulated Yb-169 source.

Due to a number of distinct advantages resulting from the relatively low energy gamma ray spectrum of Yb‐169, various designs of Yb‐169 sources have been developed over the years for brachytherapy applications. Lately, Yb‐169 has also been suggested as an effective and practical radioisotope option for a novel radiation treatment approach often known as gold nanoparticle‐aided radiation therapy (GNRT). In a recently published study, the current investigators used the Monte Carlo N‐Particle Version 5 (MCNP5) code to design a novel titanium‐encapsulated Yb‐169 source optimized for GNRT applications. In this study, the original MC source model was modified to accurately match the specifications of the manufactured Yb‐169 source. The modified MC model was then used to obtain a complete set of the AAPM TG‐43 parameters for the new titanium‐encapsulated Yb‐169 source. The MC‐calculated dose rate constant for this titanium‐encapsulated Yb‐169 source was 1.19 ± 0.03 cGy·h−1·U−1, indicating no significant change from the values reported for stainless steel‐encapsulated Yb‐169 sources. The source anisotropy and radial dose function for the new source were also found similar to those reported for the stainless steel‐encapsulated Yb‐169 sources. The current results suggest that the use of titanium, instead of stainless steel, to encapsulate the Yb‐169 core would not lead to any major change in the dosimetric characteristics of the Yb‐169 source. The results also show that the titanium encapsulation of the Yb‐169 source could be accomplished while meeting the design goals as described in the current investigators’ published MC optimization study for GNRT applications.

Peak center and area estimation in gamma-ray energy spectra using a Mexican-hat wavelet

Wavelet analysis is commonly used to detect and localize peaks within a signal，such as in Gamma-ray energy spectra. This paper presents a peak area estimation method based on a new wavelet analysis. Another Mexican Hat Wavelet Signal (MHWS) named after the new MHWS is obtained with the convolution of a Gaussian signal and a MHWS. During the transform, the overlapping background on the Gaussian signal caused by Compton scattering can be subtracted because the impulse response function MHWS is a second-order smooth function, and the amplitude of the maximum within the new MHWS is the net height corresponding to the Gaussian signal height, which can be used to estimate the Gaussian peak area. Moreover, the zero-crossing points within the new MHWS contain the information of the Gaussian variance whose valve should be obtained when the Gaussian peak area is estimated. Further, the new MHWS center is also the Gaussian peak center. With that distinguishing feature, the channel address of a characteristic peak center can be accurately obtained which is very useful in the stabilization of airborne Gamma energy spectra. In particular, a method for determining the correction coefficient k is given, where the peak area is calculated inaccurately because the value of the scale factor in wavelet transform is too small. The simulation and practical applications show the feasibility of the proposed peak center and area estimation method.

Measurement of the gamma-ray energy spectrum of the educational Kinki University Reactor (UTR-KINKI)

The gamma-ray energy spectrum of the Kinki University Reactor (UTR-KINKI) was estimated from Ge detector measurements combined with Monte Carlo N-particle transport criticality calculations. The gamma rays mainly originated from prompt fission components, although small amounts of gamma rays from (n,γ) reactions, fission product gamma rays, and activation gamma rays were detected. The averaged gamma-ray tissue kerma rate in the irradiation port during UTR-KINKI operation at 1W was calculated as 10.5cGy/h based on the estimated gamma-ray energy spectrum. This value is consistent with a previous measurement with paired ionization chambers and a tissue equivalent gas proportional counter. This result demonstrates the reliability of the estimated gamma-ray energy spectrum.

Study of gamma spectrometry laboratory measurement in various sediment and vulcanic rocks

Gamma-ray spectroscopy is the quantitative study of the energy spectra of gamma-ray sources. This method is powerful to characterize some minerals, especially to differentiate rocks which contains among Potassium, Uranium, dan Thorium. Rock contains radioactive material which produce gamma rays in various energies and intensities. When these emissions are detected and analyzed with a spectroscopy system, a gamma-ray energy spectrum can be used as indicator for mineral content of rock. Some sediment and vulcanic rock have been collected from East Java Basin. Samples are ranging from Andesite vulcanics, Tuff, Shale, various vulcanic clay and Alluvial clay. We present some unique characteristics of gamma spectrometry in various sedimentar and vulcanic rocks of East Java Basins. Details contents of gamma ray spectra give enrichments to characterize sample of sediment and vulcanic in East Java. Weathered vulcanic clay has lower counting rate of gamma ray than alluvial deltaic clay counting rate. Therefore, gamma spectrometrometry can be used as tool for characterizing the enviroment of clay whether vulcanic or alluvial-deltaic. This phenomena indicates that gamma ray spectrometry can be as tool for characterizing the clay whether it tends to Smectite or Illite

Feasibility study on real-time γ-ray spectrum / dose measurement system

Recently, medical applications of radiation have been widely spread. However, exposure of medical staffs is sometimes not focused on because treatment of patients is the first priority. It is thus important to decrease exposure for them as much as possible. The purpose of this study is to develop a system which can measure energy spectrum and dose of gamma-rays at the same time in real time in medical application spots. As a result, the medical staff could be guided to aware the risk of radiation and finally the exposure dose to them could be suppressed substantially. We first decided to use a CsI(Tl) scintillator as the gamma-ray detection device. A Multi-Pixel Photon Counter (MPPC) was attached to the scintillator to detect gamma-ray signals. Pulse height spectra were measured with several standard gamma-ray sources. The detection efficiency and energy resolution were deduced from the measured results and the detection efficiency was compared with the calculation result by MCNP5. After evaluating the response function, the energy spectrum was derived with the spectrum type Bayesian estimation and the sequential Bayesian estimation procedure. From the result, it was confirmed that the sequential Bayesian estimation could be applied to real time measurement of gamma-ray energy spectrum and dose.