Low Energy Gamma Photons Research Articles

Investigation of shielding properties of gamma and neutrons in some natural radioprotective drugs

In radiation therapy, various radioprotective materials are used to protect normal cells from damage due to ionizing radiation. Natural products such as apigenin, bergenin, caffeine, chlorogenic acid, coniferyl aldehyde, curcumin, delphinidine, and quinic acid have been found to be good radioprotectors as they have low toxicities. In order to select the best natural radioprotector, it is essential to understand the interaction of gamma and neutrons with these radioprotectors and to determine radiation shielding parameters. The radiation parameters such as mass attenuation coefficient (MAC), effective atomic number (Zeff), equivalent atomic number (Zeq), effective electron density (Neff), exposure buildup factor (EBF), and energy absorption buildup factor (EABF) have been determined for the natural radioprotectors using EpiXs and NGCal software. The estimated results show that the Zeff values of selected radioprotectors are higher in the low-energy region and lower in the high-energy region, indicating that they are suitable for shielding low-energy gamma photons. Among selected natural radioprotectors, quinic acid is the best radioprotector for shielding thermal and fast neutrons. The relationship between MAF and Zeff/Neff has been established for the first time, and it has been found that MAF for thermal and fast neutrons decreases with an increase in the Zeff/Neff values of selected natural radioprotectors.

Performance evaluation of YAlO3 scintillator plates with different Ce concentrations

Since Ce-doped YAlO3 (YAP(Ce)) scintillators have small non-proportionality, it is useful to develop a radiation imaging detector for low-energy gamma photons or X-rays. However, the YAP(Ce) performance with different Ce concentrations remains unclear. Consequently, we measured the basic performance of YAP(Ce) plates with different Ce concentrations. We used three types of YAP(Ce) scintillator plates with different Ce concentrations: 0.05% Ce, 1% Ce, and 2% Ce. The YAP(Ce) plates were 10 mm × 10 mm x 0.5 mm. We measured and compared the energy spectra, the decay times, the α-γ ratio, and the non-proportionality. We also evaluated the relation between these performances and the Ce concentrations. The light output of a YAP(Ce) showed positive correlation with the Ce concentrations, and the decay time of the YAP(Ce) showed a negative correlation with them. The energy resolution slightly improved for a YAP(Ce) with higher Ce concentrations. We found the α-γ ratio were slightly larger for higher Ce concentrations. The YAP(Ce) plate with a 2% Ce had the highest light output and the best energy resolution as well as the shortest decay time. Based on these results, the YAP(Ce) plate with a concentration of 2% Ce is a better selection for the development of radiation detectors or radiation imaging detectors for low-energy gamma photons or X-rays as well as alpha particles.

Influence of background characteristics on the optimal sample filling height in gamma-ray spectrometry

The minimum detectable activity (MDA) for gamma spectrometric measurements was studied as a function of filling height for two detectors having different background characteristics and for two sample matrices: a water sample with a low content of natural radionuclides, and zircon sand, with high activities of uranium and thorium. The zircon sand is also a material in which the self-attenuation of low-energy gamma photons will be high. The results show that for the water sample it is always favourable to completely fill the sample container. However, due to the inherent content of naturally occurring radionuclides in the zircon sand the MDA may not necessarily improve with the filling height, since an increased amount of sample will increase the background in the spectrum as well.

An ultrahigh spatial resolution radiation-imaging detector using 0.1 mm × 0.1 mm pixelated GAGG plate combined with 1 mm channel size Si-PM array

Spatial resolution of a pixelated scintillator-based radiation-imaging detector is sometimes limited by the pixel size of the scintillators. We developed a small-size pixelated GAGG scintillator using a dicing method and combined it with a small channel-size Si-PM array for the development of an ultrahigh resolution radiation-imaging detector. The developed pixelated GAGG scintillator had a pixel size of 0.1 mm × 0.1 mm arranged in 0.15-mm separations. It was combined with a Si-PM array made of 1 mm × 1 mm channels to form a radiation-imaging detector. With the developed radiation imaging detectors, the 0.1 mm × 0.1 mm pixels could be resolved for Am-241 alpha particles (5.5 MeV). The spatial resolutions of this imaging detector were better than 0.31-mm FWHM for Am-241 alpha particles and Ca-45 (maximum energy: 0.257 MeV) beta particles. The spatial resolutions for Am-241 gamma photons (60 keV) and Cs-137 X-ray (∼32 keV) were better than 0.6-mm FWHM. Separation of the images of alpha particles and gamma photons was possible using the scintillation decay time difference of GAGG between alpha particles and gamma photons. The developed ultrahigh spatial resolution pixelated GAGG radiation-imaging detector is promising for the imaging of alpha particles, beta particles, low-energy gamma photons and X-ray.

Development of an event-by-event based radiation imaging detector using GGAG: A ceramic scintillator for X-ray CT

For a radiation imaging detector, low cost, high light output and short decay time scintillator is required. Although ceramic scintillators developed for X-ray computed tomography (CT) are possible materials for this purpose, the performance of the scintillation imaging detector using ceramic scintillators was not reported. For this purpose, we tested a ceramic scintillator originally developed for X-ray CT, Gd3(GaAl)5O12:Ce (GGAG), combined with a position sensitive photomultiplier (PSPMT) to test whether an event-by-event based radiation imaging detector is possible to develop. The radiation imaging detector consists of a 0.1 mm thick GGAG plate, light guide and a 1-inch square PSPMT. The GGAG plate was optically coupled to the PSPMT with a 1 mm thick light guide between them. Anger principle was used for the position calculation of the radiations. We also conducted the comparison of the imaging detectors using 0.5 mm thick GGAG and single crystal Ce doped Gd3(Ga, Al)5O12 (GAGG) plates. The spatial resolution and energy resolution of the developed imaging detector were 0.53mm FWHM and 11.5 % FWHM for 5.5 MeV alpha particles, respectively. The uniformity of the imaging detector at the central part of the field of view (FOV) was ±11%. We could obtain variable phantom images with the developed imaging detector for alpha particles. Reasonable performance was also obtained for beta particles, low energy gamma photons and X-ray. The spatial resolution of the imaging detector used GGAG plate was twice better and distortion was smaller than that of GAGG. We conclude that GGAG ceramic scintillator is promising for the development of radiation imaging detectors.

Development of ultrahigh resolution radiation imaging detector using 1 mm channel size Si-PM array combined with 0.2 mm × 0.2 mm pixelated GAGG plate

For precise distribution measurements of gamma photons or beta particles, high resolution radiation imaging detectors are required. Reducing the size of the photodetectors combined with small pixel scintillators is a possible method to improve the spatial resolution of the scintillator based radiation imaging detectors. In this paper, we used a 1mm channel size silicon photomultiplier (Si-PM) array combined with a small pixel scintillator array and evaluated the performance for gamma photons and beta particles. For the radiation imaging detector, a Si-PM array with 1mm × 1mm channel size arranged in 8 × 8 (Hamamatsu, S13615-1025N-08) was optically coupled to a 0.2 mm × 0.2 mm pixelated GAGG plate. For 662 keV high energy gamma photons, 0.2mm GAGG pixels were clearly resolved in the position histogram. The peak to valley ratio (P/V) of the position histogram was not improved when only photo-peak events were used while it was improved when the events lower energy than the Compton edge was used. We could also resolve the position histograms for both 122 keV and 60 keV gamma photons. For beta particles, although the position histogram showed good separation for relatively low energy beta particles of Ca-45 (245 keV max), separation became worse for higher energy beta particles from Sr-Y-90 (545keV and 2280keV max). The separation of the position histogram for Sr-Y-90 improved when only lower energy events were used. Using 1mm size Si-PM array, high resolution detectors was realized for low energy gamma photons and beta particle but the spatial resolution was decreased for high energy beta particles from Sr-Y-90.

In-situ formation of holmium oxide in pores of Mesoporous Carbon Nanoparticles as substrates for neutron-activatable radiotherapeutics

Radionuclide therapy with nano-sized carriers is a very promising approach to treat various types of cancer. The preparation of radioactive nanocarriers can be achieved with minimum handling using a neutron-activation approach. However, the nanocarrier material must possess certain characteristics such as low density, heat-resistance, high metal adsorption, easy surface modification and low toxicity in order to be useful. Mesoporous Carbon Nanoparticles (MCNs) in which holmium oxide is formed in their pores by a wet-impregnation process are investigated as a suitable material for this application. Holmium (165Ho) has a natural abundance of 100% and possesses a large cross-section for capturing thermal neutrons. After irradiation of Ho-containing MCNs in a neutron flux, 166Ho, which emits therapeutic high energy beta particles as well as diagnostic low energy gamma photons that can be imaged externally, is produced. The wet impregnation process (16 w/w% Ho loading) is shown to completely prevent the leaching of radioactive holmium from the MCNs without compromising their structural integrity. In vitro studies showed that the MCNs containing non-radioactive holmium do not exhibit toxicity and the same formulation with radioactive holmium (166Ho) demonstrated a tumoricidal effect. Post-irradiation PEGylation of the MCN surfaces endows dispersibility and biocompatibility.

Improvement in minimum detectable activity for low energy gamma by optimization in counting geometry

Gamma spectrometry for environmental samples of low specific activities demands low minimum detection levels of measurement. An attempt has been made to lower the gamma detection level of measurement by optimizing the sample geometry, without compromising on the sample size. Gamma energy of 50–200 keV range was chosen for the study, since low energy gamma photons suffer the most self-attenuation within matrix. The simulation study was carried out using MCNP based software “EffCalcMC” for silica matrix and cylindrical geometries. A volume of 250 ml sample geometry of 9 cm diameter is optimized as the best suitable geometry for use, against the in-practice 7 cm diameter geometry of same volume. An increase in efficiency of 10%–23% was observed for the 50–200 keV gamma energy range and a corresponding lower minimum detectable activity of 9%–20% could be achieved for the same.

A rapid dissolution procedure to aid initial nuclear forensics investigations of chemically refractory compounds and particles prior to gamma spectrometry

A rapid and effective preparative procedure has been evaluated for the accurate determination of low-energy (40–200 keV) gamma-emitting radionuclides (210Pb, 234Th, 226Ra, 235U) in uranium ores and uranium ore concentrates (UOCs) using high-resolution gamma ray spectrometry. The measurement of low-energy gamma photons is complicated in heterogeneous samples containing high-density mineral phases and in such situations activity concentrations will be underestimated. This is because attenuation corrections, calculated based on sample mean density, do not properly correct where dense grains are dispersed within a less dense matrix (analogous to a nugget effect). The current method overcomes these problems using a lithium tetraborate fusion that readily dissolves all components including high-density, self-attenuating minerals/compounds. This is the ideal method for dissolving complex, non-volatile components in soils, rocks, mineral concentrates, and other materials where density reduction is required. Lithium borate fusion avoids the need for theoretical efficiency corrections or measurement of matrix matched calibration standards. The resulting homogeneous quenched glass produced can be quickly dissolved in nitric acid producing low-density solutions that can be counted by gamma spectrometry. The effectiveness of the technique is demonstrated using uranium-bearing Certified Reference Materials and provides accurate activity concentration determinations compared to the underestimated activity concentrations derived from direct measurements of a bulk sample. The procedure offers an effective solution for initial nuclear forensic studies where complex refractory minerals or matrices exist. It is also significantly faster, safer and simpler than alternative approaches.

Development of a pixelated GSO gamma camera system with tungsten parallel hole collimator for single photon imaging

In small animal imaging using a single photon emitting radionuclide, a high resolution gamma camera is required. Recently, position sensitive photomultiplier tubes (PSPMTs) with high quantum efficiency have been developed. By combining these with nonhygroscopic scintillators with a relatively low light output, a high resolution gamma camera can become useful for low energy gamma photons. Therefore, the authors developed a gamma camera by combining a pixelated Ce-doped Gd(2)SiO(5) (GSO) block with a high quantum efficiency PSPMT. GSO was selected for the scintillator, because it is not hygroscopic and does not contain any natural radioactivity. An array of 1.9 mm × 1.9 mm × 7 mm individual GSO crystal elements was constructed. These GSOs were combined with a 0.1-mm thick reflector to form a 22 × 22 matrix and optically coupled to a high quantum efficiency PSPMT (H8500C-100 MOD8). The GSO gamma camera was encased in a tungsten gamma-ray shield with tungsten pixelated parallel hole collimator, and the basic performance was measured for Co-57 gamma photons (122 keV). In a two-dimensional position histogram, all pixels were clearly resolved. The energy resolution was ∼15% FWHM. With the 20-mm thick tungsten pixelated collimator, the spatial resolution was 4.4-mm FWHM 40 mm from the collimator surface, and the sensitivity was ∼0.05%. Phantom and small animal images were successfully obtained with our developed gamma camera. These results confirmed that the developed pixelated GSO gamma camera has potential as an effective instrument for low energy gamma photon imaging.

Detectors of Gamma Rays and Alpha Particles Based on Ta-Doped InP Converted to the Semi-Insulating State by Annealing

InP crystals were synthesized with a Ta admixture grown by the Czochralski technique, and wafers cut from the grown crystals were converted to the SI state by high-temperature annealing. The good detection performance of such material-based detectors has been tested with alpha-particles from a 241Am source (5.48 MeV). The charge collection efficiency (CCE) of 84% and relative energy resolution at full width at half maximum (FWHM) of 5% were obtained at room temperature 295 K (RT). Low-energy gamma-photons of 122 keV from a 57Co source and gamma-photons from a 137Cs source were detected at 242 K, 272 K, and 295 K, respectively. The values of CCE 88% and FWHM 16 keV of 122 keV photons and CCE 87% and FWHM 48 keV of gamma-photons of 662 keV were obtained at reduced temperatures. A pulse-height spectrum of 662 keV gamma-photons registered at room temperature is also shown in this work.

Development of a GSO positron/single-photon imaging detector

We have developed and tested a GSO (gadolinium oxyorthosilicate) position-sensitive gamma detector which can be used with positron and single-photon radionuclides for imaging breast cancer or sentinel lymph node detection. Because GSO has a relatively good energy resolution for annihilation gammas as well as low energy gamma photons, and does not contain any natural radioisotopes, it can be used for positron imaging and lower energy single-photon imaging. The imaging detector consists of a GSO block, 2 inch square multi-channel position-sensitive photo-multiplier tube (PSPMT), and associated electronics. The size of a single GSO element was 2.9 mm × 2.9 mm × 20 mm and these elements were arranged into 15 × 15 matrixes to form a block that was optically coupled to the PSPMT. It was possible to separate all GSO crystals into a two-dimensional position histogram for annihilation gammas (511 keV) and low energy gamma photons (122 keV). The typical energy resolution was 24% FWHM and 37% FWHM for 511 keV and 122 keV gamma photons, respectively. For the positron imaging, coincidence between the imaging detector and a single gamma probe is measured. For the single-photon imaging, a tungsten collimator is mounted in front of the imaging detector. With this configuration, it was possible to image both positron radionuclides and low energy single-photon radionuclides. We measured spatial resolution and sensitivity as well as image quality of the developed imaging detector. Results indicated that the developed imaging detector has the potential to be a new and useful instrument for nuclear medicine.

A GSO positron/single-photon imaging detector

We have developed and tested a GSO position sensitive gamma detector which can be used with positron and single-photon radionuclides for imaging breast cancer or sentinel lymph node detection. Because GSO has a relatively good energy resolution for annihilation gammas as well as low energy gamma photons, and does not contain any natural radioisotopes it can be used for positron imaging and lower energy single-photon imaging. The imaging detector consists of a GSO block, 2-inch square multichannel position sensitive photo-multiplier tube (PSPMT), and associated electronics. For the positron imaging, coincidence between the imaging detector and a single gamma probe is measured. For the single-photon imaging, a tungsten collimator is mounted in front of the imaging detector. With this configuration, it was possible to image both positron radionuclides and low energyu single-photon radionuclides.

A benign uptake of 99mTc-polyphosphate after radical mastectomy.

Increased uptake of 99mTc-pp was observed in 10 patients after radical mastectomy. This unilateral localized increased activity was centered at the surgical site. The lack of tissue absorption of the low energy gamma photons of 99mTc-pp due to the absence of chest wall tissue accounted for this activity. Studies of normal patients and patients with simple mastectomies did not show this finding. A routine breast examination is recommended prior to interpreting 99mTc-pp bone scans of patients with breast cancer.