Emission Of Low-energy Photons Research Articles

A new 124Xe irradiation system for 123I production

Since 2001, Nuclear and Energy Research Institute IPEN-CNEN has produced weekly ultrapure iodine-123, using a manual irradiation system, fully developed in IPEN. Iodine-123 radiopharmaceuticals have been produced and distributed to hospitals and clinics of nuclear medicine, where several diagnostic imaging procedures for thyroid, brain and cardiovascular functions are performed. Due to the short half-life and emission of low-energy photons, this radioisotope becomes suitable for diagnosis in children. In the present work, the technical and constructive aspects of a new fully automated irradiation system, dedicated to 123I routine production, employing enriched xenon-124 gas as the target material is presented. This new system consists of a target, a water and helium cooling system, a cryogenic system, an electric power system, and a control and process monitoring unit, composed of supervisory software, connected to a programmable logic controller via personal computer. In this new concept, there is no need for human intervention during radioisotope production, reducing the possibility of eventual failures or incidents involving radioactive material. By using this new system, a specific yield of 2.70 mCi/μAh per irradiation was achieved in validation runs, and after three years of routine production of iodine-123, the system showed reliability and resilience.

Light speed variation from GRB 221009A

It is postulated in Einstein’s relativity that the speed of light in vacuum is a constant for all observers. However, the effect of quantum gravity could bring an energy dependence of light speed, and a series of studies on high-energy photon events from gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) suggest a light speed variation with E LV = 3.6 × 1017 GeV or a bound E LV ≥ 3.6 × 1017 GeV. From the newly observed gamma-ray burst GRB 221009A, we find that a 99.3 GeV photon detected by Fermi-Large Area Telescope (LAT) is coincident with the sharp spike in the light curves detected by both Fermi-Gamma-ray Burst Monitor (GBM) and HEBS under the above scenario of light speed variation, suggesting an option that this high-energy photon was emitted at the same time as a sharp spike of low-energy photon emission at the GRB source. Thus this highest energy photon event detected by Fermi-LAT during the prompt emission of GRBs might be considered as an optional signal for the linear form modification of light speed in cosmological space.

Free-Space Diffused Light Collimation and Concentration

Collimating and concentrating broad-band diffused light can increase the yield, decrease the cost, and open new opportunities for solar-generated electricity. Adherence to the second law of thermodynamics requires that collimation, and therefore the reduction of étendue or entropy, of diffused sunlight, i.e., light scattered by clouds or the atmosphere, can only occur if the photons lose energy during the process. This principle has been demonstrated in luminescent solar concentrators; solar photons are energetically down-shifted by a luminophore and the emitted photons are trapped within a transparent matrix and guided toward an edge lining solar cell. However, this process suffers from low efficiency as the photons are trapped within the waveguide for a long time, encountering many instances of accumulating loss mechanisms. Here, we theoretically describe and experimentally demonstrate the first free-space diffused light collimation system which overcomes these efficiency losses. The high photon energy solar spectrum is allowed to enter the system from all angles, whereas the re-emitted luminescent photons can only escape under a desired emission cone. We achieved this through doping a polymethylmetacrylate waveguide with Lumogen Red dye, which we cover on one side with a Lambertian reflector for photon recycling and induced randomization and on the top face with a complex multilayer dielectric nanophotonic coating stack. We experimentally found an angular concentration of 118% within the designed escape cone, where isotropic emission corresponds to 100%, thereby verifying the reduction of étendue in free space experimentally. Such free-space collimation systems will enable efficient redirection of sunlight toward solar panels, thereby increasing yield, decreasing heating through the emission of low energy photons, and expanding the range of available surfaces from which sunlight can be harvested.

A Quantum Field Theory View of Interaction Free Measurements

We propose a Quantum Field Theory description of beams on a Mach–Zehnder interferometer and apply the method to describe Interaction Free Measurements (IFMs), concluding that there is a change of momentum of the fields in IFMs. Analysing the factors involved in the probability of emission of low-energy photons, we argue that they do not yield meaningful contributions to the probabilities of the IFMs.

Preclinical Single Photon Emission Computed Tomography of Alpha Particle-Emitting Radium-223.

Objective: Dose optimization and pharmacokinetic evaluation of α-particle emitting radium-223 dichloride (223RaCl2) by planar γ-camera or single photon emission computed tomography (SPECT) imaging are hampered by the low photon abundance and injected activities. In this study, we demonstrate SPECT of 223Ra using phantoms and small animal in vivo models. Methods: Line phantoms and mice bearing 223Ra were imaged using a dedicated small animal SPECT by detecting the low-energy photon emissions from 223Ra. Localization of the therapeutic agent was verified by whole-body and whole-limb autoradiography and its radiobiological effect confirmed by immunofluorescence. Results: A state-of-the-art commercial small animal SPECT system equipped with a highly sensitive collimator enables collection of sufficient counts for three-dimensional reconstruction at reasonable administered activities and acquisition times. Line sources of 223Ra in both air and in a water scattering phantom gave a line spread function with a full-width-at-half-maximum of 1.45 mm. Early and late-phase imaging of the pharmacokinetics of the radiopharmaceutical were captured. Uptake at sites of active bone remodeling was correlated with DNA damage from the α particle emissions. Conclusions: This work demonstrates the capability to noninvasively define the distribution of 223RaCl2, a recently approved α-particle-emitting radionuclide. This approach allows quantitative assessment of 223Ra distribution and may assist radiation-dose optimization strategies to improve therapeutic response and ultimately to enable personalized treatment planning.

Photon emission by volume reflected electrons in bent crystals

We present a quantitative experimental analysis of the radiation emission of 12.6 GeV electrons moving along and across the (111) planes of a strongly bent silicon crystal with a bending radius of 0.15 m. We have measured the radiation emitted during volume reflection, which has shown to strongly enhance the emission of low-energy photons, and a convincing agreement between simulations and experimental data is found.

Simple coincidence technique for cosmic-ray intensity exploration via low-energy photon detection

Changes in cosmic-ray intensity can significantly influence the search for rare events or processes in nuclear and astroparticle physics through corresponding variations in detector background count rate. In this work, we present an approach to explore cosmic-ray intensity and corresponding cascade production of secondary particles in the detector vicinity using low-energy photon background spectra induced by cosmic rays at the earth’s surface. The coincidence system based on a plastic scintillator and an extended range HPGe detector, including a multiparameter device, was used for the acquisition of low-energy photon spectra. This system was also simulated by the GEANT4 toolkit, and the simulated and experimental spectra were compared. Single aperiodic events, as well as possible periodic behavior of low-energy photon emission were searched for.

Preserving Preclinical PET Quality During Intratherapeutic Imaging in Radionuclide Therapy with Rose Metal Shielding Reducing Photon Flux

Performing PET imaging during ongoing radionuclide therapy can be a promising method to follow tumor response in vivo. However, the high therapeutic activity can interfere with the PET camera performance and degrade both image quality and quantitative capabilities. As a solution, low-energy photon emissions from the therapeutic radionuclide can be highly attenuated, still allowing sufficient detection of annihilation photons in coincidence. Methods: Hollow Rose metal cylinders with walls 2-4 mm thick were used to shield a 22Na point source and a uniform phantom filled with 18F as they were imaged on a preclinical PET camera with increasing activities of 177Lu. A mouse with a subcutaneous tumor was injected with 18F-FDG and imaged with an additional 120 MBq of 177Lu and repeated with shields surrounding the animal. Results: The addition of 177Lu to the volume imaged continuously degraded the image quality with increasing activity. The image quality was improved when shielding was introduced. The shields showed a high ability to produce stable and reproducible results for both spatial resolution and quantification of up to 120 MBq of 177Lu activity (maximum activity tested). Conclusion: Without shielding, the activity quantification will be inaccurate for time points at which therapeutic activities are high. The suggested method shows that the shields reduce the noise induced by the 177Lu and therefore enable longitudinal quantitative intratherapeutic imaging studies.

Efficiency of 2D Photonic Crystal Emitters in Thermophotovoltaic Systems

Thermophotovoltaic (TPV) systems have the potential to convert energy in a very efficient way by using 2D photonic crystal (PhC) emitters. Recent advancements in TPV technology have developed many methods for effectively generating power. These recent advancements propose that emitters can suppress low energy photon emissions while increasing higher energy photon emissions. This can be achieved by utilising new 2D photonic crystal (PhC) structures on the surface of the emitter with varying diameter and shape.In this meta study we consider the multiple design fabrications of photonic crystal emitters and compare the efficiencies, power densities, and their potential use for converting different wavelengths into heat and power. This is done by analysing the thermodynamic factors present in the system that could potentially reduce the efficiency, and therefore power generation, of the thermophotovoltaic cell. This study found that certain shapes and materials can impact on the PhC structure and its ability to emit energy.

Emission of low-energy photons by electrons at electron-positron and electron-ion colliders with dense bunches

Usually, the emission of low-energy photons in electron-positron (or electron-ion) bunch collisions is calculated with the same approach as for synchrotron radiation (beamstrahlung). However, for soft photons (${E}_{\ensuremath{\gamma}}<{E}_{c}$ where ${E}_{c}$ is a critical photon energy), when the coherence length of the radiation becomes comparable to the bunch length, the beamstrahlung approximation becomes invalid. In this paper, we present results of our calculation for this region based on approximation of classical currents. We consider several colliders with dense bunches. The number of low-energy photons $d{N}_{\ensuremath{\gamma}}$ emitted by ${N}_{e}$ electrons per bunch crossing in the energy interval $d{E}_{\ensuremath{\gamma}}$ is $d{N}_{\ensuremath{\gamma}}=\ensuremath{\alpha}g{N}_{e}d{E}_{\ensuremath{\gamma}}/{E}_{\ensuremath{\gamma}}$, where $\ensuremath{\alpha}$ is the fine-structure constant, and the function $g$, which depends on the bunch parameters, typically is of order unity for modern colliders. In particular, for the International Linear Collider, we find that ${E}_{c}=83\text{ }\text{ }\mathrm{keV}$ and $g=5.5$ at a vanishing beam axis displacement, and $g=0.88$, ${E}_{c}=0.24\text{ }\text{ }\mathrm{keV}$ for KEKB. We also calculate the specific dependence of $d{N}_{\ensuremath{\gamma}}$ on the impact parameter between the two beam axes. In principle, the latter aspect allows for online monitoring of the beam axis displacement.

Low-energy radiative-capture reactions within two-cluster coupled-channel description

The formalism that describes radiative-capture reactions at low energies within an extended two-cluster potential model is presented. Construction of the operator of single-photon emission is based on a generalisation of the Siegert theorem with which the amplitude of the electromagnetic process is constructed in an explicitly gauge-independent way. While the starting point for this construction is a microscopic (single-nucleon) current model, the resulting operator of low-energy photon emission by a two-cluster system is expressed in terms of macroscopic quantities for the clusters and does not depend directly on their intrinsic coordinates and momenta. The multichannel algebraic scattering (MCAS) approach has been used to construct the initial- and final-state wave functions. We present a general expression for the scattering wave function obtained from the MCAS T matrix taking into account inelastic channels and Coulomb distortion. The developed formalism has been tested on the He 3 ( α , γ ) Be 7 reaction cross section at astrophysical energies. The energy dependence of the evaluated cross section and S factor agrees well with that extracted from measurement though the calculated quantities slightly overestimate data.

Energy spectrum based calculation of the half and the tenth value layers for brachytherapy sources using a semiempirical parametrized mass attenuation coefficient formulism

As different types of radionuclides (e.g., 131Cs source) are introduced for clinical use in brachytherapy, the question is raised regarding whether a relatively simple method exists for the derivation of values of the half value layer (HVL) or the tenth value layer (TVL). For the radionuclide that has been clinically used for years, such as 125I and 103Pd, the sources have been manufactured and marketed by several vendors with different designs and structures. Because of the nature of emission of low energy photons for these radionuclides, energy spectra of the sources are very dependent on their individual designs. Though values of the HVL or the TVL in certain commonly used shielding materials are relatively small for these low energy photon emitting sources, the question remains how the variations in energy spectra affect the HVL (or TVL) values and whether these values can be calculated with a relatively simple method. A more fundamental question is whether a method can be established to derive the HVL (TVL) values for any brachytherapy sources and for different materials in a relatively straightforward fashion. This study was undertaken to answer these questions. Based on energy spectra, a well established semiempirical mass attenuation coefficient computing scheme was utilized to derive the HVL (TVL) values of different materials for different types of brachytherapy sources. The method presented in this study may be useful to estimate HVL (TVL) values of different materials for brachytherapy sources of different designs and containing different radionuclides.

Angular measurement of the cobalt-60 emitted radiation spectrum from a radiosurgery irradiator.

The photon energy spectrum emanating from a Leksell Gamma Knife, Model 23004B, was measured between 0.250 and 3.5 MeV with the sources exposed. Measurements were made using a 2x2 inch NaI detector enclosed in a lead-shielded apparatus having a 1/4 inch diameter measurement aperture, which reduced the amount of radiation received by the crystal. All measurements were made one meter above the floor within a quadrant toward one side of the Gamma Knife couch. The measured spectra displayed the expected 60Co doublet of photon peaks at energies of 1.17 and 1.33 MeV. These peaks appeared in spectra beginning at approximately 50 degrees, as one proceeds from a point directly lateral to the source enclosure (0 degrees) toward the foot of the couch (90 degrees). The average photon energy of the spectrum shifts to lower values as the doublet decreases in magnitude with increasing angle until almost vanishing at an angle equal to 90 degrees. Inserting a 16 cm diameter plastic sphere phantom, provided with the Gamma Knife, into the radiation beams increases the low energy photon emissions appearing in the spectrum, especially for measurements at the foot of the couch. Implications for the design of shielding a treatment room containing the Gamma Knife, Model B, and estimation of the radiation exposure to personnel during an emergency procedure in the treatment room with the sources exposed are discussed.

Electroluminescence in insulating polymers in ac electric fields

EL (electroluminescence) in several polymeric materials was investigated in the electric field range <90 kV/mm. We used polymeric films with semi-transparent gold electrodes: low density polyethylene, polypropylene, polytetrafluoroethylene and polyvinylchloride. The EL characteristics were very low EL inception fields (2 to 20 kV/mm) which strongly depend on the material and very low energy photon emission (mainly in the red region of 1.6 to 1.8 eV). These results reveal that EL emission occurs predominantly in the metal-polymer interface region rather than in the bulk of the polymer at the applied field. We present a model of EL emission in the metal-polymer interface region to explain our results qualitatively. In this model, the mechanism of EL emission is the radiative recombination of the electrons and holes trapped at the surface states of the polymer, which causes photon emission in the red region. The EL inception field and EL intensity depend on the density of the surface states of the polymers.

Stimulated neutrino conversion in the CERN beam

We discuss the possibility of searching for anomalous magnetic transitions of neutrinos in the CERN beam induced by the absorption or emission of low-energy photons in a high-quality resonant cavity such as the LEP radio-frequency cavities. With the attainable sensitivities of the present CERN neutrino detectors, this experiment would impose strong limits on this transition and on the radiative decay lifetime of neutrinos with masses in the range of interest to the resolution of the dark matter solar and atmospheric neutrino puzzles.

Intercomparison Measurements of Incorporated Radionuclides in Man by Four Whole-Body Counters

Whole-body counting is the most suitable tool to assess the incorporation of radioactive substances. Quantitative measurements of the total body activity, however, require the careful calibration of the instrument with regard to the varying responses with different body sizes. The accuracy of the obtained results can only be checked by interlaboratory intercomparison. In this study comparative measurements were performed on eight subjects employing the whole-body counters of KFKI Budapest (Hungary), GSF Frankfurt (Germany), I'AEA and stereichisches Forschungszentrum at Seibersdorf (Austria). Gamma ray spectra obtained were evaluated for body activities of 40 K, 134 Cs, and 137 Cs. On four more subjects comparative measurements were carried out at Budapest and Frankfurt. One of these subjects showed additional 125 I thyroid burden due to a diagnostic investigation. Although these devices have different arrangements with respect to counting geometry and number of detectors and although the subjects investigated were of different size and weight, generally good agreement of measured activities. i.e. mean of deviations from the average body activity for each particular subject of less than 10%, was obtained between all laboratories. For the two devices at Budapest and Frankfurt excellent agreement was achieved even for the 125 I thyroid activity with its low energy photon emission, i.e. only about 2% deviation of the value of thyroid activity measured at Budapest from the reference value calculated from the retention function

Wideband ‘‘silicon bolometers’’ on the LSX field reversed configuration experiment

Silicon photodiode detectors, which have nearly flat energy response from 1 eV to 6 keV [R. Korde and L. Randall Canfield, Proc. SPIE 1140, 126 (1989)], were used as bolometers in the field reversed theta pinch experiment LSX. Plasma escaping from the field reversed configuration is naturally diverted to the ends of the vacuum enclosure. There it affects the bolometer measurements either by direct energy deposition or by emission of low energy photons. These two particle effects can be avoided by optimizing the location of the bolometers and restricting their field of view. Good agreement is observed between the silicon bolometers and a gold foil calorimeter.

Evaluation of a Phoswich Detector for the in Situ Analysis of 90Sr

A Phoswich detector system which employs a 3.45 mm thick by 12.5 cm diameter CaF2(Eu) crystal coupled to a 6.4 cm thick NaI(Tl) crystal was evaluated for the detection of 90Sr(90γ) in the presence of 106Ru (106Rh) and 137Cs and for its ability to measure 238pu, 239pu, 241Am and 244Cm. The radioactive species were studied, both as surface contamination and contamination distributed in sediments, as a function of overburden thickness for different materials. The CaF2(Eu) crystal detects beta or low energy photon emissions while the NaI(Tl) crystal only detects higher energy photons from radionuclide decay or bremsstrahlung radiation. As little as 9 d/m/cm2 of 90Sr as surface contamination can be measured in a 1000 second counting period in the presence of comparable concentrations of 137Cs and 106Ru. The Phoswich system is specifically designed for the measurement of 90Sr(90γ) and does not detect the transuranic species well. The operating parameters and use of the Phoswich system for identification of specific radionuclides in shallow land waste burial environments are discussed.

Emission of Low-Energy Photons in Scattering and Decay Processes and a Possible Method for Determining Electromagnetic Properties of Short-Lived States

Emission of Low-Energy Photons in Scattering and Decay Processes and a Possible Method for Determining Electromagnetic Properties of Short-Lived States

An image tube scintillation camera for use with radioactive isotopes emitting low-energy photons.

Many radioactive isotopes decay with the emission of low-energy photons, which are either (a) gamma rays or (b) x rays emitted subsequent to electron capture or internal conversion. It is impossible to define on an absolute scale the term “low-energy photon”; and, arbitrarily, in this context the term will be applied to electromagnetic radiation emitted with an energy lower than 150 kiloelectron volts. Several authors, among them Harper, Myers, Sodee, and Wagner, have investigated the usefulness of several such radioactive isotopes in the visualization of organs and anatomical structures by scintiscanning (1–6). For these procedures, radioactive isotopes emitting low-energy photons exhibit both advantages and disadvantages as compared to isotopes emitting higher energy electromagnetic radiation. The high absorbability of low-energy photons in matter provides two main advantages in scintiscanning: 1. Low-energy photons can be efficiently detected by means of detectors with a relatively low cross-sectional density. Such detectors are easy to shield, they exhibit a relatively low background due to their low cross-section for the absorption of higher energy photons, and they facilitate considerably the design of certain types of scintillation cameras. 2. The second advantage derived from the high absorbability of low-energy photons consists of their efficient collimation by means of multi-hole collimators with relatively thin septa. In such collimators, the thickness of the septa is determined by the energy of the electromagnetic radiation which is to be collimated, and one of the limiting factors in both the resolution and efficiency of a scintillation camera is contributed by the thickness of the septa used. Thus, higher collimation resolution and efficiency can be achieved with lower energy photons than with higher energy radiation. In general, the design and construction of efficient collimators for low-energy photons is simple because of the near absence of septal penetration of the radiation. Collimators for low-energy radiation are light and easy to handle. The high absorbability of low-energy photons exhibits the disadvantage in organ visualization of requiring more activity in observing deep-seated structures because of the high attenuation of the radiation in the tissues interposed between the organ and the detector. This limitation, however, was found to be of minor importance in clinical work (7, 8). The major disadvantage in the use of low-energy photon emitters for organ visualization results from the fact that scattering of lower energy, photons takes place with little loss of energy; and consequently scattered radiation cannot be as efficiently eliminated from the examination as can higher energy radiation.