Prompt Gamma Rays Research Articles

Light-transport incorporated plastic scintillator response to prompt gamma-rays for use in range verification of proton therapy

In this study, the prompt gamma-rays (PGs) produced during the interactions of proton beams of various energies have been investigated using the MCNPX2.6 Monte Carlo code. Having considered a detection setup consisting of a thick lead collimator and a commercial plastic scintillator, the event-by-event data, generated by the PTRAC card of the MCNPX code, when the scintillator is exposed to PGs have been extracted before they are used in a dedicated light transport code, PHOTRACK. The plastic scintillator response when it is moved along the phantom axis determines the flux variation of proton-induced PGs which can be further related to the longitudinal deposition energy profile of protons, i.e., the Bragg curve. The present study shows that the Bragg peak location is ∼3.7 cm after the PG peak for different proton energies of interest. The uncertainty in the Bragg peak location data is about 0.02 cm which can be improved by taking into account the precise electron-transport simulation details.

The Stellar 72Ge(n, γ) Cross Section for weak s-process: A First Measurement at n_TOF

The slow neutron capture process (s-process) is responsible for producing about half of the elemental abundances heavier than iron in the universe. Neutron capture cross sections on stable isotopes are a key nuclear physics input for s-process studies. The 72Ge(n, γ) Maxwellian-Averaged Cross Section (MACS) has an important influence on the production of isotopes between Ge and Zr in the weak s-process in massive stars and so far only theoretical estimations are available. An experiment was carried out at the neutron time-of-flight facility n_TOF at CERN to measure the 72Ge(n, γ) reaction for the first time at stellar neutron energies. The capture measurement was performed using an enriched 72GeO2 sample at a flight path length of 184 m, which provided high neutron energy resolution. The prompt gamma rays produced after neutron capture were detected with a set of liquid scintillation detectors (C6D6). The neutron capture yield is derived from the counting spectra taking into account the neutron flux and the gamma-ray detection efficiency using the Pulse Height Weighting Technique. Over 70 new neutron resonances were identified, providing an improved resolved reaction cross section to calculate experimental MACS values for the first time. The experiment, data analysis and the new MACS results will be presented including their impact on stellar nucleosynthesis, which was investigated using the post-processing nucleosynthesis code mppnp for a 25 solar mass model.

Quantitative Elemental Analysis Using Whole Spectral Information (with GA and MLR Methods) of Proton Induced Prompt Gamma-Rays Simulated Using Geant4 Toolkit

Purpose: Online determination of the elemental composition of tissues near the Bragg peak is a challenge in proton therapy related studies. In the present work, an analysis method based on the whole spectral information is presented for the quantitative determination of the elemental composition (weight %) of an irradiated target from its emitted Prompt Gamma (PG) spectrum.
 Materials and Methods: To address this issue, four test phantoms with different weights (%) of 12C, 16O, 20Ca, and 14N elements were considered. The simulated PG spectra were recorded using 3 × 3 inch NaI detectors. A library consisting of the spectra of single-element phantoms as well as the spectra of test-irradiated phantoms was produced for 30, 70, and 150 MeV incident protons using the Geant4 Monte Carlo toolkit. The elemental analysis was performed using the information of the whole spectrum by applying two methods, including the well-known Genetic Algorithm (GA) and Multiple Linear Regression (MLR).
 Results: The results show that the proposed method estimates the oxygen concentration accurately. Furthermore, the estimated weights of other elements, with both methods, agree well with nominal values in each test phantom, for the considered energies.
 Conclusion: The proposed quantitative elemental analysis of proton-bombarded phantoms using their induced PG spectrum is expected to be beneficial in treatment planning and treatment verification studies.

A long-duration gamma-ray burst with a peculiar origin.

It is generally believed that long-duration gamma-ray bursts (GRBs) are associated with massive star core collapse1, whereas short-duration GRBs are associated with mergers of compact star binaries2. However, growing observations3-6 have suggested that oddball GRBs do exist, and several criteria (prompt emission properties, supernova/kilonova associations and host galaxy properties) rather than burst duration only are needed to classify GRBs physically7. A previously reported long-duration burst, GRB 060614 (ref. 3), could be viewed as a short GRB with extended emission if it were observed at a larger distance8 and was associated with a kilonova-like feature9. As a result, it belongs to the type I (compact star merger) GRB category and is probably of binary neutron star (NS) merger origin. Here we report a peculiar long-duration burst, GRB 211211A, whose prompt emission properties in many aspects differ from all known type I GRBs, yet its multiband observations suggest a non-massive-star origin. In particular, substantial excess emission in both optical and near-infrared wavelengths has been discovered (see also ref. 10), which resembles kilonova emission, as observed in some type I GRBs. These observations point towards a new progenitor type of GRBs. A scenario invoking a white dwarf (WD)-NS merger with a post-merger magnetar engine provides a self-consistent interpretation for all the observations, including prompt gamma rays, early X-ray afterglow, as well as the engine-fed11,12 kilonova emission.

GRB 220426A: A Thermal Radiation–Dominated Gamma-Ray Burst

The physical composition of the ejecta of gamma-ray bursts (GRBs) remains an open question. The radiation mechanism of the prompt gamma rays is also in debate. This problem can be solved for the bursts hosting distinct thermal radiation. However, the events with dominant thermal spectral components are still rare. In this work, we focus on GRB 220426A, a recent event detected by the Fermi Gamma-ray Burst Monitor. The time-resolved and time-integrated data analyses yield very hard low-energy spectral indices and rather soft high-energy spectral indices. This means that the spectra of GRB 220426A are narrowly distributed. And the Bayesian inference results are in favor of the multicolor blackbody model. The physical properties of the relativistic outflow are calculated. Assuming a redshift z = 1.4, the bulk Lorentz factors Γ of the shells are found to be between and , and the corresponding photosphere radii R ph are in the range of and cm. Similar to GRB 090902B, the time-resolved properties of GRB 220426A satisfy the observed Γ–L and E p –L correlations, where L is the luminosity of the prompt emission and E p is the spectral peak energy.

Prompt gamma spectroscopy retrieval algorithm for element and density measurements accelerated by cloud computing

Prompt gamma ray in proton therapy is the product of a nuclear reaction between a proton and a target. The characteristic energies and intensities of prompt gamma lines can be used to determine the types of elements and their amounts in the target. In several previous experiments, it was demonstrated that no matter how complex the reaction cross-section is, once the energy of the incident proton and the irradiated element are determined, there is a definite linear relationship between the element concentration and the number of gamma-ray photons. However, this linear relationship is difficult to apply to medical imaging, and the nonlinear behavior of hydrogen has not been investigated so far. In this study, this linear relationship is extended to mixed elemental materials including a nonlinear case such as hydrogen, and a universal mathematical form, which is referred to as the prompt gamma spectroscopy retrieval algorithm (PGSRA), is developed. The basic assumption of the PGSRA is that the PGS of the sample material has a relationship with the molar gamma lines of the elements. For carbon and oxygen, this relationship is linear, while for hydrogen, this relationship is nonlinear. As the 2.23 MeV gamma line originates from neutron absorption radiation, the behavior of hydrogen is carefully investigated. The linear and nonlinear relationships are verified using Monte Carlo simulations with different combinations of carbon, oxygen, and hydrogen, such as PMMA, pentanediol, and ethanediol. The PGSRA developed in this work could be the first bridge between PGS and medical imaging.

Fast neutron induced gamma rays from (n,n’), (n,p) and (n,α) reactions on CaCO3

Emission of prompt gamma rays following (n,n’), (n,p) and (n,α) reactions induced by irradiation of a calcium carbonate (CaCO3) sample with a beam of fission neutrons was investigated with a modified version of the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The neutron spectrum has an average energy of 2.30 MeV and at sample position the fast neutron flux was (1.13 ± 0.04) × 108 cm−2 s−1. The measurement was performed at an angle of 90° between neutron beam and detector. In total, we claim the identification of 38 prompt gamma lines, from which we have assigned 12 to the (n,n’) reaction in calcium (7 for 40Ca, 1 for 42Ca and 4 for 44Ca), 1 to the 12C(n,n’)12C reaction, and 2 to the (n,n’) reaction in oxygen (1 for 16O and 1 for 18O). The other observed gamma lines are attributed to the 40Ca(n,p)40K reaction (20 lines) and to the 40Ca(n,α)37Ar reaction (3 lines). Relative intensities and fast neutron spectrum averaged partial cross sections of the gamma lines are presented and compared with available literature data. Our results were found to be in good agreement with available literature data but also improved and complemented it, as we have pointed out possible errors and identified new lines. Additionally, for a counting time of 12 h the detection limits of calcium, carbon and oxygen were determined as 5, 13 and 64 mg, respectively.

Demonstrative measurement of proton-nuclear reaction by deconvolving the prompt gamma-ray spectra

In proton therapy, there has been an increasing demand for measuring the employed dose distribution to improve treatment accuracy and quality. One method of estimating radiation dose in real time is to visualize the prompt gamma rays emitted during nuclear reactions between protons and nuclei in the patient’s body. However, this is difficult without accurate measurements of nuclear cross sections, that cover a 10–100 MeV energy range. Herein, we propose a novel method for determining cross section of low-energy protons with 12C and 16O by measuring the prompt gamma rays emitted from stacked slab phantoms placed along the proton path. These emitted gamma rays provide direct information on the nuclear reactions occurring at different proton energies. By applying an iterative inference using the response matrix, the contamination of various prompt gamma rays can be resolved; thus, the cross sections of various reactions were obtained at arbitrary proton energies. As a first step to this study, we applied this method to measure the nuclear reaction of protons with 12C and 16O nuclei, which are the major elements constituting the human body. The cross section of the 12C(p,p)12C∗ reaction, which produces a prominent gamma-ray peak at 4.4 MeV, reproduced the one in literature well, supporting the validity of the proposed method. Furthermore, we show that even weak prompt gamma rays can be resolved for a wide range of proton energies below 70 MeV, for which no cross sectional data have been reported so far.

Measurement of prompt gamma production from neutron capture on manganese

Prompt gamma radiation is an important part of radiation fields with neutrons. Its good description is vital for precise predictions in void swelling issues because it is a contributor in gamma heating effect. The energy of prompt gamma rays is unique for each nuclide, thus can be used as its signature. Prompt gamma activation analysis is a technique using these gammas in nuclide identification. Despite the prompt gamma importance, current nuclear data libraries describe its origins very inaccurately. Measurement of gamma leakage spectrum of manganese bath with 252Cf neutron source was performed using well-defined HPGe detector with high-density polyethylene shielding and stilbene scintillator. Stilbene measured gamma/neutron spectrum was separated by a Pulse Shape Discrimination method. MCNP6.2 simulation of the experiment was performed with ENDF/B-VIII.0 and JEFF-3.3 libraries for neutrons (and gamma production from neutron interactions) and MCPLIB04 library for photons. Analysis of results revealed that ENDF/B-VIII.0 and JEFF-3.3 description of prompt gamma radiation production is significantly discrepant. INDEN updated data for gamma production on 55Mn was tested as well and show significant improvement compared to original ENDF/B-VIII.0 data. Nevertheless, significant discrepancies up to 50% were still observed. An alternative approach using prompt gamma production tables provided by IAEA was tested as well. Its results are basically in agreement with the calculation using INDEN updated 55Mn data.

Feasibility study on rare earth ion exchange resin saturation analysis based on PGNAA technique

In this work, prompt gamma ray neutron activation analysis technique was used to monitor the REEs saturation in resin. A facility consisted of a D-T neutron generator, a BGO detector and a 3He detector was established and applied to analyze REEs (Gd and Sm) samples. Neutron self-shielding effect was also corrected. The enriched Gd and Sm in resin were close to saturation at about 400 min. The results showed a satisfactory agreement with the XRF tests, which demonstrated that PGNAA was sufficient for monitoring REEs saturation in resin.

Design of Radiation-Tolerant High-Speed Signal Processing Circuit for Detecting Prompt Gamma Rays by Nuclear Explosion

Electronic equipment in nuclear power plants and nuclear warfare is damaged by transient effects that cause high-energy pulsed radiation. There is a concern that this type of damage can even cause enormous economic losses and human casualties by paralyzing control systems. To solve this problem, this study proposes a complementary metal-oxide semiconductor (CMOS) logic-based, switching detection circuit that can detect pulsed radiations at a fast rate. This circuit improved response speed and power consumption by using the switching operation of digital logic compared with conventional circuits. Furthermore, radiation tolerance to total ionizing dose (TID) effects was achieved even in a cumulative radiation environment because of the use of the design using p-metal-oxide semiconductor field effect transistor (p-MOSFET). The proposed detection circuit was manufactured by a 0.18 µm CMOS bulk process for integration. Normal operation in the detection range of 2.0 × 107 rad(si)/s was verified by pulsed radiation test evaluations, and the tolerance properties to a radiation of 2 Mrad was verified based on cumulative radiation test evaluations.

Neutron area monitor for ambient dose equivalent (H*(10)) and effective dose (EAP) using prompt gamma rays induced in high density polyethylene with metallic external layer

Estimations of neutron ambient dose equivalent, H∗(10) and effective dose (anterior-posterior), EAP using measured prompt gamma intensities are theoretically investigated for several prompt gamma generating detection systems, each consisting of a cylindrical high density polyethylene (HDPE) covered with a layer of different materials. The neutron induced prompt gamma intensities are measured using a NaI(Tl) detector with lead as shielding. Materials like cadmium, iron, nickel, zinc, copper and lead are used as an outer layer covering the HDPE cylinder. A linear combination of the distributions of the prompt gamma intensities emitted from these materials at different incident neutron energies are subjected to multiple linear regression analyses to fit the energy dependent neutron fluence to dose conversion coefficients (DCC) as provided by the International Commission on Radiological Protection (ICRP). The aim of the present work is to explore the suitability of other elements to replace boron in the earlier used borated HDPE in the system to overcome certain practical difficulties. Different neutron energy distributions in the energy range from about 0.01 eV to 20 MeV are selected to validate the dose estimation. Among the materials used, iron, nickel, zinc and copper show promising results for the estimation H∗(10) as well as EAP as a replacement of boron for neutron energy distributions with predominant high energy components.

Timing Performances of SDD as Photodetector Candidate for Proton Therapy Application

In the proton therapy, charged particles interact with tissue depositing dose in the tumor, providing enhanced tumor coverage compared to conventional radiotherapy. However, proton range uncertainties limit the full exploitation in clinical practice of the localized dose deposition. Range and dose monitoring in real time would be beneficial to deliver safer and more effective treatments. A possible solution is to use the signature of high-energy (2–8 MeV) prompt gamma rays, produced naturally along the beam path by excited nuclei. In this article, we study the timing capability of the silicon drift detector (SDD) as a photodetector candidate to be used for the scintillator readout for high-energy gamma rays detection. The peculiar drift mechanism affects the time needed for the photogenerated charge inside the SDD volume to approach the collecting electrode. As a result, the detector output signal shows a rise time limiting usually its timing performances when used with scintillators. In this work, we first developed a simulator to predict the drift time values as a function of charge generation position. Next, we performed the experimental characterization of the SDD timing performances by directly irradiating it with laser light. We carried out spectroscopy measurements for the assessment of the electronics noise of the detector in two readout configurations: 1) single anode and 2) merged anodes. Finally, we experimentally evaluated the timing performances of the SDD at the signal levels expected in the target application, showing sub-ns timing resolution.

A thermal neutron detection system based on boron-coated straw detector with prompt gamma coincidence

Accurate measurement of the neutron flux is of crucial importance for rare event search experiments in underground laboratories. The intrinsic radioactive background of the detector becomes the limiting factor for the detection of extremely low neutron flux. In this study, a thermal neutron detection system aimed at low flux measurement was developed based on boron-coated straw (BCS) neutron detectors. The neutron events can be distinguished from the detector background by coincidence measurement of neutron and the prompt gamma ray. With state-of-the-art BCS neutron detectors and NaI(Tl) gamma detector, a system sensitivity of ∼120 cps/nv was achieved, comparable to that of the commonly used 3He counters. Based on the selected coincidence criteria, the background events were rejected to 0.1% with 45.3% of the neutrons preserved. The background accidental coincidence count rate of the system was measured as 2.3×10-5 cps, corresponding to a lower limit of measurable thermal neutron flux of 1.9×10-7 n/cm2/s. The performance of the system can be further improved by using other gamma scintillator with lower neutron absorption (such as BGO) and adding extra shielding for ambient gamma rays.

On the Self-Consistent Simulation of High-Altitude Electromagnetic Pulse

Self-consistency between Compton electrons and electromagnetic (EM) fields is an important physical mechanism in the generation and propagation of early-time high-altitude EM pulse (HEMP). This article develops an iterative self-consistent HEMP simulation scheme based on high-frequency approximation (HFA) algorithms. The self-consistent effect between electrons and fields is decoupled and neglected in the first iteration and then is taken into account by considering the results of the field as the independent fields, which affect electrons in the next iteration. The computation can be improved up to tens of times faster than the existing non-iterative method. This article provides a detailed study about self-consistent HEMP with regard to the influence of prompt gamma yield and various prompt gamma ray spectra. The saturation phenomenon caused by secondary electrons is considered as well. The self-consistent effect is significant in the source region. At ground level, it shortens the duration and reduces the amplitude of HEMP. Numerical results showed that the differences caused by self-consistency are significant in the simulation with different prompt gamma yields and prompt gamma ray of monoenergetic and spectrum.

Prompt gamma rays from fast neutron inelastic scattering on aluminum, titanium and copper

Prompt gamma rays induced by inelastic scattering of fast neutrons on aluminum, titanium and copper were measured at an angle of 90o between fast neutron beam and detector of the instrument FaNGaS, operated by Jülich Centre of Neutron Science at Heinz-Maier-Leibnitz Zentrum in Garching. The fast neutron flux was 1.40 108 cm−2 s−1 with the average energy of 2.30 MeV. Intensities and neutron spectrum averaged isotopic partial cross section for production of 214 gamma lines (22 for aluminum, 72 for titanium and 120 for copper) are presented. The results are consistent with the literature data. However, the new sets of gamma lines are recommended to replace the old datasets from fast neutrons reactors with several new lines also recognizing a few false identifications. Additionally, the detection limits of aluminum, titanium, copper, iron and indium were determined as 1.0, 0.4, 0.9, 0.5 and 1.3 mg, respectively, for a counting time of 12 h.

Design of a DT neutron source based PGNAA facility for element determination in aqueous solution

A DT neutron source-based prompt gamma ray neutron activation (PGNAA) facility for bulk sample analysis was designed and developed in this research. The aqueous samples containing chlorine and boron with known concentration were determined for the calibration curve by the facility. The neutron self-shielding effect was corrected by internal standard method. The minimum detectable concentration of boron and chlorine are 1.37 ± 0.42 and 12.51 ± 3.80 mg/L, respectively. Finally, five mixture aqueous solution samples were measured for the facility performance test. The maximum relative deviation of boron and chlorine are 4.49% and 5.32% respectively.

Compton imaging for medical applications

Compton imaging exploits inelastic scattering, known as Compton scattering, using a Compton camera consisting of a scatterer detector in the front layer and an absorber detector in the back layer. This method was developed for astronomy, and in recent years, research and development for environmental and medical applications has been actively conducted. Compton imaging can discriminate gamma rays over a wide energy range from several hundred keV to several MeV. Therefore, it is expected to be applied to the simultaneous imaging of multiple nuclides in nuclear medicine and prompt gamma ray imaging for range verification in particle therapy. In addition, multiple gamma coincidence imaging is expected to be realized, which allows the source position to be determined from a single coincidence event using nuclides that emit multiple gamma rays simultaneously, such as nuclides that emit a single gamma ray simultaneously with positron decay. This review introduces various efforts toward the practical application of Compton imaging in the medical field, including in vivo studies, and discusses its prospects.

Cramér–Rao Bound Evaluations of Compton Imager Designs for Proton Beam Range Verification

Compton imaging is an attractive tool for range verification and dose estimation in proton therapy. To investigate the application of CdZnTe-based cameras for this task, we apply the uniform Cram&#x00E9;r&#x2013;Rao bound (UCRB) to dual-plane-based designs with various interplane spacings and evaluate their bias-variance tradeoff. The investigation focuses on the 718-keV and 4.4-MeV prompt gammas emitted from proton interactions with ¹²C, and focuses on a detector geometry having two planes of <inline-formula> <tex-math notation="LaTeX">$3 \times 3$ </tex-math></inline-formula> CdZnTe crystals with a volume of <inline-formula> <tex-math notation="LaTeX">$2 \times 2 \times 1.5 \,\,\mathrm {cm}^{3}$ </tex-math></inline-formula>. When considering only interplane events, the improvement in minimum variance plateaus at 8 cm. However, when considering both intraplane and interplane events with an efficiency factor, the optimum spacing is calculated to be around 4 cm as larger spacings degrade the performance with poorer efficiency and a lower interplane to intraplane fraction. In addition, the study uses the modified UCRB based on a simulated distribution of prompt gamma rays expected from proton irradiation. The results show that the optimum spacing may be between 2 and 4 cm, depending on the specific bias-gradient norm.

OC-0628 Proton therapy treatment verification with prompt gamma rays and fast neutrons – a feasibility study

OC-0628 Proton therapy treatment verification with prompt gamma rays and fast neutrons – a feasibility study