High Intensity Gamma-ray Research Articles

The laser matter interaction in the QED regime

Contemporarily, with the rapid development of the laser techniques, the peak intensity of the laser reaches 1023 W/cm2. In this case, the laser plasma interaction enters the QED regime. With this in mind, this research demonstrates the state-of-art simulations results in the frame. Specifically, a brief introduction to the QED effect is introduced primarily. Subsequent, the progress of ultra-intensity laser, and the state-of-art facilities are discussed. Afterwards, the theoretical description of Compton scattering and Electron-Positron pairs generation are discussed. Eventually, application of high intensity gamma ray and EP pairs are presented. These results shed light on guiding further exploration of the QED physics.

Simulation of cobalt-60 production in research reactors using OpenMC Monte Carlo code

Abstract Cobalt-60 is an artificial radioisotope with a wide range of applications in many industries for its high intensity gamma-rays and longer half-life. It may be produced in research reactors from the stable isotope cobalt-59 by neutron activation when a fission neutron is absorbed in the Co-59 nucleus. The ETRR-2 research reactor is designed with an in-core neutron flux trap that accommodates space for placement of an irradiation box, which makes it suitable for the production of radioisotopes as an in-core fixed facility. This simulation study compares the production yield of Co-60 for different Co-59 pencil configurations within the irradiation box inside the in-core neutron flux trap. IAEA reference for Co-60 specifications was used to set the comparison criteria for generating different configurations. Reactor geometry and calculations were carried out using OpenMC Monte Carlo code to obtain the effective multiplication factor Keff, the flux distribution, and the production yield of Co-60 with respect to time. Results show that the ETTR-2 is capable of producing Co-60 with a specific activity of 83.89 Ci g−1 in 263 ± 14 days following the placement of eight Co-59 pencils with 0.77 cm diameter, 32 cm in height, and 74.506 g each. It was also shown that a higher production rate may be achieved by decreasing the diameter of the pencils and increasing their number while Co-59 mass is kept constant.

Model independent approach to photodisintegration of 7 Li at the range of energies of interest to BBN

One of the elements that was synthesized primordially in the standard Big Bang Nucleosynthesis is lithium. Lithium, being fragile gets easily destroyed at relatively low temperatures in the mixing process between stellar surface and hot internal layers. So that, at the end of the stellar lifetime the lithium content is believed to be depleted. Series of experimental measurements on lithium isotopes were carried out at High Intensity Gamma Ray Source (HIGS) at Duke Free Electron Laser Laboratory. More recently experiments [1]-[2] were performed, to measure the differential cross section of the photo-neutron reaction channel in photodisintegration of 7 Li, where the progeny nuclei is in the ground state as well as in excited states. The purpose of present contribution is to study the reaction channel 7 Li + γ → 6 Li + n using linearly polarized photons. The model independent irreducible tensor formalism [3]-[5] will be used to study the differential cross section of the reaction. We study the angular dependence of differential cross section by expressing differential cross section in terms of legendre polynomials. In view of the several theoretical and ongoing experimental studies, a detailed theoretical study of the spin structure of the amplitudes in 7 Li + γ → 6 Li + n and their expansion in terms of ’electric’ and ‘magnetic’ amplitudes is needed to analyze the measurements of spin observables as well as differential cross section, which leads to a better understanding of the problem at astrophysical energies

Measurement of the absolute gamma emission intensities from the decay of Th-229 in equilibrium with progeny

There are few long-lived radionuclides yielding high intensity gamma-rays emission with energies ranging from 100 keV to 500 keV that can be applied as radioactive gamma standard to calibrate HPGe detectors. Furthermore, this energy range represents the main emitted energies of the majority of radionuclides used in nuclear medicine. The Brazilian National Laboratory for Ionizing Radiation Metrology (LNMRI/IRD/CNEN) has attempted to identify radionuclides that have the potential to be used as a calibration source due to their long half-life as well as their emission spectrum. Hence, LNMRI promotes standardization studies of gamma-emitting radionuclides that meet these criteria on order to disseminate them. Thorium-229, with its well-defined energies and relatively high intensities, is one such candidate radionuclide for the energy and full-energy peak efficiency calibration of high-purity gamma spectrometers. Thorium-229 was standardized by the method of 4παβ(LS)-γ(NaI(Tl)) live timed anticoincidence counting. The emission intensities of gamma-rays associated with the decay of 229Th have been determined by HPGe gamma ray spectrometry with accuracy and precision. The results are in agreement with current literature data.

THE RADIOACTIVITY ESTIMATION OF THE IRRADIATED 13 MEV CYCLOTRON’S CONCRETE SHIELD

The Center for Accelerator Science and Technology (PSTA) planned to install K500 concrete shield in its 13 MeV cyclotron facility (DECY-13). However, fast neutrons that are generated by this cyclotron could activate materials of the concrete. It may harm the radiation workers. In this work, we conducted simulations using ORIGEN2 and PHITS computer code to estimate the formed radioactivity and the neutron flux distribution in the DECY-13 cyclotron's concrete shield. Based on the simulation, the induced radioactivity is 2.3478 × 109 Bq, while its gamma dose rate is 22.09 µSv/m2h. The most contributed isotopes are Th-233, Ho-166, Al-28, Mn-56 and Si-31. This dose is quite high. Neutron fluxes in the rear of the simulated concrete shield are also still prominent. Accordingly, it is necessary to attach neutron shielding materials which do not generate high-intensity gamma-ray. The formed radioactivity is high; but it appears from the short half-life isotopes such as Th-233, Ho-166, Al-28, Mn-56 and Si-31. Its activity will diminish quickly after the cyclotron is off. Hence, it will be safe for radiation workers.Keywords: Radioactivity, Concrete Shield, 13 MeV Cyclotron, Neutron Irradiation, DECY-13, PHITS

Comparison of HfB2 and ZrB2 behaviors for using in nuclear industry

Owing to the importance of two HfB2 and ZrB2 materials in nuclear industry, the behavior of the two materials under neutron irradiation was examined. As Boron element plays an important role in these materials, it seems that these two substances are more likely to be similar to each other in more terms. However, the results indicated that there were differences. HfB2 is a better absorbent for neutron in all energies rather than ZrB2. However, ZrB2 may become damaged or burnt-out relatively soon. The prompt gamma rays produced in ZrB2 for low energy neutron are far less than those in HfB2, but for high energy neutron, high intensity gamma ray peaks arise in ZrB2. Therefore, if one wants to use these two materials as radiation shield, he should pay attention to that point. Alpha particle spectrum and gamma rays were obtained for different energies of neutron. Half Value Layer (HVL) values for both materials and different neutron energies were also obtained.

Development of the ELISSA array: prototype testing at Laboratori Nazionali del Sud

The Extreme Light Infrastructure-Nuclear Physics (ELI-NP) facility, underconstruction in Magurele near Bucharest in Romania, will provide high-intensity andhigh-resolution gamma ray beams that can be used to address hotly debated problems in nuclear astrophysics, such as the accurate measurements of the cross sections of the24Mg(γ,α)20Ne reaction For this purpose, a silicon strip detector array (named ELISSA) will be realized in acommon effort by ELI-NP and Laboratori Nazionali del Sud (INFN-LNS), in order to measure excitation functions and angular distributions over a wide energy and angular range. A prototype of ELISSA was built and tested at INFN-LNS in Catania (Italy) with the support of ELI-NP. In this occasion, we have carried out experiments with alpha sources and with a 11 MeV 7Li beam that show up a very good energy resolution (better than 1%) and very good position resolution, of the order of 1 mm. Moreover, a threshold of 150 keV can be easily achieved with no cooling.

A Feasibility Study on the Transmutation of 100Mo to 99mTc with Laser-Compton Scattering Photons

This paper evaluates the effectiveness of producing 99Mo using the photonuclear giant dipole resonance (GDR) (γ, n) reaction. The focus of the study is a novel implementation of the photonuclear transmutation method by the use of laser-Compton scattering (LCS) gamma-ray beams to produce 99Mo. The use of LCS enables the production of energetic and high-intensity gamma rays with a tunable energy spectrum based on various facility parameters (i.e., electron energy, laser energy, and collimation angle). The combination of these three features have made the use of the LCS process for the production of 99Mo using the photonuclear (γ, n) reaction a concept deserving further investigation. In this study, rigorous optimization of the LCS spectrum is performed to maximize the overlapping of the GDR cross section and the LCS spectrum to optimize the production rate and activity of the 99Mo product. Furthermore, the unique innovation of the multiple laser extraction concept is also included in this paper in order to increase the gamma-ray intensity by a factor of 10 to 20.

Optimization of the laser-Compton scattering spectrum for the transmutation of high-toxicity and long-living nuclear waste

The laser-Compton scattering (LCS) phenomenon is one known method for producing energetic and high-intensity gamma rays with variable photon spectrums. Availability of high-intensity gamma rays has made probing the (γ,n)-based photonuclear transmutation possible and worth consideration. Parametric studies of LCS have shown that the gamma ray’s spectrum is tunable and dependent upon various facility-related parameters. In this paper, a systematic optimization study of the LCS spectrum has been performed in view of the incident laser energy, electron beam energy and collimation angle. This optimization has been done with the aim to maximize the transmutation reaction rates of long-living fission products (LLFPs) such as 129I, 135Cs, and 137Cs that have an isotopic composition of typical LWR spent fuel. In addition, the (γ,n) and (γ,2n)-reaction rates have been simultaneously calculated in order to evaluate the feasibility of photonuclear transmutation using the (γ,n)-reaction. It has been shown that careful optimization of the LCS spectrum noticeably enhances the (γ,n)-reaction rate without requiring any isotopic separation of the iodine and cesium targets. Furthermore, in order to enhance the energy efficiency of the LCS-based photo-transmutation system, a novel multiple laser-Compton scattering extraction (MULEX) concept has been introduced in this work, and it has been shown that the total production of the LCS photons can easily be increased by a factor of 10 or 20 in a single accelerator system.

Development of neutron spectrum unfolding method for advanced nuclear emulsion

In order to realize neutron spectroscopy in high-intensity gamma ray fields such as those present in spent nuclear fuel storage facilities using an advanced nuclear emulsion based on a non-sensitized OPERA film with AgBr grain sizes of 60 nm, a new neutron spectrum unfolding method has been developed. The response functions were evaluated in the neutron energy range between 0.1 and 4.5 MeV by Monte Carlo calculations. To realize a highly reliable unfolding method that does not require an initial guess spectrum, an algorithm was formulized based on the maximum entropy principle and the maximum likelihood method, and the new unfolding code MEALU was developed. The code performance was checked by analyses of mock-up data. As an example, the neutron spectrum from fresh fuel of the experimental fast reactor Joyo was calculated and track lengths were simulated using the calculated response function and the estimated spectrum. Comparison between the original neutron spectrum and the unfolded one confirmed the effectiveness of the proposed method.

Fast neutron detection under intense gamma-ray fields with novel nuclear emulsion technique

Abstract In order to measure neutron flux and energy in the presence of high-intensity background gamma rays, a new nuclear emulsion based on a non-sensitized OPERA film was synthesized, which had small AgBr grain sizes of 60, 90 and 160 nm. The sensitivity of this new emulsion, which is described in terms of the stopping power and grain density, was estimated experimentally by neutron irradiation at several energies. The response of the emulsion to gamma-ray-induced electrons was also simulated and the results were compared with experimental data obtained using a 60 Co gamma source. The results indicated that each AgBr grain has a threshold energy that must be deposited before the AgBr can develop into metallic Ag. Based on these results, the efficiency of the new emulsion in detecting gamma rays and neutrons was evaluated.

Electromagnetic dipole strength of136Ba below the neutron separation energy

The electromagnetic dipole strength of the nucleus ${}^{136}$Ba has been investigated. Two measurements were performed with electron energies of 7.0 and 11.4 MeV at the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. Photon scattering experiments on the same nucleus have been performed at the high-intensity gamma-ray source (HI$\ensuremath{\gamma}$S) facility of the Triangle Universities Nuclear Laboratory between 4.7 and 9.3 MeV. The geant4 code has been used to determine detector response and non-nuclear scattered events. Thus it is possible to account for the dipole strength in the quasicontinuum of unresolvable transitions. A statistical code was used to simulate inelastic transitions and to determine the branching ratios of transitions to the ground state. The resulting photoabsorption cross section is compared to quasiparticle random-phase approximation and relativistic quasiparticle time blocking approximation calculations.

Cross-section measurement of9Be(γ,n)8Be and implications forα+α+n→9Be in therprocess

Models of the r-process are sensitive to the production rate of 9Be because, in explosive environments rich in neutrons, alpha(alpha n,gamma)9Be is the primary mechanism for bridging the stability gaps at A=5 and A=8. The alpha(alpha n,gamma)9Be reaction represents a two-step process, consisting of alpha+alpha -> 8Be followed by 8Be(n,gamma)9Be. We report here on a new absolute cross section measurement for the 9Be(gamma,n)8Be reaction conducted using a highly-efficient, 3He-based neutron detector and nearly-monoenergetic photon beams, covering energies from E_gamma = 1.5 MeV to 5.2 MeV, produced by the High Intensity gamma-ray Source of Triangle Universities Nuclear Laboratory. In the astrophysically important threshold energy region, the present cross sections are 40% larger than those found in most previous measurements and are accurate to +/- 10% (95% confidence). The revised thermonuclear alpha(alpha n,gamma)9Be reaction rate could have implications for the r-process in explosive environments such as Type II supernovae.

Non-planar four-mirror optical cavity for high intensity gamma ray flux production by pulsed laser beam Compton scattering off GeV-electrons

As part of the R&D toward the production of high flux of polarised Gamma-rays we have designed and built a non-planar four-mirror optical cavity with a high finesse and operated it at a particle accelerator. We report on the main challenges of such cavity, such as the design of a suitable laser based on fiber technology, the mechanical difficulties of having a high tunability and a high mechanical stability in an accelerator environment and the active stabilization of such cavity by implementing a double feedback loop in a FPGA.

Development of a bunch-by-bunch longitudinal feedback system with a wide dynamic range for the HIGS facility

Electron beam coupled-bunch instabilities can limit and degrade the performance of storage ring based light sources. A longitudinal feedback system has been developed for the Duke storage ring to suppress multi-bunch beam instabilities which prevent stable, high-current operation of the storage ring based free-electron lasers (FELs) and an FEL driven Compton gamma source, the high intensity gamma-ray source (HIGS) at Duke University. In this work, we report the development of a state-of-the-art second generation longitudinal feedback system which employs a field programmable gate array (FPGA) based processor, and a broadband, high shunt-impedance kicker cavity. With two inputs and two outputs, the kicker cavity was designed with a resonant frequency of 937 MHz, a bandwidth of 97 MHz, and a shunt impedance of 1530 Ω . We also developed an S-matrix based technique to fully characterize the performance of the kicker cavity in the cold test. This longitudinal feedback system has been commissioned and optimized to stabilize high-current electron beams with a wide range of electron beam energies (250 MeV to 1.15 GeV) and a number of electron beam bunch modes, including the single-bunch mode and all possible symmetric bunch modes. This feedback system has become a critical instrument to ensure stable, high-flux operation of HIGS to produce nearly monochromatic, highly polarized Compton gamma-ray beams.

Behavior of Random Hole Optical Fibers under Gamma Ray Irradiation and Its Potential Use in Radiation Sensing Applications

Effects of radiation on sensing and data transmission components are of greatinterest in many applications including homeland security, nuclear power generation, andmilitary. A new type of microstructured optical fiber (MOF) called the random hole opticalfiber (RHOF) has been recently developed. The RHOFs can be made in many differentforms by varying the core size and the size and extent of porosity in the cladding region.The fibers used in this study possessed an outer diameter of 110 μm and a core ofapproximately 20 μm. The fiber structure contains thousands of air holes surrounding thecore with sizes ranging from less than 100 nm to a few μm. We present the first study ofthe behavior of RHOF under gamma irradiation. We also propose, for the first time to ourknowledge, an ionizing radiation sensor system based on scintillation light from ascintillator phosphor embedded within a holey optical fiber structure. The RHOF radiationresponse was compared to normal single mode and multimode commercial fibers(germanium doped core, pure silica cladding) and to those of radiation resistant fibers (puresilica core with fluorine doped cladding fibers). The comparison was done by measuringradiation-induced absorption (RIA) in all fiber samples at the 1550 nm wavelength window(1545 ± 25 nm). The study was carried out under a high-intensity gamma ray field from a 60Co source (with an exposure rate of 4x104 rad/hr) at an Oak Ridge National Laboratory gamma ray irradiation facility. Linear behavior, at dose values less than 106 rad, was observed in all fiber samples except in the pure silica core fluorine doped cladding fiber which showed RIA saturation at 0.01 dB. RHOF samples demonstrated low RIA (0.02 and 0.005 dB) compared to standard germanium doped core pure silica cladding (SMF and MMF) fibers. Results also showed the possibility of post-fabrication treatment to improve the radiation resistance of the RHOF fibers.

Copolymerization of Styrene onto Polyethersulfone Films Induced By Gamma Ray Irradiation

Radiation-induced grafting of styrene into polyethersulfone (PES) films were investigated by simultaneous method in solution using gamma-ray from a radio nuclide 60Co source. The starting materials were prepared via casting method of the polymeric solution. The grafted membranes have side chains of polystyrene which may be sulfonated to become proton conductive to be used as polymer electrolyte membrane in fuel cell. The localized energy of high intensity gamma-ray induced breaking of chemical bonds leads to free radical formation, a reactive species having a single unpaired electron. The radical start a conventional polymerization sequence comparable with that obtained with a chemical catalyst acting as initiator. The effects of grafting conditions include monomer concentration, irradiation total dose, dose rate and addition of cross linking agent, were studied by means of the techniques of structure analysis, morphology, thermal degradation and crystallinity. The degree of grafting (DOG) was analyzed by percentage of the weight increase. As a result, the reaction always follows the same pattern: DOG increases rapidly initially whilst propagation is the main reaction, then more slowly as termination becomes more frequent.

Parity assignments inYb172,174using polarized photons and theKquantum number in rare earth nuclei

The 100 % polarized photon beam at the High Intensity gamma-ray Source (HIgS) at Duke University has been used to determine the parity of six dipole excitations between 2.9 and 3.6 MeV in the deformed nuclei 172,174 Yb in photon scattering (g,g') experiments. The measured parities are compared with previous assignments based on the K quantum number that had been assigned in Nuclear Resonance Fluorescence (NRF) experiments by using the Alaga rules. A systematic survey of the relation between gamma-decay branching ratios and parity quantum numbers is given for the rare earth nuclei.

The calibration setup of the MEGA prototype at the high intensity γ-ray source

We describe the calibration measurements of the MEGA prototype, a tracking Compton and pair creation telescope. The measurements were performed at the high intensity gamma-ray source (HIγS) facility from April 21 to May 06, 2003. The main goal of this calibration was directed at higher energies, above those available from radioactive lab sources, and at polarization. A total of 15.5×10 6 triggered events at 10 energies in the range of 0.7–49 MeV and at six angles of incidence (0°–180°) were recorded.

Low-energy photodisintegration of the deuteron and Big-Bang nucleosynthesis

The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the high-intensity gamma-ray source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron–proton radiative capture reaction at energies important for Big-Bang nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations. Therefore, the uncertainty in the baryon density ΩBh2 obtained from Big-Bang Nucleosynthesis can be reduced at least by 20%.