Γ-ray Beam Research Articles

The irradiation studies on diamond-like carbon films

Diamond-like carbon (DLC) films have been deposited on glass substrates using radio-frequency (r.f.) plasma deposition method. γ-ray, ultraviolet (UV) ray and neutron beam were used to irradiate the DLC films. Raman spectroscopy and infrared (IR) spectroscopy were used to characterize the changing characteristics of SP 3C–H bond and hydrogen content in the films due to the irradiations. It showed that, the damage degrees of the γ-ray, UV ray and neutron beam on the SP 3C–H bonds are different. Among them, the damage of γ-ray on the SP 3C–H bond is the weakest. When the irradiation dose of γ-ray reaches 10×10 4 Gy, the SP 3C–H bond reduces about 50% in number. The square resistance of the films is reduced due to the irradiation of UV ray and this is caused by severe oxidation of the films. Compared with that of the as-deposited one, the IR transmittance of the films irradiated by both γ-ray and neutron beam is increased to some extent. By using the results on optical gap of the films and the fully constrained network theory, the hydrogen content in the as-deposited films is estimated to be 10–25 at.%.

Frontier of Quark-Nuclear Physics at SPring-8 and Nuclear Data

A new facility for GeV γ-ray beams in an energy range of 1.5~3.5 GeV has been constructed for developing physics with photo-nuclear reactions at SPring-8. The GeV γ-rays are produced via the inverse Compton scattering process, and are used to study the sub-nucleonic structure of the nucleon via the productions of ϕ and K + mesons. This SPring-8 project offers an unique opportunity to study the nucleon structure in view of the quark physics. The recent experimental results to observe ϕ and K + mesons are discussed to look for the physics in relation to strangeness quarks in nucleon. A new beam line for MeV γ-rays at SPring-8 to give new possibilities for the basic science, astrophysics, and nuclear structure studies is discussed.

The effect of wall thickness on the response of a spherical ionization chamber

Air-filled ionization chambers are used widely for radiation dosimetry. For some applications it is important to know the effect on the chamber response of photon attenuation and scattering in the chamber walls. Traditionally, the wall effect is determined by measuring the chamber response as a function of wall thickness and extrapolating linearly to zero thickness. We have constructed a spherical graphite chamber with variable wall thickness. The change in the chamber response with wall thickness has been measured in a 137Cs γ-ray beam. Our data show that the change in response is not linear with wall thickness, in agreement with the theoretical prediction of Bielajew (1990 Med. Phys. 17 583–7). A linear versus non-linear extrapolation of the measured data to zero wall thickness leads to a difference of almost 1% in the estimate of the wall correction factor, Kw. The value of Kw obtained using the non-linear extrapolation is in good agreement with the result obtained using Monte Carlo techniques.

Performance analysis and determination of the pwall correction factor for 60Co γ-ray beams for Wellhöfer Roos-type plane-parallel chambers

The wall perturbation correction factor pwall in 60Co for Wellhöfer Roos-type plane-parallel ionization chambers is determined experimentally and compared with the results of a previous study using PTW–Roos chambers (Palm et al 2000 Phys. Med. Biol. 45 971–81). Five ionization chambers of the type Wellhöfer PPC-35 (or its equivalent PPC-40) are used for the analysis. Wall perturbation correction factors are obtained by assuming ND,air chamber factors determined by cross-calibration in a high-energy electron and in a 60Co γ-ray beam to be equal, and by assigning any differences to the wall perturbation factor. The procedure yields a pwall value of 1.018 (uc = 0.010), which is slightly higher than the value 1.014 (uc = 0.010) formerly obtained for the PTW–Roos chambers using the ND,air method. The chamber-to-chamber variation in pwall for the Wellhöfer–Roos chambers is found to be very small, with a maximum difference of 0.3%. The effect of using new pcav values for graphite-walled Farmer-type chambers used in water in electron beams is to decrease pwall by approximately 0.5%. The long- and short-term stability of the Roos-type chambers manufactured by Wellhöfer is investigated by measurements at the IAEA Dosimetry Laboratory in Vienna, Austria, and at the Sahlgrenska University Hospital in Göteborg, Sweden. Calibrations made at the IAEA over several months show variations in the ND,w calibration factors larger than expected, based on previous experiences with PTW–Roos chambers. Measurements of the short-term stability of the Wellhöfer–Roos chambers show a marked increase in chamber response for the time the chambers are immersed in water, pointing to a possible problem in the chamber design. As a consequence of these findings, Wellhöfer is currently working on a re-design of the chamber to solve the stability problem.

天然食品用着色料の放射線殺菌に関する研究 ビートレッドの機能特性に及ぼすγ線および電子線照射の影響

For the practical use of radicidation, we studied on the effects of γ-ray and electron beam on functional properties of beet red colorant, natural colors with low heat stability and high possibility of microbe contamination.Neither γ-ray or electron beam had any significant influence on color contents and color tone of red beet products at less than 10 kGy of irradiation for the practical use. Influence of moisture content at level of less than 20% in powdered product was not observed.The results suggest that both γ-ray and electron beam irradiation is significantly effective in decontamination of powdered beet red products.

Relative biological effectiveness of boron ions on human melanoma cells

Purpose : To compare the difference in relative biological effectiveness (RBE) between 10 B ions and a 60 Co γ-ray beam for human melanoma cells using in vitro cell survival based on a clonogenic assay. Materials and methods : Cells were irradiated in vitro under aerobic conditions with 60 Co and 10 B ions with different linear energy transfer (LET) (40, 80 and 160 eV nm -1) . The dose to the cells was determined using ferrous sulphate dosimetry and an ionisation chamber. The standard linear-quadratic model and the newly proposed repairable conditionally repairable damage (RCR) model were used to calculate the RBE. Results : The RBE at 10% cell survival for 40, 80 and 160eV nm -1 boron ions compared with 60 Co were 1.98 (1.83-2.22), 2.85 (2.64-3.11) and 3.37 (3.17-3.58), respectively, of almost independence of the model used in the calculation. Conclusions : Different cell survival models may generate different RBE, especially at low doses and high cell survival levels.

Spatial distribution and polarization of γ-rays generated via Compton backscattering in the Duke/OK-4 storage ring FEL

Beams of nearly monochromatic γ-rays are produced via intracavity Compton backscattering in the OK-4/Duke storage ring FEL, the high-intensity γ-ray source (HIγS). Presently, HIγS generates γ-ray beams with an energy tunable from 2 to 58 MeV and a maximum flux of 5×10 7 γ-rays per second. The γ-rays are linearly polarized with a degree of polarization close to 100% (V.N. Litvinenko, et al., Predictions and expected performance for the VUV OK-5/Duke Storage Ring FEL with variable polarization, Nucl. Instr. and Meth. A, to be published in this proceeding) and they are collimated to pencil-like semi-monoenergetic beams with RMS energy spreads as low as 0.2%. The detailed theoretical and experimental studies of the γ-ray beam quality were conducted during the last two years (S.H. Park, Thesis, Duke University, Durham, NC, USA, 2000). In this paper, we present the theoretical analysis and the experimental results on the spatial distribution and polarization of γ-rays from the HIγS facility.

Electrical resistivity of carbon black-filled high-density polyethylene (HDPE) composite containing radiation crosslinked HDPE particles

The room-temperature volume resistivity of high-density polyethylene (HDPE)–carbon black (CB) blends containing previously radiation crosslinked HDPE powder was studied. The results showed that the room-temperature volume resistivity decreases with increasing concentration of crosslinked HDPE powder. It is considered that the crosslinked HDPE particles act as a filler that increases the CB volume fraction in the HDPE matrix. The results of an optical microscope observation indicated that the crosslinked polymer particles are dispersed in the HDPE/CB composite. This effect of the crosslinked particles is attributed to the fact that the crosslinked mesh size of the HDPE particles is so small that the CB particles cannot go inside them. The effect of 60Co γ-ray and electron beam (EB) irradiation on the positive temperature coefficient, negative temperature coefficient and electrical resistivity behavior of the blends were studied.

Energy correction factors of LiF powder TLDs irradiated in high-energyelectron beams and applied to mailed dosimetry for quality assurancenetworks

Absorbed dose determination with thermoluminescent dosimeters (TLDs) generallyrelies on calibration in 60Co γ-ray reference beams. Theenergy correction factor fECo for electron beams takes into accountthe difference between the response of the TLD in the beam of energy E andin the 60Co γ-ray beam. In this work, fECo wasevaluated for an LiF powder irradiated in electron beams of 6 to 20 MeV(Varian 2300C/D) and 10 to 50 MeV (Racetrack MM50), and its variation withelectron energy, TLD size and nature of the surrounding medium was alsostudied for LiF powder. The results have been applied to the ESTRO-EQUALmailed dosimetry quality assurance network.Monte Carlo calculations (EGS4, PENELOPE) and experiments have been performedfor the LiF powder (ρ = 1.4 g cm-3) (DTL937, Philitech,France), read on a home made reader and a PCL3 automatic reader (Fimel,France). The TLDs were calibrated using Fricke dosimetry and compared withthree ionization chambers (NE2571, NACP02, ROOS).The combined uncertainties in the experimental fECo factorsdetermined in this work are less than about 0.4% (1 SD), which is appreciablysmaller than the uncertainties up to 1.4% (1 SD) reported for othercalculated values in the literature. Concerning the Varian 2300C/D beams, themeasured fECo values decrease from 1.065 to 1.049±0.004 (1 SD)when the energy at depth in water increases from 2.6 to 14.1 MeV; theagreement with Monte Carlo calculations is better than 0.5%. For theRacetrack MM50 pulsed-scanned beams, the average experimental value offECo is 1.071±0.005 (1 SD) for a mean electron energy at depthĒz ranging from 4.3 to 36.3 MeV: fECo is up to 2% higherfor the MM50 beams than for the 2300C/D beams in the range of the testedenergies.The energy correction factor for LiF powder (3 mm diameter and 15 mm length)varies with beam quality and type (pulsed or pulsed-scanning), cavity size andnature of the surrounding medium.The fECo values obtained for the LiF powder (3 mm diameter and 15 mmlength) irradiated in water, have been applied to the EQUAL external auditnetwork, leading to a good agreement between stated and measured doses, with amean value of 1.002±0.022 (1 SD), for 170 beam outputs checked (36electron beam energies) in 13 `reference' radiotherapy centres in Europe.Such fECo data improve the accuracy of the absorbed dose TLDdetermination in electron beams, justifying their use for quality control inradiotherapy.

Review of some selected experiments on laser electron–beam interaction

The third-generation 1.5 GeV electron storage ring DELTA, dedicated to synchrotron-radiation experiments, accelerator technology and UV FEL operation, was commissioned about 2 years ago at the Dortmund University. After the first successful lasing in the visible region (470 nm) beginning of this year, it is planned to obtain lasing also in the UV near 200 nm and then later to use the high average intracavity power and natural synchronization of electron and optical pulses to produce intense beams of high-energy γ-rays by Compton backscattering. Applying these γ-rays, a photo-fission experiment of importance for nuclear astrophysics is described. Since the time resolution of high-brightness synchrotron light sources is limited to more than 10 ps, it is envisioned to test a novel technique for generating sub-picosecond X-ray pulses based on the interaction of the electrons with a co-propagating beam of femtosecond photon pulses from an external TW-laser. This technique will be applied at DELTA by using its superconducting wiggler and a permanent-magnet undulator. Simulations show that a brilliance of 10 8 photons/(s mm 2 mrad 2 0.1% bandwidth) with pulse durations of the order of 100 fs can be achieved. Using the magnetic insertions of DELTA and an external TW-laser will further allow measurements for testing laser acceleration in the ultra-high vacuum of a storage ring and of radiation damping of the beam emittance on a fast time scale. First, results of laser-beam monitoring at the stretcher ring AmPS to determine the transverse beam emittance are presented and are intended to be performed also at DELTA. For these investigations the electron beam has been scanned at 90° with a high-power laser beam, and forward-scattered Compton photons were detected to derive the beam profile.

Generation of Compton backscattering γ-ray beams

The backward scattering of laser light against high-energy electrons may be used to produce highly polarized photon beams of low background, with an energy resolution of a few percent. The general characteristics of Compton backscattering beams are outlined and the application of this technique to different electron accelerators is reviewed. The results from existing facilities are presented with an outlook to planned future installations.

Relativistic Winds from Compact Gamma‐Ray Sources. II. Pair Loading and Radiative Acceleration in Gamma‐Ray Bursts

We consider the effects of rapid pair creation by an intense pulse of γ-rays propagating ahead of a relativistic shock. Sidescattered photons colliding with the main γ-ray beam amplify the density of scattering charges. The acceleration rate of the pair-loaded medium is calculated and its limiting bulk Lorentz factor related to the spectrum and compactness of the photon source. One obtains, as a result, a definite prediction for the relative inertia in baryons and pairs. The deceleration of a relativistic shock in the moving medium and the resulting synchrotron emissivity are compared with existing results for a static medium. The radiative efficiency is increased dramatically by pair loading. When the initial ambient density exceeds a critical value, the scattering depth traversed by the main γ-ray pulse rises above unity and the pulse is broadened. This sets an upper limit to the preburst mass-loss rate of ~10-5 M☉ per year and places significant constraints on γ-ray burst progenitors. An anisotropic γ-ray flux (on an angular scale Γ-1 or larger) drives a large velocity shear that greatly increases the energy in the seed magnetic field forward of the propagating shock.

A Three‐dimensional Outer Magnetospheric Gap Model for Gamma‐Ray Pulsars: Geometry, Pair Production, Emission Morphologies, and Phase‐resolved Spectra

A three-dimensional pulsar magnetosphere model is used to study the geometry of outer magnetospheric gap accelerators, following seminal work of Romani and coworkers. The size of the outer gap is self-consistently limited by pair production from collisions of thermal photons from polar cap heating of backflow outer gap current with curvature photons emitted by gap-accelerated charged particles. In principle, there could be two topologically disconnected outer gaps. Conditions for local pair production such as local field line curvature, soft X-ray density, electric field, etc., support pair production inside an outer gap only between rin() (the radius of the null surface at azimuthal angle ) and rlim() ≈ 6rin( = 0) RL (the light cylinder radius). Secondary pairs, on the other hand, are produced almost everywhere outside the outer gap by collisions between curvature photons and synchrotron X-rays emitted by these secondary pairs. These processes produce a wide X-ray fan beam in the outgoing direction and a very narrow beam in the incoming direction for each outer gap. For pulsars with a large magnetic dipole inclination angle, part of the incoming γ-ray beam will be absorbed by the stellar magnetic field. If the surface magnetic field is dominated by a far off-center dipole moment (e.g., as in a proposed plate tectonic model), gravitational bending of photons from polar cap accelerators and their ultimate conversion into outflowing e± pairs can result in the quenching of one of these two outer gaps. Various emission morphologies for the pulsar (depending on magnetic inclination angle and viewing angle) are presented. Double-peak light curves with strong bridges are most common. From the three-dimensional structure of the outer gap and its local properties, we calculate phase-resolved spectra of gamma-ray pulsars and apply them to observed spectra of the Crab pulsar.

On-line nuclear ash gauge for coal based on gamma-ray transmission techniques

Developments and applications of on-line nuclear gauges in the coal industry are highly requested. In this work, a nuclear ash gauge for coal, based on γ-ray transmission techniques is developed. Single and dual energy γ-ray beams are used to determine the ash content of coal. The percentage ash content as a function of the γ-ray intensities transmitted through coal samples is measured and sensitivity curves are obtained. An empirical formulation relating the ash content values to the γ-ray intensities is derived. Preliminary results show that both single and dual energy γ-ray transmission techniques can be used to give a rapid on-line estimation of the ash concentration values in coal with low cost and reasonable accuracy, but the dual one is much preferable.

Observation of a highly directional γ-ray beam from ultrashort, ultraintense laser pulse interactions with solids

Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of γ rays was observed directly behind the target. The γ rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction [63Cu(γ,n)62Cu] in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of Cu62. New measurements of the bremsstrahlung radiation at 1019 W cm−2 are also presented.

Compton back-scattering of X-photons from 8 GeV electrons at SPring-8

The experimental feasibility of using an intensive photon beam at the SPring-8 for producing a high-energy γ-ray beam is examined. Compton back-scattering of the soft X-photons emitted by an undulator and reflected back by a multi-layer mirror from the electron beam can produce a quasi-monochromatic γ-ray beam up to an energy very close to 8 GeV. The intensity of the γ-ray beam in the energy range of 6.6–7.8 GeV has been estimated at 2×10 4 per second. The energy shape and the scattered angle of γ-rays produced in Compton back-scattering of the soft X-photons from an 8 GeV electron beam are calculated.

Cross-linking of amniotic membranes

Abstraet-Human amniotic membrane was cross-linked with chemical and radiation methods to investigate the effect of cross-linking on its physicochemical and biodegradation properties. Radiation cross-linking was performed with γ-ray and electron beam while chemical cross-linking was with glutaraldehyde (GA). Both γ-ray and electron beam irradiation decreased the tensile strength and elongation at break of the amniotic membrane with an increase in the irradiation dose, whereas GA cross-linking had no effect on the tensile properties. This is probably due to the scission of collagen chains through irradiation. No significant change was observed on the water content of cross-linked amniotic membranes for any of the crosslinking methods and in marked contrast with cross-linking of a gelatin membrane. A permeation study revealed that protein permeation through the amniotic membrane was not influenced by the GA concentration at cross-linking. These findings are ascribed to the structure characteristic of the amniotic membrane. The membrane is composed of a fibrous mesh structure from an assemblage of collagen fibers. It is possible that cross-linking takes place in the interior of the fiber assembly without impairing the mesh structure, resulting in no change of the water content and protein permeability. In vitro degradation of cross-linked amniotic membranes revealed that radiation cross-linking appeared to be much less effective than GA cross-linking in retarding the degradation, probably because of low cross-linking densities. GA-cross-linked amniotic membranes were degraded more slowly as the GA concentration at cross-linking increased. When the GA-cross-linked amniotic membrane was subcutaneously implanted in the rat, the tissue response was mild, similar to that of the non-cross-linked native membrane.

Assessment of heat and storage conditions on γ-ray and electron beam irradiated UHMWPE by electron spin resonance

Electron spin resonance (ESR) spectroscopic study was undertaken to explore the nature of any remaining radicals in ultra-high molecular weight polyethylene (UHMWPE) after irradiation with γ-rays and electron beams to a dose of 25 KGy in air or N 2 environment. The decay of radicals was studied by observing the ESR intensity change as a function of time. The following post-irradiation conditions were employed: (1) storage in air or N 2 at 25°C, and (2) heat treatment in air or N 2 at 80, 100, and 120°C for time intervals up to 8 h. The study suggests that radicals remaining trapped in the matrix of UHMWPE could be dramatically scavenged by heat treatment, independently of the atmosphere during irradiation and the heating process. The melting temperature and mechanical properties of irradiated UHMWPE under the experimental conditions employed were shown not to alter significantly by heat treatment, except in the presence of air.

A Compton source of high energy polarized tagged γ-ray beams. The ROKK-1M facility

The ROKK-1M facility generates high energy polarized γ-ray beams by backscattering of laser light against the high energy electron and positron beams of the VEPP-4M collider. The facility design allows to obtain backscattering of laser light on electron and positron beams separately or simultaneously. Tagging and/or collimation is applied to select a narrow energy band from the γ-quanta spectrum. Operating in a laser polarimeter mode, the ROKK1-M facility is able to measure transverse and longitudinal polarization of the electron and positron beams in the VEPP-4M collider. A description of the facility and achieved γ-ray beam parameters are presented in this paper.

Parametric study of laser Compton-backscattering from free relativistic electrons

The frontal collisions of a laser with free relativistic electrons result in Compton-backscattered γ-rays. The energy of these γ-rays is dependent on the laser and electron energy and ranges from keV to tens of MeV. In a sufficiently narrow backscattering angle the γ-rays are nearly monochromatic. Over the past 30 years there have been several attempts to produce γ-ray beams by laser backscattering from relativistic electrons. One aim is to produce γ-rays in a high MeV energy range with rates useful for nuclear physics, another for medical applications in energy range from high keV to low MeV. In order to enable conceptual studies for medical applications, a computer program IMRCBS based on the theory of laser Compton-backscattering from free relativistic electrons was written. The present document gives: (a) description of the kinematics of Compton-backscattering mechanism, and (b) parametric study of laser Compton-backscattering. The study shows, that if variable energy of γ-beam is required, then the use of a free electron laser in combination with fixed electron energy accelerator is a better combination than the use of a fixed laser energy with electron accelerator with variable energy.