Bremsstrahlung Energy Research Articles

Isomeric yield ratios in the photoproduction of 52m,gMn from natural iron using 50-, 60-, 70-MeV, and 2.5-GeV bremsstrahlung

The isomeric yield ratios for the natFe(γ,xn1p)52m,gMn reactions have been measured by the activation and the γ-ray spectroscopic methods at 50-, 60-, 70-MeV, and 2.5-GeV bremsstrahlung energies. The high purity natural iron foils in disc shape were irradiated with uncollimated bremsstrahlung beams of the Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution γ-ray spectrometry with a calibrated high-purity Germanium (HPGe) detector. In order to improve the accuracy of the experimental results the necessary corrections were made in the gamma activity measurements and data analysis. The obtained isomeric yield ratios for the natFe(γ,xn1p)52m,gMn reactions at 50-, 60-, 70-MeV, and 2.5-GeV bremsstrahlung energies are 0.27 ± 0.03, 0.33 ± 0.04, 0.34 ± 0.04, and 1.25 ± 0.15, respectively. The present results at 50-, 60-MeV, and 2.5-GeV bremsstrahlung energies are the first measurements. We found that the isomeric yield ratio of the natFe(γ,xn1p)52m,gMn reaction depends on the incident bremsstrahlung energy and the mass difference between the product and the target nucleus when we compared the present results with other experimental data at different energies.

Measurement of isomeric-yield ratios for the 197Au(γ,n)196m,gAu reactions induced by bremsstrahlung

We measured isomeric-yield ratios for the 197Au(γ,n)196m,gAu reactions with bremsstrahlung energies of 50-, 60-, 70- MeV, and 2.5-GeV at the two different electron linac of the Pohang accelerator laboratory by using the activation method. The photons were produced when a pulsed electron beam hit a thin tungsten target. The well-known photoactivation method was used and hence the induced activities in the irradiated foils were measured with the high-resolution γ-ray spectrometric system consisting of lithium drifted high-purity Germanium detector and a multichannel analyzer. The measured isomeric-yield ratios for the 197Au(γ,n)196m,gAu reactions were (4.95 ± 0.51) × 10−4, (5.72 ± 0.72) × 10−4, (6.03 ± 0.50) × 10−4, and (9.27 ± 0.83) × 10−4 for 50-, 60-, 70-MeV, and 2.5-GeV bremsstrahlung energies, respectively. The present results measured with the bremsstrahlung energy higher than 60-MeV are the first measurement.

Photofission of 235U and 237Np with Bremsstrahlung Photons below 20 MeV: Measurements of Delayed Neutron Yields and Time Spectra

Recently, new applications based on detection of delayed neutrons (DNs) or delayed photons produced during photofission have shown the need for new basic nuclear data. Indeed, available data for DNs are scarce, incomplete, and sometimes contradictory. An experimental campaign has been dedicated to DN measurements for some important actinides with a bremsstrahlung end-point energy spectrum up to 20 MeV. The experiments were carried out at the electron accelerator facility ELSA installed at the Commissariat à l’Energie Atomique (CEA) center of Bruyères-le-Châtel, France. Delayed neutrons were measured by 12 3He counters embedded in an annular polyethylene cylinder. Delayed neutron absolute yields were determined. Different irradiation-decay time combinations allowed the extraction of the averaged six-group parameters of DNs. Similarly to the nuclear reactor physics, these groups are formed by lumping DN precursors according to their half-lives. The DN time dependence is then expressed by the sum of group contributions.In this paper, DN absolute yields and six-group parameters for 235U at 15 and 18 MeV and 237Np at 15 MeV are presented. The 235U and 237Np absolute DN yields are found slightly lower than those published in the literature. For 235U, the six-group parameters show no dependence on incident electron energy from 10 to 18 MeV. In addition, the group parameters are very close to those of 237Np. This work helped to resolve the discrepancies of the photofission DN parameters for 235U while the six-group parameters for 237Np are reported for the first time.

Gluon Bremsstrahlung in Weakly-Coupled Plasmas

I report on some theoretical progress concerning the calculation of gluon bremsstrahlung for very high energy particles crossing a weakly-coupled quark-gluon plasma. (i) I advertise that two of the several formalisms used to study this problem, the BDMPS-Zakharov formalism and the AMY formalism (the latter used only for infinite, uniform media), can be made equivalent when appropriately formulated. (ii) A standard technique to simplify calculations is to expand in inverse powers of logarithms ln ( E / T ) . I give an example where such expansions are found to work well for ω / T ≳ 10 where ω is the bremsstrahlung gluon energy. (iii) Finally, I report on perturbative calculations of q ˆ .

Mass–yield distributions of fission products from photo-fission of natPb induced by 50–70 MeV bremsstrahlung

The mass–yield distributions of various fission products have been determined in the 50-, 60- and 70-MeV end point bremsstrahlung induced fission of natPb using off-line γ-ray spectrometric technique in the electron linac at Pohang Accelerator Laboratory, Korea. The mass–yield distributions are symmetric with average mass of 102.34, 102.25 and 102.03 and FWHM of 21, 22 and 23 mass unit, respectively. From the present data and literature data in the 50–85 MeV bremsstrahlung induced fission of 209Bi the following observations were obtained: (i) The average masses of the yield distributions in the 50–85 MeV bremsstrahlung induced fission of natPb and 209Bi are around 102.25 ± 0.25 and 103 ± 0.5, respectively. (ii) The FWHM of the mass–yield distributions increases from about 21 mass units at 50 MeV to 23 mass units at 70–85 MeV, which is explained from the point of increase in multi-chance fission probability with increasing excitation energy. (iii) Within the bremsstrahlung energy range of 50–85 MeV, the role of nuclear structure effect in the mass–yield distribution was observed in the photo-fission of 209Bi, whereas it was not seen in case of natPb. This may be due to the presence of so many isotopes in natPb unlike mono-isotopic 209Bi.

Measurement of isomeric yield ratios for 90Zr(γ, n) 89m,gZr, natZr(γ, xn1p) 86m,gY, and 89Y(γ, xn) 87m,g,86m,gY reactions with 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios in the photonuclear reactions of natZr(γ, n) 89m,gZr, natZr(γ, xn1p) 86m,gY, and 89Y(γ, xn) 87m,g,86m,gY by the activation method. The high-purity natural Zr and Y metallic foils in disc shape were irradiated with uncollimated bremsstrahlung beams of 50-, 60-, and 70-MeV generated from an electron linear accelerator at Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution γ-ray spectrometric system consisting of a high-purity germanium detector and a multichannel analyzer. The obtained isomeric yield ratios in the formation of 89m,gZr, 87m,gY, and 86m,gY are compared with the corresponding values found in the literature. The measured isomeric yield ratios at the bremsstrahlung energies of 50-, 60-, and 70-MeV are the first measurement except 87Y at 50-MeV bremsstrahlung.

Evolving distribution of hard partons traversing a hot, strongly interacting plasma

We present results for the evolution of the momentum distribution of a hard parton traversing a brick of quark-gluon plasma, considering both bremsstrahlung and collisional energy loss. The complete leading order transition rates are included. We find a significant modification of the evolving momentum distribution compared to results obtained by employing an approximate implementation of the collisional energy loss that uses the mean energy loss, together with momentum diffusion.

O(g)plasma effects in jet quenching

We consider the bremsstrahlung energy loss of high energy partons moving in the quark-gluon plasma, at weak coupling. We show that the rates for these processes receive large O(g) corrections from classical (nonabelian) plasma physics effects, which are calculated. In the high-energy (deep LPM) regime these corrections can be absorbed in a change of the transverse momentum broadening coefficient $\hat{q}$, which we give to the next-to-leading order. The correction is large even at relatively weak couplings $\alpha_s\sim 0.1$, as is typically found for such effects, signaling difficulties with the perturbative expansion. Our approach is based on an effective "Euclideanization" property of classical physics near the light-cone, which allows an effective theory approach based on dimensional reduction and suggests a new possibility for the nonperturbative lattice study of these effects.

The effect of magnetic field strength on the time evolution of high energy bremsstrahlung radiation created by an electron cyclotron resonance ion source

An electron cyclotron resonance (ECR) ion source is one of the most used ion source types for high charge state heavy ion production. In ECR plasma the electrons are heated by radio frequency microwaves in order to provide ionization of neutral gases. As a consequence, ECR heating also generates very high electron energies (up to MeV region) which can produce a vast amount of bremsstrahlung radiation causing problems with radiation shielding and heating superconducting cryostat of an ECR ion source. To gain information about the time evolution of the electron energies in ECR plasma radial bremsstrahlung measurements were performed. JYFL 14 GHz ECR ion source was operated in pulsed mode and time evolution measurements were done with different axial magnetic field strengths with oxygen and argon plasmas. Bremsstrahlung data were analyzed with a time interval of 2 ms yielding information at unprecedented detail about the time evolution of high energy bremsstrahlung radiation from an ECR ion source. It was observed, for example, that reaching the steady state phase of the plasma bremsstrahlung requires several hundred milliseconds and the steady state time can be different with different gases.

Photoactivation experiment onAu197and its implications for the dipole strength in heavy nuclei

The ${}^{197}\mathrm{Au}(\ensuremath{\gamma},n)$ reaction is used as an activation standard for photodisintegration studies on astrophysically relevant nuclei. At the bremsstrahlung facility of the superconducting electron accelerator ELBE (Electron Linear accelerator of high Brilliance and low Emittance) of Forschungszentrum Dresden-Rossendorf, photoactivation measurements on $^{197}\mathrm{Au}$ have been performed with bremsstrahlung endpoint energies from 8.0 to 15.5 MeV. The measured activation yield is compared with previous experiments as well as with calculations using Hauser-Feshbach statistical models. It is shown that the experimental data are best described by a two-Lorentzian parametrization with taking the axial deformation of $^{197}\mathrm{Au}$ into account. The experimental ${}^{197}\mathrm{Au}(\ensuremath{\gamma},n)$ reaction yield measured at ELBE via the photoactivation method is found to be consistent with previous experimental data using photon scattering or neutron detection methods.

Deexcitation of plasma by relativistic electrons

The characteristics of the electromagnetic radiation generated as a result of the interaction of relativistic electrons with a plasma are investigated. The main attention is paid to the analysis of the effect of broadening mechanisms on the bremsstrahlung energy spectrum of the relativistic electrons propagating in a carbon plasma upon deexcitation of its components.

Purely Angular Effects of Photon Buildup Factors for Thin Shields of Lead, Iron, Aluminum, and Water

This study investigates purely angular effects on photon buildup factors for slabs with optical thickness up to 10 mean free paths. Photon buildup factors are determined for different slabs, upon which monoenergetic photons between 50 keV and 10 MeV are incident at angles between 0 and 1.48 radians. As the incident angle is increased, the physical slab thickness is reduced to maintain a constant slant-path optical thickness relative to incident photons. This method identifies previously unexplored angular relationships between slab thickness and incident angle. Coupled electron/photon cross sections are used to account for secondary photon effects of bremsstrahlung and electron binding energies. The discrete ordinates code PARTISN is used to determine angular photon buildup factors for ten incident energies and ten incident angles for lead, iron, aluminum, and water slabs. Portions of these results are applicable to other slab geometry buildup studies.

MO-E-AUD C-07: Modeling Small Animal Micro Irradiator Orthovoltage Sources

Purpose: To model and compute spectral output, intensity, dose fall off, dose rate, and penumbra that can be achieved using industrial orthovoltage x‐rays sources used in small animal micro irradiators. Method and Materials: Using data from commercial sources as input parameters we investigated the performance of orthovoltage sources that can be used in small animal micro irradiators. We developed a pencil beam propagation code which was combined with a mouse digital phantom (MOBY‐John Hopkins Univ.) to simulate a complete small animal delivery system (source + animalmodel). We computed the source spectral output, beam filters, beam penumbra, soft tissue to bone dose ratio, dose fall off, and total dose delivered to the animalmodel. Sources covering the range of 150 to 450kVp with submillimeter focal spot were simulated. Results: We determined that a source of nominal maximum potential output of 320kVp and focal spot of 0.4×0.4 mm2 outperformed other available sources. We designed an optimum Thoraeus‐like filter to obtain a bremsstrahlung spectrum energy greater than 2 mm of Cu to increase skin spare and reduce bone dose. An average beam penumbra of 0.25mm and a dose rate of 40Gy/min were possible using this filtered beam. Higher energy sources would increase cost and shielding thickness. Lower energies sources showed limited intensities when they were aggressively filtered. Conclusion: We developed a numerical model to evaluate the radiation dose delivered by orthovoltage sources typically used in small animal irradiators. We concluded that when radiation quality, skin dose, bone to tissue dose ratio and animal throughput were considered, commercial orthovoltage sources of nominal energy of 320 keV were the best fit for conformal small animal micro irradiators. To obtain high conformality a submillimeter focal spot of 0.5×0.5 mm2 or less must be used. This work supported in part by NIH grant R21CA108677

Planar channeling experiments with electrons at the 855 MeV Mainz Microtron MAMI

Planar channeling has been studied for silicon single crystals at a beam energy of 855 MeV at the Mainz Microtron MAMI. Complex channeling patterns were observed from which the crystal orientation can unambiguously be determined. Photon spectra at (1 0 0), (1 1 0) and (1 1 1) planar channeling were recorded with a 10″ × 10″ NaI detector. The planar (1 1 0) channeling process has been studied as function of the crystal thickness in the range between 7.9 and 270 μm from which a dechanneling length of 18.0 μm and the thickness dependent rechanneling lengths were deduced, employing solutions of the Fokker–Planck equation. A signal derived from high energy bremsstrahlung exhibits a characteristic length of (32 ± 4) μm which is tentatively interpreted as the occupation length of the lowest quantum states in the planar potential. Prospects are discussed to exploit channeling of high energy electrons in periodically bent silicon single crystals for production of radiation in the hundreds keV to multi MeV range.

Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at the BNL Relativistic Heavy Ion Collider

We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a quark-gluon plasma. Our treatment of both processes is complete at leading order in the coupling and accounts for the probabilistic nature of the jet energy loss. We find that the nuclear modification factor R(AA) for neutral pi(0) production in heavy ion collisions is sensitive to the inclusion of collisional and radiative energy loss contributions while the averaged energy loss only slightly increases if collisional energy loss is included for parent parton energies E>>T. These results are important for the understanding of jet quenching in Au+Au collisions at 200A GeV at the Relativistic Heavy Ion Collider (RHIC). Comparison with data is performed applying the energy loss calculation to a relativistic ideal (3+1)-dimensional hydrodynamic description of the thermalized medium formed at RHIC.

Radiative corrections to high energy lepton bremsstrahlung on heavy nuclei

One-loop radiative corrections to the leptonic tensor in high energy bremsstrahlung on heavy nuclei are calculated. Virtual and real photon radiation is taken into account. Double bremsstrahlung is simulated by means of Monte Carlo. Numerical results are presented for the case of muon bremsstrahlung in conditions of the COMPASS experiment at CERN.

Multimode approximation for 238U photofission at intermediate energies

The yields of products originating from 238U photofission are measured at the bremsstrahlung endpoint energies of 50 and 3500 MeV. Charge and mass distributions of fission fragments are obtained. Symmetric and asymmetric channels in 238U photofission are singled out on the basis of the model of multimode fission. This decomposition makes it possible to estimate the contributions of various fission components and to calculate the fissilities of 238U in the photon-energy regions under study.

Ultra-intense Laser Plasma Interaction Studies at RRCAT, Indore

The Laser Plasma Division at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore has been engaged in research and development activities on laser plasma interaction using 10 TW, 45 fs, Ti:sapphire laser and a variety of in-house developed diagnostic systems for ultrashort laser pulses, plasma and x-ray radiation. Our recent studies include laser wakefield electron acceleration, high order harmonic generation, resonance enhancement of single harmonics, MeV energy bremsstrahlung radiation, absorption of ultrashort laser pulses in in-situ produced metal clusters, and ultrashort pulse K-shell x-ray line emission. This paper briefly describes these studies and important results obtained.

Photodisintegration studies on p-nuclei: the case of Mo and sm isotopes

In explosive stellar environments like supernovae, the temperatures are high enough for the production of heavy neutron-deficient nuclei, the so-called p-nuclei. Up to now, the knowledge of the reaction rates of p-nuclei is based on theoretical parameterizations using statistical model calculations. At the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden–Rossendorf, we aim to measure the photodisintegration rates of heavy nuclei experimentally. Photoactivation measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. First experiments on the short-lived decays following the reaction 144Sm(γ,n) are carried out using a pneumatic delivery system for rapid transport of activated samples. The activation yields are compared with calculations using cross sections from recent Hauser–Feshbach models.

Comparison of photoneutron yield from beryllium irradiated with bremsstrahlung radiation of different peak energy

In an effort to set up microtron based photoneutron source and in order to optimize the neutron yield, photoneutron production from beryllium has been studied for different volumes of beryllium irradiated by different peak energy bremsstrahlung radiation. The theoretical estimation of neutron yield has been carried out using the MCNP simulation for 8.75, 8.15 and 7.58 MeV peak energy of bremsstrahlung radiation. The experimental measurements were carried out using two types of detectors: SSNTD CR-39 and custom designed Silver wrapped GM detector. The neutron yield corresponding to beryllium of volume 381.70 cm 3 are found to be 2.13E+09, 2.00E+09 and 1.74E09 n/s (MCNP calculation values) for electrons of energy 8.75, 8.17 and 7.48 MeV, respectively. The experimental results are compared with the MCNP simulated results and are good agreement.