Bremsstrahlung Beam Research Articles

Yields of photonuclear reactions on Hg isotopes under a bremsstrahlung beam with a maximum energy of 29.1 MeV

Yields of photonuclear reactions on stable Hg isotopes under a bremsstrahlung photon beam with a maximum energy of 29.1 MeV were measured using the induced activity method. Single-neutron and single-proton reactions and the 198Hg(γ,1p1n) reaction were observed. Photoneutron reaction yields with the production of metastable states were measured.

Radiation shielding study against gas bremsstrahlung for the BMIT POE3 at the Canadian light source

A dose rate study is undertaken when gas bremsstrahlung strikes a monochromator, a copper absorber and a tungsten beam stop in the third primary optical enclosure (POE3) of the BioMedical Imaging and Therapy (BMIT) insertion device (ID) beamline 05ID-2. In the POE3, computed tomography, diffraction enhanced imaging and K-Edge subtraction monochromators are housed to conduct various diagnostic and therapeutic studies in the experimental hutch. The safety features of this beamline must be examined with great care, as this multipurpose beamline is intended for use in vivo on animals and humans. A tungsten beam stop, two safety shutters, and a lead movable wall are placed in the POE3 for the safe operation of the BMIT beamline. However, for one particular mode of operation, gas bremsstrahlung and monochromatic X-ray beams propagate closely together until the former is stopped by the tungsten beam stop while the safety shutters remain open to allow the passage of the latter to the experimental area SOE1. It is thus imperative to know the anticipated dose rate around the POE3, especially behind the back wall and on the roof. The dose rate estimates are presented based on a realistic model of the POE3 with its safety features.

3-D defect density plots of large scale structural materials with positron annihilation spectroscopy: feasibility and optimization

We investigated the feasibility of the pair-production based positron annihilation spectroscopy (PAS) technique to generate 2-D and possibly 3-D defect density images (defect density plots) of structural materials widely used in industry. After assessing the possible PAS techniques and performing MCNPX simulations on different positron production mechanisms, we chose to employ Doppler broadening analysis of the annihilation peak coupled with the pair-production method of positron creation using bremsstrahlung photon beams from a linear accelerator. First, to optimize the important parameters of the proposed experimental setup, MCNPX simulations were performed. These parameters are: thickness of the bremsstrahlung beam hardener, detector orientation, thickness of the bremsstrahlung converter, beam energy and current, etc. These parameters were studied to maximize the number of 511 keV counts in the detector and minimize the low energy background photons that Compton scatter into the detector. A Figure of Merit (FOM) was used to quantitatively track effectiveness (or ineffectiveness) of each value for all the parameters. We conducted experiments with the simulated setup and these results were compared to MCNPX calculations.

Stabilization of Relativistic Electron Beam by Dense Plasma Cloud in GOL-3 Expander

The paper presents new experimental results from the GOL-3 facility on stabilization of some beam instability modes by controlled conditions at an exit beam receiver. In the experiments the space near the beam collector in the exit expander was filled with krypton. Position and shape of the beam footprint at the exit collector was imaged using the beam bremsstrahlung. The beam shape changes were detected by a set of magnetic probes. Improvement of the beam stability due to krypton puffing was achieved. Possible mechanisms of such stabilization are discussed.

Measurement of isomeric yield ratios for 93Nb(γ,4n)89m,gNb and natMo(γ,xn1p)95m,gNb reactions with 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios for the photonuclear reactions of 93Nb(γ,4n)89m,gNb and natMo(γ,xnp)95m,gNb by using the activation method. The high-purity 93Nb and natMo metallic foils in disc shape were irradiated with uncollimated bremsstrahlung beams of 50-, 60-, and 70-MeV generated from an electron linear accelerator in 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 coupled to a PC-based 4 K multichannel analyzer. The reaction 93Nb(γ,4n)89m,gNb was studied for the first time which has no comparable literature data. The result of 95m,gNb isomeric pair was measured based on (γ,p), (γ,np), and (γ,2np) reactions which is the first measurement at the intermediate energy region of 50–70-MeV with a natMo target.

Measurement of isomeric yield ratios for the 44m,gSc isomeric pairs produced from 45Sc and natTi targets at 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios for the 44m,gSc isomeric pairs produced from different reaction channels 45Sc(γ,n)44m,gSc and natTi(γ,xnp)44m,gSc by using the activation method and γ-ray spectroscopic methods at 50-, 60-, and 70-MeV bremsstrahlung energies. The high-purity natural Sc and Ti foils in disc shape were irradiated with uncollimated bremsstrahlung beams 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 which consists of a high-purity Germanium detector and a multichannel analyzer. In order to improve the accuracy of the experimental results the necessary corrections were made in the γ-ray activity measurements and data analysis. The measured isomeric yield ratios for the 45Sc(γ,n)44m,gSc reaction are 0.20 ± 0.02, 0.21 ± 0.02, and 0.21 ± 0.02 and those for the natTi(γ,xnp)44m,gSc reaction are 0.063 ± 0.012, 0.079 ± 0.014, and 0.124 ± 0.022 at 50-, 60-, and 70-MeV bremsstrahlung energies, respectively. The obtained results are compared with the corresponding values found in the literature. We observed that the isomeric yield ratios for the 45Sc(γ,n)44m,gSc reaction increase rapidly with the increasing bremsstrahlung energies from the reaction threshold up to giant resonance region, and then those are almost constant in the energy range from about 30 to 2.5 GeV. The isomeric yield ratios for the natTi(γ,xnp)44m,gSc reaction increase with increasing bremsstrahlung energies in a wide range of bremsstrahlung energies from 50 to 2.5 GeV.

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.

Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams

Due to the clinical advantages of Intensity Modulated Radiation Therapy (IMRT) high flexibility and accuracy in intensity modulated dose delivery is desirable to really maximize treatment outcome. Although it is possible to deliver IMRT by using broad beams in combination with dynamic multileaf collimation the process is rather time consuming and inefficient. By using narrow scanned high energy photon beams the treatment outcome can be improved, the treatment time reduced and accurate 3D in vivo dose delivery monitoring is possible by PET-CT based dose delivery imaging of photo nuclear reactions in human tissues. Narrow photon beams can be produced by directing a low emittance high energy electron beam on a thin target, and then cleaning the therapeutic photon beam from transmitted high energy electrons, and photon generated charged leptons, with a dedicated purging magnet placed directly downstream of the target. To have an effective scanning and purging magnet system the purging magnet should be placed immediately after the bremsstrahlung target to deflect the transmitted electrons to an efficient electron stopper. In the static electron stopper the electrons should be safely collected independent of the desired direction of the therapeutic scanned photon beam. The SID (Source to Isocenter Distance) should preferably be short while retaining the ability to scan over a large area on the patient and consequently there are severe requirements both on the strength and the geometry of the scanning and purging magnets. In the present study an efficient magnet configuration with a purging and scanning magnet assembly is developed for electron energies in the 50–75 MeV range and a SID of 75 cm. For a bremsstrahlung target of 3 mm Be these electron energies produce a photon beam of 25–17 mm FWHM (Full Width Half Maximum) at a SID of 75 cm. The magnet system was examined both in terms of the efficiency in scanning the narrow bremsstrahlung beam and the deflection of transmitted and photon generated electrons. The simulations show that its is possible to have a scan area on the patient of up to 43 × 40 cm 2 for an incident electron energy of 50 MeV and 28 × 40 cm 2 at 75 MeV, while at the same time adequately deflecting the transmitted electron beam.

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.

Cross sections of multiparticle photonuclear reactions with 203, 205Tl isotopes

An experiment on the irradiation of the natural mixture of 203,205Tl isotopes by the bremsstrahlung beam of pulsed racetrack microtron RTM-70 (Skobeltsyn Institute of Nuclear Physics, Moscow State University) at an electron energy of 67.7 MeV was performed. The yields and integral cross sections of multiparticle photonuclear reactions with 203,205Tl isotopes were measured.

The detection of delayed [formula omitted]-rays between intense bremsstrahlung pulses for discriminating fissionable from non-fissionable materials

The detection and identification of delayed fission γ-rays emitted between intense bremsstrahlung pulses was investigated as a method to discriminate between fissionable and non-fissionable materials. Photofission and other photonuclear reactions were induced in U238, Pb, Fe and Be targets using a pulsed bremsstrahlung beam for several endpoint energies between 8 and 20MeV. In the 33ms between irradiating pulses, correlated photon energy and time spectra were collected using a high-purity germanium detector. When non-fissionable materials were irradiated, the high-energy γ-ray yield decreased a couple orders of magnitude within the first ∼12ms after the pulse. In contrast, the high-energy γ-rays emitted from the decay of fission fragments were nearly constant throughout the period between bremsstrahlung pulses. Hence, a basic energy and time discrimination provides a unique high-energy delayed γ-ray signature for fissionable material detection.

The use and characterization of a backilluminated charge-coupled device in investigations of pulsed x-ray and radiation sources

Examinations of bremsstrahlung and energetic electron beams from a novel laser plasma source motivate and assist characterization of a backthinned, backilluminated direct detection x-ray charge-coupled device (CCD), a topology that is uncommon in hard x-ray work. Behavior toward pseudomonochromatic ((55)Fe) and multichromatic ((241)Am) sources is briefly reviewed under optimized noise conditions. Results collectively establish the previously unknown functional depth structure. Several modes of usage are illustrated in approximately 4-20 keV x-ray laser plasma source investigations, where the significance of the characterization is briefly discussed. The spectral redistribution associated with this CCD topology is unfavorable, yet appropriate analysis ensures that sufficient spectral information remains for quantitative determination of broadband x-ray flux and spectra in essentially single laser shot measurements. The energy dependence of nascent electron cloud radii in silicon is determined using broadband x-rays from the laser plasma source, turning the narrow depletion depth to advantage. Finally, the characterization is used to quantify recent x-ray spectral explorations of the water jet laser plasma source operating under aspirator vacuum. These results will have key value for establishment of laboratory based ultrafast extended x-ray absorption fine structure experiments using microbolometric detectors.

DO ANGLES OF OBLIQUITY APPLY TO 30° SCATTERED RADIATION FROM MEGAVOLTAGE BEAMS?

The angle of obliquity is used in radiation shielding calculations to account for the longer path length x rays will see when obliquely incident on the protective barrier. According to the National Council on Radiation Protection and Measurements (NCRP), use of the angle of obliquity is explicitly assumed for primary radiation, so that an angle of obliquity for secondary radiation is never addressed. However, in the example section of the latest report, it specifically recommends against using an angle of obliquity for scattered radiation. To check this assumption, the existence or not of an angle of obliquity for scattered radiation has been investigated for bremsstrahlung x-ray beams of 4, 6, 10, 15, and 18 MV and for barriers consisting of concrete, lead, and steel using a Monte Carlo approach. The MCNP Monte Carlo code, v4.2C, has been used to generate scattered radiation at 30 degrees from a water phantom and incident on a secondary barrier at the same angle relative to the normal to the barrier. The barrier thickness was increased from zero to a thickness sufficient to reduce the fluence (f4 tally) to <10(-3). A transmission curve was created for each energy-barrier material combination by normalizing to zero thickness. The results for the first tenth-value layer (TVL) in concrete (5 energies) show an average angle of obliquity of 21.7 degrees +/- 5.6 degrees , and for the first two TVLs averaged 29.7 degrees +/- 3.9 degrees . The results for the first TVL in lead (3 energies) show an average angle of obliquity of 27.7 degrees +/- 4.0 degrees , and for the first two TVLs averaged 20.5 degrees +/- 5.8 degrees . There are no data in the NCRP reports for 30 degrees scattered radiation attenuated by steel with which to make a comparison.

Formation of the 178m2Hf isomer in a natural mixture of hafnium isotopes irradiated by an intense γ quantum beam (experiment)

The results of an experiment on the production of the 178m2Hf isotope by exposing a natural mixture of hafnium isotopes to an intense bremsstrahlung beam are reported. The sample under investigation was exposed to an electron beam with an energy of 30 MeV and current 200 μ A for 500 h. The spectrometric analysis of the irradiated sample using radiochemical methods for the separation of isotopes did not reveal 178m2 Hf lines.

Isomeric yield ratios for the formation of 44m,gSc in the 45Sc(γ,n), natTi(γ,xnp), natFe(γ,xn5p) and natCu(γ,xn8p) reactions with 2.5 GeV bremsstrahlung

We measured the isomeric yield ratios for the 44m,gSc isomeric pairs produced from four different photonuclear reactions 45Sc(γ,n) 44m,gSc, natTi(γ,xn1p) 44m,gSc, natFe(γ,xn5p) 44m,gSc, and natCu(γ,xn8p) 44m,gSc by using the activation method. The high purity natural Sc, Ti, Fe, and Cu metallic foils in disc shape were irradiated with uncollimated 2.5 GeV 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 45Sc(γ,n) 44m,gSc, natTi(γ,xn1p) 44m,gSc, natFe(γ,xn5p) 44m,gSc and natCu(γ,xn8p) 44m,gSc reactions are 0.25 ± 0.03, 0.43 ± 0.05, 1.38 ± 0.14, and 1.89 ± 0.21, respectively. The present result for the natCu(γ,xn8p) 44m,gSc reaction is in good agreement with the existing data. Our results for the 45Sc(γ,n) 44m,gSc, natTi(γ,xn1p) 44m,gSc, and natFe(γ,xn5p) 44m,gSc reactions are the first measurements at 2.5 GeV bremsstrahlung. The obtained results are compared with the corresponding values found in the literature. The relation between the isomeric yield ratios and the complexity of the photonuclear reactions is discussed.

A technique for measuring the quadrupole deformation parameter of transuranium nuclei

A method for determining the quadrupole deformation parameter of transuranium nuclei is presented. This method is based on giant dipole resonance splitting in the photofission cross section. The experimental setup containing an avalanche counter of fission fragments, as well as a method for reconstructing the cross section from the measured dependence of the photofission reaction yield on the endpoint energy of the bremsstrahlung spectrum, are described. The setup was tested on the bremsstrahlung beam of the MT-25 microtron at the Flerov Laboratory for Nuclear Reactions of the Joint Institute for Nuclear Research. The test results—in particular, the measured excitation function of the uranium photofission reaction—are presented.

Yields of multiparticle photoneutron reactions on the 209Bi isotope

The relative yields of multiparticle photoneutron reactions on the 209Be isotope with emission of two to seven neutrons from the nucleus are measured. The experiment was carried out with the bremsstrahlung beam from the RTM-70 pulsed race-track microtron (INP, MSU) with a maximum photon energy E = 67.7 MeV.

Multiple-beam method for object scanning

A multiple-beam method for scanning large objects is proposed, which is based on the use of multiple bremsstrahlung beams with different upper limits. Mathematical modeling is performed to compare the multiple-beam method with the double-beam method, and an advantage of the proposed technique over the double-beam method method is shown.

The photoresponse of 45Sc up to 7 MeV

High-resolution photon scattering experiments have been performed on the nucleus 45Sc at the Darmstadt superconducting electron accelerator S-DALINAC using bremsstrahlung beams with end point energies of 5.0 and 7.0MeV. Energies, absolute cross-sections and decay widths of 50 states, most of them previously unknown, have been determined. The results are compared to (γ,\( \gamma{^\prime}\)) experiments on the neighbouring closed proton shell isotope 44Ca .

Screening effect and possibility of diagnostics of atomic nuclei and electron distribution in structured material using bremsstrahlung beam of relativistic electrons

The possibility of diagnostics of atomic nuclei and electron distribution in a structured material using bremsstrahlung (BS) of relativistic electrons in the material and considering the electric field screening of nuclei by the electrons of the medium is discussed. The alternative calculation technique of the BS spectrum determining a distinctive relation between the frequency-angular BS properties and the relativistic factor of radiating electrons is considered. The dependence of the BS intensity on the screening electron distribution character is analyzed for light and heavy elements. It is shown that, in spite of a sharp decrease in the BS intensity as compared to the radiation for a bare nucleus, the screening does not completely suppress BS, which allows its use for structural analysis of a material.