End-point Energy Research Articles

Measurement of photo-neutron cross sections and isomeric yield ratios in the 89Y(γ,xn)89−x Y reactions at the bremsstrahlung end-point energies of 65, 70 and 75 MeV

Abstract The flux-weighted average cross sections of the 89Y(γ,xn; x=1–4)89−x Y reactions and the isomeric yield ratios of the 87m,gY, 86m,gY, and 85m,gY radionuclides produced in these reactions with the bremsstrahlung end-point energies of 65, 70 and 75 MeV have been determined by an activation and off-line γ-ray spectrometric technique using the 100 MeV electron linac in Pohang Accelerator Laboratory, Korea. The theoretical 89Y(γ,xn; x=1–4)89−x Y reactioncross sections for mono-energetic photonshave been calculated using the computer code TALYS 1.6. Then the flux-weighted theoretical values were obtaind to compare with the present data. The flux-weighted experimental and theoretical 89Y(γ,xn; x=1–4)89−x Y reaction cross sections increase very fast from the threshold values to a certain bremsstrahlung energy, wherethe other reaction channels open up. Thereafter it remains constant a while and then slowly decreases with the increase of cross sections for other reactions. Similarly, the isomeric yield ratios of 87m,gY,86m,gY and 85m,gY in the 89Y(γ,xn; x=2–4)89−x Y reactions from the present work and literature data show an increasing trend from their respective threshold values to a certain bremsstrahlung energy. After a certain point ofenergy, the isomeric yield ratios increase slowly with the bremsstrahlung energy. These observations indicate the role of excitation energy and its partitioning in different reaction channels.

Rigidity Theory-Based Approximation of Vibrational Entropy Changes upon Binding to Biomolecules.

We introduce a computationally efficient approximation of vibrational entropy changes (ΔSvib) upon binding to biomolecules based on rigidity theory. From constraint network representations of the binding partners, ΔSvib is estimated from changes in the number of low frequency ("spongy") modes with respect to changes in the networks' coordination number. Compared to ΔSvib computed by normal-mode analysis (NMA), our approach yields significant and good to fair correlations for data sets of protein-protein and protein-ligand complexes. Our approach could be a valuable alternative to NMA-based ΔSvib computation in end-point (free) energy methods.

Measurement of flux-weight average cross-sections of natZn(γ,xn) reactions in the bremsstrahlung end-point energies of 50, 55, 60, and 65 MeV

The flux-weighted average cross-sections of (γ,xn) reactions on natZn induced by the bremsstrahlung end-point energies of 50, 55, 60, and 65 MeV have been determined by activation and off-line γ-ray spectrometric technique, using the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The theoretical photon-induced reaction cross-sections of natZn as a function of photon energy were taken from TENDL-2014 nuclear data library based on TALYS 1.6 program. The flux-weighted average cross-sections were obtained from the literature data and the theoretical values of TENDL-2014 based on mono-energetic photon. The flux-weighted reaction cross-sections from the present work and literature data at different bremsstrahlung end-point energies are in good agreement with the theoretical values. It was found that the individual natZn(γ,xn) reaction cross-sections increase sharply from reaction threshold to certain values where the next reaction channel opens. There after it remains constant for a while, where the next reaction channel increases. Then it decreases slowly with increase of bremsstrahlung end-point energy due to opening of different reaction channels.

Electron Accelerators for Novel Cargo Inspection Methods

One of the main factors limiting the performance of conventional x-ray cargo inspection with material discrimination (MD) is the interlaced mode of system operation. Such systems use pulsed linac or betatron x-ray generators and produce alternate bremsstrahlung pulses with lower- and higher- end-point energies. Consequently, these systems provide about 50mm lower penetration than a system operated in a non-interlaced mode, have a limited range of cargo areal densities with valid MD, and cannot perform MD of objects smaller than the pulse separation. Also, the limited pulse repetition rate of x-ray generators in interlaced mode limits the radiographic image quality at nominal commercial speeds of vehicles or trains.Several new methods of cargo inspection with MD were recently introduced to address the above-mentioned limitations: dual-energy methods based on Scintillation-Cherenkov detectors [1]; multi-energy method based on intrapulse time-varying of spectral content of x-ray [1,2]; multi-energy method utilized ramping-up energy packet of short x-ray pulses [3,4]; and methods based on multi-energy betatron [5,6]. All of these methods have electron accelerators as a core element. However, the accelerator requirements and, thus, their designs, are different for each system. In this paper, we will discuss the requirements for the accelerators, provide some details about their designs, and present several novel solutions for current and future projects.

Isomer ratios for products of photonuclear reactions on 121Sb

Over the past several years various preequilibrium model approaches for nuclear reactions were developed. Diversified detailed experimental data in the medium excitation energy region for nucleus are needed for reasonable selection among these theoretical models. Lack of experimental data in this energy region does essentially limit the possibilities for analysis and comparison of different preequilibrium theoretical models. For photonuclear reactions this energy region extends between bremsstrahlung energies nearly 30–100 MeV. Experimental measurements and estimations of isomer ratios for products of photonuclear reactions with multiple particle escape on antimony have been performed using bremsstrahlung with end-point energies 38, 43 and 53 MeV. Method of induced activity measurement was applied. For acquisition of gamma spectra we used HPGe spectrometer with 20% efficiency and energy resolution 1.9 keV for 1332 keV gamma line of 60 Co. Linear accelerator of electrons LU-40 was a source of bremsstrahlung. Energy resolution of electron beam was about 1% and mean current was within (3.8–5.3) μA.

Investigation of the reaction 4Нe(γ, pn)d at energies below the meson-production threshold

Themomentum distributions of deuterons and nucleons from the reaction 4Не(γ, pn)d induced by bremsstrahlung photons whose spectrum extends up to the endpoint energy of 150 MeV weremeasured by means of a diffusion chamber placed in a magnetic field. These measurements were performed in four photon-energy intervals for deuterons and in the energy range between 100 and 150 MeV for nucleons. Angular and energy correlations of nucleons were measured at photon energies in the interval between 50 and 70 MeV. The results obtained in this way were analyzed on the basis of the quasideuteron model. The probability for final-state nucleon–deuteron interaction was estimated.

Impact of gamma-decay description on nuclear reaction characteristics

The results of the study of gamma-transition description in fast neutron capture and photofission are presented. Recent experimental data were used, namely, the spectrum of prompt gamma-rays in the energy range 2÷18 MeV from 14-MeV neutron capture in natural Ni and isomeric ratios in primary fragments of photofission of the isotopes of U, Np and Pu by bremsstrahlung with end-point energies =10.5, 12 and 18 MeV. The data are compared with the theoretical calculations performed within EMPIRE 3.2 and TALYS 1.6 codes. The mean value of angular momenta and their distributions were determined in the primary fragments 84 Br, 97 Nb, 90 Rb, 131 ,133 Te, 132 Sb, 132,134 I, 135 Xe of photofission. An impact of the characteristics of nuclear excited states on the calculation results is studied using different models for photon strength function and nuclear level density

Measurement of isomeric yield ratios for the 110Pd(γ,n)109m,gPd reaction

We measured the isomeric yield ratios for the 110Pd(γ,n)109m,gPd reaction by the activation method with the bremsstrahlung endpoint energies of 50-, 55-, 60-, 65-, and 70-MeV generated from an electron linear accelerator of Pohang accelerator laboratory. The induced γ-activities of the irradiated palladium foils were measured by a coaxial high purity germanium detector coupled to a PC-based multi-channel analyzer. The necessary corrections were made to improve the accuracy of the γ-activity measurements. The present experimental results measured with bremsstrahlung endpoint energies of 50-, 55-, 60-, 65-, and 70-MeV are 0.108 ± 0.007; 0.118 ± 0.008; 0.118 ± 0.007; 0.120 ± 0.008; 0.119 ± 0.008, respectively. The obtained results are compared with those existing in literature.

Determination of flux-weighted average cross-sections of natPb( $\gamma$ γ ,xn), 208Pb( $\gamma$ γ ,xn), and 209Bi( $\gamma$ γ ,xn) reactions using bremsstrahlung end-point energies of 50-70 MeV

The flux-weighted average cross-sections of the natPb(\(\gamma\),xn)198-204Pb reaction for the bremsstrahlung end-point energies of 50-70MeV were determined by activation and off-line \( \gamma\) -ray spectrometric technique, using the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Korea. The relative cross-sections of the 208Pb(\(\gamma\),xn)202-204Pb and 209Bi(\(\gamma\),xn)203-206Bi reactions from our earlier work were updated to absolute values and compared with the present data. The photo-neutron cross-sections of natPb, 208Pb, and 209Bi were also calculated, as a function of the photon energy using the TALYS 1.6 code. The flux-weighted average cross-sections were obtained from the theoretical values of the TALYS 1.6 code, based on mono-energetic photons, and compared with the present experimental data. The values were found to be in good agreement with the present data for the 209Bi(\(\gamma\),xn)203-206Bi, 208Pb(\(\gamma\),xn)202-204Pb, and natPb(\(\gamma\),xn)198-202Pb reactions. However, the present data for the natPb(\(\gamma\),xn)203, 204Pb reactions were higher than the flux-weighted values obtained using the TALYS 1.6 code.

Low-energy modification of the γ strength function of the odd-even nucleus In115

Photoactivation yield measurements on $^{115}\mathrm{In}$ have been performed at the ELSA facility with Bremsstrahlung photon beams over a range of endpoint energies between 4.5 and 18 MeV. The measured photoexcitation yields of the $^{115m}\mathrm{In}$ metastable state are compared with calculated yields using cross sections obtained with different models of the photon strength function. It is shown that additional photon strength with respect to the general Lorentzian model is needed at 8.1 MeV for the calculated yields to reproduce the data. The origin of this extra strength is unclear, because it is compatible with additional strength predicted in both $E1$ and $M1$ photon strength distributions by quasiparticle random-phase approximation calculations using the Gogny D1S force.

Effect of incident electron energy of beta emitter on the formation of bremsstrahlung spectra in the photon energy region of 1–5 keV

The effect of incident electron energy of beta emitter 204Tl (end-point energy=765keV) and 90Sr (end-point energy=546keV), on the formation of total bremsstrahlung spectra in thick targets, was investigated in the photon energy region of 1–5keV. Theoretical bremsstrahlung spectra were obtained from theory that describes ordinary bremsstrahlung (OB) and the theoretical model, which includes the contribution of polarization bremsstrahlung (PB) in OB in stripping approximation. The theoretical and experimental bremsstrahlung spectra were modified by applying corrections due to the range of beta particles, self-absorption of photons in target, absorption of photons in detector compounds, and backscattering of beta particle. It was observed that the experimental results were 10–15% higher than that of the theoretical model, which includes the contribution of PB in OB in stripping approximation, particularly for medium and high Z elements. The contribution of PB in OB was suppressed with the increase in the end-point energy of the beta emitters. The results reported here clearly indicate the inadequacy of stripping approximation and the need to include the term of interference of OB and PB while describing the total bremsstrahlung spectra.

Isomeric ratio of 137mCe to 137gCe produced in 138Ce(γ, n)137m,gCe photonuclear reaction induced by end-point bremsstrahlung energies from 14 to 17, 21 to 23 and at 19 MeV

The isomeric ratios in 138Ce(γ, n)137m,gCe photonuclear reaction have been measured for energy ranges from 14 to 17, 21 to 23 and at 19 MeV end-point bremsstrahlung energies by the activation method. In order to improve the accuracy of the experimental results, necessary corrections and data analysis were made in the γ-ray activity measurements. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy and the influence of channel effects. The above obtained data are the first time measurements.

Kinematic sensitivity to the Fierz term ofβ-decay differential spectra

The current most stringent constraints on exotic scalar or tensor couplings in neutron and nuclear $\beta$ decay, involving left-handed neutrinos, are obtained from the Fierz interference term. The sensitivity to this term in a correlation coefficient is usually driven by an energy-averaged kinematic factor that increases monotonically toward smaller values of the $\beta$ endpoint energies. We first point out here that this property does not hold for certain differential observables that are directly sensitive to the Fierz term, such as the $\beta$ or the recoil energy spectrum. This observation is relevant for the selection of sensitive transitions in searches for exotic couplings through spectrum shape measurements. We then point out previous errors in the exploitation of measurements of the $\beta-\nu$ angular correlation coefficient and discuss their impact on the extraction of constraints on exotic couplings.

Average cross section measurement for 162Er (γ, n) reaction compared with theoretical calculations using TALYS

Bremsstrahlung photon beam delivered by a linear electron accelerator has been used to experimentally determine the near threshold photonuclear cross section data of nuclides. For the first time, (γ, n) cross section data was obtained for the astrophysical important nucleus 162Er. Moreover, theoretical calculations have been applied using the TALYS 1.6 code. The effect of the gamma ray strength function on the cross section calculations has been studied. A satisfactorily reproduction of the available experimental data of photonuclear cross section at the energy region below 20 MeV could be achieved. The photon flux was monitored by measuring the photons yield from seven well known (γ, n) reactions from the threshold energy of each reaction up to the end-point energy of the photon beam used. An integrated cross-section 87±14 mb is calculated for the photonuclear reaction 162Er (γ, n) at the energy 9.2–14 MeV. The effective cross section estimated using the TALYS code range between 89 and 96 mb depending on the γ-strength function used. To validate the method for the estimation of the average cross-section data of 162Er (γ, n) reaction, the same procedure has been performed to calculate the average cross-section data of 197Au (γ, n) and 55Mn (γ, n) reactions. In this case, the photons yield from the rest well known (γ, n) reactions was used in order to monitoring the photon flux. The results for 162Er (γ, n), 197Au (γ, n) and 55Mn (γ, n) are found to be in good agreement with the theoretical values obtained by TALYS 1.6. So, the present indirect process could be a valuable tool to estimate the effective cross section of (γ, n) reaction for various isotopes using bremsstrahlung beams.

Photonuclear reactions on the cadmium isotopes 106,108Cd at the bremsstrahlung endpoint energy of 55.5 MeV

The gamma-activation technique was used to measure the absolute yields of photonuclear reactions on the cadmium isotopes 106,108Cd. The results obtained in this way were compared with the results of the calculations based on the statistical model. For reactions on the isotope 108Cd, agreement between these theoretical and experimental results is good, but the experimental ratio of the yields of photoproton and photoneutron reactions on the isotope 106Cd differs substantially from its theoretical counterpart. The results of our present study are discussed from the point of view of the production of bypassed nuclei in the p-process of nucleosynthesis.

Excitation of 11/2− isomeric state in 137Ce in (γ,n) reaction within 10–22MeV energy range

Isomeric yields ratios and energy differential cross-section of metastable state excitation in the [Formula: see text] reaction has been studied in the 10–22[Formula: see text]MeV end-point energy range of bremsstrahlung beams. Experimental data are compared with Hauser–Feshbach calculations performed with TALYS-1.6 statistical model code.

Pressure dependence of X-rays produced by an LiTaO3 single crystal at the pressures of 1–20 Pa

The energy spectra of X-rays produced by an LiTaO3 single crystal have been measured at pressures of 1–20Pa. The energy spectra showed that the endpoint energy and the amount of X-rays gradually increased with the decrease of pressure at 5–8Pa and abruptly increased around 4Pa and below. A maximum endpoint energy of 70keV was obtained using the LiTaO3 single crystal with 5mm thickness at a pressure of 3Pa. The change of X-rays produced by the LiTaO3single crystal was discussed in relation to the breakdown potential at the pressures.

Energy level and half-life determinations from photonuclear reaction on Ga target

Photonuclear reactions are important tools in the understanding of the nucleus. These reactions are also interesting for realizing the element creation processes in stellar environment. The use of bremsstrahlung photons generated from clinic linear accelerator is practical for performing these type of reactions. In this study, the bremsstrahlung photons with endpoint energy of 18[Formula: see text]MeV have been used for activating gallium target material. After irradiation, the transition energies and half-lives associated with the decay of [Formula: see text], [Formula: see text] and [Formula: see text] isotopes have been determined The values obtained for half-life of [Formula: see text], [Formula: see text] and [Formula: see text] isotopes are [Formula: see text][Formula: see text]min, [Formula: see text][Formula: see text]min and [Formula: see text][Formula: see text]h, respectively. It has been seen that the values are consistent with the present literature values. In addition, the new measurements of gamma-ray energies for transition energies have been obtained comparable to the literature values with good uncertainties.

Photo-neutron reaction cross-sections for natMo in the bremsstrahlung end-point energies of 12-16 and 45-70 MeV

The natZr(\(\gamma\), xn) 89-86Zr reaction cross-sections were experimentally determined at the bremsstrahlung end-point energies of 12, 14, 16, 45, 50, 55, 60 and 70MeV by activation and off-line \(\gamma\)-ray spectrometric technique using the 20 MeV electron linac (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany, and the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The natZr(\(\gamma\), xn) 89-86Zr reaction cross-sections as a function of photon energy were also calculated using the TALYS 1.4 computer code. The flux-weighted average cross-sections at the end-point energies of 12-16 and 45-70 MeV were obtained using the literature and the TALYS calculation data based on mono-energetic photons and are found to be in good agreement with the present data. It was also found that the present data and the flux-weighted literature and theoretical values for the natZr(\(\gamma\), xn) 89-86Zr reaction cross-sections increase from the threshold values to a certain energy, where other reaction channels open. This indicates the role of excitation energy. However, the increasing trend of the natZr(\(\gamma\), xn) 89,88Zr reaction cross-sections are sharper from the threshold value up to end-point bremsstrahlung energies of 17-22 MeV compared to the same for the natZr(\(\gamma\), xn) 87, 86Zr reactions. This is due to the Giant Dipole Resonance (GDR) effect besides the role of excitation energy. After a certain value, the individual natZr(\(\gamma\), xn) reaction cross-sections decrease with the increase of bremsstrahlung energy due to opening of other reactions, which indicates partitioning of energy in different channels.

On the role of energy separated in fission process, excitation energy and reaction channels effects in the isomeric ratios of fission product 135Xe in photofission of actinide elements

In this work we present the isomeric ratio of fission product 135Xe in the photo-fission of actinide elements 232Th, 233U and 237Np induced by end-point bremsstrahlung energies of 13.5, 23.5 and 25.0 MeV which were determined by the method of inert gaseous flow. The data were analyzed, discussed and compared with the similar data from literature to examine the role of energy separated in fission process, excitation energy and reaction channels effects.