End-point Energy Research Articles

Measurement of half-lives for 87m,gY and 196m,g,194Au produced from the photon and neutron induced reactions of 89Y and 197Au

We have measured the half-lives of 87mY and 87gY produced from the 89Y(γ, 2n) and 89Y(n, 3n) reactions with the bremsstrahlung end-point energy of 65 MeV and the average neutron energy of 37.2 MeV using an activation and an off-line γ-ray spectrometric technique, respectively. The bremsstrahlung photon was produced by using the 100 MeV electron linac of the Pohang Accelerator Laboratory (PAL), whereas the fast neutron was produced from the 9Be(p, n) reaction by using the 45 MeV proton of the MC-50 Cyclotron at the Korea Institute of Radiological and Medical Sciences (KIRAMS). We have also measured the half-lives of 194Au and 196m2,gAu produced from the 197Au(γ, xn; x = 1, 3) and 197Au(n, xn; x = 2, 4) reactions with the bremsstrahlung end-point energy of 60 MeV and the average neutron energy of 37.2 MeV using the same technique and the same facilities as mentioned above. The induced γ-ray activities of the irradiated samples were measured by using an energy- and efficiency calibrated high purity germanium (HPGe) detector. The spectrum analysis has been done by using the ROOT software to separate signals from background. The measured half-lives are compared with the literature values and are in general agreement with each other within the uncertainties.

Improved Value for the Gamow-Teller Strength of the ^{100}Sn Beta Decay.

A record number of ^{100}Sn nuclei was detected and new isotopic species toward the proton dripline were discovered at the RIKEN Nishina Center. Decay spectroscopy was performed with the high-efficiency detector arrays WAS3ABi and EURICA. Both the half-life and the β-decay end point energy of ^{100}Sn were measured more precisely than the literature values. The value and the uncertainty of the resulting strength for the pure 0^{+}→1^{+} Gamow-Teller decay was improved to B_{GT}=4.4_{-0.7}^{+0.9}. A discrimination between different model calculations was possible for the first time, and the level scheme of ^{100}In is investigated further.

Understanding Aldose Reductase-Inhibitors interactions with free energy simulation

Aldose Reductase (AR) reduces a variety of substrates, such as aldehydes, aldoses and corticosteroids. It is the first and rate-limiting enzyme of the polyol pathway and is an important target enzyme for diabetes-associated complications, including retinopathy, neuropathy, and nephropathy. Inhibitors targeting this enzyme are structurally different and some of them have side effects. In existing publications, computational techniques are applied to investigate the binding affinities of existing inhibitors and predicting the affinities of newly designed ligands. However, these calculations only employ coarse and approximated methods such as docking and MM/PBSA. Brute force simulations are employed to study the dynamics of the system but no converged statistics is obtained. As a result, these computations provide results not consistent with experimental values and large discrepancies exist. In the current work, we employ the enhanced sampling technique of alchemical free energy simulation to calculate the binding affinities of several ligands targeting AR. The statistical error is defined with care and the correlation in the time-series data is fully considered. The statistically optimal estimators are used to extract the free energy estimates and the predicted results are in agreement with the experimental values. Less computationally demanding end-point free energy methods are also performed to compare their efficiency with the alchemical methods. As is expected, the end-point methods are of less accuracy and reliability compared with the alchemical free energy methods. The decomposition of the free energy difference in each alchemical transformation into the enthalpic and entropic components gives further insights on the thermodynamics. The enthalpy-entropy compensation is observed in this case. As the structural data obtained from experiments are only snapshots and more details are needed to understand the dynamics of the protein-ligand system, the conformational ensemble is analyzed. We identify important residues involved in the protein-ligand binding case and short-lived interactions formed due to fluctuations in the conformational ensemble. The current work shed light on the atomic detailed understanding of the dynamics of AR-inhibitors interactions.

Beam energy measurement on LINAC-200 accelerator and energy calibration of scintillation detectors by electrons in range from 1 MeV to 25 MeV

Abstract Accurate determination of the energy of LINAC-200 fast electrons was performed using several photonuclear reactions carried out on natural Indium after conversion of electron energy in bremsstrahlung in thick Tungsten target. Natural Indium was used as an activation detector and the ratios of saturation activities R( 113m In)/R( 115m In), R( 114m In)/R( 115m In) and R(111In)/R ( 115m In) were used as a measure of the endpoint energy of the bremsstrahlung beam (and energy of electrons striking the bremsstrahlung target as well). Energy dependence of the three ratios of saturation activities were determined by using the bremsstrahlung produced by electrons accelerated by Microtron to the energies known with accuracy not worse than 0.1 MeV. Three types of scintillation detectors (LaBr3:Ce, BGO and plastic) were calibrated using electrons having energies from 1.17 MeV to 25 MeV. In low energy region photoelectrons produced by 60 Co gamma radiation in the detector itself were used, as well as high energy electrons (from 11 MeV to 25 MeV) accelerated by LINAC-200.

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. The result for 162Er(γ,n), is 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.

New and comprehensive β - and βp -decay spectroscopy results in the vicinity of Sn100

A decay spectroscopy experiment on proton-rich nuclei in the vicinity of the doubly magic Sn100 was carried out at RIKEN Nishina Center. More than 20 nuclei with 43≤Z≤50 and N≤51, produced by fragmentation reactions were investigated via analyses of β-decay, βp-decay, and subsequent γ-ray data. Owing to higher statistics, the precision on the half-lives of many of the ground states and isomers was improved. β-decay endpoint energies of 11 states in 8 nuclei were measured for the first time, and the corresponding QEC and excitation energies were generally consistent with various mass models. Many β-delayed proton emission branching ratios were measured either for the first time or with higher precision compared to literature values, and some of them differed by more than 2σ. Many of the large discrepancies were associated with nuclei with long-lived isomeric states, highlighting large systematic uncertainties involved in these measurements. Twenty-five new γ rays were observed, and ten new states are proposed with unambiguous excitation energies, spins, and parities. Most of the energies of the excited states were consistent within 300 keV or 20%, whichever was greater, compared to shell model predictions in the proton/neutron (p1/2,g9/2) model space assuming a Sr76 core. A signature of a new (1/2-) isomer in Cd97 with T1/2=0.73(7) s was found, in good agreement with shell model predictions.

Reactor neutrino spectral distortions play little role in mass hierarchy experiments

The Coulomb enhancement of low energy electrons in nuclear beta decay generates sharp cutoffs in the accompanying antineutrino spectrum at the beta decay endpoint energies. It has been conjectured that these features will interfere with measuring the effect of a neutrino mass hierarchy on an oscillated nuclear reactor antineutrino spectrum. These sawtooth-like features will appear in detailed reactor antineutrino spectra, with characteristic energy scales similar to the oscillation period critical to neutrino mass hierarchy determination near a 53 km baseline. However, these sawtooth-like distortions are found to contribute at a magnitude of only a few percent relative to the mass hierarchy-dependent oscillation pattern in Fourier space. In the Fourier cosine and sine transforms, the features that encode a neutrino mass hierarchy dominate by over sixteen (thirty-three) times in prominence to the maximal contribution of the sawtooth-like distortions from the detailed energy spectrum, given $3.2\%/\sqrt{E_\mathrm{vis.}/\mathrm{MeV}}$ (perfect) detector energy resolution. The effect of these distortions is shown to be negligible even when the uncertainties in the reactor spectrum, oscillation parameters, and counting statistics are considered. This result is shown to hold even when the opposite hierarchy oscillation patterns are nearly degenerate in energy space, if energy response nonlinearities are controlled to below 0.5\%. Therefore with accurate knowledge of detector energy response, the sawtooth-like features in reactor antineutrino spectra will not significantly impede neutrino mass hierarchy measurements using reactor antineutrinos.

On Restraints in End-Point Protein-Ligand Binding Free Energy Calculations

The impact of harmonic restraints on protein heavy atoms and ligand atoms on end-point free energy calculations is systematically characterized for 54 protein-ligand complexes. We observe that stronger restraints reduce the equilibration time and statistical inefficiency, suppress conformational sampling, influence correlation with experiment, and monotonically decrease the estimated loss of entropy upon binding, leading to stronger estimated binding free energies in most systems. A statistical estimator that reweights for the biasing potential and includes data prior to the estimated equilibration time has the highest correlation with experiment. A spring constant of 20 cal mol-1 A-2 maintains a near-native energy landscape and suppresses artifactual energy minima while minimally limiting thermal fluctuations about the crystal structure. © 2019 Wiley Periodicals, Inc.

Population cross-section of 179m2Hf from the reactions on hafnium and tantalum targets

The integral and flux-weighted average cross-sections of the 180Hf(γ,n)179m2Hf and 181Ta(γ,pn(d))179m2Hf reactions for the bremsstrahlung end-point energy of 37 MeV were determned by activation and off-line γ-ray spectrometric technique. Also by this techinque, the cross-section of the 178Hf(nr,γ)179m2Hf reaction was determined for reactor neutrons.

Binding pattern and susceptibility of epigallocatechin gallate against envelope protein homodimer of Zika virus: A molecular dynamics study

Zika virus (ZIKV) has caused an infant neurologic disorder, microcephaly, leading to a global health problem. Until now, no antiviral drug against ZIKV is commercially available. The recent studies reported that epigallocatechin gallate (EGCG) was found as a potential agent inhibiting the ZIKV entry process in Vero E6 cell. A pH-induced conformational change of the viral envelope (E) protein is a key step in such process. Herein, we focused on how EGCG could inhibit the dimeric E protein at the three possible binding sites at acidic pH condition by all-atom molecular dynamics (MD) simulations for 500 ns. The three EGCG binding sites on dimeric E protein are (i) the hinge region between domains I and III; (ii) the conserved region among flaviviruses; and (iii) the dimer interface. As a result, the binding pattern of EGCG in each pocket was presented in the mode of action of inhibition. The ligand-protein binding interactions, protein motions and binding free energies indicated that EGCG favorably interacted with the conserved region greater than the hinge region and the dimer interface, respectively. The obtained results via 4 different end-point free energy calculation methods suggested how this compound binds and prevents the rearrangement in the E protein at low pH.

Photon activation analysis of sand samples from Antalya in Turkey with a clinical electron linear accelerator

Abstract The purpose of this study is to demonstrate the feasibility of elemental analysis of sand samples by photon activation induced by high energy bremsstrahlung photons at an end point energy of 18 MeV from a clinical electron linear accelerator. The γ-ray spectra of the activated samples were collected using a high resolution spectrometer. Qualitative analysis of major and trace components of the samples (12 in total) was carried out whilst the spectra of eight of the samples were evaluated quantitatively. The contents of elements obtained by photon activation analysis were compared with values obtained by X-ray fluorescence.

Electron spectroscopy with a commercial 4H-SiC photodiode

A Commercial-Off-The-Shelf (COTS) 4H-SiC p-n photodiode (sold as a UV detector) was investigated as detector of electrons (β− particles) over the temperature range 100 °C to 20 °C. The photodiode had an active area of 0.06 mm2. The currents of the photodiode were measured in dark condition and under the illumination of a 63Ni radioisotope β− particle source (endpoint energy = 66 keV). The photodiode was then coupled to a custom-made low-noise charge-sensitive preamplifier to make a direct detection particle counting electron spectrometer. 63Ni β− particle spectra were accumulated with the spectrometer operating at temperatures up to 100 °C. The quantum efficiency of the photodiode as well as the spectrum expected to be detected were calculated via Monte Carlo simulations produced using the CASINO computer program. Comparisons between the simulated and detected 63Ni β− particle spectra are presented. The work was motivated by efforts to apply COTS technologies to develop low-cost space science instrumentation; a low-cost electron spectrometer of this type could be included on a university-led CubeSat mission for space plasma physics and magnetosphere experiments.

GaAs Spectrometer for Planetary Electron Spectroscopy

AbstractWork toward producing a radiation‐hard and high temperature tolerant direct detection electron spectrometer is reported. The motivation is to develop a low‐mass, low‐volume, low‐power, multimission capable instrument for future space science missions. The resultant prototype electron spectrometer employed a GaAs p+‐i‐n+ mesa photodiode (10 μm i layer thickness; 200 μm diameter) and a custom‐made charge‐sensitive preamplifier. The GaAs detector was initially electrically characterized as a function of temperature. The detector‐preamplifier assembly was then investigated for its utility in electron spectroscopy across the temperature range 100 to 20 °C using a laboratory 63Ni radioisotope β− particle source (end point energy = 66 keV). Monte Carlo simulations using the computer program CASINO were conducted and showed that the spectrometer had a quantum detection efficiency which increased with increasing electron energy up to 70 keV; a quantum detection efficiency of 73% was calculated. The accumulated 63Ni β− particle spectra together with CASINO simulations of the detected spectra showed that the GaAs based spectrometer could be used for counting electrons and measuring the energy deposited per electron in the detector's active region (i layer). The development of a GaAs electron spectrometer of this type may find use in future space missions to environments of intense radiation (such as at the surface of Europa for investigation of electron‐driven radiolysis of ice) and high temperature (such as at Mercury, and comets passing close to the Sun).

Ytterbium ( $\gamma$ γ , n) average cross-sections data near to photodisintegration reaction threshold

The thick foils activation technique has been applied to estimate the average cross-sections of 168,170,176Yb $(\gamma, \mathrm{n})$ reaction near to photodisintegration threshold. The $(\gamma, \mathrm{n})$ cross-sections are derived using the integrated photon flux at any energy range from the reaction threshold to the bremsstrahlung end-point energy. The photon flux is estimated using a calibration photodisintegration set of foils and taking in advance the spectrum linearity at high energies. The p-nuclei 168Yb average cross-section is $ 106 \pm 21$ mb corresponding to $E_{\mathrm{mean}} = 10$ MeV. The 170Yb average cross section is $ 117 \pm 31$ mb matching $ E_{\mathrm{mean}} = 9$ MeV while the 176Yb one is $ 123 \pm 36$ mb corresponding to $ E_{\mathrm{mean}} = 8$ MeV. The experimental results associate to statistical model simulations performed by the TALYS code. The simulated data of 168Yb ranges 83–139 mb, while 170Yb and 176Yb vary between 89–152 and 84–170mb; which agree with the measurements within uncertainties. The simulated average cross-section of natYb $(\gamma, \mathrm{n})$ reaction is $ 127 \pm 25$ mb corresponding to energy ranges 6.6-14 MeV. The simulation results based on Lorentzian $ \gamma$ -strength considerations with the density level of Fermi gas plus the constant temperature model are closest to the average cross-sections measured.

Energy loss due to defect formation from 206Pb recoils in SuperCDMS germanium detectors

The Super Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory studied energy loss associated with defect formation in germanium crystals at mK temperatures using in situ 210Pb sources. We examine the spectrum of 206Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of (6:08 ± 0:18)%, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of 19.7−0.5+0.6 eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches.

Flux weighted average cross-sections of natNi(γ, x) reactions with the bremsstrahlung end-point energies of 55, 59, 61 and 65 MeV

We measured the flux weighted average cross-sections of the natNi(γ,xn)56,57Ni and natNi(γ, pxn)55,56,57,58Co reactions with the bremsstrahlung end-point energies of 55, 59, 61 and 65 MeV by using an activation cum off-line γ-ray spectrometric technique at the Pohang Accelerator Laboratory (PAL), Korea. The natNi(γ, xn) and natNi(γ, pxn) reaction cross-sections as a function of monoenergetic photon were calculated theoretically by using the computer code TALYS-1.8. The flux-weighted average cross-sections of the natNi(γ, xn) and natNi(γ, pxn) reactions from the present work were compared with the similar data from the literature as well as the theoretical values from the TALYS-1.8 code and the TENDL-2015 data library. Both the experimental and theoretical values increase sharply from the reaction threshold to a maximum value where the next reaction channel opens. After the maximum value, individual reaction cross section decreases slowly with increase of bremsstrahlung end-point energy, which may be due to the opening of other possible reaction channels.

Isomeric yield ratio of 152m1Eu(8−)–152m2Eu(0−) produced in (γ, n) photonuclear reaction in the giant dipole resonance region

In this work, the isomeric ratio of 152m1Eu(8−)–152m2Eu(0−) produced from the 153Eu(γ, n)152Eu reaction have been measured in the whole giant dipole resonance region by the activation method. In order to improve the accuracy of the experimental results, the necessary corrections were made in the gamma activity measurements and data analysis. The results were discussed and compared with the similar data from literature to examine the excitation energy, the spin difference and the nuclear reaction channel effects and can be used for the interpretation on the structure of the nucleus and the mechanisms of nuclear reactions. The data for bremsstrahlung end-point energies of 19–23 MeV are first-time measurements.

The quality of megavoltage photon beams measured by the ratio of photoactivation and neutron capture yields

The activities of products of two photonuclear reactions (113In(γ,γ’)113mIn and 115In(γ,γ’)115mIn) and neutron capture (115In(n, γ)116mIn) were measured. The measurements were made to verify that obtained activities (as well as some of their ratios) change sufficiently with the change of the energy, so that the activation of the indium could be recommended as a sensitive test for the control of the endpoint energy (and beam quality) of bremsstrahlung beams in an energy region usually used in radiation therapy. Mikrotron photon beam was used for photoactivation, and the source of neutrons was the mikrotron tungsten target itself, at energies higher than threshold for (γ, n) reaction. At lower energies, neutrons were produced in Be target inserted in photon beam. It was obtained that sensitive index of endpoint energy variation can be obtained in a broad energy region from 5 MeV to 23 MeV by different combinations of saturation activities of three reaction products. The described measurements can be used to develop a very sensitive and simple method in a routine quality control of photon beams of megavoltage devices used in radiotherapy.

Cyclotron Production of Unconventional Radionuclides for PET Imaging: the Example of Titanium-45 and Its Applications

Positron emitting radionuclides are used to label different compounds, allowing the study of the major biological systems using PET (positron emission tomography) imaging. Although there are several radionuclides suited for PET imaging, routine clinical applications are still based on a restrict group constituted by 18F, 11C, and, more recently, 68Ga. However, with the enlarged availability of low-energy cyclotrons and technical improvements in radionuclide production, the use of unconventional radionuclides is progressively more common. Several examples of unconventional radionuclides for PET imaging are being suggested, and 45Ti could be suggested as a model, due to its interesting properties such as its abundant positron emission (85%), reduced positron energy (β+ endpoint energy = 1040 keV), physical half-life of 3.09 h, and interesting chemical properties. This review aims to introduce the role of cyclotrons in the production of unconventional radionuclides for PET imaging while using 45Ti as an example to explore the potential biomedical applications of those radionuclides in PET imaging.

High-energy radiographic imaging performance of LYSO

A comprehensive comparison of the dominant sources of radiation-induced blur for radiographic imaging system performance is made. End-point energies of 6, 10, 15, and 20 MeV bremsstrahlung photon radiation produced at the Los Alamos National Laboratory Microtron facility were used to examine the performance of large-panel cerium-doped lutetium yttrium silicon oxide (LYSO:Ce) scintillators 3, 5 and 10 mm thick. The system resolution was measured and compared between the various end-point energies and scintillator thicknesses. Contrary to expectations, it is found that there was only a minor dependence of system resolution on scintillator thickness or beam end-point energy. This indicates that increased scintillator thickness does not have a dramatic effect on system performance. The data are then compared to Geant4 simulations to assess contributions to the system performance through the examination of modulation transfer functions. It was determined that the low-frequency response of the system is dominated by the radiation-induced signal, while the higher-frequency response of the system is dominated by the optical imaging of the scintillation emission.