Ca Nuclei Research Articles

Development of activity pencil beam algorithm using measured distribution data of positron emitter nuclei generated by proton irradiation of targets containing 12 C, 16 O, and 40 Ca nuclei in preparation of clinical application

The purpose of this study is to develop a new calculation algorithm that is satisfactory in terms of the requirements for both accuracy and calculation time for a simulation of imaging of the proton-irradiated volume in a patient body in clinical proton therapy. The activity pencil beam algorithm (APB algorithm), which is a new technique to apply the pencil beam algorithm generally used for proton dose calculations in proton therapy to the calculation of activity distributions, was developed as a calculation algorithm of the activity distributions formed by positron emitter nuclei generated from target nuclear fragment reactions. In the APB algorithm, activity distributions are calculated using an activity pencil beam kernel. In addition, the activity pencil beam kernel is constructed using measured activity distributions in the depth direction and calculations in the lateral direction. (12)C, (16)O, and (40)Ca nuclei were determined as the major target nuclei that constitute a human body that are of relevance for calculation of activity distributions. In this study, "virtual positron emitter nuclei" was defined as the integral yield of various positron emitter nuclei generated from each target nucleus by target nuclear fragment reactions with irradiated proton beam. Compounds, namely, polyethylene, water (including some gelatin) and calcium oxide, which contain plenty of the target nuclei, were irradiated using a proton beam. In addition, depth activity distributions of virtual positron emitter nuclei generated in each compound from target nuclear fragment reactions were measured using a beam ON-LINE PET system mounted a rotating gantry port (BOLPs-RGp). The measured activity distributions depend on depth or, in other words, energy. The irradiated proton beam energies were 138, 179, and 223 MeV, and measurement time was about 5 h until the measured activity reached the background level. Furthermore, the activity pencil beam data were made using the activity pencil beam kernel, which was composed of the measured depth data and the lateral data including multiple Coulomb scattering approximated by the Gaussian function, and were used for calculating activity distributions. The data of measured depth activity distributions for every target nucleus by proton beam energy were obtained using BOLPs-RGp. The form of the depth activity distribution was verified, and the data were made in consideration of the time-dependent change of the form. Time dependence of an activity distribution form could be represented by two half-lives. Gaussian form of the lateral distribution of the activity pencil beam kernel was decided by the effect of multiple Coulomb scattering. Thus, the data of activity pencil beam involving time dependence could be obtained in this study. The simulation of imaging of the proton-irradiated volume in a patient body using target nuclear fragment reactions was feasible with the developed APB algorithm taking time dependence into account. With the use of the APB algorithm, it was suggested that a system of simulation of activity distributions that has levels of both accuracy and calculation time appropriate for clinical use can be constructed.

Quasifree (e,e′p) reactions on nuclei with neutron excess

We study the evolution of the $(e,{e}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{'}}p)$ cross section on nuclei with increasing asymmetry between the number of neutrons and protons. The calculations are done within the framework of the distorted-wave impulse approximation, by adopting nonrelativistic and relativistic models. We compare the results obtained with three different approaches based on the mean-field description for the proton bound-state wave function. In the nonrelativistic model phenomenological Woods-Saxon and Hartree-Fock wave functions are used; in the relativistic model the wave functions are solutions of Dirac-Hartree equations. The models are first tested against experimental data on ${}^{16}$O, ${}^{40}$Ca, and ${}^{48}$Ca nuclei, and then they are applied to calculate $(e,{e}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{'}}p)$ cross sections for a set of spherical calcium and oxygen isotopes. From the comparison of the results obtained for the various isotopes we can infer information about the dependence of the various ingredients of the models on the neutron to proton asymmetry.

A specific role of 43Ca in the enzymatic ATP synthesis

This is the first report ever on the nuclear spin selective 43 Ca 40 Ca isotope effect expressed in the Calcium affected enzymatic ATP synthesis. Once the creatine kinase (CK) catalytic sites were loaded with 43 Ca 2+ , the resulting enzyme activity goes up (2.0±0.3 – fold) compared to the CKdirected ATP synthesis rate occurred in the presence of nonmagnetic, spinless, 40 Ca nuclei. The effect manifests itself predominantly within a high concentration range (Calcium chloride,40 mM) indicating that the ATP synthesis is a spin-selective ion-radical process. Primary reaction of this path is an electron transfer between the reaction partners, С a(H2O)n 2+ ( n ≤ 4) and Ca(ADP) 3- , generating an ion-radical pair where the singlet -triplet spin conversion takes place as a result of the nuclear spin selectivity and a consequent magnetic isotope effect. This, in turn, makes an essential impact on the final reaction’s ATP yield. To the contrast, there is no any isotope effect found within a low Ca 2+ concentration range showing that the ATP synthesis proceeds in a most common nucleophylic way. The submolecular mechanisms of phenomena described and their possible applied significance are under discussion.

Calcium induced ATP synthesis: Isotope effect, magnetic parameters and mechanism

ATP synthesis by creatine kinase with calcium ions is accompanied by 43Ca/ 40Ca isotope effect: the enzyme with 43Ca 2+ was found to be 2.0 ± 0.3 times more active than enzymes, in which Ca 2+ ions have nonmagnetic nuclei 40Ca. The effect demonstrates that primary reaction in ATP synthesis is electron transfer between reaction partners, Сa( H 2 O ) n 2 + ( n ⩽ 3) and Ca 2+(ADP) 3−. It generates ion-radical pair, in which spin conversion results in the isotope effect. Magnetic parameters (g-factors and HFC constants a( 43Ca) and a( 31P)) confirm that namely terminal oxygen atom of the ADP ligand in the complex Ca 2+(ADP) 3− donates electron to the Ca( H 2 O ) n 2 + ion.

Combined model of photonucleon reactions

A combination of the semimicroscopic, exciton, and evaporation models is used to describe photonucleon reactions induced in medium-mass and heavy nuclei by photons of energy below the mesonproduction threshold. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance (GDR) at energies in the range Eγ ≲ 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region Eγ ≳ 40 MeV. The densities of particle-hole states appearing in the exciton model are calculated on the basis of the Fermi gas model. Our combined model takes into account the multiparticle emission of preequilibrium particles. The influence of isospin conservation and collective phenomena on photonucleon emission by giant dipole resonances is considered. The combined model is used to describe cross sections for photonucleon reactions proceeding on the 40,48Ca, 90Zr, 139La, 142Nd, and 181Ta nuclei, as well as difference (Eγmax = 85–55 MeV) bremsstrahlung photoneutron spectra for the 63Cu, 115In, 118Sn, 181Ta, 207Pb, 209Bi, and 235U nuclei and bremsstrahlung photoproton spectra for the 90Zr nucleus at the energies of Eγmax = 22, 25, and 34 MeV.

New versatile mechanism of enzymatic synthesis of adenosine triphosphate: theoretical foundation and experimental control

The energies of electron transfer between pyrophosphate metal complexes and hydrated metal complexes, which is the key reaction that models the radical ion mechanism of adenosine triphosphate (ATP) synthesis, were calculated. A threshold dependence of the energy on the number of water molecules n in the ion hydration sphere was established: for n < 4 the reaction is exothermic, while for n ≥ 4 it is endothermic. The switching of the energy regime accounts for the fact that ATP is synthesized only in molecular machines, enzymes, rather than in homogeneous aqueous solutions. It was predicted theoretically that the radical ion ATP synthesis may be catalyzed by not only magnesium ions as in living cells but also by calcium, zinc, barium, cadmium, and tin ions. This prediction was experimentally confirmed by the discovery of the magnetic isotope effect in the calcium- and zinc-catalyzed ATP synthesis by creatine kinase. The efficiency of ATP synthesis in the presence of ions with magnetic nuclei 43Ca and 67Zn is almost twice as high as that in the presence of the same ions with nonmagnetic nuclei 40Ca and 64Zn.

Ab initiocoupled-cluster approach to nuclear structure with modern nucleon-nucleon interactions

We perform coupled-cluster calculations for the doubly magic nuclei 4He, 16O, 40Ca and 48Ca, for neutron-rich isotopes of oxygen and fluorine, and employ "bare" and secondary renormalized nucleon-nucleon interactions. For the nucleon-nucleon interaction from chiral effective field theory at order next-to-next-to-next-to leading order, we find that the coupled-cluster approximation including triples corrections binds nuclei within 0.4 MeV per nucleon compared to data. We employ interactions from a resolution-scale dependent similarity renormalization group transformations and assess the validity of power counting estimates in medium-mass nuclei. We find that the missing contributions due to three-nucleon forces are consistent with these estimates. For the unitary correlator model potential, we find a slow convergence with respect to increasing the size of the model space. For the G-matrix approach, we find a weak dependence of ground-state energies on the starting energy combined with a rather slow convergence with respect to increasing model spaces. We also analyze the center-of-mass problem and present a practical and efficient solution.

Δ-Resonances in Ground State Properties of 2040Ca Spherical Cold Finite Nucleus at Equilibrium and under Compression

The ground state properties of the spherical nucleus 40Ca have been investigated by using constrained spherical Hartree–Fock (CSHF) approximation at equilibrium and under high radial compression in a six major shells. The effective baryon-baryon interaction that includes the Δ(1236) resonance freedom degrees to calculate nuclear properties is used. The nucleon-nucleon (N-N) interaction is based on Reid soft core (RSC) potential. The results of calculations show that much of increase in the nuclear energy generated under compression is used to create the massive Δ particles. The number of Δ's can be increased to about 2.1% of constituents of nucleus when nuclear density reaches about 1.34 times of normal density. The single particle energy levels are calculated and their behavior under compression is also examined. A good agreement has been found between current calculations and phenomenological shell model for low lying single-particle spectra. The gap between shells is very clear and L-S coupling become stronger as increasing the static load on the nucleus. The results show a considerable reduction in compressibility when freedom degrees of Δ's are taken into account. It has been found that the total nuclear radial density becomes denser in the interior and less dense in the exterior region of nucleus. The surface of nucleus becomes more and more responsive to compression than outer region.

SHELL STRUCTURE IN NEUTRON-RICH Ca AND Ni NUCLEI

The shell structure of the neutron-rich Ca and Ni nuclei is investigated by the spherical Hartree-Fock calculations with the semi-realistic NN interactions. The tensor force plays a significant role in the Z dependence of the shell structure, as is exemplified by N = 32 and N = 40. Loose binding may lead to a submagic number N = 58 in 86 Ni , assisted by the weak pair coupling.

Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields

Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the spherical Hartree-Fock calculations with the semi-realistic $NN$ interactions. Specific ingredients of the effective interaction, particularly the tensor force, often play a key role in the $Z$ dependence of the neutron shell structure. Such examples are found in N=32 and N=40; N=32 becomes magic or submagic in $^{52}$Ca while its magicity is broken in $^{60}$Ni, and N=40 is submagic (though not magic) in $^{68}$Ni but not in $^{60}$Ca. Comments are given on the doubly magic nature of $^{78}$Ni. We point out that the loose binding can lead to a submagic number N=58 in $^{86}$Ni, assisted by the weak pair coupling.

NEW CALCULATION FOR SOME GROUND STATE FEATURES OF 40Ca, 48Ca32S AND 39K NUCLEI

Some ground states features of 32 S , 39 K , 40 Ca and 48 Ca nuclei are investigated using the Hartree–Fock method with the Skyrme SKM * and SLy4 forces calculated in two different code implementations. The calculated total binding energies per particle and root mean square (rms) nuclear charge radii using the Skyrme–Hartree–Fock (SHF) + BCS method are compared with relativistic mean-field (RMF) theory and experimental values. The obtained charge density distributions from these code implementations are compared with the experimental data. Pairing effects are also included in calculations for the same nuclei. Variations of the total binding energies per particle and rms nuclear charge radii were investigated as the last shell nucleons were carried to the upper shell.

Bremsstrahlung neutrino energy loss for 24Mg, 28Si, 32S, 40Ca, 56Fe in strong electron screening

Based on Weinberg–Salam theory the bremsstrahlung neutrino energy loss for nuclei 24Mg, 28Si, 32S, 40Ca and 56Fe are investigated in strong electron screening. Our results are compared with those of Dicus' and show that the latter are higher by 2 orders of magnitude in the density-temperature region of 108 g/cm3 ≤ ρ/μe ≤ 1011 g/cm3 and 2.5 ≤ T9 ≤ 4.5. On the other hand, the factor C shows that the maximum differences are 99.16%, 99.13%, 99.12%, 99.055%, 99.040% corresponding to the nuclei 24Mg, 28Si, 32S, 40Ca and 56Fe.

PAIRING VIBRATIONS STUDY FROM TIME-DEPENDENT HARTREE-FOCK-BOGOLIUBOV FORMALISM

We study pairing vibrations in 18,20,22 O and 42,44,46 Ca nuclei solving the time-dependent Hartree-Fock-Bogoliubov equation in coordinate space with spherical symmetry. We use the SLy4 Skyrme functional in the particle-hole part of the energy density functional and a local, density-dependent pairing functional in its particle-particle (hole-hole) part. Pairing vibrations are excited by a two-neutrons transfer operator. The Fourier analysis of the time-dependent response of the expectation value of this operator in the linear regime is used to extract strength functions. The presence of the giant pairing vibration is discussed.

Multipole resonances in open-shell nuclei: Connection with direct-reaction spectroscopy

Probability distributions for the excitation of the 1ħω multipole resonances E1, M6, and M2 in the sd-shell nuclei 18O, 22Ne, 24Mg, 26Mg, 27Al, 28Si, 32S, and 40Ca were obtained by means of the spectroscopy of direct pickup reactions within the particle-core coupling (PCC) version of the multiparticle shell model. The deviation of the ground state of a nucleus featuring A nucleons from the case of closed shells or subshells manifests itself in a broad range of the energy distribution of holes among states of (A − 1) nuclei. This energy spread is the main source of the fragmentation of multipole resonances in open-shell nuclei. A comparison of PCC theoretical results with experimental data confirms the applicability of the approach used over a broad range of momentum transfers and proves the existence of connections between direct and resonance processes.

On M1-radiative transitions between analog and Gamow-Teller states

The description of M1-radiative transitions between analog and Gamow-Teller states built on the ground state of a closed-shell nucleus is given within the continuum random phase approximation. For the parent nuclei 48Ca and 208Pn the reduced probabilities and partial widths are calculated using a phenomeno-logical partially self-consistent nuclear mean field and the Landau-Migdal particle-hole interaction.

Semimicroscopic description of charge-exchange giant spin-monopole resonances

The quantitative analysis of the main properties of charge-exchange giant spin-monopole resonances is performed for closed-shell parent nuclei within the semimicroscopic approach based on the continuum version of the random phase approximation and phenomenological treatment of the spreading effect. For the first time the description of direct neutron decay of the spin-monopole resonances in the β+-channel is given together with taking into account the resonance energy shift due to the spreading effect. The results of the joint analysis of the main properties of the above-mentioned giant resonances are given for the parent nuclei 48Ca and 208Pb.

Inhibitory Mechanism of Escherichia coli RelE-RelB Toxin-Antitoxin Module Involves a Helix Displacement Near an mRNA Interferase Active Site

In Escherichia coli, RelE toxin participates in growth arrest and cell death by inducing mRNA degradation at the ribosomal A-site under stress conditions. The NMR structures of a mutant of E. coli RelE toxin, RelE(R81A/R83A), with reduced toxicity and its complex with an inhibitory peptide from RelB antitoxin, RelB(C) (Lys(47)-Leu(79)), have been determined. In the free RelE(R81A/R83A) structure, helix alpha4 at the C terminus adopts a closed conformation contacting with the beta-sheet core and adjacent loops. In the RelE(R81A/R83A)-RelB(C) complex, helix alpha3(*) of RelB(C) displaces alpha4 of RelE(R81A/R83A) from the binding site on the beta-sheet core. This helix replacement results in neutralization of a conserved positively charged cluster of RelE by acidic residues from alpha3(*) of RelB. The released helix alpha4 becomes unfolded, adopting an open conformation with increased mobility. The displacement of alpha4 disrupts the geometry of critical residues, including Arg(81) and Tyr(87), in a putative active site of RelE toxin. Our structures indicate that RelB counteracts the toxic activity of RelE by displacing alpha4 helix from the catalytically competent position found in the free RelE structure.

Lifetime measurements of neutron-rich nuclei around 48Ca with the CLARA-PRISMA setup

The lifetimes of excited states in neutron-rich nuclei around the doubly-magic nucleus 48Ca have been measured using a novel technique that combines the Recoil Distance Doppler Shift method with the CLARA-PRISMA spectrometers. This is the first time such a method is applied to measure lifetimes of neutron-rich nuclei populated via a multinucleon transfer reaction. The experimental method will be discussed and the results for Ca nuclei will be compared with realistic simulations of the CLARA and PRISMA spectrometers.

Disassembling the nuclear matrix elements of the neutrinoless ββ decay

In this article we analyze the nuclear matrix elements (NME) of the neutrinoless double beta decays ( 0 ν β β ) of the nuclei 48Ca, 76Ge, 82Se, 124Sn, 128Te, 130Te and 136Xe in the framework of the interacting shell model (ISM). We study the relative value of the different contributions to the NME's, such as higher order terms in the nuclear current, finite nuclear size effects and short range correlations, as well as their evolution with the maximum seniority permitted in the wave functions. We discuss also the build-up of the NME's as a function of the distance between the decaying neutrons. We calculate the decays to 0 1 + final states and find that these decays are at least 25 times more suppressed with respect to the ground state to ground state transition.

Spin-Isospin Resonances: A Self-Consistent Covariant Description

For the first time a fully self-consistent charge-exchange relativistic RPA based on the relativistic Hartree-Fock (RHF) approach is established. The self-consistency is verified by the so-called isobaric analog state (IAS) check. The excitation properties and the nonenergy weighted sum rules of two important charge-exchange excitation modes, the Gamow-Teller resonance (GTR) and the spin-dipole resonance (SDR), are well reproduced in the doubly magic nuclei 48Ca, 90Zr and 208Pb without readjustment of the particle-hole residual interaction. The dominant contribution of the exchange diagrams is demonstrated.