181Ta Targets Research Articles

Investigation of Reaction Cross Sections for Beams of 8Li, 8He on 28Si, 59Co, 181Ta Targets

Investigation of Reaction Cross Sections for Beams of 8Li, 8He on 28Si, 59Co, 181Ta Targets

Complete set of bound negative-parity states in the neutron-rich nucleus N18

High-resolution gamma-ray spectroscopy of 18N is performed with the Advanced GAmma Tracking Array AGATA, following deep-inelastic processes induced by an 18O beam on a 181Ta target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in 18N below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0^-_1 and 1^-_2 excitations, which provide strong constrains for cross-shell p-sd matrix elements based on realistic interactions, and help to simultaneously reproduce the ground and first-excited states in 16N and 18N, for the first time. Understanding the 18N structure may also have significant impact on neutron-capture cross-section calculations in r-process modeling including light neutron-rich nuclei.

Nucleon scattering analysis with a lane-consistent dispersive optical potential for Hf, W and Ta isotopes

Nucleon scattering on tungsten and neighboring nuclei are analyzed with a coupled-channels method based on a soft-rotator structure model. The multiple band couplings and nuclear stretching factors are built using nuclear wave functions of the soft-rotator model with the Hamiltonian parameters adjusted to reproduce the energy of low-lying collective levels of corresponding nuclei. A regional lane-consistent dispersive coupled-channels optical-model potential is derived to reproduce the neutron total cross sections, nucleon elastic and inelastic scattering angular distributions, and analyzing powers. Excellent agreement with measurements is obtained for neutron total cross sections of 182,183,184,186W, 178Hf, and 181Ta targets in the whole energy range from 100 keV to 200 MeV; other scattering data are found to be in good agreement with measurements. A deformation-dependent nuclear radius correction arising from the volume conservation condition is introduced and allowed to remove phenomenological radii dependencies on nuclear mass from the potential geometry.

Analysis of velocity distributions in projectile fragmentation reactions of 18O ions on 9Be and 181Ta targets at 35 A MeV

Up to date analysis of velocity and isotope distributions of light fragments obtained in the projectile fragmentation reactions of 18O at 35 A MeV on 9Be and 181Ta targets measured at COMBAS fragment separator at the U400 M Research Facility in JINR are presented. The results of velocity spectra analytical parameterization and isotopic ratios are compared with the ones obtained in the experiments presented in the literature. The discussion of the different mechanisms involved in these types of the reactions is given.

Total Reaction Cross Sections for 6,8He and 9Li Nuclei on 28Si, 59Co, and 181Ta Targets

Experiments with 6,8He, 9Li + 28Si, 59Co, and 181Ta reactions in the energy range of 6,8He and 9Li beams 6–36 A MeV have been preformed. Prompt neutrons and gamma radiation were registered by a 12‑detector gamma spectrometer. The values of the total reaction cross sections and the multiplicity distributions for the emission of γ-quanta and neutrons were calculated taking into account the distributions over the number of triggered detectors.

Short-range Lifetime Measurements for Deep-inelastic Reaction Products: the \(^{19}\)O Test Case

An experiment, aiming at measuring lifetimes of excited states in neutron-rich C and O isotopes, was performed at the GANIL laboratory with the use of the AGATA segmented HPGe tracking array, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The nuclei of interest were populated in transfer and deep-inelastic processes induced by an 18O beam at 126 MeV (7.0 MeV/u) on a 181Ta target. This paper contains a brief description of a novel implementation of a Monte-Carlo technique, which allowed us to obtain excited states lifetimes in the range from tens to hundreds femtoseconds for a reaction with complex initial velocity distribution, making use of the Doppler-shift attenuation method (DSAM). As a test case, we present here the analysis for two states in 19O: 2371-keV 9/2 + and 2779-keV 7/2 +, for which lifetimes of τ > 400 fs and τ = 140+50 −40 fs were obtained, respectively, in agreement with literature values. This newly developed approach will be essential for short lifetimes measurements in neutron-rich systems, exploiting intense ISOL-type beams, currently under development.

L-shell X-ray production cross sections in metal oxide thin films due to 12C, 16O and 28Si ion beams at MeV SIMS energies

Successful co-implementation of different heavy ion beam nuclear analytical techniques such as heavy ion PIXE, ERDA, MeV SIMS and RBS hinges on the availability of accurate databases of fundamental ion beam-matter interaction parameters. We report on measurements carried out to determine L-shell X-ray production cross sections in 101Ru and 181Ta due to 12C, 16O and 28Si projectile ions in the 0.2 MeV/u–1.0 MeV/u energy range. Experimental data is compared to calculations by one of the most widely implemented X-ray ionisation theories in PIXE analyses – the ECPSSR theory in its modified United Atom (UA) version. Results show fairly good agreement between experiment and theory for the 181Ta target atoms, with the level of agreement improving as the Zion/Ztarget ratio decreases and as beam energy increases. For 101Ru target atoms theoretical predictions tend to underestimate experimental data and the discrepancies increase with projectile mass and decreasing energy. The contribution of projectile electron capture (EC) to the measured X-ray production cross sections is also considered in the data analysis and discussion.

Direct detection of delayed high energy electrons from the 181Ta target irradiated by a moderate intensity femtosecond laser pulse

We depict an experimental study of delayed fast, negatively charged particles from femtosecond laser-plasma interaction at an intensity of I ∼ 1017 W cm−2. Plates of 2 mm thickness made of 181Ta (∼100% abundance) and natural W were used as targets. We distinguished certain delayed events due to detection of negative H−, C− and O− ions. However, most events which were delayed by 0.5–5 μs with respect to the instantaneous plasma formation caused by the laser pulses, were identified as electrons with energies of 3–7 keV. A comparative analysis between the tantalum and tungsten spectra was undertaken. This revealed a close similarity between the measured spectrum for tantalum and the predicted spectrum for electrons arising from to the internal conversion decay of the 6.237 keV nuclear isomeric state in 181Ta.

Projectile fragmentation of 40,48Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of 40,48Ca on 9Be and 181Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the 40,48Ca pair. The symmetry energy determined in this way depends on these structure effects.

Investigation of contribution of incomplete fusion in the total fusion process induced by 9Be on 181Ta target at near barrier energies

We have studied the relative contribution of incomplete fusion (ICF) and complete fusion (CF) in total fusion (TF) induced by 9Be on 181Ta target at energies in the vicinity of Coulomb barrier using classical dynamical model and Wong's formula in conjugation with energy dependent Woods–Saxon formula. It is found that at above barrier energies ICF contributes almost 30% in TF while at energies below the barrier qualitatively its contribution is much more than thirty percent.

Comparison of neutron doses measured by CR-39 via LET spectrometry and neutron rem meter

Neutron dose for proton induced reactions on the combination of 7Li and 181Ta target was measured using CR-39 detector and a neutron rem meter, at five different proton energies (8–24 MeV). In case of CR-39, the dose equivalent (HLET) was measured via linear energy transfer (LET) spectrometry method using the major, minor radii of each track and thickness of removed surface, whereas the rem meter provided the direct reading of ambient dose equivalent [H*(10)]. Both these quantities per incident proton were found to increase with the proton energy. The response ratio of HLET to [H*(10)] was found to be in the range of 0.15–0.3 with an average 0.20 ± 0.09.

Exploration of Adiabatic Resonance Crossing Through Neutron Activator Design for Thermal and Epithermal Neutron Formation in (99)Mo Production and BNCT Applications.

A feasibility study was performed to design thermal and epithermal neutron sources for radioisotope production and boron neutron capture therapy (BNCT) by moderating fast neutrons. The neutrons were emitted from the reaction between (9)Be, (181)Ta, and (184)W targets and 30 MeV protons accelerated by a small cyclotron at 300 μA. In this study, the adiabatic resonance crossing (ARC) method was investigated by means of (207)Pb and (208)Pb moderators, graphite reflector, and boron absorber around the moderator region. Thermal/epithermal flux, energy, and cross section of accumulated neutrons in the activator were examined through diverse thicknesses of the specified regions. Simulation results revealed that the (181)Ta target had the highest neutron yield, and also tungsten was found to have the highest values in both surface and volumetric flux ratio. Transmutation in the (98)Mo sample through radiative capture was investigated for the natural lead moderator. When the sample radial distance from the target was increased inside the graphite region, the production yield had the greatest value of activity. The potential of the ARC method is a replacement or complements the current reactor-based supply sources of BNCT purposes.

Measurement and simulation of the cross sections for the production of 148Gd in thin natW and 181Ta targets irradiated with 0.4- to 2.6-GeV protons

The cross sections for the production of 148Gd in natW and 181Ta targets irradiated by 0.4-, 0.6-, 0.8-, 1.2-, 1.6-, and 2.6-GeV protons at the ITEP accelerator complex have been measured by direct α spectrometry without chemical separation. The experimental data have been compared with the data obtained at other laboratories and with the theoretical simulations of the yields on the basis of the BERTINI, ISABEL, CEM03.02, INCL4.2, INCL4.5, CASCADE07, and PHITS codes.

Measurement and simulation of the cross sections for nuclide production in natW and 181Ta targets irradiated with 0.04- to 2.6-GeV protons

The cross sections for nuclide production in thin natWand 181Ta targets irradiated by 0.04–2.6-GeV protons have been measured by direct γ spectrometry using two γ spectrometers with the resolutions of 1.8 and 1.7 keV in the 60Co 1332-keV γ line. As a result, 1895 yields of radioactive residual product nuclei have been obtained. The 27Al(p, x)22Na reaction has been used as a monitor reaction. The experimental data have been compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.

Kaon production in nucleus-nucleus collisions at 92 MeV per nucleon

K+ production far below the free nucleon-nucleon threshold has been investigated in collisions of 36Ar on 12C, natTi, and 181Ta targets at an incident energy of 92 MeV per nucleon. The cross sections for K+ production have been inferred from the observed muon decays of positive kaons. The results are discussed in the framework of a participant-spectator model and are compared to proton induced K+ production and to subthreshold pion production experiments.

Search for new neutron-rich nuclei with a 70 A MeV 48Ca beam

The results of an experiment by the RIKEN-JINR collaboration on search for new Ne, Na, Mg, Al isotopes close to the neutron drip line are presented. We found for the first time three new neutron-rich nuclei 38Mg and 40,41Al. Some clue for particle unstability of 33Ne was also obtained. These nuclei were produced by the projectile fragmentation of a 70 A MeV 48Ca beam on a 181Ta target. The reaction fragments were analyzed by the fragment separator RIPS at RIKEN, and were unambiguously identified by measuring the magnetic rigidity, time-of-flight, energy loss and total kinetic energy.

The nuclear structure of 178Hf studied by the 181Ta(p, α) 178Hf reaction

The microscopic structures of levels in 178Hf have been studied by the 181Ta(p, α) reaction using 17 MeV protons. The reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions, yielding an overall resolution of ⩽ 20 keV (FWHM). Levels with significant populations must involve a proton in the 7 2 + [404] Nilsson orbital, which forms the ground state of the 181Ta target nucleus. The admixtures of various two-quasiproton configurations were extracted from the observed cross sections. The ground-state band is populated unusually weakly, while a large 7 2 + [404] − 7 2 + [404] strength is observed for the K π = 0 + band at 1199 keV. This is attributed to the irregular filling of Nilsson proton states in this region, whereby the 7 2 +[404] orbital appears as the ground state for tantalum as well as lutetium nuclei. For the well-known K π = 8 − bands at 1147 and 1479 keV the present results confirm in a direct manner the 9 2 −[514] π + 7 2 +[404] π admixtures proposed earlier on the basis of gamma-ray mixing ratios and log ft values. An upper limit of ∼ 5% for the 9 2 −[514] π− 7 2 +[404] π configuration in the K π = 1 − band at 1310 keV is consistent with earlier proposals that this is predominantly a 9 2 +[624] v− 7 2 −[514] v two-quasineutron band. A new K π = 1 − band has been assigned at 1513 keV, which has the main 9 2 −[514] π− 7 2 +[404] π strength. Levels previously assigned as a K π = 2 − band at 1566 keV are shown to be rotational excitations based on this new K π = 1 − band. The K π = 3 + band at 1758 keV is found to be predominantly the 7 2 +[404] π− 1 2 +[411] π configuration, while the strength for the K π = 4 + parallel coupling of the same two protons is spread over more than one band.

Measurement and QRPA calculation of the β-delayed neutron emission of 21,22N and 23,24O

Neutron-rich isotopes of nitrogen and oxygen have been produced as projectile-like fragments in the reaction of a 44 MeV/u 48Ca beam with a 173mg/cm 2 181Ta target. The fragments have been analyzed by the doubly achromatic spectrometer LISE and implanted in a semiconductor identification telescope, surrounded by a 4π neutron detector in order to observe their radioactive decay. The β-delayed neutron emission has been measured for the isotopes 21,22N and 23,24O for the first time and the β-half-lives T 1 2 and delayed neutron-emission probabilities Pn are determined. These values are discussed within the framework of a QRPA calculation. The influence of the decay energy Q β used in the calculation is examined, indicating the reliability of predicted matrix elements. Furthermore, P n values are calculated and compared to the experimental data.

Total cross sections of reactions induced by neutron-rich light nuclei

Total nuclear reaction cross-sections are determined by means of a 4π-γ method. The results cover a wide span of targets for various stable beams. The validity of the method is shown in a combined systematics including also the results of transmission-type experiments. The data are very well described by the formula developed by Kox et al. The same method is applied to secondary fragment beams produced from a 44 MeV/u22Ne beam on a 332mg/cm2 181Ta target. Using the LISE spectrometer the fragments4, 6He,6–9, 11Li,7, 9–12, 14Be,10–15, 17B11–19C,13–19N,15–21O,18– 21F and20,21 Ne are analyzed and transported to interact with a 199.4 mg/cm2 Cu target surrounded by a 4π-γ counter. The measured total reaction cross-sectionsσ R are discussed in terms of the reduced strong absorption radiusr 0 and compared with other experimental results.

β-Delayed neutron emission of the isotopes 20C, 40,41,42P, 43,44S

Very neutron-rich isotopes have been produced by the fragmentation of 55 MeV/u 48Ca projectiles from GANIL onto a 181Ta target. The nuclei were separated by means of the doubly achromatic spectrometer LISE and implanted into a semiconductor telescope for identification in Z and A. Their β-delayed neutron radioactivity is observed by means of a 4π β-n coincidence detector. The results include first measurements of the half-life T 1 2 and the neutron emission probability P n for the isotopes 20C, 40,41,42p and 43,44S. They are compared to current theoretical predictions.