Recoil Transport Research Articles

Decay measurements of43K(β−)43Ca by HRS and TAS

In this work, decay spectroscopy of neutron-rich 43 K has been performed at the Radioactive Ion Beam (RIB) facility at Variable Energy Cyclotron Centre (VECC), Kolkata by producing it with an 18-MeV alpha beam on 40 Ar gas target. The beam was delivered from the K130 Cyclotron and the gas jet recoil transport system was used to move the products to a low-background site. The β-feeding intensities were measured by both high resolution γ-ray spectroscopy and total absorption γ-ray spectroscopy methods in order to address mainly the anomalies (if any) in the feeding to ΔJ ≥ 1 levels reported earlier. The decay half-life of 43 K was also measured to be 22.4(1) hrs.

A gas-jet transport and catcher technique for on-line production of radioactive ion beams using an electron cyclotron resonance ion-source

Radioactive ion beams (RIB) have been produced on-line, using a gas-jet recoil transport coupled Electron Cyclotron Resonance (ECR) ion-source at the VECC-RIB facility. Radioactive atoms∕molecules carried through the gas-jet were stopped in a catcher placed inside the ECR plasma chamber. A skimmer has been used to remove bulk of the carrier gas at the ECR entrance. The diffusion of atoms∕molecules through the catcher has been verified off-line using stable isotopes and on-line through transmission of radioactive reaction products. Beams of (14)O (71 s), (42)K (12.4 h), (43)K (22.2 h), and (41)Ar (1.8 h) have been produced by bombarding nitrogen and argon gas targets with proton and alpha particle beams from the K130 cyclotron at VECC. Typical measured intensity of RIB at the separator focal plane is found to be a few times 10(3) particles per second (pps). About 3.2 × 10(3) pps of 1.4 MeV (14)O RIB has been measured after acceleration through a radiofrequency quadrupole linac. The details of the gas-jet coupled ECR ion-source and RIB production experiments are presented along with the plans for the future.

Nuclear Data Sheets for A = 235,239

The evaluator presents in this publication spectroscopic data and level schemes from radioactive decay and nuclear reactions studies for all nuclei with mass numbers A=235,239. A relatively small amount of new data on the level structure of nuclei with A=235,239 has been reported since the previous evaluation of this mass chain. The data presented here are mostly that from 1993Sc22 and 1992Sc18 but updated and modified as needed. A new isotope of americium, 235Am (9.9 min), which was chemically and mass separated, was identified using a He-jet recoil transport technique (1996Gu11,1997Sh21,1999Ya13), and has been included in this evaluation. A new isotope of protactinium, 239Pa (1.8 hr.) has been included in this evaluation. This nuclide was produced by bombarding uranium with 18O projectiles; it was chemically separated and its genetic relationship to its daughter nuclide 239U was well established (1995Yu01,1996Yu06). The alpha hindrance factors (HF) presented in this evaluation were calculated using values of the radius parameter (r 0) interpolated from those for even-even adjacent nuclei given by 1998Ak04.

Simulation of the implantation of recoils and displacement production in the 316 stainless steel mercury-container vessel at SNS

In this study, the focus is on the possible effect of mercury and transmuted atom recoils that are implanted into the wall of the stainless steel container vessel at SNS. Two computer codes were used: Los Alamos high energy transport (LAHET) and the stopping and range of ions in matter (SRIM). LAHET provided information of the energy distribution of the recoils upon bombardment. Also, SRIM simulated the transport of recoils through the mercury layer adjacent to the stainless steel wall and into the wall itself, and provided recoil and displacement concentration profiles in the wall. The calculated recoil and displacement concentrations in the near-surface region of the wall appear to be quite significant. The recoil and displacement concentrations per year at the surface are determined to be about 0.0015 recoil atoms/wall atom and about 17 dpa at the center of an incident proton beam. These concentrations fall to about one-half of the surface values at a penetration distance of about 0.1 μm, and the concentrations become negligibly small at 0.5 μm and beyond.

Depth distributions of sputtered atoms

The computer code OKSANA is applied to calculate the depth of origin of atoms sputtered from an amorphous Si target under ion bombardment. Most simulations refer to 2 keV Ne bombardment. The emphasis is put on the comparison of the depth distributions found by computer simulation with the profiles predicted by the analytical theory which is known to overestimate the mean escape depth. It has been shown that failing to include the coarse-grain structure of an amorphous target and some simplifying assumptions concerning the generation and transport of recoils are the main reasons for high theoretical values of the mean escape depth.

Effects of neutron heating on ignition and energy gain of laser-imploded D-T pellets

On the basis of coupled neutronic/hydrodynamic calculations, we examine the neutron heating effects on the ignition and burn propagation in laser-imploded D-T pellets. The fusionproduced neutrons deposit their energy all over the pellet region since the mean-free-path of the neutron is long. The fraction of neutron energies deposited to the central spark region during the ignition phase is too small to reduce the threshold energy of the laser for ignition. In the burn phase, the neutron heating decreases the maximum compression ratio and accelerates the plasma expansion. The inclusion of neutron heating hence decreases the pellet gain from the value in the case without neutron heating. Calculations neglecting the transport of neutron recoils overestimate the neutron heating rate in the reactor-grade pellets.

Ion beam induced modifications of TiN and Ti films on Al-3% Mg substrates

Thin titanium nitride films (50–110 nm) deposited via magnetron sputtering on Al+3 wt.% Mg substrates were irradiated with Ar, Kr, and Xe ion beams at room temperature and with energies between 0.1–0.9 MeV. Sputtering yields and interface mixing rates were determined using Rutherford backscattering (RBS) as depth profiling method. The obtained TiN sputtering yields for Ar and Xe irradiation are found to be in good agreement with predictions of the Sigmund approach. A systematic study with Ar and Xe beams revealed a correlation of the mixing rate with the parameter d/Rp, where d denotes the layer thickness and Rp the mean projected ion range. The mixing data and Monte-Carlo calculations of the collision cascades elucidate the importance of focused recoil transport, especially in the case of Xe irradiations. The results from ion mixing experiments of titanium films (70–140 nm) on Al-3% Mg with 0.1–1.0 MeV Xe beams and 0.05–0.2 MeV Ar beams support these conclusions.

Effects of nuclear elastic scattering on energetic ion transport in hot dense plasmas

Effects of nuclear elastic scattering (NES) on the transport of energetic ions in plasma spheres at densities and temperatures of interest for inertial confinement fusion are investigated on the basis of a linear Boltzmann-Fokker-Planck equation. After presenting the adopted calculational model, numerical results are given for two particular problems: (1) the deposition of 14.7 MeV proton energy in a typical deuterium sphere and (2) the inflight fusion probability for energetic deuterons in a D-T pellet. It is shown that in both cases NES effects are significant. An adequate treatment of the slowing-down process, especially consideration of the transport of NES recoils, is essential for an accurate estimation of the energy deposition and of the fusion probability. Calculations neglecting NES considerably underestimate these quantities.

Beta +-electron-capture decay of 69Se.

The ${\ensuremath{\beta}}^{+}$--electron-capture decay of $^{69}\mathrm{Se}$, produced via the $^{40}\mathrm{Ca}$${(}^{32}$S, 2pn${)}^{69}$Se reaction, has been studied by \ensuremath{\beta}-delayed proton and \ensuremath{\gamma}-ray emissions using the recoil transport helium jet technique. The established decay scheme for $^{69}\mathrm{Se}$ involves 13 up to now unreported \ensuremath{\gamma} emitting levels in $^{69}\mathrm{As}$. The total proton branching ratio has been measured to be (4.5\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$. The autocorrelation analysis of the delayed proton spectra indicates a level spacing in agreement with the back shifted Fermi gas model estimates. The Gamow-Teller beta strength distribution has been measured in 95% of the ${Q}_{\ensuremath{\beta}}$ window, up to 6.5 MeV excitation energy in $^{69}\mathrm{As}$.

Decay of 3 sec 160Hom.

The decay of /sup 160/Ho/sup m/ (3 sec) has been studied using high resolution detectors. The activities were produced using the reaction /sup 159/Tb(..cap alpha..,3n) and were transported with the help of a gas jet recoil transport system. From the observed ..gamma..-ray and K x-ray intensities, the multipolarities of all the assigned transitions have been deduced. No evidence of any other isomer of /sup 160/Ho with a half-life between 1 sec and 1 h has been obtained.

A gas-jet coupled ISOL system at VECC

A gas-jet recoil transport (GJRT) system at VECC is being extensively used for the study of short-lived nuclei. A transport efficiency of ∼70–90% has been obtained for a large number of elements at a distance of ∼40 ft using a 1.27 mm tygon capillary. For the same distance, a transit time of ∼900 ms has been obtained using a pressure differential of 1 atmosphere. To extend the capability of the present system, a mass separator coupled to the GJRT has been designed. The integrated system will consist of a GJRT system, a skimmer, an ion-source, a beam transport system and a tape-transport type detection assembly. The beam optics of a 90° analyser magnet have been computed using the code ODESSA developed at VECC. A mass resolving power of ∼600 and a dispersion of ∼2.36 m have been estimated including second order aberrations. With reduced capillary length, the facility should allow the study of nuclides with half-lives ∼100 ms.

Helium jet recoil transport setup for chemistry and nuclear applications at VECC

A gas jet recoil transport facility (GJRT) developed at VECC is described. A maximum transport efficiency of ∼ 90% has been obtained for Ni and Cu isotopes using cyclohexane as a dopant to the He carrier gas. A transit time of ∼ 1 s has been obtained at a distance of ∼ 12 m using a 1.6 mm i.d. tygon capillary and a pressure differential of 1 atm. The effect of various dopants, beam current and fluid dynamical parameters on the transport of different nuclides has been studied. The results indicate the role of the chemical aspects of the dopants and the recoils on the efficiency of transport. The usefulness of this system in determining (reaction) cross sections has been demonstrated for 60Cu, 60Zn, 61Zn and 159mHo.

Computer simulations of sputtering

Monte Carlo simulations have become a useful tool for studying ion radiation effects at or near surfaces or interfaces, such as sputtering, reflection, mixing, etc. The principal advantage of Monte Carlo calculations is that any physical process can be included directly. Also multielement and multilayer targets, even complex geometries, can be treated exactly in order to simulate realistic cases. The present paper will concentrate mainly on sputtering calculations with the Monte Carlo code TRIM, which treats ion and recoil transport in amorphous matter. It is based — as are analytic theories and most other Monte Carlo codes — on binary collisions with target atoms initially at rest. Over the past few years, the basic physical input has been greatly improved. Both the interatomic potentials and the electronic stopping powers proved to be of crucial importance even for the lowest energies occurring in recoil cascades. With the Kr-C or universal potential and the recent ZBL electronic stopping, which includes the Z oscillations, and a planar surface binding energy set equal to the heat of sublimation, realistic sputtering predictions could be obtained for most metals — without the use of any adjustable parameters.

Three-dimensional distributions of ion range and damage including recoil transport

Ion range and damage distributions — in insulators also ionization distributions — are of increasing relevance for modern semi conductor (VLSI) developments. With small dimensions also the lateral distributions need to be considered. In both longitudinal and lateral profiles, strong deviations from the commonly used Pearson IV or Gaussian distributions are found and shall be demonstrated with Monte Carlo results. In the Monte Carlo calculations the contributions of the moving recoils to ionization and damage production can be studied explicitly. In cases of heavy ions incident on a lighter target, the fluxes of recoils can be larger than the ion beam flux, and the ionization and damage profiles are drastically enhanced and shifted, due to the motion of recoils.

Influence of recoil transport on energy-loss and damage profiles

The effect of energy transport by recoils on energy-loss and damage profiles is investigated. For this purpose the well-known Monte Carlo simulation code TRIM is applied to implantation of B + and Sb + ions into silicon and to implantation of Ar + and Ga + ions into SiO 2 and PMMA at ion energies of 100 keV. Results with and without recoil transport are compared. In the case of relatively heavy ions a considerable contribution of the recoils to the energy transport in the target is found, both for electronic and nuclear effects.

The application of alpha spectrometry to the discovery of new elements heavy-ion beam bombardment

Starting with polonium in 1898, alpha spectrometry has played a decisive role in the discovery of new, heavy elements. For even-even nuclei, alpha spectra have proven simple to interpret and exhibit systematic trends that allow extrapolation to unknown isotopes. The early discovery of the “natural” alpha decay series led to the very powerful method of “genetically” linking the decay of new elements to the well-established alpha emission of “daughter” and “granddaughter” nuclei. This technique has been used for all recent discoveries of new elements, including Z = 101, thin samples suitable for alpha spectrometry were prepared by chemical methods. With the advent of heavy-ion accelerators, new sample preparation methods emerged. These were based on the large momentum transfer associated with heavy-ion reactions, which produced energetic target recoils that, when ejected from the target, could be thermalized in helium gas. Subsequent electrical deposition or a helium jet technique yielded samples that were not only thin enough for alpha spectrometry, but also for alpha and beta-recoil experiments. Many variations of these methods have been developed and will be covered in this paper. For the synthesis of element 106, an aerosol-based recoil transport technique was devised. In this most recent experiments, alpha spectrometry has been coupled with the magnetic analysis of the recoils. The time from production to analysis of an isotope has thereby been reduced to 10 −1−10 0s for helium jets and 10 1−10 3 s for rapid chemical separations. Experiments are now in progress to synthesize super heavy elements (SHE) and to analyse them with These latest techniques. Again, alpha spectrometry will play a major role, since the expected signature for the decay of a SHE is a sequence of alpha decays followed by spontaneous fission.

The evolution of 252Cf - plasma desorption mass spectroscopy

The 252Cf Time-of-Flight/Plasma Desorption Mass Spectroscopy method ( 252Cf TOF/PDMS) is an example of how technology transfer from one discipline to another can stimulate new approaches to the solutions of important problems. The 252Cf TOF/PDMS technique evolved from three technologies originally developed by Macfarlane and his co-workers to study nuclear processes: the electrostatic particle guide, the helium-jet recoil transport method, and the on-line β-recoil mass spectrometer. In this paper, these techniques are reviewed, and their contributions to the ultimate development of 252Cf TOF/PDMS are discussed.

Rapid continuous separation procedures for zirconium, niobium, technetium, bromine and iodine from complex reaction product mixtures

Fast, continuous methods for the separation of radiochemically pure samples of Zr, Nb, Tc, Br and I from fission product mixtures are described. The procedures involve multistage solvent extraction separations with the centrifuge facility “SISAK 2” connected to a gas-jet recoil transport system. The mean transport time between production and measurement amounts to 5–9 s depending on the element to be separated.

A simple, inexpensive tape system for on-line studies of short-lived nuclei transported by He-jet

A simple tape transport system is described which is used for the collection of short-lived nuclides emerging from a He-jet recoil transport system. It is based on pistons driven by compressed air and is both inexpensive and reliable, and allows accurate and reproducible positioning of the radioactive sources at the counting position.

Studies of the formation mechanism of aerosols in a gas jet recoil transport system using pure gases as carrier

A detailed study was made of the conditions under which radioactivity is transported in a gas recoil transport system using various gases. The conclusion is drawn that two conditions must be fulfilled for the formation of the radioactivity transporting aerosols. Firstly, the gas must condense partly during the expansion from the high pressure in the gas tank to the lower pressure in the transport system leading to the formation of relatively short-lived droplets of condensed gas. Secondly, the gas must contain small amounts of impurities which are present in sufficient amount even in commercially available high-purity gases. These impurities are frozen out in the cold droplets of liquefied gas. After evaporation of the droplets of liquefied gas the impurity is left behind in the form of an aerosol. Thirteen different gases were used successfully to transport radioactivity.