16O Ions Research Articles

Sensitivity in trace-element analysis by p, α and 16O induced X-rays

With direct application in mind we have investigated the sensitivity of ion-induced X-ray trace-element analysis as a function of projectile atomic number. For 3 and 5 MeV/amu p, α and 16O ions we have measured K and L X-ray yields for six elements between Cu and Pb and background radiation form matrices consisting of C, Al and V. The importance of nuclear processes and the Compton scattering of the associated γ-rays is emphasized as a limiting factor for the sensitivity when the radiation is recorded in a solid-state detector.

Identification of heavy ions in AgCl monocrystals by means of multiple coulomb scattering

The scattering constant of AgCl monocrystals was estimated by comparing the multiple Coulomb scattering of stopping 16O ions as a function of residual range in an AgCl monocrystal and in Ilford G5 nuclear emulsion. The ratio of scattering constants for the two media was found to be 1.255±0.038, as compared to the theoretical prediction of 1.273.Absence of sizeable distortion in the monocrystal was checked by measurements on fast 16O ion tracks.The reading noise level on the AgCl tracks was found to be at most equal to that in nuclear emulsion. From the observed dispersions it is estimated that a track length of 8 mm in the monocrystal should be sufficient to estimate the ion charge within one unit.

The determination of the differential energy loss of heavy ions backscattered from an infinitely thick solid target

A method is described to determine the differential energy loss of heavy ions from the spectrum of heavy ions elastically scattered from an infinitely thick target. Data over a fairly wide energy range can be obtained from a single measurement by a recursive and iterative calculation. The data obtained in this way for 16O ions in Ni and Au targets are compared to those from other measurements. They differ by less than 5% over the whole energy range investigated (7–35 MeV). The same method also allows the calculation of the elastic or inelastic cross section from known energy loss applying the recurrence formula inversely.

A study of sub-Coulomb, heavy ion, one-nucleon transfer reactions on the Z = 40 isotopes and N = 50 isotones

Sub-Coulomb one-nucleon transfer processes have been investigated. These include the transfer reactions induced by 13C ions on 90Zr, 88Sr, 92Mo and proton transfer reactions induced by 16O ions on 90, 92, 94, 96Zr. Angular distributions of all the above reactions were measured and absolute differential cross sections obtained between 90° and 180°. The variation of cross section with Q-value can be experimentally established. Variation of cross section for different fractions of the Coulomb barrier were investigated, and theoretical fits were made using the distorted wave Born approximation.

Response of NE 111 scintillator foil to transient 16O ions

The response of a thin NE 111 scintillator foil to transient 16O ions of energies between 15 and 60 MeV has been measured.

Charge collection in silicon detectors for strongly ionizing particles

Experimental results for the plasma time in a semiconductor detector are given for alpha-particles, 16O ions and fission fragments. The plasma time tp is defined as the time needed to bring all carriers under the influence of the applied field. A simple theoretical model based on diffusion and space charge limited current erosion of the track is described and results in the expression tp = 1.32 × 10−10 (n1E)13/F for a silicon detector where F is the electric field in the detector at the position of the track, n1 is the linear carrier density in the track and E is the particle energy. This gives good agreement with the experimental data for tracks longer than ⋍ 15 μm (alphas and 16O ions of energies 5.3–8.8 MeV and 22–42 MeV, respectively). The shorter tracks of fission fragments (90 MeV from 252Cf) give shorter tp values then predicted by the formula above. This is explained by transfer from cylindrical to spherical erosion geometry.

Comparison of back-scattering parameters using high energy oxygen and helium ions

For material analysis by ion back-scattering spectrometry the quality of information obtainable depends on the mass of the back-scattered ions used. Relevant parameters affecting analysis are the mass resolution, depth resolution, depth range of the ion and time of analysis. These parameters are compared here for two types of analysing ions, α-particles and 16O ions, at optimum values of ion energy. Under the energy conditions chosen, 16O ions gave a better mass resolution by a factor of about 2–4 (depending on the mass range) and a better depth resolution by a factor of between 1.5 and 2.

The new nuclide nobelium-259

A new, relatively long-lived isotope of element 102 has been produced through the bombardment of 248Cm with 18O ions at both Oak Ridge and Berkeley. A maximum of approximately 20 nb occurs in the production cross section at a bombarding energy of 93 MeV. A total half-life of 58 ± 5 min was computed from the combined data of both laboratories. Five α-particle groups have been observed in the decay with the following energies and abundances: 7.685 (11%), 7.605(14%), 7.533 (23%), 7.500 (39%) and 7.455 MeV (13%). A spontaneous-fission branch of about 20% relative to the α-emission appears to accompany the decay. The atomic number was assigned on the basis of characteristic ion-exchange column behavior; the mass assignment was made from the growth of the α-decay daughter, 255Fm, into chemically separated samples. The Z and A assignment is corroborated by Nuclear reaction data and consistent with α-decay energy systematies.

The interference of Coulomb and nuclear excitation in the scattering of 16O from 58Ni, 88Sr and 142Nd

The interference of Coulomb and nuclear excitation has been studied for 16O ions bombarding targets of 58Ni, 88Sr and 142Nd in the energy region spanning the Coulomb barrier. The measurements include elastic and inelastic (to the first 2 + state) excitation functions at 175° lab for all targets, excitation functions at 60°, 75° and 90° lab for 58Ni and 88Sr, angular distributions at 44, 50 and 60 MeV for 58Ni, and angular distributions at 52 and 60 MeV for 88Sr. From the sub-Coulomb data, B(E2) values (in units of e 2·b 2) of 0.066 ± 0.004 for 58Ni (1.45 MeV), 0.114 ± 0.015 for 88Sr (1.84 MeV) and 0.27 ± 0.03 for 142Nd (1.57 MeV) were obtained. The cross section data can be well reproduced by the optical model and the distorted-wave Born approximation with a collective model form factor for nuclear excitation. Absolute values for the real part of the optical model potential are obtained for the interaction of 16O and 58Ni in the region 1 fm to 3 fm beyond the nuclear surface. For r 0 = 1.3 fm, the DWBA fits to the data require r′ 0 > r 0, a′ < a and nuclear deformation parameters, ( βR) nucl., of 0.94 fm, 0.64 fm and 0.34 fm for 58Ni, 88Sr and 142Nd, respectively.

Reactions of 14N and 16O ions with light nuclei at Elab = 16–58 MeV

Yield curves for formation of 7Be and other radio-nuclides from bombardment of C, Al and Si targets with 16–58 MeV 14N and 16O ions were measured. The 7Be yields disagree by several orders of magnitude with Hauser-Feshbach and transition-state predictions. The other yields are in order-of-magnitude agreement with nucleon and/or α-particle evapolation calculations.

Ein computergesteuertes experiment zur Aktivierungsanalyse

The relative cross sections for different exit channels have been determined for reactions induced by bombardment of enriched 0.5 mg/cm 2 targets of 46,48Ti with 36, 39, 42, 46, 50 MeV 16O ions. They were obtained from yields of gamma rays from the residual radioisotopes. The experiment was computer controlled by CAMAC electronics.

The reorientation effect in 110Cd and 114Cd

New detailed measurements of the reorientation effect in the first 2 + state of 110Cd and 114Cd were carried out using back-scattered 4He and 16O ions. They yield Q 2 + = − 0.28±0.09 e· b with B(E2; 0 → 2) = 0.513±0.005 e 2 · b 2, or Q 2 + = − 0.03±0.09 e · b with B(E2; 0 → 2) = 0.512±0.005 e 2 · b 2 for 114Cd depending on the sign of the interference term. The results for 110Cd are Q 2 + = −(0.42 or 0.21)±0.10 e · b with B(E2; 0 → 2) = 0.432±0.006 e 2 · b 2. The deduced Q 2 + for 114Cd is approximately half of the rotational-model value.

The static quadrupole moments of the first 2 + states of 74Ge and 76Ge

The reorientation effect in Coulomb excitation has been used to determine the static quadrupole moments of the first 2 + states of the nuclei 74Ge and 76Ge. Thin foils of enriched 74Ge and 76Ge were bombarded by 25 MeV 16O ions. The relative excitation probabilities of the first 2 + states were measured as a function of projectile scattering angle. Particle-γ coincidences were used to identify the inelastic events. The data were analyzed with the aid of the coupled-channel computer program of Winther and De Boer and excitation of the first 2 + state via the second 2 + state was included in the analysis. If the interference term due to excitation via the second 2 + level is positive, such that the excitation probability is increased, then the extracted values of the static quadrupole moment are Q 2 + = −0.25 ± 0.10 b for 74 Ge and Q 2 + = −0.15 ± 0.10 b for 76 Ge . If the interference term is negative then Q 2 + = −0.17 ± 0.10 b for 24Ge and Q 2 + = −0.05 ± 0.10 b for 76 Ge .

Détecteurs en verre: Influence de la masse et de l'énergue des particules sur le diamétre des traces

Glass has been irradiated orthogonally with respect to its surface by 12C, 16O, 20Ne, 40Ar, Ni and 84Kr ions of energy per nucleon ranging up to 1.1 MeV/amu. The diameter of the etched particle tracks was measured as a function of the mass and velocity of the particle. It increases with the mass and energy of the projectile. The increase with mass is greatest between O and Ar and much smaller for heavier particles. The projectile detection threshold appears to occur in the vicinity of oxygen. Particles of charge greater than or equal to 10 and energy greater than 6 MeV are detected with 100% efficiency.

Measurement of Stopping Powers for 4He, 16O, and 35Cl ions at ~1 to ~3 MeV per Nucleon in Ni, Ge, Y, Ag, and Au

Stopping powers have been measured for 4He, 16O, and 35Cl ions at energies of ~1 to ~3 MeV per nucleon in Ni, Ge, Y, Ag, and Au foils. The absolute accuracy is of the order of ± 4%. The results are compared with the semiempirical values tabulated by Northcliffe and Schilling and with previous experimental values.

Coulomb excitation of 81Br

Coulomb excitation of the low-lying levels in 81Br was effected with 2.5 to 8.2 MeV α-particles and 33 MeV 16O ions. Gamma-ray energies and yields, γ-ray angular distributions, in one instance a γ-γ angular correlation, and Doppler-broadened γ-ray peaks were obtained. Level energies, spins, B(E2) and B(M1) transition probabilities and half-lives were deduced from these data for states at 275.9, 538.2, 566.0, 650.0, 767.1, 828.5, 836.5 and 1322.7 keV. The level properties are compared to those calculated by Stewart and Castel using an intermediate-coupling unified model.

NUCLIDES FAR OFF THE STABILITY LINE AND SUPER-HEAVY NUCLEI IN HEAVY-ION NUCLEAR REACTIONS

A review is given on the new species which have been produced in the recent years by heavy ion reactions, mainly 12C, 16O, 18O, 22Ne and 20Ne ions. The first section is devoted to the formation of neutron rich exotic light nuclei and to the mechanism of multinuclear transfer reactions responsible for this formation. In the second section dealing on medium atomic numbers a brief account is made on the discovery of proton radioactivity and some comments are made on the difficulties encountered for producing very neutron deficient isotopes like 10050Sn. The study of the region of neutron deficiency for rare earth is one of the most fruitful field for heavy ion reactions. More than fifty new isotopes have been found. A discussion is made on the possibility for going further into the neutron deficiency open by the use of Ar, Kr and heavier ions. It is shown that there is no advantage to bombard targets with ions heavier than 40Ca or 58Ni. Section 4 is devoted to heavy nuclei in the region of the neutron shell N = 126. Fission competition is discussed as well as the limitation of the compound nucleus cross section due to high angular momentum effects. Results are presented on the rotating liquid drop and the very strong diminution of fission barriers due to rotational energy. A brief review is made of the new decay families discovered by Hyde et al. [63] for light thorium and protactinium isotopes. These results are one of the great success of heavy-ion induced reactions. Section 5 reminds that all isotopes of elements beyond Z = 101 have been produced by heavyion reactions, in spite of the great fission competitionc. The last section describes the various attempts already made for the synthesis of superheavy elements. A discussion is presented on the following problems : reaction thresholds and coulomb barriers for heavily charged projectiles, complete fusion cross section as compared to the total cross section, main decay channels for excited compound nuclei in the region Z = 118, N = 184-190, fusion-fission reactions and the possibility of production of S.H. elements as fission fragments, grazing reactions and exchange of big aggregates.

An investigation of proton-rich nuclei and other products from the bombardment of 24Mg, 28Si AND 32S by 16O ions

Abstract The β- and γ-ray spectra have been studied resulting from the bombardment of 24Mg, 28Si and 32S with continuous and chopped beams of 16O ions in the energy-range of 22–33 MeV. Compound-nucleus formation is found to predominate in the reactions. Protonrich nuclei are observed via the (16O, 2n) reaction in each case. In particular the mass excess of the previously unobserved nucleus 46Cr is found to be −29.46 ± 0.03 MeV; its half-life is 0.26 ±0.06 s. The systematics of the Coulomb displacement energies of the mass triplets up to A = 46 are discussed.

Multiple coulomb excitation of γ-vibrational bands in 162Dy, 166Er, 168Er and 170Er

The 2 γ and 4 γ states in 162Dy, 166Er, 168Er and 170Er have been Coulomb excited with 45–60 MeV 16O ions. Values of B( E2; 0 → 2 γ ) were determined and the angular correlations of the de-excitation γ-rays in coincidence with the backscattered particles have been analysed to yield E2/M1 mixing ratios for the 2 γ → 2 and 4 γ → 4 transitions. From the measured branching ratios for the decay of the 2 γ and 4 γ states, values of z 2, the spin-independent mixing parameter for the γ-vibrational band, were determined. Two additional states having spin and parity assignments 0 + and 4 + have been identified in 170Er at energies of 889 and 1124 keV, respectively.

Negative parity levels in 103Rh via coulomb excitation

Low-lying negative parity levels in 103Rh were Coulomb excited with 7–10 MeV 4He ions and 36–45 MeV 16O ions to test the weak-coupling core excitation model for two-quadrupole phononcore states. A Ge(Li) detector was used to observe the de-excitation γ-rays in singles and 16O-γ coincident spectra. Gamma-ray angular distribution measurements taken during 4He ion bombardment established spin values of 5 2 and 3 2 for the 880 and 1277 keV states, respectively. The 848, 880, 920 and 1107 keV levels have properties consistent with the interpretation of coupling a 2p 1 2 proton to the 4 + and second 2 + core states. Our spectra give some indication of a level at 803 keV previously seen in inelastic proton-scattering work which could be a state arising from coupling to the two- phonon 0 + core state.