Heavy-ion Projectiles Research Articles

A simple leading particle explanation for linear momentum transfer systematics

A simple formula based on leading particle models of nucleon-nucleon collisions is used to evaluate the average momentum transfer in central heavy ion collisions at energies from 20 to 150 MeV/u. This formula, which reproduces a number of the features of the observed systematics, offers a straightforward explanation for the approximate universality of fractional linear momentum transfer as a function of velocity, the dependence of fractional momentum transfer on target mass and the greater fractional momentum transfer of the proton as compared to heavy ion projectiles.

Projectile fragments isotopic separation: Application to the lise spectrometer at GANIL

The isotopic separation of intermediate-energy (30 to 100 MeV per nucleon) heavy-ion projectile fragments is theoretically and experimentally investigated. Physical separation of nuclides is achieved through magnetic analysis ( A Z sensitivity) and differential stopping-power effects ( Z −2 sensitivity). Depending on the specific case, a complete mass and charge separation may be achieved or a few nuclides may be selected simultaneously. The projectile fragments isotopic separation method described allows us to obtain an experimental mass separation A ΔA ≈ 100 . Simple formulae are given to determine the optimum factors for the best separation and transmission of the device. First applications to the spectroscopy of exotic nuclei lead to the new observation of the beta decay of 37P at GANIL and 15B at CERN.

Forward electron ejection in H+-He, He+-He and He2+-He collisions

The dependence of the parameters (width, intensity and shape) of the cusp in the processes of electron capture to the continuum (ECC) and electron loss to the continuum (ELC) has been studied as a function of impact velocity (from 2 to 5 au) for the simple collision systems H+-He, He+-He and He2+-He. An approximately linear increase in the width (FWHM) is found in both cases. There is no difference in this respect within the error limits for He2+ (ECC) and He+ (ELC). Regarding cusp shape, similar symmetry (ELC) and asymmetry (ECC) have been observed as in the case of heavy-ion projectiles. None of the theories satisfactorily describes the experimental absolute cross sections of ECC cusp (He2+), while in the case of the He+ projectile (ELC) rather good agreement with theory can be seen in the higher-velocity region. The deviation at lower velocities in the latter case could be explained by an ECC effect present even in the case of He+. Concerning the dependence of the cusp yield on the Zp value of the projectile, Z02.5+or-0.3 was obtained from the yield in H+-He and He2+-He collisions.

"Stripping" reaction in heavy ion projectile dissociation: Extended Serber model.

The opaque Serber model is extended for ``stripping'' reaction in heavy ion projectile dissociation by incorporating a critical distance between constituent clusters in the projectile. This model describes the higher energy part of the fragment inclusive spectra. The results are discussed in comparison with the local-momentum plane-wave Born approximation calculations by McVoy and Nemes and with the Friedman model.

Radiotracers from heavy-ion fragmentation

The advent of high energy heavy-ion accelerators has introduced the new mechanism of projectile fragmentation for the production of radiotracers. Projectile fragmentation occurs when the heavy-ion projectile has a sufficient velocity to undergo a strong interaction with a target nucleus without being deflected very much from its initial trajectory. The fragmentation of 14N beams from the K500 superconducting cyclotron at Michigan State is described, a 490 MeV 14N beam was fragmented in a beryllium foil and the reaction products are stopped in (liquid) water. The water provides an additional source of 13N through fragmentation of 16O, facilitates the conversion of 13N atoms to labeled nitrate and allows the rapid transfer of the source out of the accelerator vault.

Inelastic scattering and excitation of 6Li.

Differential cross sections for elastic and inelastic $^{6}\mathrm{Li}$ scattering from $^{12}\mathrm{C}$ at ${E}_{\mathrm{c}.\mathrm{m}.=16}$ and 20 MeV, and scattering from $^{16}\mathrm{O}$ at 18.7 MeV were measured out to ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.\mathrm{\ensuremath{\approxeq}}170}$\ifmmode^\circ\else\textdegree\fi{}. Also by scattering $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ from $^{6}\mathrm{Li}$, the inelastic cross sections for the excitation of the ${3}^{+}$ (2.18 MeV) and the ${2}^{+}$ (4.31 MeV) states of $^{6}\mathrm{Li}$ and an estimate of the continuum inelastic cross sections of $^{6}\mathrm{Li}$ were determined. The inelastic data were analyzed using the distorted-wave Born approximation and coupled-channels techniques with folded real and phenomenological imaginary form factors, with the deformations derived from electron scattering. The inelastic data are well described. Coupled-channels effects due to the ${3}^{+}$ state of $^{6}\mathrm{Li}$ were found to play an important role in the scattering. The inclusion of the ${3}^{+}$ state in the coupled-channels calculations reduced the discrepancy in the normalization of the real double-folded potential between $^{6}\mathrm{Li}$ and other heavy-ion projectiles, and the imaginary potential became weaker in the surface region. The present results show that L=2 coupling in the elastic scattering is very important and that the source can be a state in either the projectile, the target, or both.

Rate of saturation of target L shell vacancy probability, pl, with projectile charge as given by coupled-channels calculations

The distribution of intensities of K.L n K α satellites is nearly binomial, with parameter p l , the mean L shell vacancy probability per electron. The chemical environment of an atom produces a shift, Δp l ,of p l from its value for an isolated target atom. Δp l tends to increase as p l increases, so for greatest chemical sensitivity one wants p l as large as possible. p l increases with Z p but, because it must remain ⩽1, p l must saturate for large Z p . Thus, little additional sensitivity is gained, for a given target and impact speed, by using heavy-ion projectiles of charge greater than some moderate value. We have made theoretical calculations of p l to provide information on the rate of this saturation. Whereas all earlier calculations have employed a single-particle model and a simple collision approximation, we use the Hartree-Fock independent Fermi particle model, which contains Pauli correlations, and refined coupled-channels collision theory. Because of a tendency toward random phases in the scattering amplitudes, the intensity distribution is nearly binomial in most cases, but has the possibility of deviating strongly when one or two channels are dominant. We show, as a typical example, p l as a function of Z p and E/ A for isolated Ar targets, where the tendency toward saturation appears for F 9+ and even for C 6+.

Systematic Spectroscopic-Factor Discrepancy in Heavy-Ion Proton-Pickup Reactions onCa40

The differential cross sections of proton-pickup reactions on $^{40}\mathrm{Ca}$ initiated by various heavy-ion projectiles have been uniformly analyzed in a distorted-wave Born-approximation model. There appears to be a spectroscopic-factor inconsistency depending on whether an odd-odd or an even-even nucleus (projectile or ejectile) participated in the reaction.

Compton profiles by inelastic ion-electron scattering

It is shown that Compton profiles (CP) can be measured by inelastic ion-electron scattering. Within the impulse approximation the binary-encounter peak (BEP) reflects the CP of the target atom whereas the electron-loss peak (ELP) is given by projectile CP's. Evaluation of experimental data reveals that inelastic ion-electron scattering might be a promising method to supply inelastic electron or photon scattering for the determination of target CP's. The measurement of projectile CP's is unique to ion scattering since one gains knowledge about wave-function effects because of the high excitation degree of fast heavy-ion projectiles.

A threshold cherenkov counter for isotopic identification of high-energy heavy ions

We have developed an apparatus for isotope identification of heavy-ion projectile fragments with energies from ≃ 330 to 600 MeV/nucleon. The detector uses a Cherenkov intensity measurement inconjunction with a measurement of magnetic rigidity to determine mass. An advantage of this technique is that it allows isotope identification of projectile fragments with higher energies than are possible for “stopping type” detectors. Higher fragment energies allow the use of much thicker targets and, therefore, provide higher sensitivity to rare isotopes. In a recent test of the apparatus using a 670 MeV/nucleon 20Ne beam and a 30 g/cm 2 aluminum target a mass resolution of σ A =0.2 amu was obtained for projectile fragments with charges 5 ⩽ Z ⩽9.

The 24Mg( 16O, 16O') reaction and triaxial structures in 24Mg

Angular distributions for the elastic and inelastic scattering of 16O from 24Mg, exciting the 2 1 + (1.37 MeV), 4 1 + (4.12 MeV) and 2 2 + (4.24 MeV) states, have been measured at E c.m. = 43.5 MeV, an energy at which resonance-like structure has been observed previously in the related 24Mg( 16O, 12C) 28Si reaction. In particular, the 4 1 +, 2 2 + doublet has been resolved for the first time for heavy-ion projectiles. The data have been well described by coupled-channels calculations within the framework of a Davydov-Filippov asymmetric rotor model for the low-lying states of 24Mg, which has been extended to include a symmetric hexadecapole shape component. The optical model potential for the 16O + 24Mg interaction was found to have a moderate real well depth and some surface transparency. The shape parameters for the nuclear potential were determined to be β (N) 2 = 0.25, γ = 22° and β 4 (N) = −0.065 and the corresponding deformation lengths are in good agreement with earlier light-ion results. The inclusion of a negative symmetric hexadecapole component leads to an improved description of the reduced transition rates. The triaxial structure of 24Mg is discussed.

Pre-equilibrium description of fast light particle emission in heavy-ion reactions

Fast light particle emissions in heavy-ion reactions are described as a pre-equilibrium process. Reactions between a “light” heavy-ion projectile and a heavy target are considered in the energy region of the incident energy / the projectile mass ⪅ 10 MeV. Calculations are carried out by an extended exciton model in which the finiteness of the time needed for the fusion process is included. The spectrum shapes of proton, alpha, deuteron and triton emissions are well explained for an example case, 14 N+ 181 Ta at 115 MeV .

Spin-Orbit Interaction Induced by Heavy-Ion Projectile Excitation

It is shown that, for heavy-ion projectiles with a cluster structure, effects due to projectile excitation generate a large effective spin-orbit interaction which can drastically alter the predictions for vector analyzing powers obtained from folding model spin-orbit potentials. Coupled-channels calculations of this effect for $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ scattering from $^{58}\mathrm{Ni}$ at ${E}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\sim}20$ MeV give a good account of experimental data.

Coulomb final state interaction and the charge effect in heavy ion projectile fragmentation at intermediate energies

In intermediate energy heavy-ion projectile fragmentation the width of the transverse momentum distribution for a given fragment mass depends on the charge number of the fragment. The greater the charge number, the smaller is the width of the transverse momentum distribution. Such a charge effect may be explained in terms of a Coulomb final state interaction between the fragment and the protons dissociated from the projectile. With simple assumptions concerning the fragmentation process, analytic expressions for the momentum dispersions are obtained and are found to give good agreement with experimental results.NUCLEAR REACTIONS Heavy ions. Projectile fragmentation. Intermediate energy. Coulomb final state interaction. Calculate ${{\ensuremath{\sigma}}_{\ensuremath{\perp}}}^{2}$, ${{\ensuremath{\sigma}}_{\ensuremath{\parallel}}}^{2}$.

Perturbation of L X-rays emitted by swift heavy-ion projectiles

Low-energy X-rays (1–4 keV) have been detected under bombardment of light-ion targets by Br ions of 70–130 MeV, at incident charge states between 9 + and 28 +. Evidence from X-ray spectra is presented that the radiation comprises L X-rays, enhanced in energy by a factor of over two by the effects of the ions' motion in the target. A qualitative discussion is given of the observed perturbations in relation to the polarising forces expected in solid and gas targets.

Isobars and isobaric analog states

A formalism for the coherent production of isobars in the periphery of a relativistic heavy ion projectile is generalized to include isobaric spin so that concomitant excitations of the target to isobar analog giant resonances may be realized. The effects of the finite isobar decay width on the total cross section is investigated.NUCLEAR REACTIONS Relativistic, HI reaction theory, coherent isobar production and IAS.

A study of long-term thermal annealing on lexan plastic track detector

We have investigated fragmentation interactions of relativistic heavy ion projectiles using the plastic nuclear track detector CR-39 (C12H18O7). Stacks with detector foils and different targets have been exposed to Au- and Pb-ions at the Berkeley BEVALAC, the GSI Darmstadt SIS, the Brookhaven AGS and the CERN SPS. These experiments have been performed with high statistical significance. Charge yields and charge correlations determined for beam energies of 1, 10.6 and 158 A GeV were investigated. Our first experiments with 1 A GeV Au-nuclei have shown that the transverse momenta of the fragments are enlarged in comparison to a simple statistical model (Goldhaber model). For the new data at higher energies, we observed a dependence of the momentum transfer on the beam energy.

Selective electron capture into highly stripped Ne and N target atoms after heavy-ion impact

Auger electron and X-ray spectra from Ne and N gas targets excited with 1.4 MeV amu-1 Ar12+, Kr15+, Xe24+, and Pb36+ ions are measured, varying the target pressure and mixing other gases into the target volume. A dramatic change of line intensities from outer-shell configurations having a KL two-electron core and a third electron in the n=4, 5, 6 shell is observed, depending on the target pressure and systematically on the target ionisation potential. This effect is explained by highly selective electron capture from neutral target atoms or molecules into outer-shell orbitals of slowly (Er<10 eV) recoiling and highly stripped target atoms with metastable core states. It turns out that selective electron capture is a dominant mechanism for the population of H-, He- and Li-like states of low atomic number (Zt<or=10) target atoms after bombardment with heavy-ion projectiles. The capture process is discussed in the framework of a simple classical model and a capture cross section in the order of 10-14 cm 2 is estimated from the experiment.

Coherent Isobar Production in Peripheral Relativistic Heavy-Ion Collisions

Theoretical estimates of total cross sections for the coherent production of isobars in a relativistic heavy-ion projectile with concomitant excitation of the target to a giant resonance at two appreciably different energies/nucleon are presented and comparisons are made to estimated experimental total cross sections for pion production.

Target fragmentation ofAu197by relativistic heavy ions

The cross sections and recoil properties of a number of target fragmentation products formed by the reactions of 4.8- and 25-GeV $^{12}\mathrm{C}$ and 7.6-GeV $^{20}\mathrm{Ne}$ with $^{197}\mathrm{Au}$ have been measured. Comparisons between these data for relativistic heavy ions and those for relativistic protons have been used to test the hypotheses of factorization and limiting fragmentation. The cross sections for most of the nuclides measured are related for different projectiles by the ratio of the total reaction cross sections. An exception is the light nuclides ($Al30$), for which enhanced yields are found for heavy-ion projectiles compared to protons. The velocities imparted to recoil fragments by the projectiles are considerably larger for the heavy ions of $\ensuremath{\sim}0.4A$ GeV than for protons, but are the same for $2.1A$ GeV $^{12}\mathrm{C}$ (25-GeV kinetic energy) and 28-GeV protons. Limiting fragmentation has not been reached at energies of $0.4A$ GeV, as shown by the large change in recoil properties with increasing energy. The projectile kinetic energy appears to be more significant as a scaling variable than the velocity for relativistic heavy ions.NUCLEAR REACTIONS $^{197}\mathrm{Au}(^{12}\mathrm{C}, X)$, ($^{20}\mathrm{Ne}$, $X$), $X=^{24}\mathrm{Na}\ensuremath{-}^{196}\mathrm{Au}$, ${E}_{^{12}\mathrm{C}}=4.8 \mathrm{and} 25$ GeV, ${E}_{^{20}\mathrm{Ne}}=7.6$ GeV; measured cross sections and recoil properties; deduced mean kinetic parameters; test of factorization and limiting fragmentation.