Carbon Projectiles Research Articles

Sub-Coulomb transfer reactions on 208Pb with carbon and oxygen projectiles

Single-neutron transfers induced by 12, 13C and 16, 17, 18O projectiles on 208Pb and the 12C( 17O, 16O) 13C reaction have been studied at energies close to the Coulomb barrier. These processes are well described by the distorted-wave Born approximation. Coupled-channels effects are found to be small. Normalization factors have been determined for all projectile and target transitions, and also for the triton-deuteron overlap by comparison with previous measurements of the 208Pb(d, t) 207Pb reaction. The root-mean-square (rms) radii of single-particle neutron wave functions in 208Pb and 209Pb were calculated using known spectroscopic factors. The distribution of the point neutron excess density in the surface region of 208Pb has been derived and its rms radius determined to be 5.93 ± 0.13 fm with a local potential model. This is in good agreement with theoretical predictions, but is considerably larger than estimates based on Coulomb energy differences. The phenomena of core polarisation by the odd particle or hole outside 208Pb is discussed using the single-particle orbitals determined in this work.

Stopping powers from the inverted Doppler shift attenuation method: Z-oscillations; Bragg's rule or chemical effects; solid and liquid state effects

With our “Inverted Doppler Shift Attenuation (IDSA)” method stopping cross sections for swift ions can be measured with an accuracy of about 1%. We report here on results with lithium and carbon projectiles in very different stopping materials. It turns out that the stopping cross section around Bohr's velocity is linearly dependent on the velocity. Stopping cross sections of elements show the expected Z 2-oscillations. With compound targets we found strong deviations from Bragg's rule which means that the stopping cross section is influenced by the chemical bonding. In electrolytic solutions effects due to ion-dipole interactions can be observed. These phenomena demonstrate the strong sensitivity of electronic stopping cross sections on the specific distribution of the outer electrons of the target atoms. Further we have modified Lindhard's formula which gives a good description of this influence.

Experimental impact-parameter-dependent probabilities forK-shell vacancy production by fast heavy-ion projectiles

The impact-parameter dependence of the probability for production of target $K$ x rays has been measured for oxygen projectiles on copper and for carbon and fluorine projectiles on argon at scaled velocities near 0.5. The O-on-Cu data were taken for 1.56-, 1.88-, and 2.69-MeV/amu O beams incident upon thin Cu foils. A thin Ar-gas target was used for 1.56-MeV/amu C and F beams, permitting measurements to be made for charge-pure ${\mathrm{C}}^{+4}$, ${\mathrm{C}}^{+6}$, ${\mathrm{F}}^{+9}$ and ${\mathrm{F}}^{+5}$ projectiles. Ar and Cu $K$ x rays were observed with a Si(Li) detector and scattered projectiles with a collimated surface-barrier detector. Comparison of the shapes of the measured $K$-vacancy-production probability curves with predictions of the semiclassical Coulomb approximation (SCA) shows adequate agreement for the O-on-Cu system. For the higher ratio of projectile-to-target nuclear charge ($\frac{{Z}_{1}}{{Z}_{2}}$) characterizing the C-on-Ar and F-on-Ar systems, the SCA predictions are entirely inadequate in describing the observed impact-parameter dependence. In particular, they cannot account for large probabilities found at large impact parameters. Furthermore, the dependence of the shapes on the projectile charge state is found to become pronounced at larger $\frac{{Z}_{1}}{{Z}_{2}}$. Attempts to account for this behavior in terms of alternative vacancy-production processes are discussed.