Charge state and stopping dynamics of fast heavy ions in dense matter

$K$-shell radiation of fast heavy ions penetrating solid matter was used to analyze the stopping dynamics of ions over more than 80% of the stopping path. The most important advantage of this method is that the data is obtained with a high spatial resolution directly from the interaction volume. In experiments $11.4\mathrm{MeV}∕\mathrm{u}$ Ca projectile were slowed down in solid quartz and low-density $\mathrm{Si}{\mathrm{O}}_2$ aerogel targets. Characteristic projectile and target spectra in the photon energy range of 1.5–4 keV were registered by means of spherically bent crystal spectrometers with high spectral and spatial resolution in the direction of the ion beam propagation. $K$-shell spectra of heavy ions induced by close collisions with target atoms provided information about the projectile charge state and velocity dynamics. The line intensity distribution of the $K$-shell transitions arising from ions with different ion charges represents the charge state distribution along the ion beam track. The variation of the line Doppler shift due to the ion deceleration in the target material was used to determine the ion velocity dynamics. The spectroscopic analysis of the stopping process was complemented by measurements of the energy loss and ion charge state distribution after the ion beam emerged from the target using a standard time-of-flight method and magnet spectrometer.

Figure 1

$K$-shell ionization cross sections of ${\mathrm{Ca}}^{q+}$ ions $(q=15\text{–}19)$ colliding with $\mathrm{Si}{\mathrm{O}}_2$ molecules as a function of the ion energy, calculated by the LOSS code [22].

Figure 2

Experimental setup for the measurements of the energy loss and charge state distribution of the ion beam by methods of x-ray spectroscopy, magnet spectroscopy and time-of-flight used simultaneously.

Figure 3

Scheme of principles of x–ray focusing spectrometer with spatial resolution based on spherically bent crystal.

Figure 4

The profile of the ${}^{48}\mathrm{Ca}$ beam charge state distribution after analyzing magnet: gray line, Ca charge state distribution after passing through the Al foil with a linear density of $13.8\mathrm{mg}∕{\mathrm{cm}}^2$; black line, Ca charge state distribution after penetration of the $0.048\mathrm{g}∕{\mathrm{cm}}^3$ aerogel target with a linear density of $13.6\mathrm{mg}∕{\mathrm{cm}}^2$.

Figure 5

(Color online) Si target $K\alpha$ spectra produced due to irradiation of $2.23\mathrm{g}∕{\mathrm{cm}}^3$ solid quartz and $0.04\mathrm{g}∕{\mathrm{cm}}^3\mathrm{Si}{\mathrm{O}}_2$-aerogel targets by $11.4\mathrm{MeV}∕\mathrm{u}{}^{48}\mathrm{Ca}$ ions under the same experimental conditions.

Figure 6

(Color online) Radiation dynamics of Ca ions with the initial energy $E_0=11.4\mathrm{MeV}∕\mathrm{u}$ slowing down in silica aerogel $(\rho =0.04\mathrm{g}∕{\mathrm{cm}}^3)$. $Y$ axis represents the ion penetration depth.

Figure 7

Ca ion velocity normalized to the light speed versus penetration depth in $\mathrm{Si}{\mathrm{O}}_2$ with a mean density of $0.04\mathrm{g}∕{\mathrm{cm}}^3$. Measured x-ray spectroscopic (squares and circles) and time-of-flight (triangles) data are compared with SRIM calculation.

Figure 8

Charge state distribution of Ca ions with initial energy of $11.4\mathrm{MeV}∕\mathrm{u}$ after emerging from the $0.023\mathrm{g}∕{\mathrm{cm}}^3$ aerogel sample with a linear density of $19\mathrm{mg}∕{\mathrm{cm}}^2$. Data were obtained by the method of magnet spectroscopy with magnet field value of $B=1.63\mathrm{T}$. The measured ion beam energy after the target $E=6.54\mathrm{MeV}∕\mathrm{u}$.