Stopping Media Research Articles

Ion impact stopping cross sections for various media (Z = 3–100)

ABSTRACTStopping cross sections (SCS) for protons, alphas and Li ions are calculated with a modified form of our earlier work by incorporating a different electron density distribution of target materials; this involves four parameters – two projectile dependent and the rest two remain fixed. The prosed model has been tested for three stripped ion (H+, He2 + and Li3 +) projectiles and found that it describes quite satisfactorily the experimental SCS data from low energies with projectile velocities nearing v = Z1v0 (with Z1 as the atomic number and v0 the Bohr velocity) up to 100.0 MeV over a wide range of stopping media with atomic numbers Z2 =3–100.

Semi-empirical model for stopping cross sections of p, α and Li ions

Absolute magnitudes of stopping cross sections (SCS) for H+, He2+ and Li3+ in various stopping media with atomic numbers Z 2 = 2 to 100 are calculated using atomic density functions from Dirac-Hartree-Fock-Slater wave functions in the Lindhard-Schraff theory [J. Lindhard, M. Scharff, Kgl. Danske Videnskab. Selskab. Mat. Fys. Medd. 27, 15 (1953)]. The newly proposed formula, characterizing projectile-specific parameters in the incident energy range considered herein, describes satisfactorily the experimental and SRIM-simulated SCS data from low energies, with projectile velocities nearing v = Z 1 v 0 (with Z 1 as the projectile’s atomic number, v 0 = c / 137, the Bohr velocity and c, the speed of light in vacuum), to high energies up to about 2.5 MeV/u.

Gas phase chemical studies of superheavy elements using the Dubna gas-filled recoil separator – Stopping range determination

Currently, gas phase chemistry experiments with heaviest elements are usually performed with the gas-jet technique with the disadvantage that all reaction products are collected in a gas-filled thermalisation chamber adjacent to the target. The incorporation of a physical preseparation device between target and collection chamber opens up the perspective to perform new chemical studies. But this approach requires detailed knowledge of the stopping force (STF) of the heaviest elements in various materials. Measurements of the energy loss of mercury (Hg), radon (Rn), and nobelium (No) in Mylar and argon (Ar) were performed at low kinetic energies of around (40–270) keV per nucleon. The experimentally obtained values were compared with STF calculations of the commonly used program for calculating stopping and ranges of ions in matter (SRIM). Using the obtained data points an extrapolation of the STF up to element 114, eka-lead, in the same stopping media was carried out. These estimations were applied to design and to perform a first chemical experiment with a superheavy element behind a physical preseparator using the nuclear fusion reaction 244Pu( 48Ca; 3n) 289114. One decay chain assigned to an atom of 285112, the α-decay product of 289114, was observed.

Debris Interaction with Different Vapors and Condensed Materials in NIF

When an ICF fuel pellet explodes, the energy produced is divided among neutrons, x rays, and target debris. This work is conducted to study how target debris as charged particles deposits its energy in the stopping media on its way out from the chamber center. An attempt is also made to verify the continuum assumption that is used in chamber gas dynamics calculations by codes like TSUNAMI. 6 refs., 7 figs.

Symmetrisation procedures for detailed balancing of classical energy transfer probabilities

In a few previous papers, we introduced a so-called fluctuation model accounting for inelastic effects in molecular energy transfers induced by collisions. This model resulted in «symmetrisation rules» to be applied to the classical expressions for energy transfer probabilities, in order to insure detailed balancing. In this paper, we show that the symmetrisation procedures can also be applied successfully to the classical equations for energy loss and radiative transitions induced by Coulomb collisions of charged particles in stopping media. The resulting expressions display correct threshold behaviours and are worthwhile to be compared with the exact QM results. The comparison demonstrates interesting conceptual improvement of the classical equations and confirms that the symmetrisation procedures—as well as the underlying fluctuation model—are of a somewhat general applicability to inelastic processes in physics.

Energy loss of 14N ions in Ni, Ag, and Cu and the lifetimes of the states at 2.3 and 3.9 MeV in 14N.

The energy loss of /sup 14/N ions in Ni, Ag, and Cu has been investigated via the inverted Doppler-shift attenuation technique in the energy range up to 3.1 MeV. Excited /sup 14/N nuclei were produced in the reaction /sup 12/C(/sup 3/He,p) /sup 14/N/sup */, and energy-loss information was obtained from the analysis of the Doppler-broadened 2.313-MeV ..gamma..-ray line, observed with a Ge(Li) detector. This analysis also yielded the lifetimes of the levels at 2.3 and 3.9 MeV in /sup 14/N, which were determined to be 97.7 +- 5.5 and 5.6 +- 1.1 fs, respectively, in reasonable agreement with previous measurements and theoretical calculations. The stopping cross sections obtained for all three stopping media are compared with existing theoretical calculations, especially with regard to the oscillations with the atomic number of the stopping medium.

Theoretical energy straggling of 252Cf fission fragments in various absorbers

A new theoretical formula of energy straggling for heavy ions such as 252Cf fission fragments in various stopping media has been calculated in terms of incident heavy ion energy, differential scattering cross-section, electronic and nuclear stopping cross-section (data taken from Lindhard and co-workers [1,2]). However, no theory yet exists which is capable of predicting straggling behaviour of fission fragments. Comparison between our theoretical predictions and the previous work of Al-Bedri [3] and Sykes [4] has been made. Good agreement has been achieved at the beginning of the range of fission fragments but towards the end of the range our theoretical results were greater than the experimental results by about 0–20%. This discrepancy could be caused by the stopping cross-section, because the experimental stopping cross-section is greater than the theoretical data by about 0–30% [5–8].

Stopping power measurements for 4–5 MeV/nucleon 16O, 40Ar, 63Cu and 84Kr in C, Al, Ni, Ag and Au

The stopping powers for ≈4 and ≈5 MeV/nucleon 16O, 40Ar, 63Cu and 84Kr have been measured in C, Al, Ni, Ag and Au media. The experimental technique consists in measuring accurately the energy of protons elastically scattered at zero degrees by the incident and degraded beams. The experimental results have been compared with stopping powers calculated in different ways. Discrepancies as large as 30% have been observed for the heaviest ions in light media (C, Al), the experimental values being higher than the calculated ones. Moreover, this comparison indicates that, from these calculations, no agreement can be obtained in the whole range of incident ions and stopping media used in the present experiment. On the contrary, a quantitative agreement was obtained by a new calculation mode which takes into account the variation of the moving ion effective charge with the atomic number of the stopping medium.

Ranges of 99Mo and 140Ba in several stopping media from the spontaneous fission of 252Cf

The average ranges of 99Mo and 140Ba in aluminium, nickel, copper and palladium ( 140Ba only) were measured from the spontaneous fission of 252Cf. The average ranges of 99Mo and 140Ba are respectively: mg Al/cm 2:3·85 ± 0·05, 3·03 ± 0·03, mg Ni/cm 2:5·53 ± 0·22, 4·45 ± 0·10, mg Cu/cm 2:6·07 ± 0·17, 4·97 ± 0·16, mg Pd/cm 2:5·81 ± 0·08, ( p140 Ba) . The measured ranges were compared with calculated ranges from kinetic energies using the modified LSS equation. A general range-energy equation is proposed, applicable to most fissioning systems and stopping media.

Theory of Effective Charge and Stopping Power for Heavy Ions

A revision of the Knipp-Teller effective-charge theory for the electronic stopping power of media for heavy ions is described. In the new theory the ion velocity is related to the mean ionization energy of the most loosely bound medium electrons as calculated from the Thomas-Fermi atomic model. The effective charge ($\ensuremath{\gamma}z$, $0<\ensuremath{\gamma}<1$, where $\ensuremath{\gamma}$ is the effective-charge parameter) of an ion with atomic number $z$ is related to the ionic kinetic energy $\ensuremath{\epsilon}$(MeV/amu) through the equation $\frac{\ensuremath{\epsilon}}{{z}^{\frac{4}{3}}}=0.0277k[{f}_{0}(\ensuremath{\gamma})+\frac{{f}_{1}(\ensuremath{\gamma})}{z}]$ where $k$ is a constant, near unity, to be determined from the empirical data for the atomic-number region of interest. Curves for ${f}_{0}$ and ${f}_{1}$ as functions of $\ensuremath{\gamma}$ are presented and an overall value of $k=1.25$ is recommended. Calculated values of the effective-charge parameter are compared to experimentally measured values for a wide range of ions, ionic energies, and stopping media. For $z>10$ the agreement is very good from $\frac{\ensuremath{\epsilon}}{{z}^{\frac{4}{3}}}\ensuremath{\approx}0.001$, where exchange corrections (ignored in the Thomas-Fermi model) become important, to $\frac{\ensuremath{\epsilon}}{{z}^{\frac{4}{3}}}\ensuremath{\approx}0.1$, where a statistical theory is no longer valid.

On the Energy Loss of Fission Fragments in Composite Systems

Accurate predictions of the energy loss of fission fragments in gaseous and solid stopping media are of considerable interest in a number of fields such as fissio-chemistry and direct energy conver...

252Cf Fission Fragment Energy Loss Measurements in Elementary Gases and Solids as Compared with Theory

Energy loss of 252Cf fission fragments in 15 gases and solids, representing a wide range of atomic numbers throughout the periodic system, has been measured using a calibrated Si surface barrier heavy ion detector. The data are used for a detailed and systematic comparison with existing theoretical treatments of the electronic energy loss mechanism showing that none of them gives overall good agreement for all stopping substances.The Bohr expression for heavy stopping substances, which shows consistent deviation from experiment for the entire range of stopping media, suggests that based on this approach, a semi-empirical modification can be derived.

Experimental problems in the Doppler-shift attenuation method

The lifetime of the first excited state of 30Si has been measured by the Doppler-shift attenuation method using Mg, SiO 2, Y, Sn, Ni and Au as stopping media. Comparison of the different results shows that the major uncertainty in such measurements stems from the inadequacies of present stopping power theory and that the r.m.s. error arising from this source will be ≈ 15 % in a typical measurement. The measured lifetime is taken as 0.336±0.025 ps.

Energy loss of heavy ions in nickel, oxygen, and nuclear emulsion

Range-energy relations for He 4, B 10, B 11, C 12, N 14, O 16, F 19 and Ne 20 ions in oxygen and nickel have been measured in the energy range 2 to 10 MeV per amu (atomic mass unit). Together with similar relations for heavy ions in nuclear emulsions, reported in an earlier paper, these have been differentiated numerically to obtain specific energy loss relations. fThe effective charge of heavy ions passing through matter, as well as the relative stopping power per atom of oxygen, nickel and emulsion, have been computed from these and compared with theoretical predictions. From this comparison, it has been concluded that fairly reliable calculations of specific energy lossesand/or range-energy relations can be made for various heavy ion species in different stopping media.