P. Tikkanen

Electronic stopping power for 7Li, 11B, 12C, 14N and 16O at energies 0.4 to 2.1 MeV/nucleon in Ta and Au, and for 12C at energies 0.4, 0.8 and 1.4 MeV/nucleon in 18 elemental solids

Abstract Stopping powers have been measured for 0.4 to 2.1 MeV/nucleon beams of 7 Li, 11 B, 12 C, 14 N and 16 O in Au and of 7 Li, 12 C and 14 N in Ta. The results are compared with the predictions of an empirical model. By application of the Doppler-shift attenuation method, the measured electronic stopping powers for 12 C in Ta and Au are used to deduce the mean lifetime 58 ± 5 fs for the 4.439 MeV level in 12 C. Deviations of the electronic stopping power from the predictions of the empirical model have been studied for 12 C at energies 0.4, 0.8 and 1.4 MeV/nucleon in 18 Z = 14–82 elemental solids by application of the Doppler-shift attenuation method and the lifetime value of the 4.439 MeV level.

High-spin spectroscopy of the 142Eu, 143Eu and 144Eu nuclei

Abstract High-spin level schemes of the 142Eu, 143Eu and 144Eu nuclei have been investigated by in-beam γ-ray spectroscopic methods using the NORDBALL Compton-suppressed multi-detector array. The previously known schemes have been extended to considerably higher spin and excitation energy, up to I ≈ 30, Ex ⩾ 9 MeV in 142Eu, I = 75 2 , Ex = 15.6 MeV in 143Eu and I ≈ 40, Ex ⩾ 16 MeV in 144Eu. The level schemes are very complicated, characteristic of spherical or slightly oblate nuclei. Also, long cascades of stretched E2 transitions have been observed in all three nuclei. Plunger and DSAM lifetime results demonstrate high collectivity values up to ∼100 W.u. (up to ∼200 W.u. in 142Eu) in these E2 cascades and they are proposed to represent several crossing collective bands with the nucleus at triaxial shape of β2 ≈ 0.25 and γ ≈ 30°. Low parts of the level schemes have been discussed within the spherical shell model. Below 5.5 MeV excitation in 144Eu and 3.5 MeV in 143Eu practically all the observed levels are interpreted with shell model configurations of respectively two or four, and one or three quasiparticles.

Stopping power for low-velocity heavy ions: (0.01-0.9) MeV/nucleon Si ions in 18 (Z = 13–79) metals

Abstract The stopping power for 29 Si ions in Al, Ti, V, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Hf, Ta, W, Re, Pt and Au has been studied in the energy region (0.01-0.9) MeV/nucleon by application of a technique of nuclear physics, the inverted analysis of Doppler-shift attenuation data. Generally, the measured values are considerably higher at low energies (less than 0.4 MeV/nucleon) and show different energy dependence than the predictions of the commonly used empirical electronic stopping powers by Ziegler, Biersack and Littmark [1] [The Stopping and Ranges of Ions in Matter (Pergamon, New York, 1985) Vol. 1]. The uncertainty of the electronic stopping powers determined is typically ±6%.

Electronic stopping power of Si and Ge for MeV-energy Si and P ions

The electronic stopping powers of Si and Ge for 0–30 MeV 29Si and 29P ions are reported. The stopping power was studied by application of a technique of nuclear physics, the inverted analysis of Doppler‐shift attenuation data. The measured values at 30 MeV are about 15% lower and at 2 MeV considerably higher than the predictions of the commonly used empirical electronic stopping powers by J. F. Ziegler, J. P. Biersack, and U. Littmark [The Stopping Power and Ranges of Ions in Matter (Pergamon, New York, 1985), Vol. 1]. The experimental nuclear stopping power was taken into account in the deduction of the electronic stopping power.

Transition strengths in the mirror nuclei 27Si-27Al

Abstract Mean lifetimes of levels in the mirror nuclei 27Si and 27Al have been measured using the Doppler-shift-attenuation (DSA) method and the reactions 12C(16O, n)27Si and 12C(16O, p)27Al. The lifetime values or limits were determined for 14 levels in 27Si and 7 levels in 27Al. For the effective stopping of recoils, the targets were prepared by implanting 12C into Ta backings. The Monte Carlo method and the experimental stopping power were used in the DSA analysis. The strengths of the analogue transitions are discussed.

Short lifetimes in 24Mg for test of rotational collectivity in shell-model wave functions

Abstract Mean lifetimes of levels in 24Mg have been measured using the Doppler-shift-attenuation (DSA) method in conjunction with the reactions 23Na(p, γ)24Mg and 12C(14N, pn)24 Mg. The lifetime values or limits were determined for 27 bound levels below the excitation energy of 11 MeV; the lifetimes of 3 levels are reported for the first time. For the effective stopping of recoils, the targets were prepared by implanting 23Na and 12C into Ta backings. The Monte Carlo method and the experimental stopping power were used in the DSA analysis. The experimental transition strengths are compared with recent shell-model calculations.

A comprehensive study of the 34S + α system

Abstract The 34 S+ α system has been studied both experimentally and theoretically. Excitation functions of the 34 S( α , γ ) 38 Ar reaction have been measured over the alpha bombarding energy range E α = 3.4–4.4 MeV. The low background provided by the 100% enriched (implanted) target allowed one to observe 10 new resonances, some of them attributed previously to the 32 S contamination of the target. Decay schemes, spin-parity values, reduced electromagnetic transition probabilities and resonance strenghts have been determined. A semimicroscopic algebraic 34 S+ α cluster model has been used to describe the new resonances together with the low-lying states of the 38 Ar nucleus. This analysis indicates that the J π = 1 − resonances may not be good candidates for the first state of a K π = 0 − band predicted to start in the E x ⋍ 10–11 MeV region.

Hydrogen in diamond-like carbon films

Abstract Properties of physical vapor deposited diamond-like carbon films and the migration of hydrogen in co-deposited samples were studied. Measurements utilizing Rutherford backscattering spectrometry and Doppler-shift-attenuation techniques were used to obtain the average mass density of the films. Distributions of co-deposited hydrogen and deuterium were measured by the nuclear resonance reaction 1 H ( 15 N,αγ) 12 C, and the elastic recoil detection technique, respectively. Secondary ion mass spectrometry was also used in combination with these two methods. It was observed that in H and CH 4 co-deposited DLC films the temperature of H release varied between 950 and 1070°C depending on the H concentration.

Short lifetimes in 29Si-29P for the test of shell-model wave functions

Abstract Mean lifetimes of levels in the mirror nuclei 29 Si and 29 P have been measured using the Doppler-shift-attenuation (DSA) method and the reactions 15 N( 16 O, np) 29 Si and 28 Si(p, γ) 29 P. The lifetime values or limits were determined for 14 bound levels in 29 Si below the excitation energy of 9 MeV and for 4 levels in 29 P below the excitation energy of 4.1 MeV. The lifetimes of 5 levels in 29 Si are reported for the first time. In order to provide effective stopping of recoils, the targets were prepared by implanting 15 N and 28 Si into Ta backings. The Monte Carlo method and experimental stopping power were used in the DSA analysis. The experimental transition strengths are compared with recent shell model calculations.

The reaction 36(α, γ)40Ar: γ-transition properties of resonance and bound states in 40Ar

Abstract The El character of the de-excitation of the 9 to 10 MeV states in 40 Ar has been studied through the reaction 36 S(α, γ) 40 Ar. Angular distributions and γ-yield asymmetries of primary transitions from the E α = 2.35 to 3.50 MeV resonances have been measured. The Doppler-shift attenuation method was used to obtain the following lifetime values: 720 ± 120 fs ( E x = 2.52 MeV), 89 ±17 (3.21), 90±17(3.511), 22 ±9 (4.33), and 105 ± 17 (4.60).