12C Ion Beams Research Articles

Recoil separator ERNA: ion beam specifications

For improved measurements of the key astrophysical reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is being developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with about 50% efficiency. Calculations of the ion beam optics including all filtering and focusing elements of ERNA are presented. Since the 12C projectiles and the 16O recoils have essentially the same momentum, and since the 12C ion beam emerging from the accelerator passes through a momentum filter (analysing magnet), the 12C ion beam must be as free as possible from 16O contamination for ERNA to succeed. In the present work, the 16O contamination was reduced from a level of 1 × 10−11 to a level below 2 × 10−29 by the installation of Wien filters both before and after the analysing magnet. The measurement of these and other beam specifications involved other parts of the final ERNA layout – sequentially a Wien filter, a 60˚ dipole magnet, another Wien filter, and a ΔE-E telescope. The setup led to a measured suppression factor of 5 × 10−18 for the 12C ion beam. The experiments also indicate that an almost free choice of the charge state for the 16O recoils is possible in the separator.

Relative biological effectiveness of accelerated heavy ions for induction of morphological transformation in Syrian hamster embryo cells.

Syrian hamster embryo cells were used to study the morphological transformation induced by accelerated heavy ions with different linear energy transfer (LET) ranging from 13 to 400 keV/micron. Exponentially growing cells were irradiated with 12C or 28Si ion beams generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC), then inoculated to culture dishes. Morphologically altered colonies were scored as transformants. Over the LET range examined, the frequency of transformation induced by the heavy ions increased sharply at very low doses no greater than 5 cGy. The relative biological effectiveness (RBE) of the heavy ions relative to X-rays first increased with LET, reached a maximum value of about 7 at 100 keV/micron, then decreased with the further increase of LET. Our findings confirmed that high LET heavy ions are much more effective than X-rays for the induction of in vitro cell transformation.

Neoplastic transformation of hamster embryo cells by heavy ions

We have studied the induction of morphological transformation of Syrian hamster embryo cells by low doses of heavy ions with different linear energy transfer (LET), ranging from 13 to 400 keV/μm. Exponentially growing cells were irradiated with 12C or 28Si ion beams generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC), inoculated to culture dishes, and transformed colonies were identified when the cells were densely stacked and showed a crisscross pattern. Over the LET range examined, the frequency of transformation induced by the heavy ions increased sharply at very low doses no greater than 5 cGy. The relative biological effectiveness (RBE) of the heavy ions relative to 250 kVp X-rays showed an initial increase with LET, reaching a maximum value of about 7 at 100 keV/μm, and then decreased with the further increase in LET. Thus, we confirmed that high LET heavy ions are significantly more effective than X-rays for the induction of in vitro cell transformation.

On the "Oxygen in Heavy-Ion Tracks" Hypothesis

Two well-known chemical systems, the Fricke (system I) and the Fricke + ethanol (system II), were irradiated with intermediate-energy 12C and 40Ca ion beams. A vertical beam allowed us to study radiation phenomena in the bulk of a stirred solution and in the motionless surface layer in contact with air. The G value of the formation of Fe3+ in system II compared to system I allowed us to distinguish between oxygenated and hypoxic conditions in the reaction zone, i.e., in our case, in the vicinity of the heavy-ion path. Our results for nonstirred solutions that are open to air indicate an oxygen deficiency in the reaction zones even for medium-intensity ion fluences. The origin of this effect is not completely clear at present. Nevertheless, it is evident that postulated mechanisms for the generation of O2 in heavy-ion tracks are not sufficient to keep an oxygenated condition in nonstirred solutions. We cannot exclude the possibility that the low oxygen enhancement ratio observed in experiments with high-LET radiation may arise, at least partly, from an insufficiency rather than an excess of oxygen.

Bone powder exposed to the action of 12C and 25Mg ion beams as investigated by electron paramagnetic resonance spectroscopy

Bovine compact bone powder was irradiated with α-particles of 241Am, 12C 6+ and 35Mg 12+ ion beams, then examined by the e.p.r. spectroscopy. The stable e.p.r. signal found is of the same characteristic as that observed in γ-irradiated bone ( g ⊥ = 2.0017, g ∥ = 1.9973, ΔH pp = 0.85 mT). Thus, the structure of radiation induced paramagnetic center in bone does not depend on the LET of radiation used. The radiolytic yields of the formation of stable paramagnetic centres in bone powder irradiated with γ-rays are G γ = 0.08 ± 0.01 while with 12C 6+ ion beams roughly about G c = 0.02, respectively.