Influence of heavy-ion bombardment on the structure of targets for atomic and nuclear interaction studies

doi:10.1016/0168-9002(89)90142-3

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Volume 282, Issue 1, 1 October 1989, Pages 206-212

https://doi.org/10.1016/0168-9002(89)90142-3 Get rights and content

Abstract

An accurate knowledge of the absolute magnitude of the energy loss of heavy ions inside targets is necessary in many experiments. The energy loss and target properties are directly correlated. Even if the initial status of a target is known, the heavy-ion bombardment may lead to a drastic change of its properties or even to its total deterioration. The degree and timescale of a possible variation depends on the type of the projectile beam and on the target properties itself, the latter being influenced by the chemical composition, the physical characteristics, and the mechanical arrangement of the target system. Structural changes of a target system limit its useful lifetime; it can be prolonged by special techniques like the application of target wobblers or target wheels. 1.6 MeV proton backscattering has been employed to investigate series of targets prior to and after their irradiation in heavy-ion beams in order to gain information on structural changes for the interpretation of experimental results obtained in heavy-ion positron spectroscopy.

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Cited by (9)

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Citation Excerpt :
Although many publications exist on the topic from the material science perspective (see for example [10,11] and references therein) and these offer important insights, one aspect of nuclear targetry often unexplored pertains to irradiation effects. Articles focusing on the characterization of nuclear targets document non-trivial physical and chemical transformations after heavy-ion beam irradiation [12,13], which can non-negligibly affect the relevant experiments. These studies are of particular interest for experiments where targets must withstand high beam intensities and doses, such as in the production of known transactinides and synthesis of new superheavy elements [14,15].
A series of enriched gadolinium (Gd, Z = 64) targets was prepared using the molecular plating process for nuclear physics experiments at the Cyclotron Institute at Texas A&M University. After irradiation with ⁴⁸Ca and ⁴⁵Sc projectiles at center-of-target energies of E_cot = 3.8–4.7 MeV/u, the molecular films displayed visible discoloration. The morphology of the films was examined and compared to the intact target surface. The thin films underwent a heavy-ion beam-induced density change as identified by scanning electron microscopy and α-particle energy loss measurements. The films became thinner and more homogenous, with the transformation occurring early on in the irradiation. This transformation is best described as a crystalline-to-amorphous phase transition induced by atomic displacement and destruction of structural order of the original film. The chemical composition of the thin films was surveyed using energy dispersive spectroscopy and X-ray diffraction, with the results confirming the complex chemistry of the molecular films previously noted in other publications.
Changes in surface composition and morphology of UF<inf>4</inf> targets during heavy ion irradiation
2004, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Citation Excerpt :
Unlike the similar swelling seen in oxides, such as SiO2 where there is a straightforward interpretation in terms of a density change due to amorphization [17], the origin of the swelling in LiF, where amorphization is thought to be less likely, is said to be more likely to arise from the formation of specific defects or defect clusters [18]. Our observations do echo those of Stiebing et al. [4], who found massive microstructural changes in UF4 targets sandwiched between C foils that had been exposed to a variety of heavy-ion beams. In some cases UF4 appeared to have migrated from some areas and piled up on others.
Aspects of the historical development of targetry for heavy ions of 0.05-2000 A·MeV at GSI
1999, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
The progressively improved GSI accelerators provide beams of heavy ions from energies of 0.05–2000 A·MeV at high particle intensities now. Therefore, a wide variety of common and new heavy-ion target techniques had to be installed and developed during the past 25 years to prepare and characterize self-supported or backed heavy-ion–targets of chemical elements and compounds from hydrogen (as polyethylene) to uranium. The thickness ranged from 2×10⁻⁶ to 20 g/cm² for beam spots of about 5 mm in diameter. Homogeneity, surface structure or individual shape had to be adapted to the needs of each experiment. Special setups were required for targets of poisonous materials, of highly enriched stable isotopes or those of radioactive species in minute amounts. The capability of thin-layer technologies was as well applied to prepare and measure stripper foils or various high-vacuum deposits for experimental or accelerator purposes.
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The brief historical review can touch only aspects of targetry at GSI. A few typical examples are included.
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1999, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
A compact detection system for heavy ions scattered in collisions at the Coulomb barrier is presented. This system, consisting of four identical, low-pressure Parallel Plate Avalanche Counter (PPAC) modules with two sensitive layers each, was built to operate in an ultra-high-vacuum environment inside the EPoS II solenoid spectrometer at GSI Darmstadt. The detector covers polar angles between 20° and 70° with respect to the beam axis, and about 80% of 2π in azimuthal angle. Segmented cathodes and a delay-line read-out allow for a determination of both angles with a precision of δΘ≈0.7° in polar and δΦ≈1.5° in azimuthal angle, respectively. The system has been proven to be capable of handling instantaneous rates of up to 5×10⁵ detected ions per second per module. It neither exhibits the degradation of detection efficiency nor loss in resolution over a 500 h period of a 6 $MeV /u^{238} U +^{181} Ta$ measurement at average luminosities of $8×10^{27} cm^{−2} s^{−1}$ .
Correlated e<sup>+</sup> e<sup>-</sup> peaks observed in heavy-ion collisions
1990, Physics Letters B
Three very narrow e⁺ e⁻ sum-energy peaks around 610, 750, and 810 keV have been observed in U+Th as well as in U+Ta collisions at beam energies around the Coulomb barrier. As no processes involving conventional atomic and nuclear physics were found to describe their origin, the data were in particular confronted with the hypothesis that the lines are due to the two-body decay of neutral objects in an e⁺ e⁺ pair. Although the 810 keV sum-energy line observed in U+Th is consistent with the prompt two-body e⁺ e⁻ decay of a neutral object if created nearly at rest in the heavy-ion center-of-mass system, the other lines require at least a considerably more complicated scenario if they are to be explained in the context of a two-body decay.
Fast determination of structure, homogeneity, and composition of targets for heavy-ion experiments from backscattering and pixe with 1.6-MeV protons
1989, Nuclear Inst. and Methods in Physics Research, A
An experimental setup has been installed to perform backscattering spectroscopy and proton induced X-ray emission for fast determinations of structures, homogeneities, and compositions including the identification of impurities in targets for heavy-ion experiments. With a well collimated beam of 1.6-MeV protons of 50 nA the measurement of a single target point takes only 5–10 min of irradiation time. Additionally, an automatic scanning of the whole target can be performed for a precise determination of the lateral distribution of these quantities. The elastic-scattering resonances for proton scattering on light elements are particularly useful for the efficient investigation of multilayer targets where the target material is sandwiched between carbon foils. The results enter into the interpretation of data from atomic and nuclear interaction studies at the UNILAC of GSI; they lead as well to developments in the preparation of heavy-ion targets for future experiments.

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Influence of heavy-ion bombardment on the structure of targets for atomic and nuclear interaction studies

Abstract

Nucl. Instr. and Meth.

Nucl. Instr. and Meth.

Phys. Rev. Lett.