Towards cooling of high-intensity ion beams

Buffer gas beam coolers may become excellent beam preparation devices for high-resolution mass separation. The small beam emittance provided makes efficient isobar resolution a realistic goal. In order to fulfill the needs of future facilities providing high-intensity beams of rare isotopes, it is desirable to increase the beam intensity limit of such devices from typically several tens of nanoamperes to microamperes. This requires the usage of high-voltage radiofrequencies in a low-pressure gas environment. A buffer gas beam cooler, dedicated to this purpose, is under development at the NSCL. The study of voltage breakdowns under such conditions and the design of an electrode system minimizing them is mandatory.      

Imprints of compound-nucleus and direct-interaction processes in energy-averaged cross sections and durations of nuclear reactions

New analytical expressions for the energy-averaged S-matrix and nuclear-reaction cross sections are obtained on the basis of the unitary S-matrix parametrization. Some approximations are analyzed when compound-nucleus cross sections are described with and without the Hauser-Feshbach formula with the partial-width-fluctuation correction. The connection of the S-matrix parameters in the Simonius representation with the dynamics of compound-nucleus processes is clarified. An explicit expression for the averaged duration of the nuclear reaction is obtained for the range of closely situated resonances. Possible methods of obtaining information on some compound-nucleus and direct-interaction characteristics from the averaged cross sections and durations are examined.     

Long-range persistence of femtosecond modulations on laser-plasma-accelerated electron beams

Laser plasma accelerators have produced femtosecond electron bunches with a relative energy spread ranging from 100% to a few percent. Simulations indicate that the measured energy spread can be dominated by a correlated spread, with the slice spread significantly lower. Measurements of coherent optical transition radiation are presented for broad-energy-spread beams with laser-induced density and momentum modulations. The long-range (meter-scale) observation of coherent optical transition radiation indicates that the slice energy spread is below the percent level to preserve the modulations.     

Phase transformation of graphite irradiated by high-intensity pulsed ion beams

The microstructure and morphology of graphite irradiated by high-intensity pulsed ion beams (HIPIB) has been studied by varying the ion current density as 200, 350 and 1500 A/cm² with one to five shots. Phase transformation from graphite to diamond-like carbon (DLC) on the HIPIB-irradiated graphite was confirmed by Raman spectroscopy where a typical broadened asymmetric peak appeared in the wavenumber range of 1100-1700 cm⁻¹. Formation of DLC on the irradiated graphite strongly depended on the HIPIB parameters and preferably took place at the medium ion current density of 350 A/cm² up to five shots. Numerical simulation of ablation process was performed to explore the transformation mechanism of DLC from graphite irradiated by HIPIB. The calculation showed that the temperature profile in irradiated graphite at 350 A/cm² is almost identical to that at 200 A/cm², showing a deeper heat-affected zone in comparison with that of 1500 A/cm². Moreover, the ablation depth per shot is around 0.8 μm at 350 A/cm², higher than that of 0.4 μm at 200 A/cm² and much lower than that of 8.4 μm at 1500 A/cm², respectively. The experimental and numerical results indicate that a proper temperature and pressure repetitively created in the top layer of ablated graphite during HIPIB irradiation facilitates the phase transformation.     

Time-reversal,nuclear reactions and molecular beams

It is pointed out, that very accurate nuclear reaction detailed balance test could be done in a single experiment using molecular beams. The feasibility of these measurements is discussed for the case of the¹³C(d, t)¹²C reaction.     

High-accuracy fluence determination in ion beams using fluorescent nuclear track detectors

We present an approach to use Al₂O₃:C,Mg-based fluorescent nuclear track detectors (FNTDs) and confocal laser scanning microscopy as a semiautomatic tool for fluence measurements in clinical ion beams. The method was found to cover a linear energy transfer (LET) range from at least L_∞(Al₂O₃) = 0.5 keV/μm to 61,000 keV/μm with a detection efficiency ≥99.83% (20 MeV protons) at particle fluences up to at least 5 × 10⁷ per cm². Our technique allows to determine the spatial fluence distribution on a microscopic scale and enables detailed track-by-track comparison studies between different fluence detectors.     

Pulse-frequency,high-intensity ion beams based on a vacuum arc

The production and investigation of pulse-frequency, high-intensity ion beams based on a vacuum arc are examined. The influence of arc discharge parameters, accelerating voltage, residual gas pressure, pulse repetition rate, and geometric dimensions of the accelerator on the ion generation efficiency is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 68–74, August, 1989.In closing, the authors express gratitude to A. R. Immel', A. L. Shipilov, and V. P. Yanovski for analyzing the implanted samples by the method of characteristic x-rays.     

Synthesis and decay properties of superheavy atoms in nuclear reactions induced by stable and radioactive ion beams

This talk consists of two parts. The first one presents the results of investigations performed in 1998-2000 in Dubna on the synthesis of superheavy nuclei in reactions induced by ⁴⁸Ca ions. The radioactive decay properties of the nuclei, indicating a considerable increase in the α-decay and spontaneous fission half-lives of the isotopes of elements 110-116 when approaching the closed neutron shell at N = 184, are given. In the second part the possible ways of advancing into the region of more neutron-rich nuclei, using stable and radioactive ion beams, are discussed. Since so far no intense radioactive ion beams are available, some experiments with stable beams are considered as a test for the suggested ideas. Received: 1 May 2001 / Accepted: 4 December 2001     

Experimental nuclear astrophysics with radioactive ion beams

Reactions involving unstable nuclei play an important role in many astrophysical sites. Radioactive ion beams provide a unique tool to investigate the structure of such unstable nuclei as well as the cross sections for many reactions of astrophysical relevance. This paper provides a brief survey of some recent results in experimental nuclear astrophysics with Radioactive Ion Beams, particularly for processes which take place during explosive hydrogen burning in novae and X-ray bursts. Some prospects for future studies at next generation facilities are also briefly discussed.     

Collimated multi-MeV ion beams from high-intensity laser interactions with underdense plasma

A beam of multi-MeV helium ions has been observed from the interaction of a short-pulse high-intensity laser pulse with underdense helium plasma. The ion beam was found to have a maximum energy for He2+ of (40(+3)(-8)) MeV and was directional along the laser propagation path, with the highest energy ions being collimated to a cone of less than 10 degrees. 2D particle-in-cell simulations show that the ions are accelerated by a sheath electric field that is produced at the back of the gas target. This electric field is generated by transfer of laser energy to a hot electron beam, which exits the target generating large space-charge fields normal to its boundary.     

Studies on ion-isotopic exchange reactions using nuclear grade ion exchange resins

The present paper deals with the study of iodide and bromide ion-isotopic exchange reactions by application of radioactive tracer technique. The specific reaction rate (per minute) of both the reactions decreases with rise in temperature and increases with concentration of ionic solution. It was observed that due to solvation effect, the iodide ion-isotopic exchange reaction take place at a faster rate than bromide ion-isotopic exchange reaction. Also for iodide ion-isotopic exchange reaction, the distribution coefficient (K _d ) values were higher than that for bromide ion-isotopic exchange reaction. The application of tracer technique was further extended for characterization of two widely used nuclear grade ion exchange resins Tulsion A-33 and Duolite ARA 9366. It was observed that the values of K _d, specific reaction rate (per minute), amount of ion exchanged (millimoles), and percentage of ions exchanged for Tulsion A-33 resins are higher than that for Duolite ARA 9366 resins under identical experimental conditions.     

Fusion using radioactive ion beams

The capture-fission cross-section is measured for the collision of the massive nucleus ¹³²Sn with ⁹⁶Zr at near-barrier energies and compared with the collision of ¹²⁴Sn with ⁹⁶Zr. This study gives insight into fusion enhancement and hindrance in systems involving neutron-rich nuclei. The dinuclear system model (DNS) calculations describe the excitation function reasonably well and if we use the barrier heights predicted by this model we can conclude that fusion hindrance (represented by extra push energy) is greater for the more neutron-rich systems.     

Extension of the Monte-Carlo code MOCADI to fusion-evaporation reactions

The Monte-Carlo code MOCADI has been extended, besides to fission and fragmentation reactions, also to fusion-evaporation reactions. The updated version includes the cross sections and the reaction kinematics for the production of evaporation residues calculated according to the statistical model code PACE2, while the atomic interaction with matter can be treated either with the code ATIMA or with the code TRIM. The present version of MOCADI can now be employed world-wide for design studies of new low-energy nuclear physics facilities and for the optimization of experiments involving fusion-evaporation reactions, e.g. mass measurements, laser spectroscopy, super-heavy synthesis.     

强流脉冲离子束辐照对不锈钢耐腐蚀性能的影响

 利用强流脉冲离子束（HIPIB）对316L不锈钢进行了表面辐照处理,研究了HIPIB辐照对其在0.5mol/L H2SO4溶液中电化学腐蚀性能的影响。极化曲线测量结果表明,HIPIB辐照能够显著提高316L的抗腐蚀性能,自腐蚀电流对辐照次数的依赖性与自腐蚀电位相比明显较强。采用扫描电子显微镜（SEM）、X射线衍射（XRD）和电子探针（EPMA）分析辐照后试样表面形貌、表面层相结构和元素分布的变化。结果表明：HIPIB辐照使试样表面光滑化,表面层产生择优取向,且发生了杂质元素的选择性烧蚀,是316L不锈钢耐电化学腐蚀性能得以提高的主要原因。     

Experimental investigations of the nuclear level density by using heavy ion reactions

The transition of the level density parameter a _off from the low excitation energy value a _off=A/8 MeV⁻¹ to the Fermi gas value a _FG ∼ A/15 MeV⁻¹ was discovered a few years ago studying particle spectra evaporated from hot compound systems of A∼ 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the lead region in which evaporation residues are tagged by low energy gammarays. Those experiments open the possibility of a detailed study of the level densities in nuclei where the shell effects are important.     

Radioactive ion beams for biomedical research and nuclear medical application

In this article a review is given on the research strategies, on experimental work and application of ISOLDE produced radionuclides used in the field of biomedicine over a period of more than 2 decades. Special attention will be directed to the radio-lanthanides for several reasons: firstly, the radio-lanthanides are three-valent metallic radionuclides which show any radiation properties we wish (single photon emission suitable for SPECT, positron emission suitable for PET, β⁻- and Auger electron emission suitable for therapy). Even the alpha decay mode (suitable for therapy in selected cases) is available in the lanthanide group. Secondly, the 15 lanthanides can be seen chemically as one single element for labelling of tracer molecules, providing the unique possibility to study systematically relationships between physico-chemical molecule parameter and a biological response without changes in the basic tracer molecule. Very recent developments in bioconjugation chemistry call for three-valent metallic radionuclides for all kinds of nuclear medical application: diagnosis, in vivo dosimetry and radionuclide therapy where the rare-earth elements will play an important role in future. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nuclear physics using unstable nuclear beams

As an application of the projectile fragmentation in high-energy heavy-ion collisions, use of the unstable nuclei as secondary nuclear beams is discussed. Results of the test experiment of secondary beam line at the Bevalac (LBL, Berkeley) is described. Clean beams of He and Li isotopes were produced with reasonable intensity. A plan of a proposed experiment, which uses the unstable nuclear beam to determine radii of unstable nuclear isotopes through a measurement of interaction cross sections, is shown.     

Probing nuclear surfaces by heavy ion reactions

An analysis of the recently measured ¹⁶O + ²⁶Mg one- and two-proton transfer reaction is given. It is shown that these reactions probe progressively deeper regions of the surface of the two colliding nuclei.     

Multi-element focused ion beams using compact microwave plasma ion source

Focused ion beams (FIB) are widely used for research and applications in nanoscience and technology. We have developed a compact microwave plasma based multi element FIB (MEFIB) system in order to widen the applications and overcome the limitations faced by conventional Liquid Metal Ion Source (LMIS) based FIB systems, that provide primarily Ga ions. The MEFIB source provides high density plasmas (∼1.5 × 10¹¹ cm⁻³) in a compact cross section. Recently the ion energy spread in the plasma meniscus from where the beams are extracted is found to be small (∼5 eV) [1–3]. The beam extraction and focusing are carried out using electrostatic multi electrode assembly. AXCEL INP and SIMION simulation codes are employed for the design of electrostatic Einzel lenses for beam focusing. The beam focal point is measured using a specially designed three slit Faraday cup and the spot size is measured by the micrography of craters formed by the focused ion beams impinging on copper and aluminium substrates. The initial experimental results show a focused beam spot size of ∼ 25 micron which is in good agreement with the simulations. By further reduction of electrode apertures and operating the second Einzel lens at higher potentials, submicron focused ion beams can be expected.