Momentum Acceptance Research Articles

States of 14C and 15C via the (18O,16O) two-neutron transfer reaction at 84 MeV

A study of the 14C and 15C states was pursued at the Catania INFN-LNS laboratory by the 12C(18O,16O)14C and 13C(18O,16O)15C reactions at 84 MeV incident energy. The 16O ejectiles were detected at forward angles by the MAGNEX magnetic spectrometer. Exploiting the large momentum acceptance (20%) and solid angle (50 msr) of the spectrometer, energy spectra were obtained with a relevant yield up to 20 MeV excitation energy. The application of the powerful trajectory reconstruction technique did allow to get energy spectra and angular distributions with resolution of about 160 keV and 0.3°. In the energy spectra several known low lying states of 14C and 15C have been observed and some unknown resonant structures at about 10.5 and 13.6 MeV in 15C and 16 MeV in 14C appear.

Fluctuations of particle yield ratios in heavy-ion collisions

We study the dynamical fluctuations of various particle yield ratios at different incident energies. Assuming that the particle production yields in the hydronic final state are due to equilibrium chemical processes ($\gamma=1$), the experimental results available so far are compared with the hadron resonance gas model (HRG) taking into account the limited momentum acceptance in heavy-ion collisions experiments. Degenerated light and conserved strange quarks are presumed at all incident energies. At the SPS energies, the HRG with $\gamma=1$ provides a good description for the measured dynamical fluctuations in $(K^++K^-)/(\pi^++\pi^-)$. To reproduce the RHIC results, $\gamma$ should be larger than one. We also studied the dynamical fluctuations of $(p+\bar{p})/(\pi^++\pi^-)$. It is obvious that the energy-dependence of these dynamical fluctuations is non-monotonic.

Beam lifetime study based on momentum acceptance restriction by movable beam scraper

The beam lifetime of the SAGA-LS electron storage ring was experimentally investigated using a movable beam scraper installed in a dispersive section. In addition to physical aperture restriction, the scraper could be used to reduce the momentum acceptance of the storage ring, enabling the evaluation of the Touschek effect. Lifetime measurements were performed with scraper scans, and the individual contributions of gas scattering and the Touschek effect were clarified. Our results confirm that the present method provides a basic understanding of lifetime limiting effects in the storage ring.

Design of an in-flight radioactive isotope beam separator for the enhancement of purity by using an energy degrader and a RF kicker

We designed an in-flight radioactive isotope (RI) beam separator with large acceptance and two-stage separation, which is a major feature for next-generation separators today. The large acceptance value made possible efficient production of RI beams while the two-stage separator allowed us to cope with the poor purity of RI beams. The first stage was used for the production and the separation of RI beams, and the second stage was used to identify RI beam species. For the designed separator, we estimated the yield and the purity of several nuclei produced in projectile fragmentation by using the code LISE++ for three different configurations — momentum analysis, momentum analysis plus an energy degrader, and addition of a radio frequency (RF) kicker. We adopted a RF kicker to increase the purity of proton-rich nuclei in the RI beams. Purifications were introduced as figures of merit for the comparison of the purity enhancements for different separation methods. When the RF kicker was combined with the energy degrader, the purifications for selected proton-rich RI beams such as 35Ca, 56Ni, 100Sn, and 129Sm turned out to be 10 ∼ 2,000 times those for the case when only the momentum analysis was used. In particular, the purifications for 100Sn and 129Sm were 2,000 and 200, respectively, for a momentum acceptance of 1%. However, in the case of neutron-rich RI beams such as 58Ca, 78Ni, 132Sn, and 162Sm, the purifications were insensitive to the RF kicker, but increased with decreasing the momentum acceptance.

The rare-RI ring

We describe the rare-RI (radioactive isotope) ring at the RI Beam Factory (RIBF). The main purpose of the rare-RI ring is to measure the mass of very neutron-rich nuclei, the production rates of which are very small (hence ‘rare RI’) and the lifetimes of which are predicted to be very short. In the rare-RI ring, there are two innovative pieces of apparatus: individual injection, which can realize the injection of 200 A MeV rare RIs one by one, and a cyclotron-like storage ring, which allows high isochronous magnetic fields with large angular and momentum acceptances. With these devices, we will achieve a 10−6 mass resolution, and will be able to access rare RIs, the production rate of which is down to 1 event/day/pnA. Construction of the rare-RI ring started in fiscal year 2012.

SAMURAI Project at RIBF

SAMURAI project aims to open a new research field in nuclear physics by the use of a large acceptance spectrometer for kinematically complete measurements of multiple particles emitted in RI-beam induced reactions. The SAMURAI spectrometer consists of a large gap superconducting dipole magnet, heavy ion detectors, neutron detectors, and proton detectors. What is special about the SAMURAI system is that projectile-rapidity protons or neutrons are detected with large angular and momentum acceptance in coincidence with heavy projectile fragments. With an effective combination of these equipments, the SAMURAI system allows us to perform various experiments: electromagnetic dissociation, various direct reactions, polarized deuteron induced reactions, and EOS studies. SAMURAI project is currently underway at RIBF. The construction of the superconducting dipole magnet will start in autumn 2010 and finish in spring 2011. The detectors are also being constructed in parallel. The first commissioning run will be performed in early 2012.

The COMBAS fragment separator

The basic ion-optical characteristics of the COMBAS fragment separator are analyzed. The momentum distributions of radioactive 6He, 8He, and 9Li nuclei obtained in the reaction 11B (33 A MeV, where A is the mass number of a particle) + 9Be (332.6 mg/cm2) have been investigated in forward-angle measurements on the COMBAS fragment separator. The momentum and angular (horizontal) acceptances of the COMBAS separator have been measured using the 6He, 8He, and 9Li beams. It has been ascertained that the images of the 6He, 8He, and 9Li nuclear beams in final achromatic focus of the separator Fa approximately twofold exceed the size of the beam on a producing target (input focus F0), at which the primary beam has a diameter of 6 mm. The intensities of 6He, 8He, and 9Li beams obtained at a 5-μA intensity of the primary 11B beam are 6.9 × 105, 2 × 104, and 4.7 × 105 particles/s, respectively. These values are sufficient for use in spectroscopic measurements. It is proposed that time-of-flight analysis of nuclear reaction products at the exit from the COMBAS separator will be used not only to measure the energy of transported particles over the whole operating range of the momentum acceptance, but also to identify them by mass A and charge Z without loss of these particles. The problem of reducing the count rates of detectors and further improvement of their energy resolution for detected particles can be solved by placing a high-resolution magnetic spectrometer past the second target accepting the secondary radioactive nuclear beams.

Performance of the improved larger acceptance spectrometer: VAMOS++

Measurements and ion optic calculations showed that the large momentum acceptance of the VAMOS spectrometer at GANIL could be further increased from ∼ 11 % to ∼ 30 % by suitably enlarging the dimensions of the detectors used at the focal plane. Such a new detection system built for the focal plane of VAMOS is described. It consists of larger area detectors (1000 mm×150 mm) namely, a Multi-Wire Parallel Plate Avalanche Counter (MWPPAC), two drift chambers, a segmented ionization chamber and an array of Si detectors. Compared to the earlier existing system (VAMOS), we show that the new system (VAMOS++) has a dispersion-independent momentum acceptance. Additionally, a start detector (MWPPAC) has been introduced near the target to further improve the mass resolution to ∼ 1 / 220 . The performance of the VAMOS++ spectrometer is demonstrated using measurements of residues formed in the collisions of 129Xe at 967 MeV on 197Au.

Beam transport line with scaling fixed field alternating gradient type magnets

A scaling fixed field alternating gradient (FFAG) accelerator provides large momentum acceptance despite the fact that magnetic guiding fields are constant in time. Optical functions are identical over the large momentum range as well. We have designed a straight beam transport line (BTL) using a scaling FFAG type magnet which has a field profile of ${y}^{k}$, where $y$ is the horizontal coordinate and $k$ is the magnetic field index. This FFAG-BTL has very large momentum acceptance and optical functions that, practically speaking, do not depend on momentum. We also designed a dispersion suppressor at the end of the line by combining unit cells with a different field index $k$ so that the momentum dependence of orbit location should be eliminated at the exit. An obvious application of this design is the BTL after an FFAG accelerator to a patient in a hadron therapy facility or to a target in general. This could be an alternative to the conventional BTL with solenoids or quadrupoles because of the strong focusing nature of a quadrupole and the large momentum acceptance like a solenoid.

A large acceptance spectrometer for reaccelerated radioactive beams at the proposed facility for rare isotope beams (FRIB) in the USA

A large acceptance ray-tracing spectrometer is being designed in order to fully exploit the research opportunities that will be offered by reaccelerated radioactive beams in the energy range 6–15MeV/nucleon from the proposed facility for rare isotope beams (FRIB) in the USA. The preliminary design of the spectrometer has been benefitted by several similar instruments in Europe (e.g. VAMOS, PRISMA, MAGNEX). The design is of QQD type (quadrupole–quadrupole–dipole) with two large-bore quadrupoles and a large-gap 70° bending magnet offering an angular acceptance around 50msr and a momentum acceptance of 10%. The maximum magnetic rigidity is 2.5T-m, providing a range appropriate for the most neutron-rich products expected from binary reactions with reaccelerated radioactive beams. The spectrometer will play an important role in nuclear structure and reaction studies, combined with gamma-ray and particle detector arrays around the target.

Broadband single-shot electron spectrometer for GeV-class laser-plasma-based accelerators

Laser-plasma-based accelerators can provide electrons over a broad energy range and/or with large momentum spread. The electron beam energy distribution can be controlled via accurate control of laser and plasma properties, and beams with energies ranging from approximately 0.5 to 1000 MeV have been observed. Measuring these energy distributions in a single shot requires the use of a diagnostic with large momentum acceptance and, ideally, sufficient resolution to accurately measure narrow energy spread beams. Such a broadband single-shot electron magnetic spectrometer for GeV-class laser-plasma-based accelerators has been developed at Lawrence Berkeley National Laboratory. Detailed descriptions of the design concept and hardware are presented, as well as a performance evaluation of the spectrometer. The spectrometer covered electron beam energies raging from 0.01 to 1.1 GeV in a single shot, and enabled the simultaneous measurement of the laser properties at the exit of the accelerator through the use of a sufficiently large pole gap. Based on measured field maps and third-order transport analysis, a few percent-level resolution and determination of the absolute energy were achieved over the entire energy range. Laser-plasma-based accelerator experiments demonstrated the capability of the spectrometer as a diagnostic and its suitability for measuring broadband electron sources.

The heavy-ion magnetic spectrometer PRISMA

PRISMA is a tracking magnetic spectrometer for heavy ions [1], designed for the A = 100 − 200, E = 5 − 10 MeV · A heavy-ion beams of the XTU Tandem-ALPI-PIAVE accelerator complex, and for possible use with future radioactive beams [2]. Its most interesting features are its large solid angle of 80 msr and momentum acceptance ± 10%, mass resolution 1/300 via TOF, energy resolution up to 0.1% and rotation around the target in a large angular range (−20° to +130°). These performances will be made possible by software reconstruction of the ion tracks using the position, time and energy signals from the entrance and focal plane detectors.

The dynamics of bunched laser-cooled ion beams at relativistic energies

We discuss the axial dynamics of laser-cooled relativistic C3+ ion beams at moderate bunching voltages. Schottky noise spectra measured at a beam energy of 122 MeV/u are compared to simulations of the axial beam dynamics. Ions confined in the bucket are addressed by the narrow-band force of a laser beam counter-propagating to the ion beam, while the laser frequency is detuned relatively to the cooling transition frequency in the rest frame of the bucket.At large detuning comparable to the momentum acceptance of the bucket, the axial dynamics can be well explained by the secular motion of individual non-interacting ions. At small detuning, corresponding to a small axial momentum spread Δpaxial/paxial < 10−6 of the ions, the measured Schottky noise spectra can no longer be explained using an approach which neglects the ion-ion interaction. Instead, the model fails when the ion bunch enters the space-charge dominatedregime, at which the mutual Coulomb-energy of the ions becomes comparable to the kinetic energy of the ions.

Proton–proton physics in ALICE

The ALICE experiment has several unique features which makes it an important contributor to proton–proton physics at the large hadron collider, in addition to its specific design goal of studying the physics of strongly interacting matter in heavy-ion collisions. The unique capabilities include its low transverse momentum (pt) acceptance, excellent vertexing, particle identification over a broad pt range and jet reconstruction. In this paper, a brief review of ALICE capabilities is given for studying bulk properties of produced particles which characterize the underlying events, and the physics of heavy-flavour, quarkonia, photons, di-leptons and jets.

Carbon/proton therapy: A novel gantry design

A major expense and design challenge in carbon/proton cancer therapy machines are the isocentric gantries. The transport elements of the carbon/proton gantry are presently made of standard conducting dipoles. Because of their large weight, of the order of $\ensuremath{\sim}100\text{ }\mathrm{\text{tons}}$, the total weight of the gantry with support structure is $\ensuremath{\sim}600\text{ }\mathrm{\text{tons}}$. The novel gantry design that is described here is made of fixed field superconducting magnets, thus dramatically reducing magnet size and weight compared to conventional magnets. In addition, the magnetic field is constant throughout the whole energy region required for tumor treatment. Particles make very small orbit offsets, passing through the beam line. The beam line is built of combined-function dipoles such as a nonscaling fixed field alternating gradient (NS-FFAG) structure. The very large momentum acceptance NS-FFAG comes from very strong focusing and very small dispersion. The NS-FFAG small magnets almost completely filled the beam line. They first make a quarter (or close to a quarter) of an arc bending upward and an additional half of a circle beam line finishing so that the beam is pointed towards the patient. At the end of the gantry, additional magnets with a fast response are required to allow radial scanning and to provide the required position and spot size. The fixed field combined-function magnets for the carbon gantry could be made of superconducting magnets by using low temperature superconducting cable or by using high temperature superconductors.

Emittance growth mechanisms for space-charge dominated beams in fixed field alternating gradient and proton driver rings

Systematic space-charge resonances are found to cause substantial emittance growth in proton driver rings and non-scaling fixed field alternating gradient (FFAG) accelerators. To avoid systematic nonlinear resonances, the phase advance of each cell must avoid π/2 and π/3. This limits the betatron tune range and the momentum acceptance for non-scaling FFAG accelerators. The emittance growth factor (EGF), defined as the ratio of final emittance to the initial emittance, is found to obey scaling properties in the linear space-charge tune shift parameter, the tune ramping rate, and stop-band widths of random quadrupole and skew-quadrupole errors.

Production of rare isotope beams with the NSCL fragment separator

Rare isotope beams at the National Superconducting Cyclotron Laboratory are produced by projectile fragmentation of medium energy primary beams on beryllium targets. The fragments of interest are selected by the A1900 high-acceptance fragment separator. The A1900 consists of superconducting magnets: four 45° dipoles and eight quadrupole triplets with a maximum magnetic rigidity of 6Tm. A momentum acceptance of Δp/p=5% with a solid angle acceptance of ΔΩ=8msr makes the A1900 one of the highest-acceptance separators in the world. Detector systems installed within the device allow tracking and unambiguous identification of individual isotopes. During the first three years of operation of the A1900, more than 200 different rare isotope beams approaching both the neutron and proton driplines have been delivered to experiments.

Summary of experimental studies, at CERN, on a positron source using crystal effects

A new kind of positron sources for future linear colliders, where the converter is an aligned tungsten crystal, oriented on the 〈111〉-axis, has been studied at CERN in the WA103 experiment with tertiary electron beams from the SPS. In such sources the photons resulting from channeling radiation and coherent bremsstrahlung create the e+e− pairs.Electron beams, of 6 and 10GeV, were impinging on different kinds of targets: a 4mm thick crystal, a 8mm thick crystal and a compound target made of 4mm crystal followed by 4mm amorphous disk. An amorphous tungsten target 20mm thick was also used for the sake of comparison with the 8mm crystal and to check the ability of the detection system to provide the correct track reconstruction. The charged particles coming out from the target were detected in a drift chamber immersed partially in a magnetic field. The reconstruction of the particle trajectories provided the energy and angular spectrum of the positrons in a rather wide energy range (up to 150MeV) and angular domain (up to 30°). The experimental approach presented in this article provides a full description of this kind of source. A presentation of the measured positron distribution in momentum space (longitudinal versus transverse) is given to allow an easy determination of the available yield for a given momentum acceptance. Results on photons, measured downstream of the positron detector, are also presented. A significant enhancement of photon and positron production is clearly observed. This enhancement, for a 10GeV incident beam, is of 4 for the 4mm thick crystal and larger than 2 for the 8mm thick crystal. Another important result concerns the validation of the simulations for the crystals, for which a quite good agreement was met between the simulations and the experiment, for positrons as well as for photons. These results are presented after a short presentation of the experimental setup and of the track reconstruction procedure.

Drift chamber with a c-shaped frame

We present the construction of a planar drift chamber with wires stretched between two arms of a c-shaped aluminum frame. The special shape of the frame allows to extend the momentum acceptance of the COSY-11 detection system towards lower momenta without suppressing the high-momentum particles. The proposed design allows for construction of tracking detectors covering small angles with respect to the beam, which can be installed and removed without dismounting the beam-pipe. For a three-dimensional track reconstruction a computer code was developed using a simple algorithm of hit pre-selection.

Biological effects of radioactive 9C-ion beams on cells

The distinguishing feature and current technique progress of tumor treatment with heavy-ion beams is introduced in the paper. Additional superiority to tumor treatment from a radioactive ion beam (RIB) is emphatically discussed. The experimental research of the radioactive 9C-ion beams aimed at tumor treatment at Heavy Ion Medical Accelerator in Chiba (HIMAC), National Institute of Radiological Sciences (NIRS), Japan is described in detail, including production of the beams, optimization of parameters, distribution of depth dose, survival effect of cell and comparison of RBE between 9C- and 12C-beams. Results show that under 40 mm thick Beryllium target and 10 mm thick aluminum degrader at full (5%) momentum acceptance, the production rate and purity of the produced 9C-beams are 9.07×l06 and 82.88% respectively with the primary 12Cbeams of 430 MeV/u and 1.8×l09 pps. A uniform irradiation field with homogeneity up to 89.6% inside central area 10 mm in diameter is obtained by using spot scanning. In this case, the dose rate at the entrance is 0.5 Gy/h. In survival experiment of cells, the average relative biological effectiveness (RBE) of 9C-beams is 5.28 and 2.93 for 12C-beams in the region around Bragg peak. The RBE of 9C-beams is 1.8 times higher than that of 12C-beams. It indicates that cell-killing efficiency of 9C-beams is stronger than that of {u12}C-beams. 9C-beams are more efficacious for tumor treatment than 12C-beams.