Search Results (24 total)

The four electron stripping stages leading to fully stripped gold ions in the Relativistic Heavy Ion Collider (RHIC) are briefly described. The third stripper, which removes 46 electrons from the Au³¹⁺ ions leading to heliumlike Au⁷⁷⁺, offers the greatest challenges in terms of energy loss and induced energy spread. These problems are described in detail as well as recent advances in the design and performance of this stripper. Measurements performed with several carbon and aluminum strippers show general agreement with a semiempirical model but small systematic deviations suggest that some model adjustments may be in order. The best performance is predicted and obtained with a combined carbon-aluminum foil system. Measurements showing the enhanced performance in the alternating gradient synchrotron are described. The stripper that removes the last two electrons has also been improved and the results of relevant calculations and measurements are presented.

Acceleration of polarized protons in the energy range of 5 to 25 GeV is challenging. In a medium energy accelerator, the depolarizing spin resonances are strong enough to cause significant polarization loss but full Siberian snakes cause intolerably large orbit excursions and are also not feasible since straight sections usually are too short. Recently, two helical partial Siberian snakes with double pitch design have been installed in the Brookhaven Alternating Gradient Synchrotron (AGS). With a careful setup of optics at injection and along the energy ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances otherwise encountered during acceleration to maintain a high intensity polarized beam in medium energy synchrotrons. The observation of partial snake resonances of higher than second order will also be described.

Two partial Siberian snakes were used to avoid all the spin imperfection and vertical intrinsic resonances in the alternating gradient synchrotron (AGS) at Brookhaven National Laboratory. However, the horizontal betatron motion can cause polarization loss resulting from the nonvertical stable spin direction in the presence of two partial snakes. This type of resonance, called a horizontal intrinsic spin resonance, was observed and systematically studied in the AGS. A simplified analytic model and numerical simulation have been developed to compare with experimental data. Properties of the horizontal intrinsic resonance are discussed.

Errors in delivering a uniformly distributed radiation dose to biological and material samples exposed to charged particle beams are a significant problem for experimenters. In this paper, we discuss data collected on the uniform beam distributions produced for NASA’s Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), using a method that was conceived theoretically and tested experimentally at BNL. This method [N. Tsoupas , Nucl. Sci. Eng. 126, 71 (1997)] of generating uniform beam distributions on a plane normal to the beam’s direction relies only on magnetically focusing the transported beam; no collimation of the beam is required or any other type of interaction of the beam with materials other than the target material. The method compares favorably with alternative methods of producing such distributions, and it can be applied to the entire energy spectrum of charged particle beams that are delivered to the NSRL’s experiments by the Booster for the Alternating Gradient Synchrotron at BNL.

The Brookhaven Relativistic Heavy Ion Collider (RHIC) has been providing collisions of polarized protons at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during acceleration from injection to 100 GeV. However, the intrinsic spin resonances beyond 100 GeV are about a factor of 2 stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were first accelerated to the record energy of 205 GeV in RHIC with a significant polarization measured at top energy in 2005. This Letter presents the results and discusses the sensitivity of the polarization survival to orbit distortions.

An 11.4% partial Siberian snake was used to successfully accelerate polarized protons through a strong intrinsic depolarizing spin resonance in the Alternating Gradient Synchrotron (AGS). No noticeable depolarization was observed. This opens up the possibility of using a 20% to 30% partial Siberian snake in the AGS or other medium energy proton synchrotrons to overcome all weak and strong depolarizing spin resonances.

A spin matching method to cure intrinsic coupled spin resonances in the AGS is proposed and explored using an extension of the existing DEPOL program algorithm. The extension of DEPOL to handle linear coupling in the polarized beam acceleration is documented. Data collected from recent polarized proton experiments in the AGS are compared with the predictions derived from the extended DEPOL program.

Response is made to J. A. MacLachlan's preceding Comment [Phys. Rev. ST Accel. Beams 4, 017001 (2001)]. We are gratified to see that high quality simulations, as presented by MacLachlan, verify our experimental results.

This paper summarizes the low-loss design for the Spallation Neutron Source accumulator ring [“Spallation Neutron Source Design Manual” (unpublished)]. A hybrid lattice consisting of FODO arcs and doublet straights provides optimum matching and flexibility for injection and collimation. For this lattice, optimization focuses on six design goals: a space-charge tune shift low enough (below 0.15) to avoid strong resonances, adequate transverse and momentum acceptance for efficient beam collimation, injection optimized for desired target beam shape and minimal halo development, compensation of magnet field errors, control of impedance and instability, and prevention against accidental system malfunction. With an expected collimation efficiency of more than 90%, the uncontrolled fractional beam loss is expected to be at the 10^-4 level.

By modulating the rf voltage at near twice the synchrotron frequency, the longitudinal bunch shape can be modulated. This method can be used to shorten bunches. We show experimentally that the bunch shape can be modulated while preserving the longitudinal emittance when the rf voltage modulation is turned on adiabatically. Experimental measurements will be presented along with theoretical predictions.

A new type of spin depolarization resonance has been observed at the Brookhaven Alternating Gradient Synchrotron (AGS). This spin resonance is identified as a strong closed-orbit sideband around the dominant intrinsic spin resonance. The strength of the resonance was proportional to the 9th harmonic component of the horizontal closed orbit and proportional to the vertical betatron oscillation amplitude. This “hybrid” spin resonance cannot be overcome by the partial snake at the AGS, but it can be corrected by the harmonic orbit correctors.

A coherent spin resonance excited by an rf dipole was used to overcome depolarization due to intrinsic spin resonances at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. We found that our data are consistent with a full spin flip of a polarized proton beam, without emittance growth, at Gγ  =  12+ν_z and 36-ν_z, by adiabatically exciting a vertical coherent betatron oscillation using a single rf dipole magnet. The interference pattern observed between the intrinsic spin resonance and the coherent spin resonance agrees well with multiparticle spin simulations based on a simple two-resonance model. The interference pattern can be used for beam diagnostics.

Data obtained by the associated production of Λ hypernuclei through the (π⁺,K⁺) reaction are presented for a wide range of mass numbers. The special features which make this reaction useful are pointed out. The reaction is shown to be an excellent probe of Λ single-particle states, as demonstrated by the excitation of deeply bound states which are interpreted as the weak coupling of a Λ to neutron-hole states of the core. The Λ binding energies and ground-state production cross sections for _Λ⁹Be, _Λ¹²C, _Λ¹⁶O, _Λ²⁸Si, _Λ⁴⁰Ca, _Λ⁵¹V, and _Λ⁸⁹Y are presented.

A search for nuclear-bound states of the η meson has been carried out. Targets of lithium, carbon, oxygen, and aluminum were placed in a π⁺ beam at 800 MeV/c. A predicted η bound state in ¹⁵O^*(E_x≈540 MeV) with a width of ≅ 9 MeV was not observed. A bound state of a size ⅓ of the predicted cross section would have been seen in this experiment at a confidence level of 3σ(P>0.9987).

Near-barrier excitation functions for 2n, 3n, 4n, 5n, 2n1p, 3n1p, and 4n1p evaporation from ²⁰⁴Rn following the fusion of ³⁵Cl+¹⁶⁹Tm, ⁴⁸Ti+¹⁵⁶Gd, and ⁶⁵Cu+¹³⁹La are compared between reactions and with statistical decay codes. First and second gamma multiplicity moments were obtained for all three systems at 50 MeV excitation energy. General agreement with statistical decay code predictions is found in all cases.

High-resolution total reaction excitation functions for ¹⁶O+ ¹²C and detailed angular distributions for the reaction ¹²C(¹⁶O,α)²⁴Mg have been measured. The interplay between (fifteen) resonance amplitudes and l-window (background) amplitudes is emphasized. Spin assignments, obtained from the α₀ data, are dominated by values of 8ℏ and 9ℏ while the grazing partial wave varies from l=5 to l=10 over the energy range studied. Elastic widths for the low-energy resonances indicate a dinuclear molecular nature; higher-energy resonances appear to originate from a more complex nuclear configuration.

Evidence for the presence of alpha-particle clustering in ²¹⁸Ra comes from a number of observables: binding energy, S_2n, Q_α, E_x(J^π), θ_α², and F_α. That this clustering is a signature for the new dipole collectivity suggested by Iachello and Jackson follows from observation of simultaneous enhancement of selected E 1, E 2, and E 3 deexcitation transition matrix elements; of these the E 1 enhancement is most pronounced as would be expected for dipole collectivity.

The magnetic moments of the 2₁⁺ states in ^186,188Os and ^194,196Pt isotopes have been measured by the transient field technique at ion recoil velocities 1.6≲v / v₀≲2.8. The transient field was assumed to follow the parametrization proposed by Shu et al. for ions in the range 8<Z<62. The g factors obtained for osmium isotopes g(¹⁸⁶Os)=0.262(15) and g(¹⁸⁸Os)=0.300(15) are in excellent agreement with independent Mössbauer and external field measurements, indicating that the adopted parametrization is valid up to Z=76. However, the same analysis yields g factors for the platinum isotopes which are smaller than previously reported: g(¹⁹⁴Pt)=0.203(6) and g(¹⁹⁶Pt)=0.213(21).

NUCLEAR REACTIONS ^186,188Os(³²S, ³²S′)^186,188Os(2₁⁺), ^194,196Pt(³²S, ³²S′)^194,196Pt(2₁⁺); E_s∼80 MeV; enriched targets; measured W(θ,B,∞) through polarized iron; deduced g(2₁⁺).

The magnetic moments of the 2₁⁺ states of ^120-130Te isotopes have been measured by the thin-foil transient field technique. The resulting magnetic moments are discussed in the light of predictions of the vibrational, the quasiparticle, and the interacting boson approximation models.

NUCLEAR REACTIONS ^120-130Te (³²S, ³²S′) ^120-130Te(2₁⁺); E_S∼80 MeV; enriched targets; measured W(θ,B,∞) through polarized iron; deduced g(2₁⁺).

Angular correlations in the ⁷⁰Ge(p,p^′γ)⁷⁰Ge reaction have been measured for two of the five substructures nested in the reported 1 / 2⁺ intermediate structure in ⁷¹As centered at E_p=5.05 MeV. The spins of both substructures were determined as being 5 / 2 or greater casting doubt on the interpretation of this cluster of states as an example of intermediate structure.

NUCLEAR REACTIONS ⁷⁰Ge(p,p^′γ)⁷⁰Ge, E=4.95 to 5.19 MeV. Deduced spins of resonances at E=5.04 and 5.14 MeV. Enriched target.

Evaporation residues from the fusion of ³²S and ¹¹²Sn at E_³²S=160 MeV were studied using an energy-mass spectrometer. The velocity selector of the energy-mass spectrometer was first utilized to measure summed fusion products as a function of velocity setting and reaction angle. In-flight mass separation of the fusion products with the energy-mass spectrometer identified masses 141, 140, and 139 from the evaporation of three to five nucleons from the ¹⁴⁴Dy compound nucleus. Absolute cross-section measurements are compared to theoretical predictions of the statistical evaporation model. Velocity, angular and charge state distributions of evaporation residues are also compared to calculated values.

NUCLEAR REACTIONS ³²S + ¹¹²Sn fusion, E=160 MeV, σ(v, θ). Compared mass, velocity and angular distributions of evaporation residues to statistical particle evaporation theory. Compared charge-state distribution of fusion products to semiempirical predictions.

Absolute differential cross sections of the ²⁸Si(p,p^′)²⁸Si^* (1.78 MeV) reaction have been measured for 12 scattering angles and at 88 different energies between bombarding energies of 3.0 to 5.2 MeV. In addition, 53 absolute cross sections of the ²⁸Si(p,p^′γ)²⁸Si angular correlations in the spin-flip geometry were also measured over the same energy region. From these and other data, the partial proton decay widths and phases of 14 resonances in ²⁹P were determined between excitation energies of 5.50 and 7.90 MeV.

NUCLEAR REACTIONS ²⁸Si(p,p₁), measured σ(E,θ), E=3.0-5.2 MeV. ²⁸Si(p,p₁γ), measured p-γ correlations in the spin-flip geometry, determined partial proton decay widths, Γ_lj, for 14 resonances. Calculated reduced widths.

Excitation functions have been measured for inelastic proton scattering from the 1.78 MeV, 2⁺ first excited state of ²⁸Si between 3.1 and 5.7 MeV. Two previously unidentified resonances corresponding to states in ²⁹P with excitation energies of 6.577 and 7.272 MeV have been observed. Triple angular correlations in the Goldfarb-Seyler geometry have been measured as a function of energy over all the resonances observed in the inelastic excitation function. Information obtained from the angular correlation data has been combined with previous information concerning these states to allow J^π assignments for 9 of the 11 states observed.

NUCLEAR REACTIONS ²⁸Si(p,p₁), measured σ(E), E=3.1-5.7 MeV. ²⁸Si(p,p₁γ), measured p-γ correlations, deduced J^π of ²⁹P levels.