High-resolution Magnetic Spectrometer Research Articles

Measurement of the exclusive D( p, e+e−) 3He and D( p, γ) 3He reactions at 98 and 176 MeV

A high resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive ( p, e + e −) and ( p, γ) reactions on deuterium at 98 and 176 MeV. The ( p, e + e −) cross sections, obtained at 40° and 80°, are compared with the corresponding data for the ( p, γ) reaction measured with the same apparatus. At small virtual photon masses the ( p, e + e −) cross sections show significant enhancement over what is expected from model calculations, a behaviour which has earlier been observed also for the 11B( p, e + e −) 12C reaction.

Hypernuclear physics with stopped K− at DAΦNE

The FINUDA experiment will start data taking in 1997 to study hypernuclear physics by a large acceptance. high resolution magnetic spectrometer at DAΦNE, the Frascati o-factory. Physics motivations and goals besides the expected performances are described.

Penetration of relativistic heavy ions through matter

New heavy-ion accelerators covering the relativistic and ultra-relativistic energy regime allow us to study atomic collisions with bare and few-electron projectiles. High-resolution magnetic spectrometers are used for precise stopping-power and energy-loss straggling measurements. Refined theories beyond the Born approximation have been developed and are confirmed by experiments. This paper summarizes the large progress in the understanding of relativistic heavy-ion penetration through matter, which has been achieved in the last few years.

The three-spectrometer facility at the Mainz microtron MAMI

A set-up of three high-resolution magnetic spectrometers, for simplicity named A, B and C, has been built as the central facility for the precise determination of double and triple coincidence cross sections of hadron knock-out and meson production through the scattering of electrons at the Mainz microtron MAMI. The spectrometers A and C with point-to-point optics in the dispersive plane and parallel-to-point optics in the non-dispersive plane have a solid angle of 28 msr and a momentum acceptance of 20 and 25%, respectively. They each consist of a quadrupole, a sextupole and two dipole magnets, reaching maximum momenta of 735 and 550 MeV/c, respectively. The spectrometer B has a solid angle of 5.6 msr and a somewhat reduced momentum acceptance of 15%, but it reaches a maximum momentum larger than that of the MAMI electron beam (855 MeV/c). It consists of a single-clamshell dipole magnet with point-to-point optics in both planes. Each spectrometer is equipped with a position-sensitive detector system consisting of four planes of vertical drift chambers, two planes of plastic scintillators and a threshold gas Cherenkov detector. The operational experiences demonstrate that all three spectrometers exceed the specifications. Selected results of double (e, e′ x) and triple (e, e′ x 1 x 2) coincidence experiments, x 1 and x 2 standing for charged hadrons, are presented, which demonstrate the performance of the whole set-up.

The FINUDA experiment at DAΦNE

FINUDA is a large acceptance, high resolution magnetic spectrometer dedicated to hypernuclear physics. The experiment is in an advanced stage of construction and will run in 1997 at DAΦNE, the Frascati o-Factory. Motivations, physics goals and expected performance are illustrated.

Hypernuclear physics with the FINUDA spectrometer at DAΦNE

The FINUDA experiment will start data taking in 1997 to study hypernuclear physics by a large acceptance, high resolution magnetic spectrometer at DAΦNE, the Frascati φ-factory. Physics motivations and goals besides the expected performances are described.

Radiative proton capture to discrete states in 31N at 98 and 176 MeV

A high resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p,γ) reaction on 12C at 98 and 176 MeV. We present angular distributions of the differential cross section for transitions to the ground state and the first three excited states of 13N. The distributions from these four states are compared with predictions from a microscopic continuum shell model calculation using a realistic finite-ranged effective interaction with tensor components. In general, reasonable agreement is obtained for reactions to states described by p shell single particle wave functions, but poor agreement is obtained for transitions described by sd shell single particle wave functions. Nevertheless we find, however, that the dominant reaction mechanism is a direct capture process. We also compare the (p,γ) data with existing data on the exclusive (p,π) reaction at 185 MeV revealing notable differences between the two reactions.

Methane dehydrogenation and aromatization in the absence of oxygen on [formula omitted]: A study on the interaction between Mo species and HZSM-5 by using 27Al and 29Si MAS NMR

By using a high-resolution solid state nuclear magnetic resonance spectrometer with 27Al and 29Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al 2(MoO 4) 3. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by 27Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The Si Al ratio measured from 29Si MAS NMR further confirms the dealumination process observed by 27Al MAS NMR. The MAS NMR results give us an evidence that Al 2(MoO 4) 3 crystallites are much less active for the reaction.

The 112Cd laboratory: An extension. E0 strengths, multiphonon states and coupled vibrations

The structure of 112Cd was investigated using the 111Cd( n th, γ) and 110Pd(α,2n) reactions. High resolution crystal and magnetic spectrometers as well as different Compton-suppressed spectrometers were used. The results were combined with published data resulting in a complete level scheme over a large range of spins and excitation energies. The interpretation of the data was performed in the framework of the interacting boson model (IBM). A special effort was put in the interpretation of E0 data and an attempt was made to identify multiphonon and 2 1 + ⊗ 3 1 − states.

First measurement of the exclusive ( p, e+e−) reaction

We present the first data on the exclusive ( p, e + e −) reaction in a nucleus. Cross sections for populating the ground state and first excited state in the residual nucleus are presented for the reaction 11B( p, e + e −) 12C at 98 MeV. The e + e − momentum vectors were measured with a high-resolution magnetic pair spectrometer. The distributions of the virtual photon invariant mass and of the direction of the electron in the virtual photon rest system are compared with a simple single-nucleon model. The ( p, e + e −) cross sections are compared with corresponding data for the ( p, γ) reaction obtained with the same apparatus. The ( p, e + e −) cross sections show substantial enhancement over what is expected from the simple model.

Electroproduction of neutral pions on the proton

The double-differential coincidence cross section for the reaction 1H(e,e′π 0)p has been measured at Q 2 = 0.1 (GeV/ c) 2 for a range in the invariant energy W of 1 to 14 MeV above threshold in order to determine the s-wave multipoles E 0+ and L 0+. The experiment was performed with a 525 MeV electron beam of the Amsterdam Pulse Stretcher and a cryogenic hydrogen target. The scattered electron and the recoiling proton were detected in two high-resolution magnetic spectrometers. By using a recent LET prediction for the relevant combinations of p-wave multipoles, values for E 0+ and L 0+ were extracted from the cos ϑ π ∗ and cos φ π ∗ dependent terms in the cross section. The data are compared to calculations from Chiral Perturbation Theory and from several Lagrangian models. All models give a fair to good description of L 0+. ChPT gives also a good description of E 0+, but the Lagrangian models tend to underestimate its value. The data for the angle-independent part of the cross section indicate that the value for the 2 M 1+ + M 1− combination of p-wave multipoles is overestimated by a recent ChPT prediction.

Study Mo/HZSM-5 Catalysts by NMR

By using high-resolution solid state Nuclear Magnetic Resonance spectrometer with Al-27 and Si-29 probes, the interaction between Mo species and HZSM-5 of Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminium in the zeolite can be easily extracted by the introduction of Mo species. The extract ability of framework aluminium by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al-2(MoO4)(3). The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The MAS NMR results give us an evidence that Al-2(MoO4)(3) crystallites are much less active for the reaction.

Radiative proton capture to discrete states in 12C at 98 and 176 MeV

A high-resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p, γ) reaction on 11B at 98 and 176 MeV. We present angular distributions of the differential cross section for transitions to the ground and first three excited states of 12C. The distributions from the three lowest lying states are compared with predictions from a microscopic continuum shell-model calculation using a realistic finite-ranged effective interaction with tensor components. Exchange current effects are examined in detail as both Δ(1232) isobar and pion exchange currents are rigorously included. In general, a good theoretical description of the data is obtained. The predominant reaction mechanism involves photon emission by the nucleonic one-body current.

Design and performance of a high resolution electrospray ion source for a magnetic sector mass spectrometer with a heated capillary inlet

The design and performance of an electrospray ion source for a high resolution magnetic sector mass spectrometer that utilizes a heated capillary has been presented. Low pressure, high sensitivity, stable electrospray, low flow rates, and low electronic noise were important factors in achieving high resolution electrospray mass spectrometry. A unit mass resolution has been achieved for biomolecules with MW > 12,000, and an accuracy of 1.4 ppm has been achieved for the average molecular weight of bovine insulin.

The three-spectrometer setup for (e,e'x) coincidence experiments at the Mainz microtron MAMI

A setup of three high-resolution magnetic spectrometers has been built up as the central facility for the precise determination of electron scattering cross sections in coincidence with hadrons. The operational experiencies with two of the spectrometers, A and B, demonstrate that both spectrometers exceed the specifications. With A and B, a series of ( e, e′x ) coincidence experiments were successfully performed. The third spectrometer, C, will be ready for operation in late autumn 1994.

The three-spectrometer setup for (e,e'x) coincidence experiments at the Mainz microtron MAMI

A setup of three high-resolution magnetic spectrometers has been built up as the central facility for the precise determination of electron scattering cross sections in coincidence with hadrons. The operational experiencies with two of the spectrometers, A and B, demonstrate that both spectrometers exceed the specifications. With A and B, a series of (e, e′x) coincidence experiments were successfully performed. The third spectrometer, C, will be ready for operation in late autumn 1994.

Determination of metabolites of a novel platinum anticancer drug JM216 in human plasma ultrafiltrates

The present study describes the application of on-line liquid chromatography-electrospray ionisation in conjunction with a high resolution magnetic sector mass spectrometer to identify metabolites of a platinum(IV) anticancer drug JM216 bis(acetato)amminedichloro(cyclohexylamine)platinum(IV)] in human plasma. Four metabolites were identified following incubation of JM216 in human plasma: JM118 [amminedichlorocyclohexylamineplatinum(II)], a platinum(II) complex; JM383 [bis(acetato)amminedihydroxo(cyclohexylamine)platinum(IV)]; JM518 [bis(acetato)amminechloro(cyclohexylamine)hydroxoplatinum(IV)] and its isomer JM559. The platinum complexes mass spectra were dominated by the natriated [M + Na] + ion. Elemental compositions of these natriated ions were confirmed by accurate mass measurement on a magnetic sector mass spectrometer in the course of LC/MS analysis. This study demonstrates the capability of direct LC-ESI/MS with accurate mass measurement for analysis of platinum complexes in biological samples. Our results suggest that LC-ESI/MS is a powerful technique for structure elucidation of novel metabolites, and could make valuable contributions to drug metabolism research.

Energy loss straggling of 0.5-MeV protons specularly reflected from a SnTe(001) surface

Energy spectra of 0.5-MeV protons specularly reflected from a SnTe(001) surface are measured with a high-resolution magnetic spectrometer ( ΔE E ∼ 0.1% ). Position-dependent energy loss straggling is derived from the observed energy distributions of the reflected protons. The obtained position-dependent straggling is compared with the theoretical ones caused by plasmon excitations and single electron collisions. The agreement between the experimental and theoretical results is reasonably good. Contrary to the energy loss itself, contribution of the single electron collisions is dominant for the energy loss straggling.

Fragmentation and splitting of Gamow-Teller resonances in Sn(3He,t)Sb charge-exchange reactions, A=112-124.

Fragmentation and splitting of the Gamow-Teller (GT) strength has been observed in a systematic study of the ${(}^{3}$He,t) charge-exchange reaction at E${(}^{3}$He)=200 MeV over the entire range of stable Sn isotopes. Triton energy spectra were observed with a high-resolution magnetic spectrometer at angles near \ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{} where \ensuremath{\Delta}L=0 transitions are enhanced. Excitation energies, widths, 0\ifmmode^\circ\else\textdegree\fi{} cross sections, and strengths B(GT) were determined. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components, expected to be dominant near A=118 at the onset of the filling of the 1${\mathit{h}}_{11/2}$ neutron orbital, could not be observed. This may be due to the fact that the total widths of the resonances of 5--6 MeV exceed the predicted splitting. A comparison of the 0\ifmmode^\circ\else\textdegree\fi{} cross sections for the transitions to the Gamow-Teller resonances and the isobaric analog states leads to strengths B(GT) for the main Gamow-Teller components of typically 65% of the sum-rule value of 3(N-Z). Three to four additional Gamow-Teller fragments (``pygmy resonances'') were observed in all final nuclei at lower excitation energies. The excellent energy resolution of the experiment made it possible to observe a pronounced fine structure in these low-lying resonances which is believed to be due to coupling to two-particle--two-hole doorway states. Also seen with all target nuclei was a systematic sequence of strong ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${1}^{+}$ states near the ground states in all Sb isotopes (${\mathit{E}}_{\mathit{x}}$=0 to 220 keV). In addition, strong \ensuremath{\Delta}L=1 resonances were observed in all nuclei at excitation energies of typically 20 MeV. Furthermore, nonresonant background from quasifree charge exchange was observed. An average of \ensuremath{\sim}85% of all excess neutrons seems to contribute to this background in approximate agreement with results from (e,e'p) experiments.

High resolution study ofhyperon-nucleon interactions by associated strangeness production in pp collisions

The associated strangeness production in pp collisions was studied at bombarding energies of 2.3 and 2.7 GeV by detecting the outgoing K + particles with a high resolution magnetic spectrometer at forward angles up to 23.5° laboratory angle. The kaons were separated from an immense background of protons and pions by a highly resolving TOF electronics addition to vetoes from Čerenkov detectors utilizing either β differing Čerenkov light cones in lucite or different thresholds for light production in aerogel. The hyperon-nucleon missing mass spectra obtained show strong deviations from pure phase space which is ascribed to final state interactions of the pΛ and the Nσ systems. The structures found are discussed and compared with results from K −d → π −YN experiments, with theoretical calculations in the frame of OBE models, and with the prediction of sharp strange dibaryon resonances from several quark-bag models.