C.T.A.M. de Laat

An improved parametrization of the optical potential for pionic atoms

We extended the parametrization of the phenomenological optical potential for pionic atoms by allowing for an isospin-dependence of the absorption parameters. Least squares fits to the 140 selected pionic atom data are performed. The new parameter set indicates a significant isospin dependence and is able to provide a simultaneous description of shifts and widths for the previously problematic deeply bound 3d-orbits in elements such as 181Ta, natRe, natPt, 197Au, 208Pb and 209Bi.

Anomalous strong interaction shifts and widths of the 3d state in pionic Pt and Au

Abstract The poinic 4f → 3d X-ray transitions in Pt and Au have been observed. The strong interaction monopole shifts ϵ o and widths Γ o of the 4f and 3dd levels have been deduced. For the pionic 4f levels standard optical potentials predict the experimental values quite well, whereas the deeper bound 3d states have shifts and widths that are smaller by a factor of about two than the theoretical predictions.

A study of the strong interaction effects on pionic 3d and 4f levels in 181Ta, natRe, natPt, 197Au, 208Pb, 209Bi and 237Np

Abstract The pionic X-ray spectra of 181 Ta, nat Re, nat Pt, 197 Au, 208 Pb, 209 Bi and 237 Np have been investigated to obtain data for a systematical study of the pionic 3d and 4f levels. In order to reduce background the experimental method has been improved by using an array of Compton suppression BGO-shields and neutron time-of-flight discrimination. The widths of the pionic 3d levels are observed to be narrower by a factor 1.5 than theoretical predictions obtained with standard optical potentials. A deviation is also found for the strong interaction quadrupole shift, ϵ 2 , for both the 4f and 3d orbits. A possible explanation for the smaller width, Γ 0 (3 d ), can be found by extending the parametrization of the optical potential with absorption terms.

Strong interaction effects in pionic 208Pb

Abstract The X-ray spectrum of pionic 208 Pb has been measured. The deduced values of the strong interaction monopole shift with respect to the point Coulomb energy are ϵ 0 (4f) = 1.49±0.02 keV and ϵ 0 (3d) = 19.4±1.2 keV. The observed s strong interaction absorption widths of this spherical nucleus are found to be Γ 0 (4f) = 1.25±0.02 keV and Γ 0 (3d) = 47.0±3.6 keV. Important in the analysis of the pionic 4f level is the intensity balance for this level, giving an additional check on the measured absorption width of the pionic 4f level. For the more peripheral 4f state the measured strong interaction shifts and widths are well explained by standard optical model calculations. The values for the 3d state, however, are not in agreement with these calculations.

The quadrupole moment and strong interaction parameters from muonic and pionic X-ray studies of 237Np

Abstract The X-ray spectrum of muonic and pionic 237Np has been investigated with muons and pions stopped in a NpO2 target. The nuclear spectroscopic quadrupole moment was determined to be Q=3.886±0.006 b from the splittings of the muonic 5g→4f hyperfine complexes. The B(E2)↓-values for the first and second excited states were evaluated as 3.17±0.08 and 2.77±0.10 e2b 2, respectively. A comparison between the muonic and pionic 5g→4f hyperfine complexes yields the strong interaction parameters for the pionic 4f state. For the first time a change of sign as function of Z for the strong interaction quadrupole shift ϵ2(4f) has been observed. The standard optical model predictions agree reasonably well with the measured strong interaction monopole optical shift, ϵ0(4f), and width, Г 0 (4f) , while they disagree with the experimental value for ϵ2. A stronger s-wave repulsion in the potential could explain this effect.

A time projection chamber with microstrip read-out

Abstract The design and testing of a novel detector for heavy-ion physics in the intermediate-energy regime is described. This detector consists of a large drift chamber with microstrip read-out in combination with thick plastic scintillators. With this system particle identification and energy determination with high spatial resolution and multiple hit capacity is achieved.

Remote handling of TEXTOR diagnostics using CORBA as communication architecture

Abstract At the Forschungszentrum Julich, an upgrade of the existing distributed system for data acquisition (DAS) at the fusion experiment TEXTOR94 is under development. DAS is currently restricted to VAX/VMS and DECNET based communications, but it is planned to add UNIX based systems, and to open the local network for an improved wide area network access for remote operations. Therefore, the DAS system is to be equipped with a suitable client/server interface, which is able to cope with the various computer platforms and operating systems involved. For this purpose, the common object request broker architecture (CORBA) will be used. CORBA is an object oriented, standardized architecture for distributed systems, which provides a high degree of modularity in software design and allows for flexible implementations. It is to act as a connecting link between the existing system and new extensions. In order to provide the desired client/server functionality for the data acquisition tasks, the components of the system (diagnostic, database, etc.) are modelled by CORBA interfaces. Processes for diagnostic control and data readout in the existing OpenVMS systems are aimed at to be accessible by CORBA server implementations. The corresponding client implementations will be developed for the operating system platforms most frequently used at TEXTOR94. Communication between clients and server will be based on TCP/IP and are to be managed by CORBA. By this standardized way, remote control of diagnostic instrumentation becomes possible in a multiplatform computer and wide area network environment. At a later stage it is intended to integrate the system into a ‘virtual control room’ environment, which should enable the participation of cooperating institutions in the full experimental program of TEXTOR94.

Deeply bound 1s and 2p states in pionic atoms

Abstract New results were obtained on pionic 1s levels in 24Mg, 27Al and 28Si, on 2p states in 93Nb and natRu, as well as on 3d states in 93Nb, natRu, natAg and natCd. For the first time the predicted repulsive shifts for the pionic 2p level have been observed. The following values were obtained for the strong-interaction shifts and widths (all values in keV); 24Mg: e1s0 = −80.5 ± 0.6 and Γ1s0 = 24.3 ± 1.6; 27Al: e1s0 = −115.5 ± 1.4 and Γ1s0 = 28.8 ± 1.2, 28Si: e1s0 = −131.6 ± 2.0 and Γ1s0 = 41 ± 4;93Nb: e2p0 = −11 ± 3, Γ2p0 = 64 ± 8, e3d0 = 0.74 ± 0.02 and Γ3d0 = 0.402 ± 0.016; natRu: e2p0 = −48 ± 7, Γ2p0 = 77 ± 24, e3d0 = 1.39 ± 0.08 and Γ3d0 = 0.75 ± 0.08; natAg: e3d0 = 1.94 ± 0.07 and Γ3d0 = 1.44 ± 0.05 and natCd: e3d0 = 2.14 ± 0.09 and Γ3d0 = 1.65 ± 0.07. The results are in reasonable agreement with the predictions of the standard optical potentials.

Muon attachment in prompt fission of237Np

The probabilities of muon attachment to fission fragments in the prompt fission of237Np have been determined as a function of fragment mass and total kinetic energy release in a (μ−,f1f2e−)-coincidence measurement. A strong dependence of the attachment probability on the fragment mass is observed. The experimental results are compared with theoretical predictions.

The probability of prompt and delayed fission of muonic237Np

Fission fragments from the reaction237Np(μ−,γ,f) have been measured in coincidence with muonic X-rays. The efficiency of the fission fragment detector is determined from (μ−,γ,f)-data of the same experiment. The total fission probability perμ-stopPt has been measured as well as the fission probabilities Pf of the non-radiative muonic (3d→1s)- and (2p→1s)-transitions; the latter has been divided into two parts leading to different mean excitation energiesE:Pt=(54±17)%,Pf(3d→1s)=(41±21)%,Pf(2p→1s,E=6.218 MeV)=(61±19)%, andPf(2p→1s,E=6.525 MeV)=(57±18)%. The influence of the muon on the fission barrier is discussed. The fission probability after muon capture is compared with a calculated value using a distribution of nuclear excitation energies following muon capture and the fission probability as measured in a238U(3He,αf)-reaction.