H. Matthäy

The angular distribution of final state interacting n-p pairs in the reaction p+d → p+p+n

Abstract The three-particle reaction p+d → p+p+n has been investigated systematically at a deuteron bombarding energy of 52.3 MeV. Kinematically complete experiments have been carried out by detecting the two protons in coincidence. The kinematical conditions were chosen predominantly to observe the effect of the n-p final state interaction. All the data are analysed in terms of the Watson-Migdal model of final state interactions. At specific kinematical conditions the impulse approximation turns out to be a more general and better description. An angular distribution was obtained for the production of singlet and triplet final state interacting n-p pairs with zero relative energy in the n-p subsystem. A relation is derived which connects the measured angular distribution for triplet final state interaction in the three-nucleon reaction quantitatively with the angular distribution of elastic p-d scattering. The systematic study proves that values of the nucleon-nucleon scattering lengths can be extracted with a high degree of reliability from three-particle reactions under properly chosen kinematical conditions.

Energy spectra of neutrons emitted following the absorption of stopped negative pions in light nuclei

Abstract Energy spectra of neutrons emitted following the absorption of stopped negative pions in carbon, nitrogen and oxygen were measured from about 2.5 MeV up to the kinematical limit. The experiments were carried out at the biomedical pion channel πE3 of the Swiss Institute for Nuclear Research (SIN). The evaporation part of the spectra was extrapolated to zero energy using the formula of Le Couteur. Various parameters like mean neutron energies and neutron multiplicities are given. The data are compared with experimental data obtained by other authors and with results of intranuclear cascade calculations.

Proton-proton final-state interaction in the three-nucleon reaction p+d → p+p+n

Abstract The three-nucleon reaction p+d → p+n+n has been investigated at a deuteron bombarding energy of 52.3 MeV. A kinematically complete experiment was carried out with the aim to observe the proton-proton final-state interaction. By using the Watson-Migdal model a proton-proton scattering length of a pp = −7.5 ± 0.5 fm is extracted from the measurements.

Isospin mixing of the 1+ doublet in 12C determined by low-energy pion scattering☆

With the Low Energy Pion Spectrometer (LEPS) at PSI the inelastic scattering of 50 MeV positive and negative pions to the 1+ excitations at 12.71 MeV (T = 0) and 15.11 MeV (T = 1) in 12C has been measured in the angular range 35°−105°. The angular distributions are in good agreement with impulse approximation calcculations. From the double ratio of the 1+ cross sections for π+ and π− scattering an isospin mixing matrix element of H01 = 157 ± 35 keV is derived. In contrast to a previous study of this reaction these results do not question the validity of the impulse approximation at low energies.

Normalisation of scattering cross sections for low-energy pions☆

Abstract Reliable cross section normalisation of the low-energy scattering of pions has been the source of one of the great weaknesses in that experimental field. Here we describe techniques used at the Low-Energy Pion Spectrometer (LEPS) at PSI/SIN to provide normalisations with a precision of the order of several percent.

Test of a pion range monitor using the radiative capture of pions on protonsπ−p→nγ

SummaryThe present paper demonstrates that neutron-photon pairs from radiative capture of stopped pions on chemically bound protons can be used to measure the range of negative pions within phantoms or a patient. Experimental results are given for a polyethylene and a water target of realistic size as well as for a Rando phantom. Monte-Carlo calculations were carried out in order to study the influence of various sizes of treatment volumes, detector geometries and neutron scattering within the targets upon the accuracy of the pion range determination. The results reveal clearly that a pion range monitor for the control of therapy plans and for actual patient irradiations can be designed according to the proposed principle. The absorbed dose required for a measurement is of the order of 0.1 Gy for a single pion beam if one aims at an accuracy of range determination of a few millimeters.

The deuteron break-up in the reaction dd → dpn at 52 MeV

Abstract The three-particle reaction dd → dpn has been investigated systematically at an energy of 52 MeV. Proton-deuteron and neutron-deuteron coincidences have been measured in kinematically complete experiments in order to study the angular dependence of the np final state interaction and of pd and nd quasifree scattering. The experimental results show that the angular distribution for the production of np pairs with zero relative energy can be predicted absolutely from elastic dd scattering. No indication of violation of isospin conservation is found in the experiment. The measured angular distributions for nd and pd quasifree scattering are identical within the experimental errors over a wide range of angles. Their shape is similar to the distribution of elastic nucleon-deuteron scattering. Significant deviations between the pd and nd coincidence spectra (measured under identical kinematical conditions) have been observed only at forward angles, indicating the influence of the Coulomb force on the break-up mechanism. In order to analyze the spectra and angular distributions, different model calculations have been carried out.

Precision measurements of low-energy pion scattering on sulphur isotopes

A precise measurement of the elastic and inelastic π±-scattering from 32S and 34S at Tπ = 50 MeV has been performed with the LEPS spectrometer at PSI. Exploiting the enhanced isospin sensitivity of low-energy pions, we obtain a difference in neutron r.m.s.-radii between isotopes of 34rn - 32rn = 0.06(1) fm from the elastic scattering. Analysis of the angular distributions of inelastic scattering to the 21+- and 22+-excitations in 34S yields a ratio of neutron to proton matrix elements of Mn/Mp = + 1.17(9) and - 0.4(2), respectively. The latter result is at variance with previous investigations, but agrees with recent shell model calculations.

Visualization ofπ− andπ+ stopping density distributions in one and two dimensions

SummaryA technique suitable for mappingπ± stopping density distributions in patients or phantoms is described. As a position sensitive detector a multiwire proportional chamber with a slit or a hole collimator in front was applied. Results using a water and a Rando phantom are presented for various momenta and momentum band widths of theπ± beam. To our knowledge the two-dimensional visualization of aπ− stopping density distribution was realized for the first time.

Coulomb-nuclear interference in the scattering of pions on 12C at 76 MeV

Abstract The differential cross sections for elastic scattering of positive and negative pions on 12C at 76 MeV have been measured in the Coulomb-nuclear interference region. The results have been compared with calculations, which represent a new more rigorous treatment of the Coulomb corrections.