van Marc-Jan Goethem

Dynamical effects in proton–proton bremsstrahlung for non-coplanar geometries

Abstract The proton–proton bremsstrahlung process, including both coplanar and non-coplanar kinematics, has been measured with polarized protons of 190 MeV. High-precision cross sections and analyzing powers have been obtained. Cross sections as a function of non-coplanarity angle are presented and show large variations of dynamical origin. Non-coplanar analyzing powers have been measured for the first time and are compared to theoretical predictions.

Photon Production in Heavy-ion Collisions Close to the Pion Threshold

Abstract We report on a measurement of hard photons ( E γ >30 MeV) in the reaction Ar+Ca at 180 A MeV at an energy in which photons from the decay of π ° mesons are dominating. Simultaneous measurement with the TAPS spectrometer of the photon spectrum and photon-photon coincidences used for the identification of π ° enabled the subtraction of π ° contribution. The resulting photon spectrum exhibits an exponential shape with an inverse slope of E 0 =(53±2 (stat) −5 +8 (syst) ) MeV. The photon multiplicity equal to (1.21±0.03 (stat) +0.3 −0.2 (syst) )·10 −2 is roughly one order of magnitude larger than the value extrapolated from existing systematics. This enhancement of the hard photon production is attributed to a strong increase in the contribution of secondary np collisions to the total photon yield. We conclude that, on average, the number of np collisions which contribute to the hard photon production is 7 times larger than the number of first chance np collisions in the reaction Ar+Ca at 180A MeV.

Proton energy and scattering angle radiographs to improve proton treatment planning: a Monte Carlo study

The novel proton radiography imaging technique has a large potential to be used in direct measurement of the proton energy loss (proton stopping power, PSP) in various tissues in the patient. The uncertainty of PSPs, currently obtained from translation of X-ray Computed Tomography (xCT) images, should be minimized from 3–5% or higher to less than 1%, to make the treatment plan with proton beams more accurate, and thereby better treatment for the patient. With Geant4 we simulated a proton radiography detection system with two position-sensitive and residual energy detectors. A complex phantom filled with various materials (including tissue surrogates), was placed between the position sensitive detectors. The phantom was irradiated with 150 MeV protons and the energy loss radiograph and scattering angles were studied. Protons passing through different materials in the phantom lose energy, which was used to create a radiography image of the phantom. The multiple Coulomb scattering of a proton traversing different materials causes blurring of the image. To improve image quality and material identification in the phantom, we selected protons with small scattering angles. A good quality proton radiography image, in which various materials can be recognized accurately, and in combination with xCT can lead to more accurate relative stopping powers predictions.

Coherent Bremsstrahlung in \alpha + p Reactions at 50 MeV\nucleon

Bremsstrahlung emitted in the α + p reaction at 50 MeV/nucleon was studied using a 200 MeV α -particle beam and a liquid hydrogen target. Double-differential photon cross sections were measured over a wide range of angles and energies. Coherent bremsstrahlung was found to be strong for all photon energies. The cross section is enhanced at the highest photon energies and is characteristic of direct capture to the unbound 5 Li ground and first excited state. With direct capture as a limiting case of coherent bremsstrahlung a consistent reaction picture can be obtained.

Probing Few-body Systems with Bremsstrahlung

A series of bremsstrahlung measurements have been performed at KVI with the 190 MeV polarized proton beam of the new superconducting cyclotron, AGOR. The aim of these measurements is to investigate the dynamics of interactions involving intermediate off-shell nucleons. Nucleon-nucleon bremsstrahlung is the most fundamental process used for such studies as it involves the strong interaction between two nucleons and the well-known electromagnetic interaction. The present experiment provides the most accurate data on the proton-proton system. In addition the first exclusive proton-proton virtual-bremsstrahlung data ever is presented. The accuracy of the real bremsstrahlung data is high enough to investigate higher-order effects such as the virtual Δ-isobar and meson-exchange currents. None of the microscopic calculations is able to describe the data both in magnitude and in shape. The virtual-bremsstrahlung data are integrated over the detector acceptance. This same integration is done for two different soft-photon calculations for comparison.

Hard photon and neutral pion production in cold nuclear matter

Abstract The production of hard photons and neutral pions in 190 MeV proton induced reactions on C, Ca, Ni, and W targets has been for the first time concurrently studied. Angular distributions and energy spectra up to the kinematical limit are discussed and the production cross-sections are presented. From the target mass dependence of the cross-sections the propagation of pions through nuclear matter is analyzed and the production mechanisms of hard photons and primordial pions are derived. It is found that the production of subthreshold particles proceeds mainly through first chance nucleon–nucleon collisions. For the most energetic particles the mass scaling evidences the effect of multiple collisions.

Measurements of the virtual bremsstrahlung in the p+p and p+d systems

Virtual bremsstrahlung yields measured in \(\vec p + p \to p + p + {e^ + } + {e^ - }\) and \(\vec p + d \to {}^3{\text{He}} + {e^ + } + {e^ - }\) are presented. The experiments were performed with a 190 MeV polarized proton beam obtained from the cyclotron AGOR at KVI in Groningen. Differential cross sections, response functions and analyzing po- wers were obtained for both reactions in exclusive measurements in which all outgoing particles were measured in a coincidence setup between SALAD and TAPS. The data are compared with gauge-invariant calculations using a NN T-matrix fitted to elastic phase-shifts. For pp→ppe + e - a reasonable agreement is found for all measured virtual-photon invariant masses, M γ >15 MeV/c2 up to 80 MeV/c2. For the pd→3He e + e - angular distributions, the calculations un- derestimate the data for θCM >100° similar to what is found in the real-photon capture reaction.

Channel Selection in Proton-Deuteron Bremsstrahlung at 190 MeV

For the first time an exclusive proton-deuteron bremsstrahlung experiment has been performed in which all the exit channels can be identified separately. Preliminary results indicate we are able to identify the different exit channels with high accuracy. For the 3 and 4-body final state, no high quality calculations are available at the present time.

Results from proton-proton bremsstrahlung measurements at 190 MeV

A series of bremsstrahlung measurements have been performed at KVI with the 190 MeV polarized proton beam of the new superconducting cyclotron AGOR. The aim of these measurements is to investigate the dynamics of interactions involving intermediate off-shell nucleons. Nucleon-nucleon bremsstrahlung is the most fundamental process used for such studies as it involves the strong interaction between two nucleons and the well-known electromagnetic interaction. The present experiment provides the most accurate experiment to date on the proton-proton system. The accuracy is high enough to investigate higher order effects such as the virtual Δ-isobar and meson exchange currents. Surprisingly, none of the microscopic calculations is able to describe the data both in magnitude and in shape.