31 research outputs found
Anisotropic inverse Compton scattering of photons from the circumstellar disc in PSR B1259-63
The gamma-ray binary system PSR B1259-63 consists of a 48 ms pulsar orbiting
a Be star. The system is particularly interesting because it is the only
gamma-ray binary system where the nature of the compact object is known. The
non-thermal radiation from the system is powered by the spin-down luminosity of
the pulsar and the unpulsed radiation originates from the stand-off shock front
which forms between the pulsar and stellar wind. The Be star/optical companion
in the system produces an excess infrared flux from the associated
circumstellar disc. This infrared excess provides an additional photon source
for inverse Compton scattering. We discuss the effects of the IR excess near
periastron, for anisotropic inverse Compton scattering and associated gamma-ray
production. We determine the infrared excess from the circumstellar disc using
a modified version of a curve of growth method, which takes into account the
changing optical depth through the circumstellar disc during the orbit. The
model is constrained using archive data and additional mid-IR observations
obtained with the VLT during January 2011. The inverse Compton scattering rate
was calculated for three orientations of the circumstellar disc. The predicted
gamma-ray light curves show that the disc contribution is a maximum around
periastron and not around the disc crossing epoch. This is a result of the disc
being brightest near the stellar surface. Additional spectroscopic and
near-infrared observations were obtained of the system and these are discussed
in relation to the possibility of shock heating during the disc crossing epoch.Comment: 15 pages, 14 figures and 4 tables. MNRAS in press. Updated
references, correction of typos in a few of the equations in sec. 5.2 and
appendix, and other minor typo correction
Nuclear-fission studies with relativistic secondary beams: analysis of fission channels
Nuclear fission of several neutron-deficient actinides and pre-actinides from
excitation energies around 11 MeV was studied at GSI Darmstadt by use of
relativistic secondary beams. The characteristics of multimodal fission of
nuclei around 226Th are systematically investigated and interpreted as the
superposition of three fission channels. Properties of these fission channels
have been determined for 15 systems. A global view on the properties of fission
channels including previous results is presented. The positions of the
asymmetric fission channels are found to be constant in element number over the
whole range of systems investigated.Comment: 16 pages, 3 figures, background information on
http://www.gsi.de/charm
An international multi-center investigation on the accuracy of radionuclide calibrators in nuclear medicine theragnostics
Background: Personalized molecular radiotherapy based on theragnostics requires accurate quantification of the amount of radiopharmaceutical activity administered to patients both in diagnostic and therapeutic applications. This international multi-center study aims to investigate the clinical measurement accuracy of radionuclide calibrators for 7 radionuclides used in theragnostics: 99mTc, 111In, 123I, 124I, 131I, 177Lu, and 90Y. Methods: In total, 32 radionuclide calibrators from 8 hospitals located in the Netherlands, Belgium, and Germany were tested. For each radio
Preparation and characterization of a sample and study of the reaction
The Ar(n,)S reaction has been studied for the first time. A sample containing Ar atoms, was produced at the ISOLDE facility at CERN. The number of Ar atoms in the layer was determined by measuring the Ar -activity using a primary standardization method. Subsequently, the sample was irradiated with thermal neutrons at the High Flux Reactor of the ILL. An upper limit of 0.29~b was obtained for the Ar(n,)S reaction cross-section