EXPERIMENTAL STUDIES OF TRANSMUTATION OF 129 I BY SPALLATION NEUTRONS USING JINR DUBNA PHASOTRON
An intensive beam of 660 MeV protons was directed towards a lead target (not surrounded by shielding or neutron reflectors) for 10 minutes. On the top of the target were placed detectors and iodine samples. The neutron field and the transmutation of I were studied by the neutron activation analysis method. First simulations were compared to the experimental data. 1 Description of the experiment The collaboration ”Energy plus transmutation” works on benchmark experiments intended to test simulation programs, which shall be used in design of Accelerator Driven Systems. The work consist of a series of similar experiments, of which each is concentrated on a specific topic. Generally said, we study production of neutrons by spallation reactions on massive targets, their transport, and use for transmutation. Our experimental setups consist of heavy metal (Pb, W, Bi, U) targets of cylindrical shape to which a narrow beam of relativistic protons is directed. In the target protons cause spallations of heavy nuclei to nucleons, and smaller fractions of nucleus. Relativistic nucleons cause further spallations, and mostly neutrons of all energies from thermal up to the energy of the proton beam exit the target sideways. Such neutron production shall be used in the devices called ADS (Accelerator Driven Systems), which will be able to use a wider spectrum of nuclear fuel (Th, nuclear waste from thermal reactors), and their waste should be much less radioactive than the waste from thermal reactors. These systems cannot be built in smaller scale as a test model, and the accelerators to be added to the reactors will not be a cheap extension. That is why we need the precise descriptions of what will be going on in these systems. Our experiments are simplified setups of them, and are used as benchmark tests for the computer simulations that will be used to describe larger and more complicated systems. One of the experiments was held on Dubna Phasotron in December, 2003, and was focused on the studies of short-lived iodine isotopes production. We needed to make our measurements as soon as possible after the irradiation, and use as intensive proton beam as possible. The proton beam was provided by Dubna Phasotron, which accelerated the intensive proton beam to the energy 660 MeV. The beam was directed to the bare lead
First nuclear activation experiments using the new accelerator NUCLOTRON in Dubna
Abstract First nuclear activation experiments have been carried out using the new accelerator for relativistic particles NUCLOTRON in Dubna. The distribution of neutrons emitted during the irradiation with 0.65, 1.0 and 1.5 GeV protons from a lead target (∅ = 8 cm, l = 20 cm) and moderated by surrounding paraffin of 6 cm thickness was studied with radiochemical sensors along the beam axis on top of the moderator. Small 139Lasensors of approximately 1 g each were used to measure essentially the thermal neutron fluence at different depths near the surface: i. e. on top of the moderator, in 10 mm deep holes and in 20 mm deep holes, respectively. The reaction 139La (n, γ) 140La (τ1/2 = 40.27 h) was studied using standard procedures of gamma-ray spectrometry and data analysis. The induced activity of 140La increases strongly with the depth of the hole inside the moderator. Its activity distribution along the beam direction on top of the moderator has its maximum about 10 cm downstream the entrance of the protons into the lead and the activity increases about linearily with the proton energy. Some comparisons of the experimental results with model estimations based on the LAHET code are also presented. The experiments were carried out in the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna, Russian Federation.
Two-dimensional gravitational anomalies, Schwinger terms and dispersion relations
Abstract We are dealing with two-dimensional gravitational anomalies, specifically with the Einstein anomaly and the Weyl anomaly, and we show that they are fully determined by dispersion relations independent of any renormalization procedure (or ultraviolet regularization). The origin of the anomalies is the existence of a superconvergence sum rule for the imaginary part of the relevant formfactor. In the zero mass limit the imaginary part of the formfactor approaches a δ-function singularity at zero momentum squared, exhibiting in this way the infrared feature of the gravitational anomalies. We find an equivalence between the dispersive approach and the dimensional regularization procedure. The Schwinger terms appearing in the equal time commutators of the energy momentum tensors can be calculated by the same dispersive method. Although all computations are performed in two dimensions the method is expected to work in higher dimensions too.