V.I. Shvedunov

POLARIZATION BREMSSTRAHLUNG OF RELATIVISTIC ELECTRONS IN ALUMINIUM

Abstract The spectral-angular distribution of the polarization bremsstrahlung of relativistic electrons crossing a thin aluminium foil is measured. The earlier predicted strong difference between polarization bremsstrahlung properties for amorphous and polycrystalline targets is observed for the first time.

SUPPRESSION OF POLARIZATION BREMSSTRAHLUNG OF RELATIVISTIC ELECTRONS MOVING THROUGH AN AMORPHOUS CARBON FOIL

Abstract The suppression effect of relativistic polarization bremsstrahlung in an amorphous carbon foil is observed for the first time. A theoretical explanation for this effect is discussed.

Novel race track microtron end magnets

Abstract We are designing a large volume, high-precision, high-reliability 1 T dipole magnet that requires no power. This hybrid magnet uses iron to shape the gap field and permanent magnet material to excite the iron (i.e., put iron poles and surfaces onto desired scalar potentials). This structure is surrounded by an iron yoke box, thus producing the smallest size with the least cost without contaminating the environment with stray fields. To satisfy the beam optics conditions for a specific Race Track Microtron (RTM) design, the magnet has a reverse field (and potential) pole over the entire beam entrance/exit width. The scalar potentials of both the main and reverse field poles are passively adjustable (i.e., without using power) over a small range which allows the two-magnet RTM system to be tuned.

Performance of the 6 MeV injector for the Moscow racetrack microtron

Abstract The 6 MeV injector for the Moscow racetrack microtron is described. The work presents the accelerator description, the rf power supply system and results of the computer simulation. The method of injector tuning and experimental results are discussed.

Operational experience with room temperature continuous wave accelerator structures

Abstract The paper reports the results of the computer simulation of parameters of the on-axis coupled accelerator structure for the continuous wave racetrack microtron. The operational experience with the accelerating sections on the basis of the on-axis coupled structure is described.

Photoproton energy spectra and isospin effects in the decay of highly excited states of Ni isotopes

Abstract The technique of the difference proton spectra is used to study the decay properties of highly excited states of the 58 Ni and 60 Ni isotopes in the energy region of the giant dipole resonance. The proton transition strengths to specific final states from particular initial states have been extracted. Experimental data are interpreted in terms of isospin splitting of the giant dipole resonance.

A mobile racetrack microtron

Abstract Motivated by our need for a light source for our Nitrogen and Carbon Cameras, we have designed and are building a rugged compact 70 MeV RaceTrack Microtron (RTM) with simplified beam optics and tuning, improved beam parameters, and decreased capital and operating costs. The principal innovations that permit this are rare earth permanent bending magnets and a narrow rectangular biperiodic accelerating focusing structure. We describe here our machine as optimized using beam dynamics simulations.

A mobile light source for carbon/nitrogen cameras

Abstract The pulsed light source for carbon/nitrogen cameras developed to image concealed narcotics/explosives is described. This race-track microtron will produce 40 mA pulses of 70 MeV electrons, have minimal size and weight, and maximal ruggedness and reliability, so that it can be transported on a truck.

Decay channels of the giant dipole resonance in 26Mg

The energy spectra of photoprotons from 26Mg have been measured with bremsstrahlung at five values of the end-point energy Eγmax, namely, at 19.5, 20.5, 22.0, 24.5 and 27.0 MeV. Using the difference spectra technique, we have determined the main decay channels of the states of the giant dipole resonance (GDR) of 26Mg. The photoproton spectra have been used to obtain the cross sections for the formation of the final nucleus of the 26Mg(γ, p)25Na reaction in its various states. The magnitude of the configurational splitting of the GDR of 26Mg has been estimated. Relevant data from other studies have been utilized to calculate the isospin components of the GDR of 26Mg within the framework of a combined model for the decay of the giant resonance, with isospin taken into account. A new isospin interpretation of the cross sectios for the photoproton and photoneutron reactions on the 26Mg nucleus is proposed.

A combined model for decay of the giant dipole resonance

Abstract A simple model for decay of the giant dipole resonance is described that takes into account the semidirect, pre-equilibrium, and equilibrium mechanisms of the photonucleon emission. The semidirect photoeffect is treated within the framework of the R -matrix theory in the shell model. The wave function for the doorway dipole state is constructed using the generator procedure that offers the possibility to obtain simple formulas for a calculation of the semidirect component of the photonucleon spectra. The problem of the inclusion of isospin effects is treated. A reasonable agreement between theoretical and experimental photoproton spectra has been obtained.