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Relativistic Particle Interactions with Tungsten Crystals

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Investigations of Relativistic Charged Particle Interactions with Tungsten Crystals and Development of Monochromatic X-ray Source

Tech Area / Field

  • PHY-ANU/Atomic and Nuclear Physics/PhysicsnPHY-PFA/Particles, Fields and Accelerator Physics/PhysicsnPHY-SSP/Solid State Physics/Physics

Status
8 Project completed

Registration date
27.03.2001

Completion date
21.06.2007

Senior Project Manager
Lapidus O V

Leading Institute
Institute of Physical-Technical Problems, Russia, Moscow reg., Dubna

Supporting institutes

  • Institute of Solid State Physics, Russia, Moscow reg., ChernogolovkanTomsk Polytechnical University / Nuclear Physics Institute, Russia, Tomsk reg., TomsknJoint Institute of Nuclear Research, Russia, Moscow reg., Dubna

Collaborators

  • Hiroshima University/Graduate School of Advanced Sciences of Matter, Japan, Higashi-HiroshimanInstitute of Particle and Nuclear Studies, Japan, Ibaraki

Project summary

The main goal of the project.

Development of high-quality tungsten crystals. Investigation of the interaction of relativistic nuclei and electrons with crystals, including channelling and deflection of nuclei in a bent crystal, parametric X-radiation (PXR) of nuclei and electrons, and the electromagnetic dissociation of nuclei in crystals. Development of a monochromatic X-radiation source using the PXR effect from relativistic electrons in crystals. The beams of relativistic nuclei of the Nuclotron (LHE JINR) and relativistic electrons (NPI TPU) will be used for the experimental studies.

Cultivation of high-quality tungsten crystals

The most important part of the project is to increase structure perfection of the cultivated tungsten crystals of large dimensions.

The technology of solid-state re-crystallisation of tungsten ingots, 15-16mm in diameter and up to 100mm in length, and methods of manufacturing crystal plates from the ingots were developed at the Institute of Solid-State Physics (Chernogolovka) and at the Institute of Physical and Technical Problems (Dubna). The technologies allowed us to fabricate tungsten plates, cut along the (110) crystal planes with rather large dimensions of 10Ч20mm2 and 0.2-3mm in thickness, which possess a low mosaic spread of about 1ґ and a dislocation density of 104-105mm—2.

For further improvement of the tungsten crystal parameters, required for successful fulfilment of the project tasks and other basic and applied physical research, accomplishment of the following is planned:

 Development of the technology of tungsten crystal purification, which is cheaper than existing technology.

An increase in integral chemical purity of the initial tungsten material can increase the dislocation agility and, therefore, facilitate their removal from the crystal.


 Reduction of the temperature gradients during the high-temperature re-crystallisation annealing of tungsten ingots.

For this purpose, a specially-designed annealing furnace will be developed and used instead of heating by electron beam.


Channelling and deflection of relativistic nuclei in tungsten crystals

Within the project the nuclei dechannelling lengths in a bent crystal, as a function of their energy and charge, will be investigated. Crystal bending gives angular deflection of channelled particles and, thus, good potential to study the channelling process itself, realizing the angular involution of particle dechannelling.

Nowadays, silicon crystal deflectors are regularly used to form charged particle beams for experimental studies in high-energy physics and for the deflection and extraction of high-energy charged particle beams from accelerators. Silicon crystals have mainly been used as beam deflectors because of their record parameters of crystal structure perfection.

At the same time, a considerable increase in the deflector efficiency for large angles of particle deflection could be achieved using heavy instead of silicon crystals, which have stronger internal electric fields. Tungsten crystals have very suitable parameters for this purpose because they have small amplitudes of lattice atom vibrations and a high melting point.

Further improvement of the technologies developed for tungsten crystal cultivation allows one to hope for the successful investigation of tungsten deflectors at the Nuclotron beams of accelerated nuclei with energies up to 6GeV/u. In addition to the direct extraction of the Nuclotron beam, the use of crystal as an element of a slow extraction system, instead of the electrostatic septum, will be investigated.

Parametric X-radiation in a tungsten crystal

Parametric X-radiation (PXR) arises due to diffraction of the eigen electromagnetic field of a relativistic particle in a crystal. Under diffraction, the virtual photons become the real ones emitted at Bragg angles. PXR was observed for the first time on the 900MeV electron beam in Tomsk, and was later widely investigated in many laboratories all over the world, using electron beams of different energies from a few MeV up to several GeV.

PXR in a crystal can be an alternative for generation of monochromatic X-radiation with regulating parameters at rather inexpensive moderate-energy electron accelerators. With the tungsten crystal as the conductor it will be possible to avoid the effects connected with electric charge deposition under irradiation. Also, tungsten has a very high melting temperature that allows it to be heated by intensive electron beams without a loss in generated radiation intensity.

Work is planned for development of an X-ray source using PXR in a crystal at the Nuclear Physics Institute, Tomsk Polytechnical University (NPI TPU), where a series of priority results in experimental studies of PXR were obtained.

According to the theory, PXR intensity depends on the particle charge as Z2. Until now only one experimental attempt was made to observe PXR generated by particles other than electrons. However, in this experiment, which was performed at IHEP (Protvino) on a 70GeV proton beam with a silicon crystal, the observed width of spectrum maximum was much larger than one could have expected. Within the framewok of the studies of new tungsten crystals as deflectors with the circulating beam of the Nuclotron, PXR generated by nuclei in the crystals will be simultaneously investigated.

Electromagnetic dissociation of relativistic nuclei in a crystal

Channelling of the relativistic nuclei in a crystal permits us to avoid their central collisions with the nuclei of the crystal atoms. Therefore, the peripheral process of electromagnetic dissociation (EMD) for the channelled nuclei can be observed with almost no background, owing to strong interactions.

For weakly bound nuclei like deuteron (binding energy 2.26MeV) or beryllium (binding energy 1.65MeV), EMD can be observed at Nuclotron energies. The EMD cross-section is proportional to the square of the charge of the target nucleus and, therefore, is greater in a heavy crystal like tungsten.

An experimental study of the deuteron EMD in a tungsten crystal is planned at the external beams of the LHE accelerator complex. The process of electromagnetic dissociation of the relativistic deuterons channelled in a crystal can be used to produce a relativistic neutron beam with considerably narrower angular and energy distributions than at dissociation in an amorphous target.

 

Expected Results and their Application.

 

The project is dedicated to fundamental research in the field of nuclear physics, namely, the physics of charged particle interaction with crystals, and in the field of solid state physics, the results of which are directed to applications in nuclear physics experiments.

– Tungsten crystals with an extremely low dislocation density and mosaic spread will be produced. In addition to beam deflectors, single crystals can be used for physics experiments, for which tungsten crystals are promising. Possible applications are the following:

– aligned crystal targets as electron-positron converters for producing high-energy positron beams;
– aligned crystal targets for gamma-astronomy and spectrometry of ultra-relativistic photon and electron beams;
– aligned crystal targets for producing quasi-monochromatic X-ray by using the PXR effect at an intense electron beam irradiation;
– bent crystal targets for producing polarized ultra-relativistic electron, positron, and photon beams;
– bent crystal targets to study the magnetic moments of short-lived particles;
– bent crystals to form secondary particle beams at high-energy proton accelerators (to direct neutrino beams to the outlying detectors).


– New tungsten deflectors of charged particle beams with higher efficiency compared to silicon ones will be made and investigated. Their use will enhance the possibilities of high-energy physics research and the efficiency of using the expensive beam time of the accelerators.

– The experiment on observation of the parametric X-radiation from heavy charged particles (relativistic nuclei) will be performed for the first time. The results obtained can be useful to study the beam parameters, like angular spread and component structure, through the observation of PXR arising in a thin crystal.

– The source of monochromatic X-radiation will be developed using the PXR effect from the moderate-energy electrons in a tungsten crystal.

– The experiment on observation of the electromagnetic dissociation of relativistic deuterons under channeling in a tungsten crystal will be performed. This process can be used for generation of relativistic neutron beam with small angular and energy spread for nuclear physics experiments.

Realisation of goals and tasks of ISTC.

he project is devoted to fulfil the basic research for peaceful purposes. The employees of the participating institutions involved earlier into development of the nuclear weapon components and their delivery methods will carry out the main part of the project works. The main part of the participants are refugees from the Institute of Physics and Technology (Sukhumi) and from the Scientific Research Institute of Radioisotope Devices (Riga). Therefore, the project meets the ISTC goals related to redirecting their skills to peaceful activities.

The suggested broad participation of the foreign collaborators in the works on the project will help the integration of these employees into the international scientific community.

Scope of Activities.

– Development of methods to decrease the dislocation density and mosaic spread of growing tungsten crystals (the technology for tungsten powder purification and the method of crystal annealing in super-high vacuum). Improvement of the tungsten deflector fabrication.

– Experimental studies of tungsten deflectors for direct extraction of circulating nuclear beam from the Nuclotron and its possible use as an element of the slow beam extraction system.

– Investigations of parametric X-radiation from relativistic nuclei in a tungsten crystal during the experiment on the beam extraction by a bent crystal from the Nuclotron. Conclusions on PXR of the relativistic nuclei as the monochromatic X-ray source being by-product of penetration of the relativistic nuclei through a crystal target (during extraction or deflection).

– Investigations of parametric X-radiation from 100–500 MeV electrons in a W crystal using the internal electron beam of the synchrotron (Tomsk) and the beams of microtrons with the energy up to 6.5 MeV. Development of a monochromatic X-ray source using PXR effect for electrons in a tungsten crystal.

– Experimental studies of electromagnetic dissociation of the relativistic deuterons (EMDD) under channeling in a tungsten crystal at the external beams of the LHE JINR accelerator complex.

The role of Foreign Collaborators.

The participation of foreign collaborators in the works on the project will help to integrate the project participants who were involved earlier with the development of nuclear weapon into the international scientific community.

Within the frame of the proposed project, the co-operation with foreign collaborators will be carried out through information exchange, comments to the technical reports, and organisation of joint workshops and seminars.


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