Fast Scintillators for Security Devices
Fast ZnS:Te based Scintillators for Customs Control and Security Systems
Tech Area / Field
- PHY-SSP/Solid State Physics/Physics
- INS-DET/Detection Devices/Instrumentation
3 Approved without Funding
Vavilov State Optical Institute (GOI), Russia, St Petersburg
- MolTech, Germany, Berlin
Краткое описание проектаWith the resistance of all the civilized world to international terrorist organizations mounting, the problem of security for the world community is gaining in importance from year to year. One of the more common devices employed by security services is the x-ray scanner, widely used at airports for luggage check. This device is basically a combination of a source and detector of x-rays, the detector comprising a scintillation unit and a photo sensor.
The analysis of present day requirements the scintillation detectors for x-ray scanners must meet shows that the functionality of security systems can be enhanced by achieving a substantially improved image quality and response rate of the scintillation element. Among the better known today scintillation materials employed in this class of devices are the CsI:Tl and ZnSe:Te monocrystals with the characteristic decay time of up to 1000 ns and from 3-5 to 30-50 μs respectively.
The project's objective is the development of tellurium doped zinc sulfide (ZnS:Te) based scintillators with response rate and effectiveness surpassing the already known, and the creation of composite panels based on these scintillators for the enhanced resolution detectors.
The foundation for launching such a research has been laid by the results gathered in investigating the characteristics of experimental ZnS:Te samples obtained by the authors in the 90's that allowed to establish the following: when excited by α-particles with the energy of 5.3 MeV, 4 mm thick optical polycrystalline ZnS:Te delivers, compared to monocrystalline CsI:Tl, pulse amplitude 1.6 times as high and the signal's rise and fall time at the output 6 times as short (3-10 ns and ≤250 ns respectively.)
To complement the good scintillation characteristics, the material is non-hygroscopic, it is highly transparent to its own emission and is mechanically strong. As was shown by the published and patent-protected research results (Invention patent RF No. 2173469 of 14.05.1999 «A method for detection and registration of charged particles», authors E.I. Gorokhova, G.P. Tyurin, O.A. Khristich), ZnS:Te stands out favorably in comparison not only with CsI:Tl but also with ZnSe:Te as its parameters in the time domain are much better.
Expected Results and Their Application
The proposed project belongs to the applied research category.
Carrying out the project's complex research will result in a manufacturing technology for fast and highly effective ZnS:Te scintillators and in the creation on their basis of composite panels for the enhanced resolution detectors.
The employment of ZnS:Te in the scintillation detectors of x-ray scanners will allow to step up the devices operating rate and to improve image quality, thus enabling the detection of objects of minimal sizes. It is difficult yet to estimate the market share of the proposed scintillator material, but without a doubt, ZnS:Te is commercially viable. This is evidenced by the fact that the projected value of the share of scintillation detectors in the market volume can be estimated as 1,500,000 euro per year with a certain tendency to grow.
The research carried out earlier allows to conclude with certainty that the detectors based on this material can find high demand not only as components of security and control systems but also in nuclear physics for counting charged particles across a wide spread of energies and masses, including the charged high energy particles of space origin.
Thanks to a unique quality of zinc sulfide, that of a record low gamma-sensitivity of ZnS:Te (alpha/beta ratio is 1), its application in other areas is also possible. Of a considerable benefit to high-speed counting of thermal neutrons in the high energy physics would be the employment of ZnS:Te in powder form in composite ZnS:Te - 6LiF screens as a successor to the presently used ZnS:Ag-6LiF composite screens of the ND type from Applied Scintillator Technologies (Great Britain, Harlow) which are characterized by rather powerful slow components in the glow.
Qualifications of Project Participants match the project's task.
To achieve a successful realization of the project’s objective the institute has at its command highly competent personnel, the experience of many years of developing luminescent, scintillation, and optical ceramics, the results obtained in manufacturing and researching the properties of ZnS:Te-based scintillators, the required process and research equipment.
Over the years 1997-2004 the team was involved in carrying out ISTC projects (# 392.1, #392.2, #2381). Project # 2381 was a partner project and was funded by PHILIPS Research Laboratories (Annex IV). The projects yielded the development of a hot pressing technology for scintillation ceramics (Gd2O2S:Pr,Ce; Gd2O2S:Tb,Ce) employed in medical x-ray equipment. The proposed project continues the line of research directed at still further developing the technology of hot pressing for the new scintillation ceramics.
Meeting ISTC Goals and Objectives
The proposed project is fully in line with ISTC goals and objectives. It opens an opportunity for the weapons scientists and specialists of FGUP NITIOM VNC "S.I. Vavilov GOI" to redirect their abilities toward civil implementations and to support the applied research aimed at creating new fast scintillation materials for the advanced systems of customs control and security. Realization of the project will facilitate a broader and stronger affiliation between Russian and foreign specialists and will work toward transition to a civil oriented market economy.
Scope of Activities
The project's overall work effort is 10,725 person-days and is determined by the major tasks to be accomplished:
- Optimization of the composition and conditions of synthesis of raw ZnS:Te powder.
- Investigation of the influence of process parameters on properties of polycrystalline optical ZnS:Te scintillator.
- Determination of optimal process parameters for hot pressing and physical vapor deposition of polycrystalline optical ZnS:Te scintillator.
- Development of a manufacturing technology for fast high-effectiveness scintillators based on ZnS:Te.
- Selection of the conditions for machining ZnS:Te based composite scintillation panels and of the technological methods involved in their fabrication.
- Investigation of the luminescent and application characteristics of ZnS:Te based scintillation elements.
Role of Foreign Collaborators/Partners: consultations at project draft stage, exchange of scientific and technical information, discussion of obtained results and clarification of further directions of research, joint workshops and consultations.
Together with MolTech GmbH it is planned to investigate the conditions required for machining ZnS:Te based scintillators, to test-run various technological methods of manufacturing ZnS:Te based composite scintillator panels, to examine the properties of composite scintillator panels fabricated by different methods.
Technical Approach and Methodology
ZnS:Te will be produced by the advanced methods of hot pressing and physical vapor deposition widely used by the author team in developing luminescent and optical materials based on various compounds.