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Exposing electrons — the positron way
ND T Abstracts Positron annihilation methods for determining the spatial distribution of plastic damage in metal and alloy components are described. The relationship between the damage distribution and the associated residual stress variation, as measured by diffraction, is considered with reference to typical cases using ideal samples. The results can be correlated with the known thermomechanical histories and suggest such nondestructive measurements may have application in optimising the design and extending the service life of engineering components. A recently developed transportable positron annihilation system, which could he used in the field in conjunction with X-ray diffraction stress measurements, is briefly outlined. 37738 Watson, A. Exposing electrons - the positron way New Scientist, Vol. 113, No. 1545, pp. 40-43 (29 Jan. 1987) Gamma ray emission from e ~ n / p o s i t r o n annihilations can yield valuable information about the distribution and movement of electrons within metals and semiconductors and hence about defects and dislocations in their crystal structures. Positrons can be used as nondestructive testing tools to determine failure of materials. Positron diffraction would be a powerful analytic tool for the future if ~ c h e r s could produce a beam of slow positrons easily and copiously. 37123 Doring, C.; Andreeff, A.; Bertram, M.; Brauer, G. Lattice defects in plastically d e f o r m e d v a n a d i u m silicide single
crystals studied by positron annihilation Journal of Physics C, Vol. 20, No. 18, pp. 2627-2633 (30 Jun. 1987) The influence of plastic deformation of vanadium silicide single crystals on positron annihilation parameters (Doppler broadening of the annihilation line, positron lifetime) has been studied and the results compared with measurements of the electrical resistivity ratio r(20 K). The experimental results can be explained in terms of interactions of point defects and dislocations based on the monotype model of dislocation climbing developed for intermetallic compounds and the established fact of there being a large lattice expansion below an edge dislocation in vanadium silicide. Vanadium silicide dislocations are found to have a higher trapping cross section than the (vanadium) vacancies. 36604
Varshney, V.P.: Gupta, D.K.
Semiempirical stopping power equations for positrons Journal of Applied Physics, Vol. 60, No. I, pp. 461-463 (Jul. 1986) A semiempirical equation for the total stopping power for positrons in elements, compounds, and alloys have been found which is valid in ther energy region from 0.01 to I000 MeV. Values of the total stopping power obtained by the present approach are in good agreement with the theoretical values recently reported by Berger and Seltzer (National Bureau of Standards Internal Report No. 82-2550-A (1982)) within a 5% discrepancy.
prototype light-guides on BGO crystals. The axial resolution will be about 5-6 mm. 36583 Dahlbom,M.; Hoffman, Ed. P r o b l e m s in signal-to-noise ratio for a t t e n u a t i o n c o r r e c t i o n in
high resolution PET IEEE Transactions on Nuclear Science, Vol. NS-34, No. 1, pp. 288-293 (Feb. 1987) In high resolution Positron Emission Tomography (PET), the number of events required for a high signal-to-noise ratio in the measured attenuation correction is an order of magnitude higher (50-100 million) than that required for the emission image. This is due to the large number of elements in the attenuation correction sinogram (e.g. 50,000) and the large attenuation factors through the thicker sections of the body (e.g. 50). Another major contribution to noise in high resolution PET is contamination of true coincidences by accidentals and their subtraction from the prompt coincidences. In this work three methods which reduce noise in the measured attenuation are evaluated. The methods are: (1) optimization of energy threshold, (2) processing of random sinogram before subtraction and (3) spatial averaging of the transmission sinogram before performing attenuation correction. 36582
Schotanus,P.; Eijk, C.W.E.; Hollander, R.W.; Pijpelink,
J. Development s t u d y of a new gamma camera IEEE Transactions on Nuclear Science, Vol. NS-34, No. 1, pp. 272-276 (Feb. 1987) Energy, time and position resolution have been studied, for 511 kev annihilation radiation detected in a 15 can diameter, 8 mm thick BaF/sub2/ crystal coupled to a multiwire proportional chamber filled with TMAE. Properties of other UV scintillators have also been studied. 36580 Wong, W. Dynamic energy-window d a t a collection for p o s i t r o n emission
tomography camera 1EEE Transactions on Nuclear Science, Vol. NS-34, No. 1, pp. 364-368 (Feb. 1987) Recent efforts in improving the image of the PET camera are focusing at improving the 'intrinsic' detection resolution of the camera by using small detectors. However, such improvements have not been accompanied by the necessary corresponding improvement in counting statistics. As a result the high resolution image is noisy and the clinically 'usable' resolution is much worse than the 'specification' resolution measured with millions of counts collected on a point source. This paper presents theoretical model calculations based on a new dynamic energy- window data collection method which has the potential to increase the true counts collected by multiple images thereby reducing image noise and increasing resolution.
A s l a n t i n g light-guide a n a l o g decoding high resolution detector for positron emission tomography camera IEEE Transactions on Nuclear Science, Voi. NS-34, No. 1, pp. 280-284 (Feb. 1987) This paper present the feasibility and performance achievable with slanting light-gnide detectors. With a crystal-photomuitiplier ratio of 6/1, the intrinsic resolution was found to he 4.0 mm using the first non-optimized
36578 Derenzo, S.E.; Budinger, T.F. Recent developments in positron emission t o m o g r a p h y ( P E T ) instrumentation University of California, Berkeley (United States) LBL-21556, DE87- 000046, 27pp. (Apr. 1986) This paper presents recent detector developments and perspectivesfor positron emission tomography (PET) instrumentation used for medical research, as well as the physical processes in positron annihilation, photon scattering and detection, tomograph design considerations, and the potentials for new advances in detectors.
Each entry in NDT Abstracts consists of the serial number in the National NDT Centre Information Store for identification purposes; the title of the paper, book or report; the name of the author; the name of the source journal or document and the abstracts. Where necessary, author's names and the title of foreign journals have been transliterated into the Latin alphabet according to British Standard BS 2979:1958.
Information Service, US Department of Commerce, Springfield, Virginia 22151, USA. British and foreign standards can be obtained from Sales Department, British Standards Institution, 101 Pentonville Road, London N1 9ND; and British and foreign patents from the Patents Office Sales Branch, Block C, Station Square House, St Mary Cray, Orpington, Kent BR5 3RD.
Availability of Publications
Information-retrieval Service
Most papers listed may be obtained as loans or copies via local library or direct from Loans Department, British Library Document Supply Centre, Boston Spa, Wetherby, Yorkshire LS23 7BQ. Details of the British Lending Library's UK and International Services may be obtained from The Director, British Library Lending Division. Technical reports are also available from the Loans Department of the British Lending Library and in the USA from the National Technical
All entries are indexed in a computerized retrieval system, located at Harwell, which allows rapid searching of information relevant to any particular inspection problem. This service is available to both UK and overseas organizations through the National NDT Centre's Qualtis Subscription Scheme - further details are available from Phil Lawrence on Abingdon (0235) 433391.
Wong, W.; Jing, M.; Bendriem, B.; Hartz, R.; Mullani, N., Gould, K.L.; Michel, C. 36584
~C 1994 United Kingdom Atomic Energy Authority
NDT&E International 1994 Volume 27, Number 5
291
crystals studied by positron annihilation Journal of Physics C, Vol. 20, No. 18, pp. 2627-2633 (30 Jun. 1987) The influence of plastic deformation of vanadium silicide single crystals on positron annihilation parameters (Doppler broadening of the annihilation line, positron lifetime) has been studied and the results compared with measurements of the electrical resistivity ratio r(20 K). The experimental results can be explained in terms of interactions of point defects and dislocations based on the monotype model of dislocation climbing developed for intermetallic compounds and the established fact of there being a large lattice expansion below an edge dislocation in vanadium silicide. Vanadium silicide dislocations are found to have a higher trapping cross section than the (vanadium) vacancies. 36604
Varshney, V.P.: Gupta, D.K.
Semiempirical stopping power equations for positrons Journal of Applied Physics, Vol. 60, No. I, pp. 461-463 (Jul. 1986) A semiempirical equation for the total stopping power for positrons in elements, compounds, and alloys have been found which is valid in ther energy region from 0.01 to I000 MeV. Values of the total stopping power obtained by the present approach are in good agreement with the theoretical values recently reported by Berger and Seltzer (National Bureau of Standards Internal Report No. 82-2550-A (1982)) within a 5% discrepancy.
prototype light-guides on BGO crystals. The axial resolution will be about 5-6 mm. 36583 Dahlbom,M.; Hoffman, Ed. P r o b l e m s in signal-to-noise ratio for a t t e n u a t i o n c o r r e c t i o n in
high resolution PET IEEE Transactions on Nuclear Science, Vol. NS-34, No. 1, pp. 288-293 (Feb. 1987) In high resolution Positron Emission Tomography (PET), the number of events required for a high signal-to-noise ratio in the measured attenuation correction is an order of magnitude higher (50-100 million) than that required for the emission image. This is due to the large number of elements in the attenuation correction sinogram (e.g. 50,000) and the large attenuation factors through the thicker sections of the body (e.g. 50). Another major contribution to noise in high resolution PET is contamination of true coincidences by accidentals and their subtraction from the prompt coincidences. In this work three methods which reduce noise in the measured attenuation are evaluated. The methods are: (1) optimization of energy threshold, (2) processing of random sinogram before subtraction and (3) spatial averaging of the transmission sinogram before performing attenuation correction. 36582
Schotanus,P.; Eijk, C.W.E.; Hollander, R.W.; Pijpelink,
J. Development s t u d y of a new gamma camera IEEE Transactions on Nuclear Science, Vol. NS-34, No. 1, pp. 272-276 (Feb. 1987) Energy, time and position resolution have been studied, for 511 kev annihilation radiation detected in a 15 can diameter, 8 mm thick BaF/sub2/ crystal coupled to a multiwire proportional chamber filled with TMAE. Properties of other UV scintillators have also been studied. 36580 Wong, W. Dynamic energy-window d a t a collection for p o s i t r o n emission
tomography camera 1EEE Transactions on Nuclear Science, Vol. NS-34, No. 1, pp. 364-368 (Feb. 1987) Recent efforts in improving the image of the PET camera are focusing at improving the 'intrinsic' detection resolution of the camera by using small detectors. However, such improvements have not been accompanied by the necessary corresponding improvement in counting statistics. As a result the high resolution image is noisy and the clinically 'usable' resolution is much worse than the 'specification' resolution measured with millions of counts collected on a point source. This paper presents theoretical model calculations based on a new dynamic energy- window data collection method which has the potential to increase the true counts collected by multiple images thereby reducing image noise and increasing resolution.
A s l a n t i n g light-guide a n a l o g decoding high resolution detector for positron emission tomography camera IEEE Transactions on Nuclear Science, Voi. NS-34, No. 1, pp. 280-284 (Feb. 1987) This paper present the feasibility and performance achievable with slanting light-gnide detectors. With a crystal-photomuitiplier ratio of 6/1, the intrinsic resolution was found to he 4.0 mm using the first non-optimized
36578 Derenzo, S.E.; Budinger, T.F. Recent developments in positron emission t o m o g r a p h y ( P E T ) instrumentation University of California, Berkeley (United States) LBL-21556, DE87- 000046, 27pp. (Apr. 1986) This paper presents recent detector developments and perspectivesfor positron emission tomography (PET) instrumentation used for medical research, as well as the physical processes in positron annihilation, photon scattering and detection, tomograph design considerations, and the potentials for new advances in detectors.
Each entry in NDT Abstracts consists of the serial number in the National NDT Centre Information Store for identification purposes; the title of the paper, book or report; the name of the author; the name of the source journal or document and the abstracts. Where necessary, author's names and the title of foreign journals have been transliterated into the Latin alphabet according to British Standard BS 2979:1958.
Information Service, US Department of Commerce, Springfield, Virginia 22151, USA. British and foreign standards can be obtained from Sales Department, British Standards Institution, 101 Pentonville Road, London N1 9ND; and British and foreign patents from the Patents Office Sales Branch, Block C, Station Square House, St Mary Cray, Orpington, Kent BR5 3RD.
Availability of Publications
Information-retrieval Service
Most papers listed may be obtained as loans or copies via local library or direct from Loans Department, British Library Document Supply Centre, Boston Spa, Wetherby, Yorkshire LS23 7BQ. Details of the British Lending Library's UK and International Services may be obtained from The Director, British Library Lending Division. Technical reports are also available from the Loans Department of the British Lending Library and in the USA from the National Technical
All entries are indexed in a computerized retrieval system, located at Harwell, which allows rapid searching of information relevant to any particular inspection problem. This service is available to both UK and overseas organizations through the National NDT Centre's Qualtis Subscription Scheme - further details are available from Phil Lawrence on Abingdon (0235) 433391.
Wong, W.; Jing, M.; Bendriem, B.; Hartz, R.; Mullani, N., Gould, K.L.; Michel, C. 36584
~C 1994 United Kingdom Atomic Energy Authority
NDT&E International 1994 Volume 27, Number 5
291