Studies towards improved focusing methods of photoelectron autoradiography

Since the discovery of radioactivity, due to the photographic action of the emitted radiations, by Becquerel in 1896, the photographic plate has been an important tool in the detection of electrons. Although overshadowed by electronic counting devices, it still plays an important role, since the developed image gives a more detailed distribution of the radioisotope in the specimen under observation. The technique of autoradiography utilises the photographic action of all the emitted ionizing radiations for locating the radioactive material in a sample, and was first used by Lacassagne and Lattes (l ) in 1925. The general procedure is to introduce the active isotope into the system and to select the specimen to be studied, which is then placed in contact with a suitable photographic material and left for exposure. After processing, the location of the radioactive material can be deduced by studying the image, but the latter is not sharp since it is difficult to achieve intimate contact between the specimen and recording film. This method gives autoradiographs with a resolution of 50 to 100 microns(2) . An improved method was achieved by Evans(3), who floated sections of his material on to a photographic plate which was then dried out and left for exposure. The resolving power of this method was estimated to be 5 to 6 microns. Belanger and Leblond(4) obtained similar resolution by coating sections with liquefied emulsion at 37° C. These methods suffer from many disadvantages. The activity has to be firmly fixed in the emulsion so that subsequent treatment will not leach it out; also there is a danger of artifacts caused by diffusion and pressure, and the inactive substances in the specimen often render the emulsion grains developable. In the stripping plate technique described by pe1c(5) and others, the emulsion is mounted on a thin support (cellulose esters have been used) and the latter shields the emulsion from abrasion and chemical action, but this advantage is gained at the expense of resolution. There have been many refinements of the method. Berriman, Herz, and Stevens(6) using a new, fine grain emulsion 4 microns thick on top of ordinary emulsion have obtained a resolution of 200 lines per mm. Gomberg(7) has developed a method called wet process autoradiography and claims a resolution down to 1 micron, but there is a corresponding loss in resolution when a protective coating is used to shield the one micron thick sensitized layer, formed on the surface of the specimen, from direct interaction with the chemicals used in forming the film. None of these methods employs direct magnification, although Fink(8) mechanically enlarged the specimen between lead sheets in a rolling mill, before the autoradiograph was taken. Optical magnification of the image is employed, but when this is greater than 10x, the silver grains appear as groups of hazy smudges, irregularly distributed, and no longer give a true picture. The only way to get direct magnification is to use a focusing method, in which the electrons emitted from the specimen pass through a suitable magnetic field and form an image on the photographic plate some distance from the specimen. In this method the whole system is in vacuo. Emission microscopes, in which the object constitutes the source of electrons, have been used for a long time, but these did not employ a radioisotope as a source of electrons. According to Lawrence(0) , sections have been placed in magnetic fields in an attempt "to pull the /3 -rays straight out and get real cell definition" but magnetic fields are not intense enough for this. In 1947, Marton and Abelson(10) described a method called tracer micography in which monoenergetic internal conversion electrons from a radioactive source were focused by a magnetic lens, producing a magnification of 1.6x. With their apparatus, using a 1 milli curie per mm2 source of Ga67 at a numerical aperture of 0.04 radians, satisfactory blackening of a plate was obtained after a 1 hour exposure. They obtained a best resolution of 30 microns, and proposed after-acceleration of the electrons to reduce exposure time, spherical aberration, and possibly chromatic aberration. At the same time, a similar instrument was developed in Edinburgh(11), (12) with which a resolution of 5 to 10 microns was obtained at a magnification of 7x. An attempt has been made to improve this instrument, and to study the principles on which its operation depends; also to evaluate the potential of such an instrument in the field of autoradiography. The work involved is described in the following chapters

Spacelab- A Critical Review

A review of the Spacelab Programme from the point of view of a potential user is provided. In this context, the promise of Spacelab prior to the start of its development is compared with it currently estimated performance. A critical assessment of the utilisation of Spacelab is also included. Typical topics discussed include services provided for users (e.g. payload capability, available power and energy, thermal control) and operational aspects (e.g. mission duration, mission costs, participation by experimenter). Although, generally, there is good agreement with the initial specification, areas for concern are identified as power available to experiments, flight duration, data storage and most importantly operational costs

How close are formal and informal work?

Purpose: Recent changes in the UK to the regulation and modes of work in the formal and informal economies are considered. Research in this field has tended to remain in silos (treating formal economy working conditions separately from research on the informal economy. The question is whether the means of work and benefits to the worker for formal and informal work are now as different as the former images of formal and informal economy work imply under a ‘jobs-for-life’ economy. This leads in to a consideration of whether the current aim of government regulation of the informal economy – to formalise it – is actually of benefit to workers, as might be supposed. Design/methodology/approach: The article considers recent research findings on the formal and informal economy, using official government statistics for the UK and more detailed European studies on the informal economy. Findings: The article argues that formal employment in the UK is becoming more casualised, with less associated benefits to employees. Though it is still of benefit to the state to formalise informal work (to increase tax take), some of the links between formalisation and a good working environment for workers are being broken, which may lead to the informal economy becoming more popular and require different priorities in regulation. Originality/value: The article argues that we need to change our assumptions and image of work in the formal economy, compared to that in the informal economy

Asteroid belt and jupiter flyby mission study final report

Asteroid belt and Jupiter flyby mission stud

A European Approach to the Utilisation of Spacelab

The Spacelab Utilisation Programme conceived in Europe to encourage the use of Spacelab and to provide a ready access to space for European experimenters is summarised in concept and content. Within this programme four Demonstration Missions are planned to illustrate the usefulness of Spacelab and these are briefly described. In addition, considerable work has been done in Europe on possible payloads for Science and Applications. Some examples of these are provided

European Use of Space Shuttle

Europe\u27s association with the Space Shuttle started in 1973 when the European Space Agency (ESA) signed a Memorandum of Understanding with NASA for the development in Europe with European funds of Spacelab. In addition, it was agreed that ESA would provide approximately one half of the first Spacelab payload which will be carried on the SL-1 mission in September 1983. Further usage of Spacelab is foreseen either in missions dedicated to European countries or in missions shared with NASA. Also, it is anticipated that European space projects will make use of the launch and recovery capability of the Space Shuttle when these services are considered to be cost attractive. Finally, augmentation of the Shuttle\u27s capabilities is another likely area of participation through the provision of a European-built upper stage. This paper summarises these activities both from an ESA-NASA point of view and from the outlook of bilateral (i.e. NASA-ESA Member State) co-operation

Herstelbemiddeling in twee gevangenissen: positieve effecten op stoppen met misdaad? (Recovery mediation in two prisons: positive effects on stopping crime?)

Over the last twenty years, research on desistance from crime and on restorative justice has grown rapidly and both have emerged as exciting, vibrant, and dynamic areas of contemporary criminological interest. While the implementation of restorative justice practices in Europe has been essentially victim-oriented, there has always also been an emphasis on including the moral and social rehabilitation of the offender. This more offender-centred approach to restorative justice and its practices is not limited to the evaluation of its ability to reduce crime, but is to be seen within the connection between reparation, resettlement (reintegration into the community after sentence), and desistance from crime. This article examines, from a broad perspective, but including some data from research on victim-offender mediation in prison, the capacity of restorative justice interventions to impact positively on offenders’ likelihood of stopping committing criminal offences

Exploring recent developments in restorative policing in England and Wales

The evolution of the policing role over the last decade has led to 33 police forces in England and Wales integrating restorative justice practices, in one form or another, into their responses to minor crime committed for the first time by both youths and adults. Most recently, this reform dynamic has been used in response to more serious offences committed by persistent offenders and expanded to include all stages of the criminal justice process. Despite the significant positive rhetoric that surrounds the adoption and use of restorative justice, there are a number of procedural and cultural challenges that pose a threat to the extent to which restorative justice may become embedded within the policing response. This article explores these developments and highlights where potential problems for implementation may arise as well as some strategies to overcome them