464 research outputs found
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
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