Aspects of the resorcinol-formaldehyde condensation
- Authors: Waldron, Ronald Augustus Frank
- Date: 1954
- Subjects: Resorcinol , Formaldehyde
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4514 , http://hdl.handle.net/10962/d1013460
- Description: An attempt was made to producea -β or Ϫ - resorcinyl alcohol from disubstituted resorcinyls. To accomplish this 3,5-dibromo-β-resorcylic acid was reacted with lithium aluminium hybride, a mild reducing agent, in an attempt to reduce the acid group to the alcohol group. This disubstituted resorcinol was recovered unchanged. 3,5-dibromo-β-resorcyl-aldehyde was reduced by lithium aluminium hydride, but, instead of the alcohol forming, resinification took place. 2-methyl- 4-ethylresorcinol and 4,6-diethyrecorinol were reacted with formaldehyde under alkaline and acidic conditions. In each case a resin formed. The above experlments indicated that condensation took place in the meta position of the resorcinol molecule. Trimethylresorcinol was therefore reacted with formaldehyde under alkaline conditions, resulting in a small quantity ot the alcohol derivative. A better yield of the alcohol derivative was obtained by the hydrolysis or the chloromathyl derivative. In pursuing this line, a seres of new compounds and their derivatives were prepared. The condensation of the alcohol derivative with trimethylresorcinol and also with resorcinol was investigated.
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Defoe and Scottish politics after union
- Authors: Gathorne, R
- Date: 1954
- Subjects: Defoe, Daniel, 1661?-1731 -- Political and social views , Scotland -- History -- 1689-1745
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2605 , http://hdl.handle.net/10962/d1011941
- Description: It would indeed have been a difficult matter for anybody possessing a taste for self-expression, a facility with words and an insatiable imagination to avoid becoming involved in political controversy in England during the early part of the Eighteenth Century. For one who, in addition, was confident in his ability to solve problems of state of whatever complexity it was clearly an impossibility. Daniel Defoe's close connection with politics during the first years of the Eighteenth Century involved him in numerous hardships. In later years it brought him much less fame than his excursions into fiction; but it was the means of providing him, albeit sparsely at times, with sufficient money to keep his creditors at bay. On more than one occasion the protection he gained helped to rescue him from imprisonment. Intro., p. 1.
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Rhodes University Graduation Ceremony 1954
- Authors: Rhodes University
- Date: 1954
- Language: English
- Type: text
- Identifier: vital:8088 , http://hdl.handle.net/10962/d1004398
- Description: Rhodes University Graduation Ceremony in the Grahamstown City Hall on Friday , 2nd April, 1954, at 8 p.m. [and] Graduation Ceremony held in April 1954: University College of Fort Hare. Graduation Ceremony. April 23rd, 1954. , Ceremony to commemorate the fiftieth anniversary of the Foundation of Rhodes University College and congregation for the conferment of honorary degrees, City Hall, Grahamstown, Friday, 24th September, 1954, at 11:15 a.m.
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Some aspects of the insect ecology of citrus orchards
- Authors: Smithers, Courtenay Neville
- Date: 1954
- Subjects: Citrus -- Diseases and pests , Insect pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5883 , http://hdl.handle.net/10962/d1013231
- Description: After a brief introduction, the species of Citrus on which the investigations were carried out are mentioned. This is followed by an account of the methods of collection used, and a discussion of their relative merits. The main method used was that in which the trees were fumigated with hydrocyanic acid gas, and the insects falling from the trees were taken up on sheets. The location of the areas where collections were made are then given. An annotated list of the species taken by the fumigation method follows, and the numerical data obtained at the same time regarding the species present is given in an abbreviated form and discussed. A more detailed discussion of the relative abundance of the species is then undertaken. The discussion of the ecology of the insects commences with the insects listed according to their activities, so far as known, and an account of five trees of striking faunal differences is given. A broader discussion of citrus ecology is then given, based on the data previously presented; this ends with a short reminder of the inherent 'oneness' of the insect with its environment.
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Some measurements of the conductivities of dilute potassium chloride solutions
- Authors: Faure, Abraham
- Date: 1954
- Subjects: Potassium chloride
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4471 , http://hdl.handle.net/10962/d1011787
- Description: A constant temperature room has been constructed in which the thermoregulator is controlled by a temperature-sensitive resistance. A thermostat has been constructed in which the 0 temperature is controlled to within 0.001°C. A precision conductance bridge has been built in a very convenient form. Improvements include the replacement of the telephone as null detector by a cathode ray oscilloscope, and the use of a resistance-capacity phase-shift oscillator, which gives a good wave-form. An automatic recycling conductance water still has been built which regularly gives water with a conductivity less than 0.09 micromhos per cm. The conductivities of dilute KCl solutions have been measured, taking special care to prevent errors due to the adsorption of KCl on the surface of glass. Two cells were used for these measurements : a modified Jones cell, and a special conductimetric titration cell. The modified Jones cell has given results in good agreement with the generally-accepted values. The results of the conductimetric titration cell do not agree well with the generally-accepted values; the greatest difference (for the most dilute solution) is 0.4%. The reason for this is not known.
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Studies in the comparative anatomy and systematic importance of the hexapod tentorium
- Authors: Hudson, Gerda Bland
- Date: 1954
- Subjects: Insects -- Anatomy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5858 , http://hdl.handle.net/10962/d1012457
- Description: During a study of the morphology of the orthopteroid Hexapoda between the years 1939-1941, it appeareded to the writer that further investigation into the structure of the insect tentorium was necessary. The early entomologists laid the foundation or our knowledge or the tentorium but during the latter half of the last century little was added in this particulart field. Comstock and Kochi (1902), as far as the writer is aware are the only workers who have published a paper devoted entirely to the skeleton of the bead of insects, and they did much to clarify both nomenclature and existing knowledge of this structure at that time. Berlese (1909) described a typical tentorlum as observed in orthopteroid Hexapoda and then considered the variations of the tentorium which occur in other groups of insects. Some confusion then appears to have arisen amongst workers, over the origin of the dorsal arms which were erroneously considered by some to be cuticular invaginations and not secondary outgrowths of the anterior tentorial arms. Certain morphologists amongst them, Hoke (1924) Denis (1928), Snodgrass (1928, 1935), Hansen (1930), Walker (1933) Imms (1934), and Symmons (1952), have done much towards improving our knowledge of the tentorium, but all too frequently workers offer brief and inadequate descriptions of this structure in otherwise comprehensive investigations of the insect head. Themain objects in this study are threefold, vlz. (1) The claification of nomenclature (2) The examination and the interpretation ot the tentorium in certain groups of insects. (3) The deliberation as to whether the tentorium is of phylogenetic significance, and thus of use in assessing various schemes of insect classification which have been presented. Introduction, p. 1-2.
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Studies on the behaviour of Anomala opacicollis (Pér)
- Authors: Miles, Peter Wallace
- Date: 1954
- Subjects: Anomala -- Behavior -- Zimbabwe , Anomala -- Control -- Zimbabwe , Anomala -- Larvae -- Zimbabwe , Scarabaeidae -- Zimbabwe , Beetles -- Control -- Zimbabwe , Tobacco -- Diseases and pests -- Zimbabwe , Tobacco industry -- Zimbabwe , Insecticides -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5901 , http://hdl.handle.net/10962/d1013514
- Description: [Summary]: The larvae of Anomala opacicollis (Pér), of Melolonthid and of other Rutelid species, attack tobacco in Southern Rhodesia, and are more commonly called "whitegrubs". Whitegrubs are widespread in the sandveld areas where tobacco is grown and, at the Trelawney Station of the Tobacco Research Board of Southern Rhodesia, where this work was done, A. opacicollis was the predominant species. An account o£ the one year life cycle is given. The adults eat the leaves of various indigenous trees and an account of an experiment on the food preferences of A. opacicollis adults is given, and the main food sources in the Trelawney area are listed. An experiment is described which shows that the beetles prefer to lay their eggs in the veld or in manured broken land rather than in normal ploughed lands. The larvae are erratically distributed in lands and experiments on larval movement suggest that this is mainly due to concentration of the larvae at discrete concentrations of organic matter in the soil. The temperature and moisture condition of the top 3" of soil are found to be those which attact the larvae. It is suggested that tho larvae prefer and move to soil which contains the lowest amount of moisture which keeps the soil air spaces saturated. lt appears that the preferred temperature decreases with increasing soil moisture content and it is suggested that this is due to the respiratory requirements of the larvae. Soil pH, compaction and fertiliser content and the presence of plants do not appear to influence larval movements. A theory is developed concerning the mechanism of movements in the soil and it is suggested that, in the absence of a continuous gradient, the speed but not the direction of movement is influenced by conditions to which the larvae are sensitive. Evidence in support of thie theory is given. Studies on the survival of larvae at different soil moisture contents and temperatures show that conditions in the top 3" of soil are not likely to be lethal in spite of the high temperatures and low moisture contents found there. The relation of whitegrub behaviour to agricultural problems is discussed. Other workers published evidence indicating that early ploughed lands were attractive to whitegrubs; this is shown not to be the case and the previous evidence is re-interpreted. Such lands tend to contain concentrations of whitegrubs round the borders. The reason for this is discussed and it is suggested that lands should be ploughed early to confine whitegrub infestations in this manner. Soils low in fertility through repeated cultivation are commonly believed to contain more whitegrubs than virgin soil. However, behaviour studies suggest that it is the activity and not the size of the population which is affected by soil fertility. The time at which tobacco is planted is known to determine the extent of subsequent whitegrub damage. The reason for this is to be found in the life cycle of whitegrubs and the results of an experiment on time of planting in relation to whitegrub damage are given. Some insecticides are shown to be more repellant than others to A. opacicollis larvae and the influence of this fact on the assessment of soil insecticide effectiveness in the field is discussed. Reference is made to a method developed by the writer for the determination of insecticide effectiveness under the conditions of erratic whitegrub distribution which normally occur.
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The chemistry of naturally occurring long chain unsaturated compounds
- Authors: Silk, M H
- Date: 1954
- Subjects: Compounds, Unsaturated
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4518 , http://hdl.handle.net/10962/d1014332
- Description: [From Introduction, p. 3] Raw marine oils are subject to considerable variation in composition with season and are moreover very unbalanced oils for direct use in the paint industry. Further refining is undertaken chiefly by Messrs Marine Oil Refiners of Africa Ltd., whose factory is situated at Simonstown. In their plant marine oils and others are treated by the Solexol process involving counter current extraction of the oil with liquid propane in a tower over which a temperature gradient is maintained. The process achieves the removal of a large proportion of the relatively saturated glycerides, the natural antitioxidants, and the relatively highly unsaturated components, all of which are detrimental to the eventual formation of good paint films. The segregated marine oil from the Solexol process is then bodied or polymerised at high temperatures to yield a "drying oil" which is used as a substitute for bodied linseed oil in paints. The chemical reactions taking place during the polymerisation and drying of these oils are of an exemely complex nature, and for their understanding it is necessary to have an accurate knowledge of the chemical nature of the component fatty acids in the natural glycerides ... The term "marine oils" in this work should be understood to mean marine fish body oils, marine mammal oils being excluded from consideration.
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The determination of the solubility of mercurous chloride at 25°C
- Authors: Dry, Mark Eberhard
- Date: 1954
- Subjects: Mercuric chloride
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4463 , http://hdl.handle.net/10962/d1011576 , Mercuric chloride
- Description: After the publication of the paper by Gledhill and Malan in which precision conductance techniques were used for the first time in the determination of the solubility of silver chloride, Dr. N.H. Perton of Christchurch College, New Zealand, wrote to Gledhill and suggested that the same methods might be rewarding if applied to the determination of the solubility of mercurous chloride. A review of the Chemical literature showed that the values for the solubility of mercurous chloride were not at all consistent. Into., p. 1
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The polarographic determination of trace elements in blister and refined copper
- Authors: Eve, Adrian John
- Date: 1954
- Subjects: Copper , Polarographs , Polarography
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4467 , http://hdl.handle.net/10962/d1011769 , Copper , Polarographs , Polarography
- Description: In the complete analysis of copper the following impurities are generally determined: silver, gold, lead, arsenic, antimony, selenium, tellurium, iron, zinc, cobalt, nickel, oxygen, sulphur, and, less commonly, tin and phosphorus. The actual copper content varies around 99.0% in blister copper; in the refined metal the content is somewhat higher, usually over 99.9%. The concentrations of the individual impurities vary from tenths to thousandths of one per cent.
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The rehabilitative value of sub-economic housing as illustrated by Schauder Township, Port Elizabeth, Cape Province, Union of South Africa, 1938-1948
- Authors: Stoker, F M L
- Date: 1954
- Subjects: Housing rehabilitation -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3389 , http://hdl.handle.net/10962/d1014554
- Description: [From Introductory discussion]. The modern approach to any sociological problem is characterised by the attempt to analyse the contributory factors in such a way that their inter-active association is clearly discernible. The simple concept of "single cause and effect" is now recognised to be a traversity of social fact. Social Pathology, therefore, may be said to attempt to isolate the multiple factors involved in a given situation, and to endeavour to determine thelr mode of inter-action in order that remedial techniques may be applied effectively. Slum conditions are obviously pathologic, by which it is understood that the environment imposes strains upon the individual to which there is ineffective adjustment. The rehabilitation of such a population would involve the converse process, restoring individuals to a condition where they are able to cope in every respect with the demands of life at their respective class levels. It is very rare indeed that only a single factor is involved in a social pathological condition and for this reason it is quite possible that one- sided efforts at rehabilitation - such as the attempt to re-house ALL slum dwellers in sub-economic houses - have a tendency to increase the pathology in another direction. Rehabilitation must therefore be based on multi-factorial analysis in which allowance is, as far as possible, made for the inter-connection of each of the individual deviations from the normal. The aim of this thesis is to evaluate the effect of good housing conditions on the 2335 Coloured slum families re-housed in sub-economic houses at Schauder Township, Port Elizabeth, from the time that these houses were first available for occupancy.
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A critical study of the evidence of Andries Stockenstrom before the Aborigines Committee in 1835, viewed in the light of his statements and policies before 1935
- Authors: Urie, J M
- Date: 1953
- Subjects: Stockenstrom, Andries, 1792-1864 , Eastern Cape (South Africa) -- History -- 19th century
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2617 , http://hdl.handle.net/10962/d1013416
- Description: In recent years, increasing interest has been taken in the career of Andries Stockenstrom. Detailed study of his policy as Landdrost of Graaff-Reinet , as Commissioner-General of the Eastern Districts, and as Lieutenant-Governor, has brought about a realization of the soundness and value of much of his work. This appreciation of the sterling qualities of Stockenstrom's character- despite his undoubtedly difficult temperament - has led to the tacit assumption that the accusations which were levelled against him, and the odium in which he was held in Albany, after his evidence before the Aborigines Committee 1835 -1836, were largely the result of unfortunate newspaper propaganda. That evidence, it is implied - coming as it did at a time when public opinion was peculiarly sensitive to criticism - was in fact, not as black as it had been painted. Yet the events of the period between the Commissioner-Generalship and the Lieutenant- Governorship have not only coloured the judgment upon Stockenstrom of almost every writer on South African history, but so influenced contemporary public opinion as to materially impair the efficiency of his Lieutenant-Governorship. In writing this thesis, it has heen my purpose to make a detailed study of such material as is available for the period 1833-1836, and to endeavour, by an analysis of the evidence more particularly in the light of the years before 1833, to set this significant period in Stockenstrom' s career in its right perspective.
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A preliminary investigation of the ecology of the Larger Kleinmond River Estuary, Bathurst District
- Authors: Brown, Alexander Claude, 1931-2005
- Date: 1953
- Subjects: Kleinemonde River Estuary (South Africa) , Estuaries -- South Africa , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5904 , http://hdl.handle.net/10962/d1014611
- Description: Introduction. On the coast of the Bathurst Division, Eastern Cape Province, some 42 miles south- east of Grahamstown, lie two estuaries opening within a few yards of one another. These are known as the Kleinemonde. This paper embodies the results of an ecological survey of the fauna of the Larger Kleinmond Estuary. The chief concern has been the aquatic fauna but animals living along the banks have also been dealt with as far as possible, as have the birds. This is the second of South Africa's blind estuaries to be studied, the Klein River, Hermanus, having been investigated in 1947-49 by workers from the University of Cape Town. Though common in South Africa, blind estuaries are rare in parts of the world such as Europe, and present an almost entirely new field of research for the ecologist. It is hoped, therefore, that the investigation of the Kleinmond Estuary and a comparison with the results obtained from the Klein River, Hermanus, will add to our knowledge of this subject and be of service to future investigators. The history of the Kleimnond River is worthy of mention, for the lagoon was not always blind and shallow. The early maps of the 1820 settlers show the river as a navigable stream; sailing vessels anchored out at sea and sent lighters up what was then known as the Lydendoch River to collect fresh meat. The area at the mouth of the river was called Port Jessie. In these early days the region abounded with game. Hippo and elephant were common. the former inhabiting deep pools in the upper reaches of the river; pools which have since completely silted up. Constant ploughing of the slopes adjoining the river has caused vast amounts of soil to be washed by rains into the stream, and today what was within living memory a deep, clear stream is a shallow, blind and muddy river, a reflection of man's destructive methods of farming. These changes must have had a far-reaching effect on the fauna of the estuary; an effect about which we can, alas, only speculate. It is perhaps significant that though rich in numbers, the fauna is poor in species, tunicates and echinoderms being apparently entirely absent. The work involved in this survey was undertaken between September 1952 and November 1953, under the direction of Professor J . Omer-Cooper of Rhodes University, frequent and regular visits being made to the estuary. The entire month of February, 1953, was spent on the shore of the lagoon, so that animals could be observed over a continuous period. The starting date of the survey was particularly fortunate, as on September 28th, 1952, the river came down in flood and broke through the sand-bar separating the lagoon from the sea. The work thus began at a definite point in the estuarine cycle, the importance of which it is hoped to show.
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Rhodes University Graduation Ceremony 1953
- Authors: Rhodes University
- Date: 1953
- Language: English
- Type: text
- Identifier: vital:8087 , http://hdl.handle.net/10962/d1004397
- Description: Rhodes University Graduation Ceremonies in the Grahamstown City Hall on Friday , 27th March, 1953 at 8 p.m. [and] University College of Fort Hare Graduation Ceremony April 17th, 1953.
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Studies in chromium complexes
- Authors: Friend, Maurice Temple
- Date: 1953
- Subjects: Complex ions , Chromium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4474 , http://hdl.handle.net/10962/d1011892 , Complex ions , Chromium
- Description: In this work physical and analytical methods have been used to investigate the potassium salts of certain dioxalato chromium (III) complexes. The solid potassium salts of the trioxalatochromiate and the cis and trans dioxalatodiaquochromiates together with a salt corresponding to potassium dioxalatosulphatoaquochromiate were prepared. The mono- and dihydroxo derivatives of the cis and trans dioxalatochromiates were also obtained in aqueous solution. The methods of preparation and analysis used are described. Spectrophotometric absorption curves obtained on solutions of these salts using a Beckman Spectrophotometer are in agreement with results of previous workers, and the new absorption curve obtained from a solution of the solid cis dioxalatodiaquochromia salt shows that it is pure and gives additional proof of the completeness of the trans - cis isomerisation. Summary, p. i.
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Studies in chromium complexes
- Authors: Cooper, Desmond Rudolph
- Date: 1953
- Subjects: Chromium , Complex ions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4523 , http://hdl.handle.net/10962/d1014707
- Description: The chemistry of co-ordination compounds in general has played an important role in the development of the modern theory of valency, but the properties of complex salts between chromium and organic compounds containing carboxyl and amino- groups are of additional interest because of their bearing on the theory of certain technological processes such as chromium plating and, in particular, chrome-tanning. Owing to the rapid development of valence theory over the last two decades the technological chemist finds himself at a disadvantage vis-a-vis his academic counterpart in attempting to interpret the results of researches relating to these compounds as he must rely on the less powerful "classical" approach to his problems. Hence the need was felt for a brief survey of modern concepts of valency in terms of wave mechanics. For a more extended study the reader may consult the appropriate references and text books.
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Studies on Paragus (Diptera, Syrphidae)
- Authors: Stuckenberg, B R
- Date: 1953
- Subjects: Syrphidae , Diptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5887 , http://hdl.handle.net/10962/d1013321
- Description: As several new species are described in this thesis its full value can only be realised by its publication, and it has therefore been prepared with that end in view. The subject matter is divided into two parts, each of which has been treated quite independently of the other. Both parts are presented here in the form in which they have been offered for publication. The first paper consists of a systematic study of a complex of species within the genus Paragus. It includes descriptions of four new species, a new subspecies, an allotype, and redescriptions of two incompletely defined species. This paper has been offered for publication in the Transactions of the Royal Entomological Society of London. The second part consists of a study of all the Ethiopian species of Paragus except those covered by the first paper. It includes the definition of a new subgenus, and descriptions of two new species and three allotypes. It has been sent for publication in the "Revue Zoologie et Botanique de Africaine" at the invitation of Dr. P. Basilewsky of the Musee du Congo Belge, Tervuren.
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The chemistry of the wattle tannins
- Authors: Roux, David Gerhardus
- Date: 1953
- Subjects: Tannin plants , Tannins , Wattles (Plants)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: vital:4492 , http://hdl.handle.net/10962/d1013098
- Description: Four species of acacia of Auatralian origin are associated with the wattle industry in South Africa. Black wattle, Acacia mollissima willd., is the most important of these and is today almost exclusively cultivated. The tree grows successfully only in a limited area of rich soil and high rainfall and is easily affected by adverse conditions caused by insect pests, frost damage and drought. Expansion of the area under cultivation is therefore, not feasible, although the world demand for vegetable extracts far exceeds the available supply. The remaining species such as green (Acacia decurrrens willd.) and silver wattles (Acacia dealbata Link.) possess many desirable characteristics which resist such adverse factors. Their barks, however, give reddish extracts, which are considered unsuitable for tannery usage because of the red colour they impart to the leather. Hybridisation studies, involving the crossing of green and silver wattle with the black, and aimed at produc1ng progenies containing many of the desirable characterlstics of the parent plants, are thus a natural result and have been in progress for a considerable period. Summary, p. i.
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The petrology of the Khale dolerite sheet
- Authors: Eales, Hugh V
- Date: 1953
- Subjects: Petrology -- Botswana , Diabase -- Botswana
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5076 , http://hdl.handle.net/10962/d1014853
- Description: In the hills and in the plain of the Khale area are exposed two sheets of quartz-dolerite, the upper sheet being locally mushroom-shaped. The rock corresponds loosely with the Downes mountain type of dolorite, and contains numerous horizons of coarse-grained dolorite-pegmatite. The plagioclase felspars are described with special reference to the variation of grain-size, the features of zoned crystals, and the possible causes of a peculiar brown clouding in the basic zones of the crystals. Phenocrysts of augite and pigeonite, as well as plagioclase are recorded in the chilled contact rock. The micrometric data indicate that the mineral composition of the specimens is largely governed by the oxidation state of the iron, and that the Soret effect has caused the marginal rock to be enriched in basic elements. Hydrothermal veinlets composed largely of chlorite occur in both the dolorite and the country rock, and evidence suggests that veins of both residual material and mobilised granite occur in the upper finer-grained dolorite.
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The response of pure organic crystals to ionising radiations
- Authors: King, J W
- Date: 1953
- Subjects: Inorganic scintillators , Crystals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5529 , http://hdl.handle.net/10962/d1012641 , Inorganic scintillators , Crystals
- Description: The introduction contains introductory remarks on scintillation counters together with a brief description of the exciton theory believed to be the means of primary energy migration within organic crystals. Part I contains a review of the data published on the reletive responses of different organic crystals and the attempted correlations of these results with the molecular structures of the different phosphors. From data which may be accepted as being both reliable and suitable for comparison it is concluded that theories involving correlations between phosphor efficiencies and molecular structures may be tested only if the efficiency data has (i) been extrapolated to give results for crystals of very small thickness and {ii) been obtained at very low temperatures. Part II contains accurate calculations based on the exciton theory proposed by Birks (1951 ) to account for the response of crystals to different types of ionising radiations. Satisfactory agreement is obta1ned with all the avalable experimental data in the literature. In part III an account is given of the response of organic crystals observed by the author for low-energy ⋉particles, and of the similar behaviour found by Taylor et al, (1951 ) for low-energy electrons. A possible extension of the theory described in part II, allowing for the escape of excitons through the crystal surface is given accounting for this behaviour. An exciton mean free path in anthracene, terphenyl and stilbene of about 3 - 7/u is obtained. Results were obtained with strong ⋉-particle sources which could not be explained. in terms ot normal response of the phosphor used. This effect was inventigatea as described in part IV, and it is shown that photons are produced in air, glass and quartz when these materials are irradiated by ⋉particles. This luminescence was probably responsible for the "scintillations" which Richards and Cole (1951) have ascribed to thin films of various materials. Problems requiring further investigation are indicated.
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