摘要:

In order to take full advantage of liquid scintillation measurements for low level radioactivity, a large part of the solvent should be synthesized from the material of the sample to be counted. This procedure has been applied to three natural radioactivity dating a large part of the solvent should be synthesized from the material of the sample to be counted. This procedure has been applied to three natural radioactivity dating methods. For carbon-14, the most sensitive and practical of the various liquids investigated is benzene. The compound, in addition to being a good liquid scintillation solvent, contains 92% carbon. The work on the synthesis of benzene for carbon-14 dating is now complete with yields approaching 100% and less than eight hours total chemical preparation time. Furthermore, the isotope effect for carbon has been proven to be small and reproducible to better than 1/2%.

ISSN:0369-1152    

DOI:10.1080/15421406808082917

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The emission produced by mutual annihilation of a pair of triplet excitons in single crystalline anthracene was observed to be an indicator of low level gamma-ray dose. Under steady red light illumination the blue emission intensiv Fris related to gamm-ray dose D by F−1/2= a + bD in the range 300R to 104R. Independent measurements show the effect cannot be due to changes in absorption in the red region, changes in quantum yield of fluorescence, nor to changes in the specific rate of triplet interaction. An interpretation based on dose induced quenchers and the long range of triplet excitons is given. By use of mulitple techniques an individual single crystal of anthracene can be used as a wide range dosimeter; triplet-triplet annihilatin in the range 102to 104R, space charge limited photo-current in the range 103to 106R, fluorescence quenching in the range 105to 108R, and absorption spectroscopy above 107R.

ISSN:0369-1152    

DOI:10.1080/15421406808082918

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The variation of light intensity with the time following excitation by gamma rays has been measured for a quaterphenyl compound whose solubility was enhanced by substitution of alkyl groups. The decay curves, measured by use of a probability-sampling technique, were analyzed to yield preliminary estimates of the time constants τ1 related to energy transfer from solvent to solute, τ2 related to the rapidly decaying component from the singlet state, and τ3 related to the slower component which is probably due to excimers. A solution (∼65 g/liter, γ = 1.12 × of 11, 44-bis(2-butyloctyloxy)-p-quaterphen (QP-G12) in toluene shows τ1∼ 0.05 nsec, τ2 ∼ 1.4 nsec, and τ3 ∼ 11.4 nsec. The intensity of the slow component (mean life τ3) is about 20% of that of the fast component (mean life τ2). This is about a third of the slow/fast ratio measured for 2,5-diphenyloxazone (PPO) in toluene at the same mole fraction. This indicates that QP-GI2 does not form excimers as readily as PPO does. For bothsolutes, measurement shows that τ1, varies about as the reciprocal of the concentration, as expected. For the same mole fractions, moreover, the fact that the value of τ1 for QP-G12 is only about half that for PPO indicates that the rate of transfer from solvent molecule to solute is higher for QP-G12 than for PPO. The QP-G12 has a higher light output and shorter τ1 and τ2 than the plastic Naton 136 which is commonly used for delayed-coincidence measurements. Preliminary attempts to exploit this advantage led to improved time resolution; for 511-keV gamma-rays, the full width at half maximum was about 0.25 nsec and the slope of the decay curve was τ1/2∼ 0.037 nsec.

ISSN:0369-1152    

DOI:10.1080/15421406808082919

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Several attempts have been made to produce a plastic scintillator based on epoxy resins instead of styrene or vinyl toluene. The advantages of such a system are many. The shrinkage on polymerization would be an order of magnitude less than styrene. Combined with low vapor pressure and a smaller exotherm, this would mean that scintillators could be easily cast into complex and readily reproducible shapes. Since the epoxies are cross-linked systems, such a scintillator would have greater dimensional stability, greater resistance to high temperature and to chemical or solvent attack, and essentially no tendency to stress crack or surface craze. It might be possible to operate such scintillators directly immersed in strong solvents, which could be very advantageous in many chemical and biological experiments. In addition, epoxy resins systems can be easily tailored for special applications by the addition of modifying agents such as flexibilizers.

ISSN:0369-1152    

DOI:10.1080/15421406808082920

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The paper deals with the problem: What properties are requested from an organic scintillator solute and what structural principles are given to realize, or at least to influence them especially by looking at the p-oligophenylene series? According to their importance and also in respect to more or less special purposes one can distinguish the following sequence:

ISSN:0369-1152    

DOI:10.1080/15421406808082921

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

2-Arylindenes (2),3-aryl-1,2-dihydronaphthalene(3),3-aryl-l,2-dihydro-4-methylnaphthalenes (4), 2-aryl-6-phenylindenes (5), 2-aryl-3-methyl-6-phenylindenes (6), 2-aryl-3,4-dihydro-6-phenylnaphthalene (7), 2-aryl-3,4-dihydro-lmethyl-6-phenylnaphthalenes(8), 2-aryl-3H-benz[e]indenes (9), 3-aryl-1,2-dihydrophenanthrenes (10), and 3-aryl-l,2-dihydro-4-methylphenanthren (11) in which the substituent aryl group was phenyl (a), l-naphthyl (b), 2-naphthyl (c), or 4-biphenylyl (d) were synthesized and tested as liquid scintillator solutes in toluene at various concentrations. Fluorescence spectra in toluene and ultraviolet absorption spectra were also determined. It was found that the compounds having the ethylenic double bond in a five-membered ring were better scintillators at low concentrations than those having the ethylenic double bond in a six-membered ring; however, at increased concentration the six-membered ring systems surpassed the fivemembered ring systems in scintillation efficiency. In addition, the presence of a methyl group on the ethylenic carbon adjacent to that holding the substituent aryl group had a profound decreasing effect on the scintillation efficiency in the sixmembered ring compounds but no decreasing effect on the five-membered ring compounds.

ISSN:0369-1152    

DOI:10.1080/15421406808082922

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The advantages of using a secondary solute in plastic and liquid scintillators, and the manner in which such solutes define scintillation performance, are reviewed. Potential secondary solutes of general structure Ar1-X-Ar2-X-Ar1, where X is an oxadiazole, oxazole or 5-phenylpyrazoline group, were synthesized and their spectra1 and scintillation properties were measured. The relationship between the molecular structure of these compounds and their spectral properties is examined. It is postulated that anomalous spectral displacements which were observed can be explained in terms of the distorting effect of the heterocyclic groups on the conjugated system. A procedure is outlined forthedirect measurement of the reabsorption by a solute of its own fluorescence emission. The contribution of reabsorption to light attenuation in practical scintillators is discussed and a model experiment is proposed to determine the extent of this contribution.

ISSN:0369-1152    

DOI:10.1080/15421406808082923

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Measurements of the relative scintillation yields of some liquid organic systems were carried out with several highly soluble scintillator solutes. Self quenching was observed at high concentrations with some of the solutes, but not with others. The results were correlated with the ability of the solute molecules to come together, in a special configuration, close enough to form an association. A study of the atomic models of the solute molecules showed that those moleculeswith chromophor systems which were non-coplanar, or co-planar but shielded by substituent groups, did not produce self quenching. However, those solute molecules with unprotected co-planar chromophor systems did produce self quenching at high solute concentrations.

ISSN:0369-1152    

DOI:10.1080/15421406808082924

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A study has been made of the quenching properties of alcohols inliquid scintillator solutions. Sixteen alcohols,n-C-1-n-C-10, and branched chain alcohols up to C-5 were studied in two of the more common scintillator solutions (toluene and dioxane base), using carbon-14 and tritium. Irrespective of the composition of the scintillator and independent of the activity, the quenching decreased with increasing molecular weight of the quenching agent when expressed on a volume basis. The converse is true when the composition is expressed on a molar basis. Branched chain alcohols show a decreasing quenching ability with increasing substitution on the alpha-carbon. Quenching properties of binary mixtures of alcohols are intermediate between the quenching curves of the pure alcohols. The quenching behavior of the alcohols was compared with that of compounds containing the same number of carbons but different functional groups. Quenching is dependent not only upon the number of molecules but also on the steric factors affecting the functional group primarily responsible for the quenching.

ISSN:0369-1152    

DOI:10.1080/15421406808082925

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

In the use of fluorescing organic compounds as solutes for liquid scintillators several factors must be considered. The photon yield of the scintillators must be high, the spectral matching to the photomultiplier sufficient and the fluorescence decay time should be short. Besides these physical properties also some practical requirements must be fullfilled. The solubility in the solvent used should be high and the scintillator should be as little affected by quenching agents as possible. For convenience in handling and sufficient shelf life of the solutions, the photochemical degradation of the scintillator must be negligible.

ISSN:0369-1152    

DOI:10.1080/15421406808082926

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor