Milton Burton

Comparison of High‐Energy and Ultraviolet‐Radiation Induced Luminescence in Liquid Systems

Luminescence induced by Co60‐gamma excitation of some organic solvent‐solute pairs has been compared with 2537 A excitation as to dependence of intensity on solute concentration and on concentration of an added quencher. The solutions studied were 1,6‐diphenylhexatriene in benzene, p‐terphenyl in benzene, and p‐terphenyl in toluene. The quencher was bromobenzene. The energy‐transfer parameter Q of the Kallmann‐Furst theory and the quenching constant were obtained for each of the systems. Within an estimated experimental error of about 5%, Q was unaffected by change in source of excitation. The efficiency of quenching was found to be greater for Co60‐gamma than for uv excitation for the two systems involving p‐terphenyl. With diphenylhexatriene as solute, however, the quenching constant was unchanged. These results argue against a mechanism of energy exchange involving charge transfer. The high rates of transfer and quenching are consistent with a picture of the solvent involving the existence of small ord...

Ultraviolet Lamp for the Generation of Intense, Constant‐Shape Pulses in the Subnanosecond Region

A commonly available mercury contact relay is modified to make a uv lamp which yields a spark with approximately 100 times the intensity of the original relay and with constant characteristic risetime of 0.4 nsec, decay time of 0.55 nsec, and half‐width of 0.5 nsec. The lamp can be used not only for fluorescence decay‐time studies, but also for electrical applications in the subnanosecond region. It has been operated in the range 3 to 50 000 pulses per second.

Luminescence Decay Times. Concentration Effects

The optical properties (e.g., absorption spectrum, fluorescence spectrum, luminescence decay) of solutions of 2,5‐diphenyloxazole (PPO) and p‐terphenyl in benzene and cyclohexane are reported as functions of solute concentration. The absorption spectra of the solutions, when plotted as extinction coefficient vs wavelength, are unaffected by scintillator concentration, but the fluorescence spectrum of PPO solutions is affected in both intensity and shape. The luminescence decay of all solutions studied is nonexponential and can be resolved into the sum of two exponential decays. The fluorescence spectra and decay curves are affected by oxygen.The interactions between excited and unexcited molecules and between unexcited molecules themselves and the effect which these interactions have on the optical properties of luminescent solutions are examined. The experimental results can be adequately explained by a mechanism which involves formation of transient dimers by an interaction between excited and unexcited...

The Ferrous Sulfate Radiation Dosimeter: A Calorimetric Calibration with Gamma Rays

The ferrous sulfate radiation dosimeter (herein called the Fricke dosimeter) has been recalibrated by a calorimetric method in which assumptions regarding energy absorbed in the glass and the heat capacity of the calorimeter have been eliminated. The 100‐ev yield, G(Fe++→Fe+++), is 15.8±0.3 for Co60 gamma radiation in agreement with the Hochanadel‐Ghormley value. The result is compared with other G values reported in the literature and it is recommended that the low value be adopted for Co60 gamma radiation and for electrons in the 1—2 Mev range.

γ‐Radiolysis of Liquids at High Pressures. I. Aqueous Solutions of Ferrous Sulfate

The γ radiolysis of aerated and deaerated, acid solutions of ferrous sulfate has been studied at 20° and applied pressures in the range 0 to 6.34 kbar. Over the entire pressure range, G(Fe+++)=8.1±0.1 and G(H2)=4.1±0.1 in deaerated solutions containing 0.8N H2SO4, 1 mM NaCl and 2 mM Fe++. Radiolysis of deaerated, 0.8N H2SO4 solutions of dichromate gives G(O2)=0.78±0.02 over the whole pressure range. It is concluded from such results, and observation of a similar pressure independence of G(Ce+++) in the ceric sulfate dosimeter, that primary yields in water radiolysis are invariant as pressure varies from 0 to 6.34 kbar. In aerated ferrous solutions, G(H2), G(Fe+++), and G(—O2) vary with pressure, ferrous concentration, and acid concentration in such a manner as to indicate an effect of pressure on the competition between Reactions [1] and [2]: H+O2→HO2, H+H++Fe++→Fe++++H2. Analysis of the results, for aerated ferrous solutions containing 0.8N H2SO4 and 1 mM NaCl, gives k1/k2≈1000 at atmospheric pressure an...

Anomalously High Specific Rates of Diffusion‐Controlled Reactions: Luminescence Quenching in Liquid Systems

Quenching constants (γs′) and specific rates of quenching (kq) of uv‐ and high‐energy sensitized luminescence by carbon tetrachloride in de‐aerated solutions of p‐terphenyl in benzene and in cyclohexane are given. Values for kq in benzene ranging as high as 3.6×1010M—1 sec—1 appear, in first approximation, to be quantitatively explicable on the basis of current theoretical treatment. However, the cyclohexane results (kq>3×1011M—1 sec—1) are clearly anomalously high and are not suggested by current theory; some speculation as to the cause of such results is included.

Effect of Density in Radiolysis of Ammonia

A study of the effect of density on the radiolysis of ammonia at 137-C reveals sharp decreases in G(H2) and G(N2) in the density region ~0.05 to 0.15 gm cc-1. At densities less than ~0.05 gm cc-1, G(H2) = 6.2, and G(N2) = 2.0; at densities exceeding 0.15 gm cc-1, G(H2) and G(N2) are about 1.5 and 0.4, respectively. It is notable that the G values begin to level off at densities well below the critical density of 0.235 gm cc-1. The results are interpreted in terms of the Magee-Funabashi theory of ion clusters. It is assumed that the formation of such clusters reduces the probability of dissociative neutralization of ions by permitting the energy of neutralization to be spread over the molecules of the cluster. Although this interpretation is consistent with the observed density dependence of G(-- NH3), contributions from other effects, in particular deactivation of excited species, may also be involved.

Measurement of Nanosecond Scintillation Decay Times

An experimental method for measuring scintillation decay times of the order of nanoseconds is described. The method involves a repetitive time selection technique; i.e., in a sense, it is the electronic equivalent of the original Becquerel phosphoroscope. The complete circuitry is shown and some illustrative results are given.

Effect of Added Quenchers in Organic Scintillator Solutions: Organometallics

Quenching constants (γs and γx) are given for a variety of perphenyl metals (Si, Ge, Sn, Pb, Sb, and Hg) and for mercury dimethyl acting on benzene and cyclohexane solvents and p‐terphenyl and DPA scintillators. Specific rates are calculated for the quenching processes and are found to break into the following classes: <7×109 M—1 sec—1 corresponding to spin‐perturbation‐induced quenching (with a probability factor less than unity, according to Umberger—LaMer calculations) and ≧3×1010 M—1 sec—1 (exceeding such calculated values), corresponding to highly favored excitation‐transfer processes. The latter high values can be explained in terms of the domain theory of liquid scintillator solutions. Specific rates in the intermediate range for GePh4, and perhaps for SiPh4, acting on solvents are consistent with resistance to high‐energy irradiation and with the attendant probability that long‐lived excited states of such quenchers actually transfer excitation to the scintillator.Anomalously high quenching consta...

Effect of Added Quenchers in Organic Scintillator Solutions: Aromatic Halides

Luminescence‐intensity measurements, as affected by quencher concentration, solvent and scintillator, yield information on quenching constants, on specific rates of quenching, on mechanism of quenching, on contrast between quenching of solvent and quenching of scintillator, and on contrast between quenching in benzene as solvent and quenching in cyclohexane as solvent. For a number of aromatic bromides (and for iodobenzene), excitation transfer appears to be involved in the quenching process; in those cases the specific rates are higher than may be expected for simple diffusion‐controlled reactions. Typical specific rates (kq) are ≃ or >2.5×1010 M—1 sec—1 in benzene. The donor states from which excitation is transferred are not identified. In cyclohexane, calculated kq values are very much higher with an implication that the mechanism of the quenching process is quite different in such cases. Some of the results can be explained in terms of the theory of solvent domains; the data for cyclohexane suggest t...