HIGH ENERGY INDUCED FLUORESCENCE IN LIQUID ORGANIC SOLUTIONS (ENERGY TRANSPORT IN SOLUTIONS).

110 Pages·3.816 MB·English

by  FURST, MILTON

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,G7 M lton.. 192l<»» t.
1qr2 ? energy- induced Huorescence in
liquid organic solutions (energy
^ transport in solutions;
iv,103p« tables, diagrs.
; Thesis (ih .u .) - N.5f,U.p Graduate
j School, 1952*
Bibliography.* po102-l03*
CW A7 _
j..Fluorescence o 2<>3.oiution (Chemistsy)
3• Dissertations, Academic - -
1952« I .T itle . IIo T itle : nergy
transport in solutions.
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THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED.
IIBRARY i?F
NEW YORK UNIVERSITY
university heights
HIGH ENERGY INDUCED FLUORESCENCE IN LIQUID ORGANIC SOLUTIONS*
(ENERGY TRANSPORT IN SOLUTIONS)
MILTON FURST
■Nevaiae» 80, 1961
( \ S' %-
A dissertation in the department of Physics submitted in
partial fulfillment of the requirements for the degree of
Doctor of Philosophy at New York University.
•This work was supported by Signal Corps Contract No. DA?6-
039 SC-5487
Acknowledgments
To Professor Hartmut Kallmann for proposing the prob­
lem and for his vary fine guidance and advice.
To Professor Walter F, C, Ferguson for the loan of
his quart* spectrograph.
To iidna, my wife, for her patience in typing the thesi*.
ii
Table of Content*
Page Ho.
Acknowledgments ii
1* Introduction 1
11. Previous Experiments 2
III. Experimental Arrangements 4
(a) Gamma Kay measurements 5
(b) Measurements with Alpha Particles 10
(c) Gamma Bay and Alpha Particle Spectra 13
IV. Basic Experimental Results
(a) Solvent Emission 14
(b) Effects of Solute 17
(c) Physical Efficiencies 21
(d) Spectra 24
(e) Mixed Solutions and Absorption 25
(f) Concentration curves for Various Solutions 53
Parameter Representation 40
V. Theoretical Considerations
(a) Concentration Curves 55
(b) Quenching 59
(c) L&iergy Transport and Trapping 65
(d) Alpha Particle Modifications 72
VI. Discussion and Analysis of Results
(a) Physical Efficiencies of Solutions 74
(b) Extrapolated Intensities 76
Li i
Table of Contents (Continuation)
Page ITo.
(c) Parameter Identifications 79
(d) Beaction Probabilities 80
(e) Internal Quenching and Light Btoission 82
(f) Alpha Particle Parameters 88
(g) Limitations and Deviations 92
(h) Experiment on Self Quenching 94
VII, Summary 99
VIII, Bibliography 102
iv
IIIGU ENERGY INDUCED FLUORESCENCE IN LIQUID ORGANIC SOLUTIONS
(ENERGY TRANSFORT IN SOLUTIONS)
1. Introduction
Detection and measurement of high energy radiation by means
of scintillation counters has become very widespread in the short
(1)
period since their introduction in 1947 by H. Kallmann .
These devices have been limited to the use of crystals until quite
(2,3)
recently • Such crystal counters are not well suited for meas­
urements of very weak or very penetrating radiations since efficient
large size clear crystals are difficult to make. They require precise
and minute temperature control in addition to a very high degree of
chemical purity. These factors also greatly increase the cost of
such crystals.
By the use of liquid scintillation counters however,
these deficiencies can be overcome. Efficient liquid solutions for
high energy radiation can be used in comparatively large quantities
and still remain clear for the transmission of the fluorescent light,
With suitable arrangements they can be used for the detection of various
types of high energy radiation and are especially valuable for
measurements with cosmic rays. On account of the ease with which
conditions in different solutions can be varied, they also provide
the possibility for the study of the fundamental processes connected
with fluorescence. -By means of such an investigation better solutions
can perhaps be made and an understanding of the basic mechanisms
1
which are involved can he gained*
The investigation reported here is concerned with the
fluorescence mainly of " simple”, dilute, liquid organic solutions •
consisting of a single solute dissolved in a single solvent. The
variation of the fluorescent intensity of these solutions with the
concentration of the solute is determined experimentally for a large
number of solutions using both gamma and alpha excitation. A mech­
anism is then proposed to explain these experimental results theo­
retically. The parameters connected with the theoretical formulation
are then evaluated to fit the experimental determinations. By
study of the variation of these parameters in the different solutions
some of the basic ideas about the physical processes can be tested
and further insight into the processes can be obtained*
II. Previous Experiments
There has been a great deal of study of the fluorescence
of liquid solutions employing light rather than high energy as the
excitation source. An excellent review of this work including a very
extensive bibliography is presented in a book by P. Pringsheim^).
However, fluorescence in liquid solutions induced by high energy
radiation has essentially been neglected. The experiments which are
reported here show many sim ilarities with those using light but also
many differences. Outstanding among these is the function of the
solvent. Vith light, the fluorescence of the solute occurs by means
of the direct absorption of the light energy by the solute molecules.
The solvent acts mainly as the agent for distributing the solute
2
molecules without taking any active part in the emitting and absorb­
ing processes. The differences found with different solvents in
light experiments are mostly due to variations in quenching prop­
erties of the solute molecules brought about by the influence of the
solvent. With high energy radiation on the other hand, the solveht
has a fundamental part in the fluorescent process. Here the fluo­
rescence i3 sometimes of the same order of magnitude as with good
crystals while the corresponding solute concentration is far too
small to account for the light intensity by means of direct absorp­
tion of the energy by the solute molecules. Therefore a transport
of energy from the solvent to the fluorescent solute molecules was
suggested as a postulate. (See Section V).
High energy studies with organic and inorganic crystals
are more numerous. However there is certainly no direct correlation
between the fluorescence of substances in solid foim and the same
substances in solutions. Thus substances like diphenyl acetylene
and anthracene which are among the most efficient fluorescent sub­
stances in crystalline form are poor or mediocre in solutions. On
the other hand, phenyl oc-naphthylamine is not very good in solid
form but is among the most efficient in solution. Also solid naph­
thalene when melted becomes a poor fluorescent material whereas a
solution of phenyl at-naphthyl amine in phenyl ether becomes worse
upon the solidification of the solvent.
Itoergy transport in crystals is known experimentally to
(5)
take place over distances of 100 atomic diameters and more ,
Such a transport of energy can be carried out by free electrons
3
moving in the crystals or by migration of the excitation energy from
(6,7)
one molecule to the other. Becent experiments with ultra1
violet light have shown for example that the fluorescent emission of
naphthalene crystals can he increased hy the addition of 0*01 to 0.1
percent of anthracene; also there is a shift in spectrum from that of
naphthalene to that of anthracene. Similar results were obtained
with other organic crystals where the fluorescent wavelengths of the
contaminant are longer than those of the host material. Excitation ef­
fects produced by high energy radiation on the same types of crystals
were similar, The relative direct excitation of the contaminant in
these cases is approximately proportional to the relative mass that is
present; nevertheless the shift and the increase occur. The bulk ma­
terials in the case of crystals are good fluorescent substances, V/ith
liquid solutions the situation is somewhat different since the pure
solvents are poor fluorescent substances on account of quenching effects.
A fast transfer of energy from the solvent to the solute molecules
followed by trapping of the energy in the solute is necessary for ex­
plaining the sizeable light emission found in the experiments described
below.
III. Experimental Arrangements
The measuring apparatus used in the investigation was not
very complicated. It consisted mainly of a commercial photometrio in­
strument containing a photomultiplier to obtain adequate light sensitivity;
it was purchased from the Photovolt Corporation, N.Y.C. (iTodel 512 M).
4