No abstract

A T the March, 1952, Massachusetts Institute of Technology Conference on Physical Electronics we reported on the behavior of field dependent fluorescence of zinc silicate phosphor. Fluorescence could be obtained only when the electric field had an ac component. The fluorescence observed in our samples was interpreted as being due to field emission, either cold emission or Zener tunneling at regions of high field intensity. The need for the presence of an ac component was ascribed to the existence of space charge associated with traps in the semiconducting vitreous phosphor. These assumptions also explained the anomalous behavior of the radiation as the temperature of the semiconductor was increased above 200°C.Additional experimental results have now been obtained. The samples consist of a thin strip of glass, 0.01 cm wide and about 2 cm long placed between two conducting electrodes so that the electric field is applied across the width of the strip. The glass has a low softening point, and the Zn 2 Si04:Mn phosphor is imbedded in it. The radiation is observed from a cross section in a plane perpendicular to the plane of the strip. Aluminum, silver, and graphite were used for the electrodes, the graphite giving the best performing sample as far as the efficiency of fluorescence is concerned. The vitreous mixture is a semiconductor with a resistance between 5 and 100 megohms/cm 2 at room temperature. However, the resistance is a function of the temperature and depends on the frequency of the applied potential.Observation with a low power microscope shows that the radiation is emitted from the interface between the electrode and the vitreous phosphor.The lowest potential for which radiation is observed varies between 100 v and 500 v depending on the thickness and other parameters of the sample. At a fixed potential the light output varies slightly with the frequency. For a frequency variation of the applied field from 120 cps to 16 kc/sec the light output varies by a factor less than 5. At 60 cps the light output varies roughly as the square of the potential in the range from 100 v above the low voltage cutoff to the crystal breakdown potential. The low voltage cutoff is defined arbitrarily as the potential at which radiation is first observed. Possibly a more sensitive photocell arrangement, such as a photomultiplier, would detect radiation at a potential lower than the presently observed cutoff.These observations further substantiate the hypothesis that field emission is responsible for the phenomena. The transport of charge from deep-lying energy levels across the interface barriers excites the phosphor component of the glass matrix near the potential barrier at the interface. The value of this electric field across the interface will depend, of course, on the dielectric constant of the glass matrix and on the rate of conduction of the charge through the semiconducting glass matrix to the opposite electrode.It is interesting to note that Piper and Williams 1 in their recent studies on the electroluminescence of ...

The 0 1 7 and Fl9 nmr spectra of OzF2 and what has been referred to as 03Fz have been studied. The results for 02F2 were as expected: one fluorine line and one oxygen line. For OaFz three 0 1 7 lines were observed; one of the three was shown to be due to OzFz and the other two, which were of equal intensity, were attributed to 03F2. The F 1 9 spectra of OIF2 consisted of two closely spaced lines and as in the 0 1 7 case, one of these lines was attributed to OzF2. The nrnr shows conclusively that what has been called 0 8 2 is truly a mixture of O2Fz and 04Fz.number of oxygen fluorides have been reported,

As part of a prospective diagnostic protocol, patients suspected of having pancreatic cancer had systemic and portal venous blood samples assayed, in coded batches, for peptide hormones and enzymes thought to be of potential value as tumor markers. An average of 111 patients were tested for each candidate marker. Results were analyzed by dividing patients into three groups according to the definitive diagnoses. These were pancreatic cancer (32% of patients), other cancers (27%), and benign diseases (41%). Although elevated mean levels of fasting plasma glucose and serum alkaline phosphatase were found in the pancreatic cancer group, there were no significant differences in the mean levels of any of the candidate markers studied in the three groups. The diagnostic values of normal and elevated levels of each candidate marker studied have been calculated. None has proven to be as useful as the serum level of pancreatic oncofetal antigen, fasting plasma glucose, or serum alkaline phosphatase in the diagnosis or exclusion of pancreatic cancer.

The electron paramagnetic resonance of color centers in additively colored KCl crystals is measured carefully to observe the effects of optical bleaching at room temperature. Earlier measurements on the F cent~r are confirmed and the s.usceptibility is measured at 78° and 300 0 K over five decades of power, includlllg the very low power regIOn. The width and the saturation properties of the individual multiplets are studied in detail and the technique of making EPR measurements on inhomogeneously broadened lines is discussed. A calculation is presented which shows that a slight departure from a Lorentzian multiplet shape can account for the saturation data.The bleached crystals show a resonance which has a width of 35 gauss and a different rate of saturation than the F center. This resonance is associated with the B band which appears in the optical absorption.