Search

We are currently constructing a prototype, large-area, gamma-ray detector for conducting vehicle-mounted, mobile-search operations. The system is unique in that it relies on imaging to discriminate point sources of interest from the natural background variations. In a non-imaging instrument the background fluctuations mimic the signature seen from real sources at a distance and one is limited in sensitivity to detecting only those sources that overwhelm the local background variations --not just the counting statistics associated with a given measurement. The net result is that a larger detector is generally not more sensitive to detecting sources in the world at large. [1, 2] In a previous publication [3] we reported on the detection of a 1-mCi source at more than 80 meters from the detector using a proof-of-principle instrument (see Fig. 1) constructed to demonstrate how imaging removes the size limit on search instruments. In this report we document a systematic effort using the same detector to demonstrate that imaging detectors can reliably detect weak radiation sources at many 10's of meters. Specifically, we collected data on a 1-mCi {sup 137}Cs source 65 m from the path of the search instrument.

The renewal of the Ulysses mission to the year 2001, and the failure of Mars Observer, once more leave the Interplanetary Network with only two widely spaced components. We have therefore developed and begun to build a small GRB detector for the Russian Mars ’96 mission. The first flight unit has now been delivered to Russia for spacecraft tests. Three interesting features of this experiment are first, that it measures both particles and gamma rays, second, that it is not much larger than a Walkman (hence the name), and third, that it is being constructed with support only from discretionary funds at a number of institutes. We discuss the types of measurements that Burstman will make, as well as the quantity and quality of the small error boxes that will be obtained during the two year (nominal) Mars ’96 mission.

Pionic X-rays have been observed when negative pions are stopped in a hydrogen gas target. The intensity of the K lines has been found to be about 0.12 X-ray/pion stopped; moreover we found K α /K = 0.53 ± 0.04.

We descril'e here an assembly target-X-ray detector that is particularly suitable for detecting muonic and pionic X-rays in the range 1.3–10 keV. Some of the main features of the system are described.

Bei der Messung der Lebensdauer von Positronen in fester Materie findet man einen langlebigen Anteil, der auf die Bildung von Triplettpositronium zuruckgefuhrt wird. Die Lebensdauer dieses langlebigen Anteils wurde in Polystyrol gemessen, der Einflus eines Magnetfeldes auf diese Lebensdauer wurde bestimmt und ist in Ubereinstimmung mit dem aus dem Zeeman-Effekt des Positroniums berechneten Wert.

Lithium-drifted germanium detectors have been fabricated in the form of a cylindrical annulus. The forming of the annular shape was made feasible by using a spark cutting machine. The annular shape, being highly symmetrical, permits standardization of the techniques of gamma spectroscopy.

A muon beam was passed into a target of 55 atm argon with a magnetic field in the beam direction, and the decay positrons were counted as a function of the magnetic field, which was varied from l00 to 5800 gauss. The ratio of the positron counting rate for a dummy target to that for the gas target is plotted vs. the magnetic field and compared with theoretical curves for various values for the hyperfine structure separation DELTA nu of the 1 /sup 2/S/sub 1/2/ state of the muonium formed. The results indicate that all the muons form muonium and that DELTA nu lies between 2250 and 9000 Mc. (D.L.C.)

Since 1972 a pioneer experimental set-up was built, and successively used at CERN,1) in order to perform a precise measurement of the energy difference S1 between the 2S1/2 and 2P3/2 levels 2–4) of the helium muonic ion (μ4He)+. We report here on the present status of the experiment, giving preliminary results on S1.

Publisher Summary This chapter discusses the properties of atoms. The chapter deals with the methods of obtaining, observing, detecting, and analyzing the spectra of atoms in the optical region. The best presently developed means of measuring wavelength in this region are much more accurate than those of measuring intensity. Polarization is considered mainly in connection with methods of observing and analyzing the transverse Zeeman effect where the chapter deal with two orthogonal plane polarizations. Finally, only a brief mention is given of the techniques for studying light sources which vary in brightness with time, that is, of time-resolved spectroscopy. A further limitation of the chapter is that it will be confined to the experimental methods of optical atomic spectroscopy. Any source of radiation in the “optical” regions can be considered a potential source for spectroscopic studies. Sources of continuous radiation find their principal application as sources of background against which discrete or sometimes continuous absorptions can be measured. The ideal source for this application would have constant intensity structureless spectral distribution over the region of the spectrum under study, and zero intensity elsewhere.