Characteristics of a tapered undulator for the X-ray absorption fine-structure technique at PLS-II

An in-vacuum undulator (IVU) with a tapered configuration was installed in the 8C nanoprobe/XAFS beamlime (BL8C) of the Pohang Light Source in Korea for hard X-ray nanoprobe and X-ray absorption fine-structure (XAFS) experiments. It has been operated in planar mode for the nanoprobe experiments, while gap-scan and tapered modes have been used alternatively for XAFS experiments. To examine the features of the BL8C IVU for XAFS experiments, spectral distributions were obtained theoretically and experimentally as functions of the gap and gap taper. Beam profiles at a cross section of the X-ray beam were acquired using a slit to visualize the intensity distributions which depend on the gap, degree of tapering and harmonic energies. To demonstrate the effect of tapering around the lower limit of the third-harmonic energy, VK-edge XAFS spectra were obtained in each mode. Owing to the large X-ray intensity variation around this energy, XAFS spectra of the planar and gap-scan modes show considerable spectral distortions in comparison with the tapered mode. This indicates that the tapered mode, owing to the smooth X-ray intensity profile at the expense of the highest and most stable intensity, can be an alternative for XAFS experiments where the gap-scan mode gives a considerable intensity variation; it is also suitable for quick-XAFS scanning.

Whorwell et al's “Physiological Effects of Emotion: Assessment Via Hypnosis”

“Assessment of the physiological effects of physical and emotional stress has been hampered by a lack of suitable laboratory techniques. Since hypnosis can be used safely to induce specific emotional states of considerable intensity, we studied the effect on distal colonic motility of three hypnotically induced emotions (excitement, anger, and happiness) in 18 patients aged 20–48 years with irritable bowel syndrome. Colonic motility index was reduced by hypnosis on its own (mean change 19.1; 95% CI 0.8, 37.3; P < 0.05) and this change was accompanied by decreases in both pulse (12; 8, 15) and respiration (6; 4, 8) rates (P < 0.001 for both). Anger and excitement increased the colonic motility index (50.8; 29.4, 72.2; and 30.4; 8.9, 51.9, respectively; P < 0.01 for both), pulse rate (26; 22, 30; and 28; 24, 32; P < 0.001 for both), and respiration rate (14; 12, 16; and 12; 10, 14; P < 0.001 for both). Happiness further reduced colonic motility although not significantly from that observed during hypnosis alone. Changes in motility were mainly due to alterations in rate than in amplitude of contractions. Our results indicate that hypnosis may help in the investigation of the effects of emotion on physiological functions; this approach could be useful outside the gastrointestinal system. Our observation that hypnosis strikingly reduces fasting colonic motility may partly explain the beneficial effects of this form of therapy in functional bowel disorders.”

Do centers of origin have a center?

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

22 GHz Observations of Southern H2O Sources

The discovery of three new H20 sources associated with HII regions is reported. Observations of other southern H20 sources show, in several instances, considerable intensity changes over a 20-month interval.

On the use of laser light sources in schlieren-interferometer systems

In the recording of refractive index fields, the exceedingly high monochromatic brightness of laser light sources opens up new possibilities where applications to very fast or highly self-luminous phenomena are concerned. The properties of laser light, however, pose special problems, as well as presenting special opportunities. These are examined in relation to schlieren recording, deflexion mapping, shadowgraphy and interferometry. The ultimate aim is the development of a ‘versatile' optical system which is capable of fulfilling all these functions with only minor readjustments in its optical components. This is achieved, for laser light, without either the expensive apparatus, or the considerable intensity losses with which such systems are otherwise associated.

Geomorphological Investigations in the Torngat Mountains of Northeastern Labrador-Ungava

... The central area of study lay athwart the Labrador-Quebec boundary on the watershed between Nakvak Brook, which drains into Saglek Fiord, and the Koroksoak (Korok) River, which flows westwards into Ungava Bay. ... Attention was concentrated on an extensive system of lateral moraines and kame terraces which slope eastwards from the watershed towards the head of Saglek Fiord. Similar systems were examined in the through-troughs to the south. The whole complex represents the late-Pleistocene limits of trunk glaciers flowing through the mountains towards the east and supplied by an ice cap of continental proportions west of the height of land. At this stage the higher summits stood as nunataks well above the level of the ice, and an extensive series of ice-dammed lakes was held against the western slopes of the highland finding outlets over ice-free cols into the Atlantic. Detailed studies in the watershed area provide a chronology of the final emergence of the area from the last ice sheet, and the draining of the ice-dammed lakes. A final stage was represented by a mass of ice in the lower valley of the Koroksoak which dammed a lake to the level of the col, at 1,050 feet, whence it drained into Nakvak Brook and ultimately into the Atlantic. Glacial erratics, found on summits up to 4,000 feet above sea level, corroborate the conclusions of the previous summer's work suggesting that at some stage the highest summits were inundated by ice flowing from the west. The data compiled from the two summers' work prompt the conclusion that during late-Pleistocene times the Torngat Mountains were influenced by two distinct glaciations, separated by an interglacial period of considerable intensity. The final glaciation, during which large areas remained ice-free, is tentatively correlated with the "classical" Wisconsin of central North America whereas the date of the preceding glacial period is uncertain. It may be the equivalent of the Illinoian Glaciation, or even be of post-Sangamon age, and in this case be comparable with a cold phase tentatively identified in central North America, which is older than the "classical" Wisconsin Glaciation, and is separated from the latter by a warmer period. Reconnaissance from the air during flights along the Labrador coast and some distance inland suggests that these general conclusions might well be applicable to the entire coastal zone of Labrador. ...

The β -ray spectrum of radium E

The problem of the β -ray spectrum of Ra E is too familiar now to require more than brief introduction. Owing to the eminent experimental suitability of this substance, its β -ray spectrum has been investigated widely, and various workers have given summaries of the results up to date, e.g. O’Conor (1937) and Martin and Townsend (1939). Most work has been done on the upper limit or on the form of the intermediate part of the spectrum, with fairly concordant results. Only a scanty amount of work has been done on an accurate investigation of the lower regions of the spectrum, where the experimental difficulties are much greater on account of the necessity of avoiding scattering in the source and along the track of the particles in the spectrograph, and of reducing the absorption in the window of the counter. Richardson (1934) first demonstrated by cloud chamber measurements, using a satisfactorily thin source mounting, that there is a considerable intensity of slow electrons between 15 and 60 ekV, and that the ordinate of the energy distribution curve is about as high in this region as at the previously estimated maximum. However, on account of straggling and other causes, it would be extremely difficult to determine exactly the form of the energy spectrum below 100 ekV by cloud chamber methods, and most other work has been done by semicircular magnetic deflexion with Geiger counters for registration of the particles. The results of chief importance are those of Alichanian and Zavelsky (1937) and of Flammersfeld (1937, 1939). In the discussion below the conclusion is reached that in both these sets of investigations the source mountings were quite satisfactory even down to 30 or 20 ekV, but that in the former the thickness of the counter window (1 µ cellulose acetate) can scarcely be regarded as small enough for measurements below 50 ekV, whilst in the latter absorption effects in the 0.3 µ Zaponlak window must begin to enter between 30 and 20 ekV.* Moreover, in both cases the spectrographs are not sensibly free from scattering. The experiments to be described below were made in an attempt at a precise and direct observation of the undistorted spectrum, especially below 100 ekV, and it is believed that the results do represent a practical realization of this ideal, down to the region of 20 ekV at least, without the need for the application of corrections of any kind.

The first spark spectrum of platinum

In 1929, Dr J. J. Livingood and myself attempted unsuccessfully to analyse the first spark spectrum of platinum. That failure was chiefly due to the lack of adequate observations in the Schumann region. The spectrum should, of course, be similar to Ni II and Pd II, both of which were previously analysed in the laboratory, but in the third long period the excitation energies have increased to such a point that the chief lines of the transition MATHS FORMULA are mainly below λ2000. Their observation requires a vacuum spectrograph, which we did not have at that time. Observations Down to the limit of transmission of air, the spectra of the arc and spark were photographed with the 21 ft. grating, and the wave-lengths were measured against iron standards. It was found necessary to use graphite electrodes for the arc, because of the fact that it is very difficult, if not impossible, to run an arc between pure platinum rods. One is much more apt to get a glow discharge in which the cathode is hot, the anode cold and the spectrum that of air. In the Schumann region also, arc-spark observations were the chief source of the data. A modification of the method described by Selwyn (1929) was used, and excellent spectra were obtained down to the fluorite limit at λ1240. The modification ensures an image of the source at the slit and makes the elimination of oxygen from the flowing nitrogen much more complete. The arc in pure nitrogen runs at 10-15 V higher potential than it does in air, and produces the second spark spectrum of some elements with considerable intensity. A diagram of the attachment is shown in fig. 1. The spectrograph is of conventional type employing a glass grating of 2 m. radius and 30,000 lines per inch. The spectrum can be photographed from λ500 to λ 2250. Hilger Schumann plates and Ilford Q, plates were used, the latter being practically perfect for the longer wave-lengths.

Spectrum of the afterglow of sulphur dioxide

Following a previous investigation of the afterglow of carbon dioxide it was decided to examine sulpur dioxide under similar conditions of experiment. An afterglow of considerable intensity and duration had, in fact, already been noted by Professors Sir J. J. and G. P. Thomson as occurring when sulphur dioxide was excited in a ring discharge, but no observations on its spectrum appear to have been recorded. Strutt has recorded an afterglow when ozone is passed over sulphur, but no glow was recorded with sulphur dioxide. The spectrum yielded by SO 2 in vacuum tubes varies greatly according to the conditions of excitation. With sufficiently powerful condensed discharges and a rather low pressure of the gas the molecules are dissociated into atoms and the spectrum consists of lines of oxygen and sulphur. With uncondensed discharges of moderate intensity and a suitable pressure of gas, the spectrum shows a strong system of bands degraded to the red which have been analysed by Henry and Wolff and attributed to the diatomic molecule SO; these bands are most intense in the region λ 2442 to λ 3941. Still weaker excitation yields an entirely different system of bands extending from the blue to about λ 2000, and there is evidence that these bands are due to undissociated molecules of SO 2 . The absorption of SO 2 is characterized by a large number of bands, which are most intense in the region λ 2800 to 3150. Owing to the continuous spectrum emitted by the gas during electrical excitation, this absorption may appear superposed on the emission spectrum in some forms of discharge tube. Recently Lotmar has reported on a band system excited in SO 2 by fluorescence.

The absorption of hard monochromatic γ -radiation.—Part II

Thorium C" emits in very considerable intensity a monochromatic γ-ray of very high quantum energy (2·649 × 10 6 e -volts) free from any other radiation of quantum energy greater than 0·786X 10 6 e -volts, so that it can be isolated by filtering through a few centimetres of lead. Experiments by Tarrant, Meitner and Hupfeld, Chao and by Jacobsen on the absorption of these rays are in agreement in leading to the conclusion that the scattering formula of Klein and Nishina is a good approximation for the elements of low atomic number. The absorption coefficients of the heavy elements, however, indicate that a new mode of γ-ray absorption is occurring, which may be nuclear in origin.