Electron Sensitive Emulsions Research Articles

A track physics model of radiation action

A model of radiation action by energetic heavy ions, inspired by a study of particle tracks in electron sensitive emulsion, has been successfully applied to many radiation effects in condensed matter, yielding quantitative descriptions and occasional predictions. Radiation effects are attributed primarily to secondary electrons. Each detector is imagined to be a collection of targets whose radiosensitivity is represented parametrically. We avoid a mechanistic description of detector response so as to retain the global character of the model. Attention is focussed on the structure of particle tracks, on the radial deposition of dose about an ion's path by “δ-rays”, and on action cross sections.

A New Wide Field Electrographic Camera as an Optimum Detector for Schmidt-Type Telescopes

The electrographic (E.G.) camera is one of the most powerful modern detectors having high sensitivity, extended spectral response, extreme spatial resolution, low background, no threshold, good linearity and large dynamic image. A combination of highly uniform electric and magnetic fields produces distortion-free and extremely sharp images which are recorded by electron sensitive emulsions (Figure 1).

Large Window Spectracon

IN the Spectracon1 electronographic image tube, in the form now used for spectrographic recording, the image area is restricted to a rectangle 30 mm × 5 mm to enable a very thin (4 µm) mica Lenard window to be used which will support not only atmospheric pressure but also the pressure required to keep the electron-sensitive emulsion in intimate contact with the external mica surface when recording the image electrons.

Mica windows for electronographic image tubes

The curvature of and stress in rectangular and circular thin mica windows in a vacuum tube are analysed and it is shown that a circular window has advantages. A method of pressing an electron-sensitive Melinex-based emulsion against a circular window is described and the results of tests on actual windows are reported. Details are given of the method used for making a vacuum-tight seal between mica and chrome-iron.

Preparation of Electron Sensitive Emulsion Plates in the Laboratory

Preparation of Electron Sensitive Emulsion Plates in the Laboratory

Two Proposed Experiments for the Detection of the Dirac Monopole

A magnetic monopole may be detected by its deflection in an electric field or by the character of the ionization it produces. The electric deflection experiment may be performed in a helium bubble chamber where helical (or spiral) tracks whose axes are parallel to the 0-lines would be certain evidence for the discovery of the monopole. Previous studies of the ionization have emphasized thnt the Bragg tail would be missing from a monopole track, as compared to a charged particle. This conclusion must be modified because of the thin-down of tracks of heavy nuclei. The tracks of heavy nuclei thicken and then thin down as they approach the end of their range. The tracks of monopoles are wedge-shaped, thinning down continuously as they approach the end of their range. Since the track width is due to knock-on electrons, or delta rays, any search for the monopole using this criterion must be conducted with electron-sensitive emulsions. (auth)

METHODS OF PREPARATION AND CHARACTERISTICS OF NUCLEAR EMULSIONS

Details are given for some kinds of nuclear emulsions which can be prepared by simple laboratory methods. The characteristics of these emulsions have been compared with Ilford nuclear emulsions. The properties of proton sensitive nuclear emulsions N-2, N-3 are about the same as. those of "Ilford C2". Nuclear emulsions for detecting thermal neutrons "N-2 loaded with boron or lithium" seem better than "Ilford C2 loaded with boron or lithium". The sensitivity of electron sensitive emulsion N-4 is of the same order as that of emulsion "никфи P" and "Ilford G5". The hypersensitized electron sensitive emulsion N-5 is also discussed.

The nature of the taper tracks of heavy ions in nuclear emulsions

The thinning down of the tracks of heavy ions as they approach the end of their range in electron sensitive photographic emulsion, can he quantitatively explained on the assumption that the thickness of the developed track is due mainly to δ-rays which no longer have sufficient range at low ion velocities to broaden the track.

The -disintegration of RaD

Electron-sensitive nuclear emulsion impregnated with RaD citrate was used. RaD events associated with β-particles of RaE were studied to determine the total number of developed grains produced in each RaD event. An analysis of the resulting grain-count distribution provides evidence of the occurrence of a ground-state to ground-state β-process in RaD with an intensity of 15.5 ± 3.5% of all disintegrations. The total intensity of excitation of the 46.5 keV state of RaE is thus 84.5 ± 3.5% and the intensity of conversion electrons from this state is 81 ± 4%. The last of these values is consistent with the results previously published by Wu, Boehm and Nagel and by Cranberg.

Meson Showers and High-Energy Interactions in Light and Heavy Nuclei

A study has been made of nuclear disintegrations produced in electron-sensitive emulsions exposed to cosmic radiation at 80 000 ft. Of 93 stars containing more than three shower particles, 29 were interpreted as being induced in the light nuclei C, N, O, and 64 in the heavy nuclei Ag and Br. The low-energy tracks appear to be emitted isotropically from a slowly moving nucleus and the forward collimation of the remaining tracks is discussed. The average numbers of shower particles from the heavy and light nuclei are 7.7 and ${6.4}_{5}$, respectively, and it is shown that these figures are consistent with multiple processes of meson production. The difference between the angular distributions of shower particles from heavy and light nuclei is discussed on the assumption that it is mainly due to scattering.

The Origins of Background Tracks in Shielded Electron-Sensitive Emulsions

The Origins of Background Tracks in Shielded Electron-Sensitive Emulsions

The Energy Spectrum of Positrons from the Decay of theμ-Meson

The energy of the positrons from $301\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\rightarrow}\ensuremath{\beta}$ decays have been determined in electron sensitive emulsions by measuring the multiple scattering of the positron tracks. The annihilation properties of the charged particle emitted in the decay of the ${\ensuremath{\mu}}^{+}$ meson confirm its identity as a positron. This spectrum has a maximum about 36 Mev and a nonzero cutoff at the high energy end. A statistical analysis of the data, using the Michel theory, yields a value of $\ensuremath{\rho}=0.41\ifmmode\pm\else\textpm\fi{}0.13$.

XXXI. On photometry in thick nuclear emulsions

Abstract Photometric methods of determining the ionization produced by a charged particle in passing through nuclear emulsions are discussed and a technique based on measuring the mean width of a track is described. The method has been tested by applying it to a study of the heavy primary component of cosmic radiation. It is concluded that the photometry of tracks produced by charged particles passing through electron sensitive emulsions may be used as a sensitive measure of the specific ionization for values of the rate of loss of energy less than 30 mev/g/cm2. and greater than 200 mev/g/cm2. Similar methods can also be applied for identifying multiply charged particles, if they are arrested in the emulsions, and if the length of their tracks exceeds 200 µ.

CXXIV. Nuclear transmutations produced by cosmic-ray particles of great energy.—Part VI. Experimental results on meson production

Summary An analysis has been made of the secondary particles ejected from nuclear disintegrations observed in electron sensitive emulsions exposed to the cosmic radiation at 68,000 ft. Scattering and grain density measure-ments have been carried out on the tracks of 2000 particles associated with these stars. In addition, the grain density and angular distribution of 3070 shower particles and 1508 “grey” tracks have been measured. For 200 stars, the energy of the primary particle which produced the disintegration was measured. A detailed analysis was made of such events. Single fast τ-mesons of kinetic energy less than 1 BeV. are found to interact strongly with nuclear matter. An estimate of the frequency of occurrence of neutral mesons was made from a consideration of the energy balance in stars of low multiplicity, n s .

Measurements of Mass Ratios in Nuclear Emulsions

IN an earlier communication in Nature1, we have described a method of measuring photoelectrically the density of tracks in nuclear emulsions. It is analogous to the method of grain counts and can be used with electron-sensitive emulsions where the overlapping of individual grains prevents the use of the latter method. We have compared the residual ranges of particles from regions of their tracks which show the same projected area per unit length, that is, the same average track width. From these comparisons we have calculated the mass ratios. This corresponds to the method used by Lattes, Occhialini and Powell2 in grain counting.

THE EMISSION OF RADIOACTIVE NUCLEI IN COSMIC RAY STARS

It has been found that a certain proportion of the fragments emitted in cosmic ray stars formed at about 85,000 ft. consists of radioactive nuclei, i.e., in electron sensitive photographic emulsions, tracks of electrons with energies of several mega electron volts can be seen originating at the end of the track of the fragment. Details of such events are given, together with energy measurements for the disintegration electrons made by the multiple Coulomb scattering method. The significance of the results, and possible identification of the fragments, are discussed.

XLV. The processing of thick photographic emulsions.

Summary An attempt has been made to determine satisfactory processing conditions for Ilford G5 electron-sensitive emulsions up to 600 μ in thickness. The penetration and temperature characteristics of metol-hydroquinone, para-aminophenol, and p-diaminophenol developers have been investigated. The observations show that a p-diaminophenol developer gives satisfactory results and a suitable procedure for processing is described. In addition the problems of fixing, washing and drying, have been studied.

Use of liquid nuclear research emulsion in track autoradiography.

IN a recent communication, King, Harris and Tkaczyk1 described the use of liquid electron-sensitive emulsions in the autoradiography of biological specimens. We have used such emulsions for some time in investigations aiming at precise localization of radioactive isotopes in biological specimens by means of track autoradiography. In this communication we present some aspects of the technique which may be of interest to workers in this field.

EMISSION OF NUCLEI IN COSMIC RAY STARS

One of the more interesting features of cosmic ray stars is that [Formula: see text] nuclei are ejected occasionally in the nuclear disintegrations. Such nuclei are characterized by the fact that, at the end of their range, they suffer radioactive decay (τ = 0.9 sec.) into [Formula: see text], which immediately splits up into two oppositely directed α-particles, giving what is usually referred to as a hammer track. In this investigation numerous examples have been observed of the emission of such nuclei in stars in photographic emulsions, the stars having from 2 to 60 prongs. In particular, it has been shown that the energy spectrum of the α-particles forming the hammer tracks is in good agreement with that observed by other workers, and also with experiments made, using the cloud chamber technique, indicating that the [Formula: see text] in this disintegration is formed in the excited state. When an electron sensitive emulsion is used it is shown that the hammer track is accompanied by the [Formula: see text] disintegration electron. The energy spectrum of the [Formula: see text] nuclei is plotted, and the mechanism of the formation is discussed for both large and small stars.

Photo-electric Measurements of the Density of Tracks in Nuclear Emulsions

GRAIN-COUNTING is an important method for the study of charged particles in photographic emulsions. The method is well suited for the Ilford C 2 emulsion and others of a similar kind, but does not work for heavily ionizing particles in electron-sensitive emulsions, for example, the Ilford G 5. We have measured the density of the tracks in such cases by a photo-electric method.