Suitable Shielding Research Articles

Glass Combustion Bomb

A glass combustion bomb is described which has proved invaluable in working out suitable combustion conditions for inorganic materials. It is possible to observe relative combustion temperatures, rates of burning, melting of sample or combustion products, spattering, fuse wire temperature, etc., and to study the effects of these at different pressures and sample arrangements. It is imperative that suitable shielding be in place before the bomb is used. (B.O.G.)

In-vivo disometry with miniature glass rods.

A glass rod microdosimeter (1 × 6 mm.), utilizing the concept of radiophotoluminescence (1), is being used for human in vivo measurements in all modes of radiation therapy. Due to its miniature size and integrating ability, it is an ideal dosimeter for medical use (2). The undesirable feature of energy dependence in the range of 200 kev to 1.3 Mev is being corrected by a suitable gold shield designed by the authors (3). A fluorimeter electronic reader, with modifications designed by the U. S. Naval Research Laboratory, assures reproducible and stable results. In human subjects with cancer, the miniature dosimeters were placed with ease in the pharynx, the esophagus, the bladder, and other deep organs. Technics were devised to introduce these units directly into tumors and normal body tissues. In all the clinical experiments, there was a remarkable degree of correlation between the dosimeter reading and the calculated dose when beam irradiation (260 kv, 1000 kv, cobalt 60), radium implants, or isotope ther...

On the reduction of the dark current of photomultipliers

Two methods are used for reducing the rate of dark current pulses of photomultipliers; the reduction is equivalent to a cooling of about 100° C. The two methods are: the reduction of the sensitive area of the photocathode and the application of a suitable shield potential to a layer on the outer surface of the envelope. In the course of the investigation of the shield effect the stability conditions of the multiplier and the effect of the shield potential on the pulse height distribution were studied.

The stability of the calibration of liquid sample Geiger-M ller counter tubes

It is possible to construct equipment for the automatic counting of radioactive samples in solution by placing each sample in a different counter tube of the liquid sample type (CV2145) and switching to each tube in turn. The day-to-day variation of the calibration factor of such tubes, which is the main source of error in the method, is found to be ±0.6%. Background errors due to γ-radiation from samples in adjacent tubes are reduced to less than 0.1% by suitable lead shielding. The results are also relevant to the use of liquid sample counters as calibrated secondary standards for the absolute assay of radioactive isotopes.

Influence of cosmic radiation on induced carcinogenesis in mice.

Since Figge1 reported that cosmic rays accelerate the process of carcinogenesis, there has been renewed interest in the possible biological action of this radiation2. Figge claimed that an increase in cosmic radiation, produced by screening with a suitable lead shield, appeared to reduce the length of the latent period preceding the appearance of palpable tumours in mice which had previously been inoculated subcutaneously with 20-methylcholanthrene. These original investigations were carried out at sea-level.

-Ray Spectrum of Radio-Helium

IN order to investigate the energy distribution of the -rays from radio-helium1, we have employed an expansion chamber constructed by Dr. J. C. Jacobsen and kindly lent to us. In the middle of the top plate, a thin-walled brass cylinder (0.05 gm. per cm.2, 1.5 cm. diameter) was inserted, into which an activated beryllium cylinder could be dipped. The latter was made of beryllium powder (0.12 gm. per cm.2) stuck on to a brass tube (0.1 gm. per cm.2) and could be moved automatically from a position around a neutron source (beryllium-radon) to the position in the Wilson chamber in 0.4 sec., this movement also starting the timing arrangement for expansion and light. A suitable lead shielding was arranged which cut down the electrons due to the -rays to a number small compared with the number of -rays. The radioactivity induced in the brass tube carrying the beryllium is negligible as the latter is exposed to the neutrons only for a few seconds at most every minute.

Quantum mechanics of electrons in crystal lattices

Introduction .–Through the work of Bloch our understanding of the behaviour of electrons in crystal lattices has been much advanced. The principal idea of Bloch’s theory is the assumption that the interaction of a given electron with the other particles of the lattice may be replaced in first approximation by a periodic field of potential. With this model an interpretation of the specific heat, the electrical and thermal conductivity, the magnetic susceptibility, the Hall effect, and the optical properties of metals could be obtained. The advantages and limitations inherent in the assumption of Bloch will be much the same as those encountered when replacing the interaction of the electrons in an atom by a suitable central shielding of the unclear field, as in the work of Thomas and Hartree. In the papers quoted a number of general results were given regarding the behaviour of electrons in any periodic field of potential. To obtain a clearer idea of the details of this behaviour with a view to the application in special problems, however, it appeared worth while to investigate the mechanics of electrons in periodic fields of potential somewhat similar to those met with in practice and of such nature that the energy values W and eigenfunctions Ψ of the wave-equation can actually be computed. It is the purpose of this article to discuss a case where the integration is possible. In Section 1 the energy values and in Section 2 the wave-functions in their dependence on the binding introduced by the potential field are discussed for the one dimensional problem. In Section 3 the matrix elements of the linear momentum, which furnish the electric current associated with the various stationary states, are well as the probability of radiative transitions between these states, are evaluated. In Section 4 the results are extended to the three dimensional case and those features considered which one may expect to find in the case of more general periodic fields of potential. Section 5 deals with some applications to physical problems.