A comparison between a TESQ accelerator and a reactor as a neutron sources for BNCT

In this work, the performance of an accelerator-based neutron source design has been compared with that of a modern fluoride-filtered reactor-based epithermal beam having near-optimal quality for treatment of deep seated tumors in relation to its applicability for BNCT. The accelerator is a Tandem-Electrostatic-Quadrupole (TESQ) accelerator which is a design under development at the National Atomic Energy Commission (CNEA) in Buenos Aires, Argentina based on the ⁷Li(p,n)⁷Be reaction, relatively close to its energy threshold. The reactor is the Massachusetts Institute of Technology reactor upgraded with a Fission Converter Beam (MIT-FCB) and improved with an 8 mm thick ⁶Li filter. The comparison has been done by means of data reported on the MIT-FCB + ⁶Li filter performance and MCNP simulations on our TESQ design considering the neutron fluxes provided by the two sources and the doses delivered in a human phantom by both devices. The results show a deeper advantage depth (AD) for the TESQ which turns out to be a promising alternative to a reactor-based BNCT treatment.     

The effect of a changing fuel solution composition on a transient in a fissile solution

This paper presents an extension to a point kinetics model of fissile solution undergoing a transient through the development and addition of correlations which describe neutronics and thermal parameters and physical models. These correlations allow relevant parameters to be modelled as a function of time as the composition of the solution changes over time due to the addition of material and the evaporation of water from the surface of the solution. This allows the simulation of two scenarios. In the first scenario a critical system eventually becomes subcritical through under-moderation as its water content evaporates. In the second scenario an under-moderated system becomes critical as water is added before becoming subcritical as it becomes over-moderated. The models and correlations used in this paper are relatively idealised and are limited to a particular geometry and fissile solution composition. However, the results produced appear physically plausible and demonstrate that simulation of these processes are important to the long term development of transients in fissile solutions and provide a qualitative indication of the types of behaviour that may result in such situations.     

Effectiveness of a system of rod absorbers in a reactor fitted with a reflector

The conditions of criticality and the distributions of the neutron flux for a homogeneous thermal-neutron reactor with a system of absorbing rods are obtained in the two-group approximation. The rods extend through the entire depth of the reactor and are situated around the circumference of the active zone or radial reflector at a uniform distance from one another. The results of the calculation are presented.The author expresses his gratitude to Ya. V. Shevelev for discussing basic questions connected with this work, and also to N. N. Ponomarev-Stepnii and E. S. Glushkov for aid and critical remarks. Numerous and difficult calculations were performed by R. V. Kulev, to whom the author is very grateful.     

Signal Coupling from a Semiconductor Detector to a Cold Resistance Preamplifier Through a Cable or a Delay - Line Transformer

The behavior of a charge-sensitive preamplifier exhibiting a stabilized cold resistance at the input port is analyzed in view of its application as a low-noise termination for a cable or a delay-line transformer. Its use in conjuction with a remote semiconductor detector of large capacitance is discussed. Results obtained with different values of cable length, detector capacitance and shaping time constants are given. It is concluded that such a preamplifier can be successfully employed in several circumstances associated with silicon live targets in high-energy experiments.     

Benchmarking a diffusion code for a cylindrical-core reactor

The distorted-buckling method, proposed by us previously, allows the benchmarking of a diffusion code by comparing it with an analytic model in either 2 or 3 dimensions. Here, the method is applied to the case of a cylindrical TRIGA-type reactor to compare the fluxes predicted by an analytic model of the core and reflector, to those predicted by the code CITATION. The match is everywhere excellent. ©     

Thermal stresses in a cylindrical shell containing a circular hole or a rigid inclusion

The thermal stress problem of a circular discontinuity in a cylindrical shell has been solved by continuum approach. Two types of discontinuities are considered: (i) a circular hole and (ii) a circular regid inclusion. The effect of a uniform temperature or a linearly varying temperature across the thickness has been studied. The problem is converted into an equivalent boundary value problem and boundary conditions are specified around the discontinuity. The results are presented in a graphical form for ready use.     

An integral model for a severe accident at a nuclear plant with a containment

Translated from Atomnaya Énergiya, Vol. 71, No. 1, pp. 8–13, July, 1991     

Hard x-radiation accompanying a discharge in a gas

In this paper it is shown that a powerful gas discharge at low pressure is accompanied by the emission of hard X-ray quanta. The radiation is observed in the discharge in various gases. The main properties of the radiation are studied, and consideration is given to a possible mechanism of origin of the effect observed.The authors regard it as their pleasant duty to express their gratitude to L. A. Artsimovich for valuable discussions, and also to S. A. Chuvatin for aid in carrying out the experiments.     

Intermittent increase of electron current on a probe during a discharge in a magnetic field

An account is given of preliminary results in a study of the influence of a magnetic field on electron diffusion in a plasma. An intermittent increase was observed in the ratio of the electron current in the probe to the ion current at some critical value of the magnetic field intensity. According to the preliminary data, the critical magnetic field changes proportionally to the gas pressure. These facts evidently indicate the existence of two qualitatively different mechanisms for the transverse movement of the electrons, one of which is diffusion by collision.In conclusion, I wish to thank P. M. Morozov for his assistance and interest in this work, and also S. Sinotov, for taking part in the measurements.     

Resonance ionization in a gas cell: a feasibility study for a laser ion source

A laser ion source based on resonance photo-ionization in a gas cell is proposed. The gas cell, filled with helium, consists of a target chamber in which the recoil products are stopped and neutralized, and an ionization chamber where the atoms of interest are selectively ionized by the laser light. The extraction of the ions from the ionization chamber through the exit hole-skimmer setup is similar to the ion-guide system. The conditions to obtain an optimal system are given. The results of a two-step one-laser resonance photo-ionization of nickel and the first results of laser ionization in a helium buffer gas cell are presented.     

直角弯头连接的竖直管与水平管中的淹没问题

本文介绍了由直角弯头连接的竖直管与水平管内淹没与流向反转问题的实验研究，根据实验结果，分析了弯头对淹没与流向反转的影响，将所得实验结果与竖直管的实验结果进行了比较，分析了水平管长度对淹没过程的影响，以及这种管路中淹没消失滞后的问题，采用无因次量对实验数据进行了处理，给出了表达淹没开始点，淹没消失点和全部携带点的关系式。