ISSN 00204412, Instruments and Experimental Techniques, 2010, Vol. 53, No. 6, pp. 788–791. © Pleiades Publishing, Ltd., 2010. Original Russian Text © A.V. Isaev, A.V. Yeremin, N.I. Zamyatin, E.V. Zubarev, A.N. Kuznetsov, O.N. Malyshev, O. V. Petrushkin, A.V. Sabel’nikov, A.I. Svirikhin, M.L. Chelnokov, V.I. Chepigin, S.N. Dmitriev, 2010, published in Pribory i Tekhnika Eksperimenta, 2010, No. 6, pp. 16–20.
NUCLEAR EXPERIMENTAL TECHNIQUE
Detecting System of the Setup for Studying Chemical Properties of Superheavy Elements Using the Gas Chemistry Techniques A. V. Isaeva*, A. V. Yeremina, N. I. Zamyatinb, E. V. Zubarevb, A. N. Kuznetsova, O. N. Malysheva, O. V. Petrushkina, A. V. Sabel’nikova, A. I. Svirikhina, M. L. Chelnokova, V. I. Chepigina, and S. N. Dmitrieva Joint Institute for Nuclear Research Flerov Laboratory of Nuclear Reactions b Veksler and Baldin Laboratory of High Energy Physics ul. JoliotCurie 6, Dubna, Moscow oblast, 141980 Russia *email:
[email protected] a
Received March 31, 2010
Abstract—A setup for studying the physicochemical properties of superheavy elements in experiments involving gas transport systems is described. The setup is composed of four detecting modules with semicon ductor detectors; systems of data acquisition, storage, and processing; a cooling system for semiconductor detectors; and a vacuum system. In each detecting module, there are two oppositely located fourstrip semi conductor detectors. The detecting system is capable of detecting with a high efficiency α particles and spon taneous fission fragments produced in decays of superheavy elements. DOI: 10.1134/S0020441210060035
INTRODUCTION Synthesis of relatively longlived isotopes of super heavy elements from the Periodic Table has entailed rapid development of investigations aimed at chemical characterization of new elements and studying their properties [1]. The first experiments of this type were devoted to chemical characterization of elements 112 and 114 synthesized in complete fusion of 48Ca and 242,244Pu, using the gas chromatography method [2, 3]. The idea behind this method is as follows. Products of complete fusion reactions (new elements) in an actinide target bombarded with accelerated 48Ca ions escape from the target, slow down in the target chamber in an inert gas atmosphere, and are transported by the gas flow toward the detectors either as elements (if these ele ments are volatile) or as volatile chemical compound (in this case, an appropriate chemical agent is supplied into the target chamber together with the inert gas). Depending on particular experimental conditions, either cooling of detector assemblies with a gradient temperature distribution along the gas current direc tion [4] or uniform cooling of all detectors can be used. In some cases, the detector surface is coated with a thin evaporated layer of certain chemical elements in order to determine the specific chemical properties of superheavy elements. The aim of these experiments is to study the chem ical and physicochemical properties of superheavy elements (such as volatility and adsorption heat on dif ferent surfaces), the influence that the relativistic
effects due to an increase in the electron speed on a K shell upon a substantial increase in the nuclear charge have on these properties, and the properties of the radioactive decay. Progress in the gas chemistry methods is largely associated with the development of new detecting sys tems capable of meeting the requirements of a modern experiment. In this paper, we describe a setup prepared for experiments at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research. DESCRIPTION OF THE SETUP The developed setup consists of the detecting, cooling, vacuum maintenance, data acquisition, visu alization, and processing systems. The detecting sys tem is fixed in place on holders mounted into the vac uum chamber 32 cm in diameter and 13 cm in height. The detectors are cooled to the required temperature using the LAUDA PROLINE RP890 facility [4]. The vacuum chamber is used to maintain thermal stability of the detectors. Teflon capillary tubes are connected to the detecting system on two sides to pump the gas containing atoms of elements under investigation through this system. The detecting system (Fig. 1a) is composed of four modules with two silicon fourstrip semiconductor detector in each (Fig. 1b). The design of the detecting module has been developed by the Veksler and Baldin Laboratory of High Energy Physics of the Joint Institute for Nuclear Research. It consists of a heatconducting metal casing, a ceramic plate– support of a silicon detector (with uniform thermal
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DETECTING SYSTEM OF THE SETUP FOR STUDYING CHEMICAL PROPERTIES
(а)
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(b) Fig. 1. (a) Detecting assembly of four modules and (b) single disassembled detecting module.
expansion coefficients), and a printed circuit board for ultrasonic welding of detector contacts. The design of the detector module has the following characteristic features: —the detector module, being demountable, con sists of two symmetric halves; —the construction of the module and the technol ogy for assembling the detector crystal allows a tem perature gradient of up to 40°С to be created in a sin gle module without damaging the detector; and —all external contacts of the module are made by soldering the connector wires at “floating” mechani cal positioning of the module in the entire construc tion, which ensures a high structural reliability. The metal cases with an irregular shape were pro duced by the OAO Volzhskii Electromechanical Plant (Dubna, Moscow oblast) with a high precision ensur ing interchangeability of these components. The area of a single detector is 17 × 42.5 mm2, and its thickness is 300 µm. Each detector has four strips with a sensitive area of ~15 × 10 mm2 each. To deter mine the adsorption coefficient of superheavy ele ments and/or their decay products on noble metals, each detecting strip has an evaporated gold coating with an area of 13 × 8 mm2 and a thickness of ~100 µg/cm2. Under the operating conditions, the separation between the parallel detector pairs inside a module is 2 mm. The gas volume inside the detecting system is ~6 cm3. The total detection efficiency of the detectors for α particles and fission fragments from decays of nuclei penetrating into the assembly is ~92 and ~80% of 4π, respectively. The difference in the detection efficiency for α particles and fission fragments is explained by the substantial difference in their range in the gas gap between the detectors. The topology of the detector crystals was designed by the Research Institute of Material Science and INSTRUMENTS AND EXPERIMENTAL TECHNIQUES
Technology (Zelenograd, Moscow oblast) in coopera tion with the Veksler and Baldin Laboratory of High Energy Physics with allowance for the specific requirements of our experiments (a thin entrance win dow of the detector, the possibility of washing the detector surface, etc.). The silicon detector crystals were produced by the Research Institute of Materials Science using the planar technology. The main param eters of the silicon detectors are as follows: —thickness of the boronimplanted p+ layer,
