The role of chemical reactions in the Chernobyl accident

It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80–110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000°C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.     

The chernobyl accident: Air radioactivity measurements in Italy

Summary The data of the air radioactivity collected in the period 26/4–25/5, 1986 after the Chernobyl accident are presented. In particular the network of the sampling stations and the analyses carried out are briefly described. The meteorological situation responsible for the long-range transport of the pollutants from the place of emission to our country is also shown. Then the data of the air radioactivity are discussed and finally some observations on the functioning of the network are done.

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Riassunto Si presentano in questa nota i dati di radioattività dell'aria raccolti nel periodo 26/4–25/5, 1986 a seguito dell'incidente di Chernobyl. In particolare, dopo una breve descrizione della rete che ha effettuato i rilevamenti e delle modalità di campionamento, si analizza la situazione meteorologica responsabile del trasporto dei radionuclidi dal luogo di emissione fino al nostro paese. Si presentano poi i dati relativi alla contaminazione riscontrata nelle varie località. Segue una breve discussione sull'andamento dei dati e si chiude con alcune osservazioni sullo stato della rete e sulla necessità di un suo potenziamento.

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Резюме Приводятся данные по радиоактивности воздуха, собранные в период 26/04–25/05 1986 г. после аварии в Чернобыле. В частности, описываются система станций сбора проб и приведенные анализы. Также рассматривается метеорологическая ситуация, вызвавшая перенос загрязняющих веществ на большие расстояния от места выброса в Италию. Обсуждаются данные по радиоактивности воздуха и анализируются некоторые наблюденния функционирования системы станций сбора проб.

     

Study of the medium- and long-range transport analysing the data of the Chernobyl accident

Summary In the present work we analyse the meteorological factors that characterized the transport and deposition on the ground of the radionuclides from the Chernobyl nuclear power station over Northern Italy during the accident in April–May 1986. The aim of our study is to test some computational procedures and meteorological analyses specific for a comprehensive study of long-range pollution transport problem. By reconstructing the particle trajectories of the radioactive Chernobyl plume, we determined the most probable starting and arrival date of the plume and the level over the source. Moreover, analysis of the meteorological configuration up-and downwind the Alps permitted us to explain the temporal displacement between different kinds of measured fall-out.

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Riassunto Nel presente lavoro si analizzano i fattori meteorologici che hanno caratterizzato il trasporto e la deposizione sull'Italia Settentrionale del materiale radioattivo fuoriuscito dalla centrale nucleare di Chernobyl durante l'incidente di aprile-maggio 1986. Lo studio ha avuto come scopo quello di verificare e mettere a punto procedure di calcolo e di analisi di dati meteorologici finalizzate ai problemi di trasporto d'inquinanti a lunga distanza. La ricostruzione delle traiettorie percorse dalla nube radioattiva ha permesso di determinare la data di partenza e di arrivo piú probabile della nube e l'altezza di livellamento sopra la sorgente. Inoltre considerazioni sulla situazione meteorologica sopra e sottovento le Alpi hanno permesso di spiegare lo sfasamento temporale tra i diversi tipi di fall-out misurati.

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Резюме В этой работе мы анализируем метереологические факторы, которые характеризуют транспорт и оседание на землю радионуклидов в Севертоной Италии после аварии на Чернобыльской АЭС в апреля-мае 1986 г. Цель этой работы проверить некоторые вычислительные приемы и метереологический анализ, предлагаемые для исследования проблем транспорта загрязнений на большие расстояния. Реконструируя траектории частиц радиоактивного выброса в Чернобыле, мы определяем наиболее вероятные данные для выброса и уровня над источником. Более того, анаяиз метереологической ситуации в Альпах позволил объяснить временные смещение мезду различными типами измеренных радиоактивных выпадений.

     

The Chernobyl accident: the radioactive contamination in the area of Lake Como and in other Northern Italy sites

Summary The radioactive cloud released during the Chernobyl accident reached the Po Plain and Lombardy in the night of April 30, 1986; the cloud remained in the northern Italian skies for a few days and then disappeared either dispersed by winds or washed by rains. The evidence in the atmosphere of radionuclides as tellurium, iodine, cesium was promply observed by the Istituto di Fisica. The intense rain, in the first week of May, washed the radioactivity and the fallout contaminated the land, soil, grass and vegetables. The present work concerns the overall contamination of the Northern Italy territory and in particular the radioactive fallout in the Alpine region. Samples of soil have been measured at the gamma-spectroscope; a linear correlation is found between the radionuclide concentration in soil samples and the rain intensity, when appropriate deposition models are considered. A number of measurements has been done on Lake Como ecosystem: sediments, plankton, fishes and the overall fallout in the lake area have been investigated.

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Riassunto La nube radioattiva sprigionatasi nel corso dell'incidente al reattore nucleare di Chernobyl si è dispersa nei cieli lombardi fra la notte del 30 aprile 1986 e i primi giorni di maggio. La presenza di radioelementi nell'aria—tellurio, iodio, cesio—è stata osservata dalle numerose stazioni operanti nella pianura padana. Le piogge dei primi giorni di maggio, cadute soprattutto nelle zone prealpine, hanno trascinato al suolo consistenti quantità di radioelementi. Al fine di rilevare la correlazione fra pioggia e ricadute sono stati prelevati oltre un centinaio di campioni di terreno; i contenuti di radioelementi, e in particolare il cesio, sono misurati a mezzo di spettrometro gamma e risultano in buon accordo con i modelli di deposizione. Si rilevano particolarmente elevati i livelli di ricaduta nella zona del lago di Como e delle adiacenti vallate; un esame dei contenuti di radioelementi nell'ecosistema lacustre completa l'analisi.

     

Application of SSNTDs to investigations of radiation accident after-effects

Track methods and devices used for studies conducted after radiation accidents are considered. Solid State Nuclear Track Detectors (SSNTDs) are applied for measurements of contamination in soil, water, biological and other objects of alpha-emitting radionuclides, as well as for estimation of neutron doses by means accident dosimeters. Known radiation accidents (Chernobyl a.o.) and potential emergencies (sunken submarine “Komsomolets”, nuclear reactors) are discussed. Some result of SSNTD application at after-accident period are presented.     

一种辐射声场近似计算方法——单元辐射叠加法

提出一种基于表面振速预报辐射声场的近似方法——单元辐射叠加法。研究表明,声传递向量中的每项元素等于对应单元以单位速度振动、其它单元振速都为零时的辐射声压,即刚性障板上活塞面以单位速度振动时的辐射声压。在此基础上,利用刚性障板上单位速度振动活塞面的辐射声压直接建立表面振速与辐射声压之间的传递关系,根据这个传递关系对表面振速进行加权、求和便得到总的辐射声压。计算时采用规则形状障板面去拟合实际障板面,以规则形状障板上振动活塞面的辐射声压去近似实际障板上振动活塞面的辐射声压。相对于边界元方法,该方法在计算速度与存储空间上具有很大的优势。计算表明该近似方法是合理的、可行的。     

An approximate method to acoustic radiation problems: element radiation superposition method

An approximate method is brought forward to predict the acoustic pressure based on the surface velocity. It is named Element Radiation Superposition Method （ERSM）. The study finds that each element in Acoustic Transfer Vector （ATV） equals the acoustic pressure radiated by the corresponding surface element vibrating in unit velocity and other surface elements keep still, that is the acoustic pressure radiated by the corresponding baffled piston vibrating in unit velocity. So, it utilizes the acoustic pressure radiated by a baffled piston to establish the transfer relationship between the surface velocity and the acoustic pressure. The total acoustic pressure is obtained through summing up the products of the surface velocity and the transfer quantity. It adopts the regular baffle to fit the actual baffle in order to calculate the acoustic pressure radiated by the baffled piston. This approximate method has larger advantage in calculating speed and memory space than Boundary Element Method. Numerical simulations show that this approximate method is reasonable and feasible.     

Dosimetry problem in the case of accidental combined irradiation and its possible solution by the example of the consideration of the effect of a number of radiation factors during the Chernobyl accident

The paper is devoted to the radiation monitoring problem under conditions of accidental multifactorial irradiation during nuclear reactor accidents, including real-time monitoring. An algorithm of the corrections for the contributions to the effective equivalent dose (in addition to the main (gamma) irradiation) of the external beta irradiation and internal irradiation of incorporated iodine-131 decay is proposed.     

Magnetic moment measurements of picosecond states: New results and open problems

The temperature dependence of the precession of the angular correlation of decay gamma rays from swift¹⁵⁰Sm (2 ₁ ⁺ ) ions traversing a gadolinium foil has been found to be proportional to the foil magnetization, supporting the assertion that the transient hyperfine magnetic field acting on these ions is proportional to the magnetization of the hosts (iron or gadolinium). Similar experiments on¹⁹⁴Pt (2 ₁ ⁺ ) ions traversing iron and gadolinium foils are consistent with both the magnetic moment obtained from Rutgers experiments on iron and with a hyperfine field at Pt ions larger for gadolinium than for iron foils, in agreement with the Chalk River parametrization for heavy nuclei traversing gadolinium foils. Finally, the magnetic moments of the 2 ₁ ⁺ states in^144–150Nd,^145,150Sm and¹⁵²Gd have been measured. These data support the evidence of shell closure atZ=64 forN≤88 andZ=50 forN>90.     

Simulation of the radiation fields from ionizing radiation sources inside the containment in an accident

In the present work, a set of codes used for simulations of the radiation fields from ionizing radiation sources inside the containment in an accident is described. A method of evaluating the gamma dose rate from a space and energy distributed source is given. The dose rate is calculated by means of the design point kernel method and using buildup factors. The code MCU-REA with the ORIMCU module is used for the burnup calculations.     

Intercomparison of radiation measurements on STS-63

A joint NASA Russia study of the radiation environment inside the Space Shuttle was performed on STS-63. This was the second flight under the Shuttle-Mir Science Program (Phase 1). The Shuttle was launched on 2 February 1995, in a 51.65° inclination orbit and landed at Kennedy Space Center on 11 February 1995, for a total flight duration of 8.27 days. The Shuttle carried a complement of both passive and active detectors distributed throughout the Shuttle volume. The crew exposure varied from 1962 to 2790 μGy with an average of 2265.8 μGy or 273.98 μGy/day. Crew exposures varied by a factor of 1.4, which is higher than usual for STS mission. The flight altitude varied from 314 to 395 km and provided a unique opportunity to obtain dose variation with altitude. Measurements of the average east-west dose variation were made using two active solid state detectors. The dose rate in the Spacehab locker, measured using a tissue equivalent proportional counter (TEPC), was 413.3 μGy/day, consistent with measurements made using thermoluminescent detectors (TLDs) in the same locker. The average quality factor was 2.33, and although it was higher than model calculations, it was consistent with values derived from high temperature peaks in TLDs. The dose rate due to galactic cosmic radiation was 110.6 μGy/day and agreed with model calculations. The dose rate from trapped particles was 302.7 μGy/day, nearly a factor of 2 lower than the prediction of the AP8 model. The neutrons in the intermediate energy range of 1–20 MeV contributed 13 μGy/day and 156 μSv/day, respectively. Analysis of data from the charged particle spectrometer has not yet been completed.     

Controversial problems of measurements within quantum mechanics

It is explained why quantum mechanics applies principally to single systems and not to ensembles. A thorough analysis of thought-experiments shows clearly that irreversibility is connected with the storing of information rather than with the act of measurement. In order to avoid paradoxes one has to admit that the wave function does not represent the state of the system in itself, but information acquired in consequence of a complete measurement. The meaning of the time-energy uncertainty relation for stable systems is discussed.     

Lifetime and time-resolved fluorescence measurements with aco synchrotron radiation

For the first time storage ring synchrotron radiation has been used as a repetitive source for time spectroscopy. Very fast fluorescence decays (shorter than 1 nsec) have been measured with an accuracy of the order of 10%, by the Single Photon Counting technique. Also fast protolytic reactions occuring in the excited state of 2-naphthol and fluorescein have been investigated by the Delayed Coincidence technique (time-resolved fluorescence). Storage ring synchrotron radiation characteristics are compared with those of the nanosecond flash lamps, conventionally used for this kind of measurements.     

Efficient and accurate method for radiation transfer problems

An efficient method of analysis, which utilizes trial functions based on Case's eigenvalues, is developed for solving radiation transfer in an absorbing and scattering homogeneous semi-infinite plane-parallel medium subjected to externally incident radiation. Expressions for the forward and backward intensities, reflectivity and total radiation intensity are included. Numerical results are given and compared involving different forms of the externally incident radiation on the boundary surface. It is shown that the solution converges rapidly to the exact results and that lower-order solutions predict values of the physical parameters that are accurate to five figures in all values of the single-scattering albedos in the range 0.1 ≤ ω ≤ 1. The method has been also used to get approximate formulae for calculating Chandrasekhar's characteristic H-functions and their moments.     

New method for solving radiation transfer problems in emitting, absorbing, and scattering media

The proposed method is based on a novel technique for approximating the angular dependence of the radiated intensity. The entire range of solid angles is divided into N cells, which are symmetric relative to the center of the sphere. In each of the cells the radiation is assigned in the form of the P ₁ approximation, and a system of differential equations is obtained to determine the set of local zeroth and first moments. In some special cases the proposed approach can be regarded as a generalization of the discrete-ordinates method, which makes it possible to solve the problem of selecting the weights in the quadrature formulas in a natural manner. The effectiveness of the method is demonstrated in two one-dimensional test cases. It is shown that in these cases fairly high accuracy is achieved in the solution of the problem already for N=2. Zh. Tekh. Fiz. 67, 1–7 (September 1997)     

Spectral diffuse reflectance measurements of gadolinia, silica thin film systems using synchrotron radiation

Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic.     

Laser and absorption saturation measurements of Cr crystals, pumped by broadband pulsed 940 nm radiation

The characteristics of a 940 nm pumped Cr⁴⁺:forsterite laser have been investigated using a pulsed colour centre laser as the excitation source. Laser threshold, slope efficiency and temporal behaviour have been determined for high and low Cr⁴⁺ doped material. 940 nm pumping is found to be more efficient than 532 and 730–770 nm excitation. Discrepancies with 1064 nm pumping are attributed to excited state absorption. Absorption saturation measurements have been used to assess the potential applications of Cr⁴⁺:forsterite, Cr⁴⁺:YAG and Cr⁴⁺: Lu₃A1₅O₁₂ (LuAG) as passive Q-switches for Nd lasers in the 940 nm region.