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Remote monitoring of emission activity level from NPP using radiofrequencies 1420, 1665, 1667 MHz in real time
Journal of Environmental Radioactivity 115 (2013) 69e72
Contents lists available at SciVerse ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Remote monitoring of emission activity level from NPP using radiofrequencies 1420, 1665, 1667 MHz in real time Gennady Kolotkov*, Sergei Penin V.E. Zuev Institute of Atmospheric Optics SB RAS, Laboratory of Optical Location, 1, Academician Zuev Square, Tomsk 634021, Russia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 September 2011 Received in revised form 29 June 2012 Accepted 6 July 2012 Available online 9 August 2012
The Fukushima nuclear accident showed the importance of timely monitoring and detection of radioactive emissions released from enterprises of the nuclear fuel cycle. Nuclear power plants (NPP) working continuously are a stationary source of gaseaerosol emissions which presented in a ground surface layer persistently. Following radioactive emission, untypical effects can be observed, for example: the occurrences of areas with increased ionization, and increased concentration of some gases caused by photochemical reactions. The gases themselves and their characteristic radiation can be markers of radioactivity and can be monitored by a passive method. Hydrogen atom (H) and hydroxyl radical (OH) are formed in a radioactive plume by radiolysis of water molecules and other hydrogen-containing air components by the high energy electrons from beta-decay of radionuclides. The hydrogen atom and hydroxyl radical can spontaneously radiate at 1420 MHz and 1665e1667 MHz respectively. The passive method of remote monitoring of radiation levels using radio-frequencies of H and OH from radioactive emissions of NPP is described. The model data is indicative of the monitoring of radiation levels using these frequencies. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
Keywords: Environmental monitoring Passive method Radioactive emission NPP Hydrogen atom Hydroxyl
1. Introduction The work is devoted to the problem of remote monitoring of radioactivity level in a nuclear power plant (NPP) emission. The method of environmental monitoring of atmospheric emission from radiochemical plant (RCP) based on spontaneous emission detection of hydrogen atom (H) at a frequency of 1420 MHz was proposed in the work (Penin and Chistyakova, 1997). In the paper (Chistyakova et al., 1997) the experiments in a nuclear reprocessing plant and theoretical study conducting based on radionuclide isotope Kr-85 only. The results of field experiments from the article (Chistyakova et al., 1997) showed the feasibility of detection of the hydrogen atom line radiation in the plume of emission from RCP. The observed increase of radiation intensity at 1420 MHz can be explained by the process of electron multiplication as the result of radionuclide decay. This effect was ignored in the work of Penin and Chistyakova (1997). In this paper we taking into account isotopes of Ar, Kr, Xe and radioactive iodine in the process of generation not only hydrogen atom, but also hydroxyl radical. It is necessary to note that emissions from nuclear fuel cycle enterprises, including both NPP and RCP, differ in isotope composition
* Corresponding author. Tel.: þ7 3822 491546. E-mail address: [email protected] (G. Kolotkov).
(Kolobashkin and Rubcov, 1999). Necessity of taking into account many electron generations is because secondary, tertiary and further electrons have sufficient energies to ionize environment calling photochemical reactions in the atmosphere with appearance of radioactivity marker by which spontaneous emission is determined a radioactivity level of emission from NPP (Kolotkov et al., 2006). As an additional marker of radioactivity it is suggested to use hydroxyl spontaneously radiating (1665e1667 MHz) at the same frequency range as hydrogen atom. 2. Kinetics of H and OH under influence of ionizing radiation of beta-decay electron In routine operation of an NPP a particular set of beta radionuclides (isotopes Ar, Kr, Xe and iodine) are emitted to the atmosphere and are ever presented in the vicinity of the NPP (Kolobashkin and Rubcov, 1999). Beta decay electron traveling through molecules or neutral atom of the air can emit a photon without losing all its kinetic energy or remain free or it can absorb a photon acquire additional kinetic energy. The electron is slowed down in the field of the ion or neutral atom and loses a part of its energy in the radiation process. These freeefree transitions are called bremsstrahlung, having a continuous emission and absorption spectrum. This energy can cause photochemical reactions. Further we analyzed potential reactions inducing to H and OH generation.
0265-931X/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2012.07.004
70
G. Kolotkov, S. Penin / Journal of Environmental Radioactivity 115 (2013) 69e72
Fig. 1 illustrates the total concentration distribution of multiplication electrons by energies for Ar41, Kr85, Xe133 and I131, calculated in the work of Kolotkov et al. (2006), where Ne is a sum of energies of the ninth generation of electrons in 1 cm3 of air; and E is an energy of electron, keV. These calculations were carried out using recurrence relation by SpencereFano formulas which defined probability of electron collisions in above-threshold region of energy (Spencer and Fano, 1954) and under these assigned conditions: -
basic mechanism of electron production is ionization; electroneelectron and electroneion collisions are neglected; dissipative process is not considered; atoms in the air are at rest state before collision; and interaction occurs in the homogeneous medium (N2, O2, H2O).
The Fig. 1a shows that electrons with small energies (<10 keV) constitute a considerable part of the total amount of electrons. Fig. 1b shows the electron energy distribution of small energies for better presentation. These electrons introduce the considerable contribution to a bremsstrahlung quantity e the basic mechanism of radiation influence on atmospheric components. The sharp decrease is observed at small energies. This is can be explained that it is necessary to consider effects of an electron attachment in this case, which are not considered within the limits of the presented model. 2.1. Photochemical processes: generation of H and OH The concentration of hydrogen atom in the atmosphere is negligibility small below a level of 10 km, because radiation is critical for the photolysis of atmospheric gases and the generation A), is completely absorbed by ozone in of O (l e wavelength < 2900 the stratosphere is situated between 10 km and 30 km (Okabe, 1978). Hydrogen atom escapes from Earth’s gravity into space, because of its light weight (Tiwary and Colls, 2010). Generation of hydrogen atom is caused by photolysis of the following compounds: methane (SO4), ammonia (NH3), molecular hydrogen (O2), and formaldehyde (OSOP), hydrogen sulfide (H2S) and water (O2P). The total concentration of these molecules in the atmosphere constitutes w1019e1020 m3. We shall consider the reactions generating hydrogen atom only, and the conditions of their behavior (Okabe, 1978).
Initial processes of methane photolysis by radiation at
l e 1100e1600 A can be presented as: CH4 /CH3 þ H CH4 /CH2 þ H2 ; H2 /H þ H; CH4 /CH þ H2 þ H:
Three main initial processes for the photolysis of radiation in range of the near and vacuum ultraviolet for ammonia are:
NH3 /NH2 þ H at l< 2800 A
(1)
NH3 /NH þ H2 at l< 2240 A
(2)
NH3 /NH þ H þ H at l< 1470 A
(3)
Processes (1e3) are more probable for the dissociation at wavelength <2800 A. The main initial photochemical process for the formaldehyde photodissociation is:
HCHO/H þ HCO threshold wavelength le3500 A : Initial process for the hydrogen sulfide photodissociation, at a near UV e range, is:
H2 S/H þ SH at l< 3170 A: The main initial process for water photodissociation in range of wavelengths 1200e1900 A is:
H2 O/H þ OH at l< 1357; 2420 A:
(4)
Molecular hydrogen, nascent as a result of secondary, can dissociate in the atmosphere under the radiation act over the range 844.7e1108 A: H2 /H þ H. Concentration of hydroxyl strictly depends on solar radiation but will not exceed 106e107 cm3 at a release height (Rohrer and Berresheim, 2006). In the standard atmosphere OH is formed in the result of the reaction sequences:
O3 þ hn/O2 ð1 Dg Þ þ Oð1 DÞ at l< 320 nm; Oð1 DÞ þ H2 O/2OHðz5%Þ Oð1 DÞ þ M/OH þ Mðz95%; ground state transition Oð3 PÞ; N2 and O2 in the air; Oð3 PÞ then forms O3 Þ;
Fig. 1. The total energy distribution of electrons.
where M ¼ CH4, H2, N2, or O2. Notice that the reaction rate of OH radical formation by photolysis of O3 is fortunately restricted by small amounts of solar radiation <320 nm in the troposphere. Other sources of OH are: nitrous acid (HONO), hydrogen peroxide (H2O2), methane peroxide (CH3OOH), reaction nitric oxide (NO) and radical hydro peroxide (HO2), or reaction ethylene and ozone. As has been shown in Li et al. (2008) the major natural source of tropospheric hydroxyl part is the reaction NO*2 with water vapor. If the main part of NO*2 reacts with water vapor then the following processes of generation OH take place:
G. Kolotkov, S. Penin / Journal of Environmental Radioactivity 115 (2013) 69e72
NO2 þ hn/NO*2 at l< 4200 A; NO*2 þ M/NO2 þ M; where M ¼ N2, O2 or H2O
NO*2 þ H2 O/OH þ HONO: The HONO photolysis gives additional OH:
HONO þ hn/OH þ NO at l< 3900 A: On the basis of the considered reactions it is possible to conclude that the radiation with wavelengths from 844.7 A to 4200 A make the greatest contribution to the generation of hydrogen atom and hydroxyl. By the formula Ed ¼ hc/l (Okabe, 1978), we determine the dissociation energy lies in the range 2.95e14.68 eV. Thus the equilibrium concentration of atoms O and OH depends on the processes of generation and recombination. 3. Estimation of H and OH concentration in the emission plume region
dQn ¼
8e2 y2 =3c3 $neff dn; erg sec1
3.1. Photochemical processes: recombination of H and PO These estimates show that about 1015 atoms of hydrogen in one m per second are formed in the result of the decay of the listed above isotopes in the emission plume. Knowing the recombination rate of hydrogen atoms allows estimate the stationary concentration from the equation (Okabe, 1978): 3
1=2
NHðnonstatÞ =2k
;
OH þ CO/H þ CO2 recombine about 70%; k ¼ 1:5 1013 ðT=300Þ0:6 cm3 mol1 s1 ; HO2 þ NO/OH þ NO2
where e is the electron charge, C, c is the light speed, cm s1, y is the electron speed, neff ¼ Nystr is the effective frequency of collisions (N is the number of atoms in 1 cm3, str is the transport scattering cross-section, cm2). In order to find power Qn which the electron radiates in the interval of wavelengths dn it is necessary to sum dn over all collisions. Assuming the diffusion to be isotropic, the electron deceleration time w106 s and taking into account results presented in Kolotkov et al. (2006), after summation we obtain the amount of energy from 0.1 to 2$1012 erg cm3 emitted in the wavelength interval 844.7e4200 A.
NH ¼
process is the main mechanism of disappearance of hydrogen atoms under normal atmospheric conditions the equation (5) is true. In this case, the stationary concentration of O in the plume is w1014 m3. The hydroxyl radical, OH, is a significant chemical species of HOx family and plays key role in atmospheric chemistry. Extremely high reactivity of OH and strong dependence on time of day, latitude and humidity are part of the complexity in the precise definition of OH concentration (Rohrer and Berresheim, 2006; Li et al., 2008; Sedunov, 1991). The average background concentration is about 1012 atoms m3. We consider the bremsstrahlung of law-energetic electrons is the major mechanism of radiation effects on atmospheric constituents and in view of the generation of OH in the reaction (4), thus the generation rate is 1015 m3 s1. There are two main sink reactions of OH in the troposphere (Plane, 2009; Seinfeld and Pandis, 2006; Sander et al., 2011):
H þ O2 ðþMÞ/HO2 ðradical hydroperoxideÞ
For calculation of the energy radiated by an electron in the given interval of wavelengths, it is possible to apply classical electrodynamics which yields the result, quite fit for estimations. As collisions of electrons with atoms occurs rarely (in comparison with the frequency of the radiated electromagnetic wave), it is possible to consider the consecutive collisions as independent, and the energy radiated at many collisions is simply the sum of the energies radiated by the separate collisions. As the act of scattering occurs very quickly in comparison with the period of the field oscillation, it is possible to write down the formula for the quantity of the bremsstrahlung electron energy in the frequency interval dn per second (Zel’dovich and Raizer, 1966; Kolotkov et al., 2006):
71
(5)
where NH is the stationary concentration of hydrogen atoms, k is the recombination coefficient m3 molecule1 s1. From experimental data, it is known that the constant of recombination rate for neutral hydrogen atoms under standard conditions, about 1013e1014 m3 mol1 s1 (Okabe, 1978). If a recombination
(6)
It is necessary to note that reduction of OH in the first cycle.
OH þ CH4 /CH3 þ H2 O z30% OH reacts by this way; k ¼ 7 1015 cm3 mol1 s1 CH3 þ O2 ðþMÞ/CH3 O2 CH3 O2 þ NO/CH3 O þ NO2 CH3 O þ O2 /CH2 O þ HO2 ðformaldehydeÞ CH2 O þ hvðl < 338 nmÞ/HCO þ H H þ O2 /HO2 HCO þ O2 /CO þ HO2
(7)
Then 3 HO2 radicals react with NO and generate 3 OH / chain reactions: HO2 þ NO/OH þ NO2 . If the NO concentration is smaller than peroxides generation rate then scavenged by atmospheric water particles. As OH recombination rate is small compared with OH generation rate and the cycles reactions (6) and (7) lead to OH regeneration, then we could assume that hydroxyl concentration slightly increase. Thus, OH concentration is about 1015 m3.
4. Estimation of spontaneous radiation intensities from the plume emission Radiation intensity (line) is defined by radiative transition probability Ank and by the following formula: S ¼ EnkAnk, where E ¼ h$Dn (h e Planck’s constant, Dn e transition frequency). The energy of hyperfine splitting of the lowest orbital energy state of hydrogen atom is equal 9.412$1023 J for Dn ¼ 1420.4057517 MHz. The probability of spontaneous transition is w3$1015 s1. Thus the radiation power emitted by one atom is 2.824$1037 W. As the concentration of hydrogen atoms in one cubic meter of the emission plume is about 1014 atoms, then the power radiated in volume of 1 km3 at 1420 MHz frequency is about 1013 W. As mentioned before, the characteristic emissions of H and OH could be used for detection of an activity level of NPP plume. Beside of H emission could use emission of OH radicals at the frequencies: 1612, 1665, 1667 j 1721 MHz. The number of radio lines is explained by existence of nuclear spin of hydrogen atom. The summary table for 4 radio lines of OH present below (Haar and Pelling, 1974) (Table 1).
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G. Kolotkov, S. Penin / Journal of Environmental Radioactivity 115 (2013) 69e72
7. Conclusion
Table 1 Pivot table of OH emission lines. Frequency (MHz)
Einstein coefficient A (1011 s1)
Energy of hyperfine splitting (1025 J)
Radiated power (1035 W)
1612.231 1665.40 1667.358 1720.533
1.289 7.103 7.698 0.940
10.7 11.0 11.0 11.4
1.3792 7.8133 8.4678 1.0716
It is thought that the fundamental frequencies of spontaneous transition are 1665e1667 MHz and the radiation power of emitted by hydroxyl molecule is about 1034 W. Thus the emission volume of 1 km3 radiates 2 1010 W at 1665e1667 MHz range. In work of Penin and Chistyakova (1997), the experimental data are presented which show the feasibility of detection of the radiation at 1420 MHz from the nuclear reprocessing plants at distances up to 30 km. Thus these intensities would be quite sufficient for detection of radionuclides release from NPP at the distance of several kilometers.
The radiant intensity at the frequencies of 1420 MHz and 1665e1667 MHz is enough for monitoring the amount of radionuclide released from NPP at the distance of 10 km and more from the source in real time. This weak electromagnetic radiation at the frequencies could be measured by a dual-channel 1.3e1.8 GHz radiometric complex. The design of the microwave radiometer is simplified as the hydrogen atom and hydroxyl spontaneously radiate in the same spectral range. Within the contract with TRIO Consulting Incorporation the development of the scheme and production of the full-function on-board dualchannel 1.3e1.8 GHz radiometric complex was performed.
Acknowledgments We appreciate invaluable comments made by Dr. S. C. Sheppard as well as anonymous reviewers.
5. Doppler spectral broadening for OH and H References It is well-known fact that there is the broadening of a spectral line of the emitting particle moving toward or away from observer. Such line broadening Dn (cm1) is defined by formula: Dn ¼ 7:16$107 $no $ðT=MÞ1=2 , where n0 is the wave number of central wavelength, T is the gas temperature in K, and M is the atomic mass. The Doppler width of the OH lines (1665e1667 MHz) at T ¼ 300 K is equal to 10.5$107 cm1 or 31.5 kHz. The Doppler width of the H line (1420 MHz) does not exceed of 150 kHz because the energy of translational motion of hydrogen atom <2 eV (Penin and Chistyakova, 1997). 6. Substantiation of use of 1420 and 1665e1667 MHz radiofrequencies The troposphere is practically transparent to the microwave radiation with these frequencies. The atmospheric attenuation is low at the microwave range from 1 to 10 GHz. The noise background is less than 1021 W m2 in this spectral range 1e10 GHz and the attenuation due to atmospheric absorption is less than 2 dB. The frequency bands 1400e1427 and 1660.5e1668.4 MHz are used for search for intentional emissions of extraterrestrial origin. That means any transmissions are not recommended according to the recommendation 702 of ITU (International Telecommunication Union) (ITU, 2008) and prohibited by countries all over the world: USA, Great Britain, Russia and etc.
Chistyakova, L.K., Chystyakov, V.Yu., Losev, D.V., Penin, S.T., 1997. Microwave radiation of atomic hydrogen in plumes of radioactive emissions from nuclear reprocessing plants. Microw. Opt. Technol. Lett. 16 (4), 225e260. Haar, D.T., Pelling, M.A., 1974. Interstellar hydroxyl and water masers and formaldehyde masers and dasars. Rep. Progr. Phys. 37 (4), 481e561. ITU, 2008. Radio Regulations, Edition of 2008, vol. 3. Kolobashkin, V.M., Rubcov, P.M., 1999. Radiating Characteristics of the Irradiated Nuclear Fuel. Energoatomizdat. Kolotkov, G.A., Penin, S.T., Chistyakova, L.K., 2006. Degradation of fast electrons energy and atomic hydrogen generation in an emission plume from atomic power stations. In: Proceeding SPIE, 616025, pp. 1e12. Li, Sh., Matthews, J., Sinha, Am., 2008. Atmospheric hydroxyl radical production from electronically excited NO2 and H2O. Science 319 (5870), 1657e1660. Okabe, H., 1978. Photochemistry of Small Molecules. John Wiley & Sons, New York. Penin, S.T., Chistyakova, L.K., 1997. Generation and dynamic of atomic hydrogen radiation in atmosphere and in emission plume of nuclear reprocessing plants. Atmos. Ocean Opt. 10 (1), 73e81. Plane, J., 2009. Lecture: Chemistry of the Earth’s Atmosphere. A General Introduction. ERCA. Rohrer, F., Berresheim, H., 2006. Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation. Nature 442, 184e187. Sander, S.P., et al., 2011. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies. Evaluation Number 17. JPL Publication 10-6, Jet Propulsion Laboratory, Pasadena. Sedunov, U.S., 1991. Atmosphere. Gidrometeoizdat. Seinfeld, J.H., Pandis, S.N., 2006. Atmospheric Chemistry and Physics: from Air Pollution to Climate Change, second ed. John Wiley & Sons Inc.. Spencer, L.V., Fano, U., 1954. Energy spectrum resulting from electron slowing down. Phys. Rev. 93 (6), 1172e1181. Tiwary, A., Colls, J., 2010. Air Pollution: Measurement, Modelling and Mitigation. Routledge, Taylor & Francis group, Abingdon, Oxon, UK. Zel’dovich, Y.B., Raizer, U.P., 1966. Physics of Shock Waves and the HighTemperature Hydrodynamical Phenomena. In: Izdat Phys-Math. Sciences.
Contents lists available at SciVerse ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Remote monitoring of emission activity level from NPP using radiofrequencies 1420, 1665, 1667 MHz in real time Gennady Kolotkov*, Sergei Penin V.E. Zuev Institute of Atmospheric Optics SB RAS, Laboratory of Optical Location, 1, Academician Zuev Square, Tomsk 634021, Russia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 September 2011 Received in revised form 29 June 2012 Accepted 6 July 2012 Available online 9 August 2012
The Fukushima nuclear accident showed the importance of timely monitoring and detection of radioactive emissions released from enterprises of the nuclear fuel cycle. Nuclear power plants (NPP) working continuously are a stationary source of gaseaerosol emissions which presented in a ground surface layer persistently. Following radioactive emission, untypical effects can be observed, for example: the occurrences of areas with increased ionization, and increased concentration of some gases caused by photochemical reactions. The gases themselves and their characteristic radiation can be markers of radioactivity and can be monitored by a passive method. Hydrogen atom (H) and hydroxyl radical (OH) are formed in a radioactive plume by radiolysis of water molecules and other hydrogen-containing air components by the high energy electrons from beta-decay of radionuclides. The hydrogen atom and hydroxyl radical can spontaneously radiate at 1420 MHz and 1665e1667 MHz respectively. The passive method of remote monitoring of radiation levels using radio-frequencies of H and OH from radioactive emissions of NPP is described. The model data is indicative of the monitoring of radiation levels using these frequencies. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
Keywords: Environmental monitoring Passive method Radioactive emission NPP Hydrogen atom Hydroxyl
1. Introduction The work is devoted to the problem of remote monitoring of radioactivity level in a nuclear power plant (NPP) emission. The method of environmental monitoring of atmospheric emission from radiochemical plant (RCP) based on spontaneous emission detection of hydrogen atom (H) at a frequency of 1420 MHz was proposed in the work (Penin and Chistyakova, 1997). In the paper (Chistyakova et al., 1997) the experiments in a nuclear reprocessing plant and theoretical study conducting based on radionuclide isotope Kr-85 only. The results of field experiments from the article (Chistyakova et al., 1997) showed the feasibility of detection of the hydrogen atom line radiation in the plume of emission from RCP. The observed increase of radiation intensity at 1420 MHz can be explained by the process of electron multiplication as the result of radionuclide decay. This effect was ignored in the work of Penin and Chistyakova (1997). In this paper we taking into account isotopes of Ar, Kr, Xe and radioactive iodine in the process of generation not only hydrogen atom, but also hydroxyl radical. It is necessary to note that emissions from nuclear fuel cycle enterprises, including both NPP and RCP, differ in isotope composition
* Corresponding author. Tel.: þ7 3822 491546. E-mail address: [email protected] (G. Kolotkov).
(Kolobashkin and Rubcov, 1999). Necessity of taking into account many electron generations is because secondary, tertiary and further electrons have sufficient energies to ionize environment calling photochemical reactions in the atmosphere with appearance of radioactivity marker by which spontaneous emission is determined a radioactivity level of emission from NPP (Kolotkov et al., 2006). As an additional marker of radioactivity it is suggested to use hydroxyl spontaneously radiating (1665e1667 MHz) at the same frequency range as hydrogen atom. 2. Kinetics of H and OH under influence of ionizing radiation of beta-decay electron In routine operation of an NPP a particular set of beta radionuclides (isotopes Ar, Kr, Xe and iodine) are emitted to the atmosphere and are ever presented in the vicinity of the NPP (Kolobashkin and Rubcov, 1999). Beta decay electron traveling through molecules or neutral atom of the air can emit a photon without losing all its kinetic energy or remain free or it can absorb a photon acquire additional kinetic energy. The electron is slowed down in the field of the ion or neutral atom and loses a part of its energy in the radiation process. These freeefree transitions are called bremsstrahlung, having a continuous emission and absorption spectrum. This energy can cause photochemical reactions. Further we analyzed potential reactions inducing to H and OH generation.
0265-931X/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2012.07.004
70
G. Kolotkov, S. Penin / Journal of Environmental Radioactivity 115 (2013) 69e72
Fig. 1 illustrates the total concentration distribution of multiplication electrons by energies for Ar41, Kr85, Xe133 and I131, calculated in the work of Kolotkov et al. (2006), where Ne is a sum of energies of the ninth generation of electrons in 1 cm3 of air; and E is an energy of electron, keV. These calculations were carried out using recurrence relation by SpencereFano formulas which defined probability of electron collisions in above-threshold region of energy (Spencer and Fano, 1954) and under these assigned conditions: -
basic mechanism of electron production is ionization; electroneelectron and electroneion collisions are neglected; dissipative process is not considered; atoms in the air are at rest state before collision; and interaction occurs in the homogeneous medium (N2, O2, H2O).
The Fig. 1a shows that electrons with small energies (<10 keV) constitute a considerable part of the total amount of electrons. Fig. 1b shows the electron energy distribution of small energies for better presentation. These electrons introduce the considerable contribution to a bremsstrahlung quantity e the basic mechanism of radiation influence on atmospheric components. The sharp decrease is observed at small energies. This is can be explained that it is necessary to consider effects of an electron attachment in this case, which are not considered within the limits of the presented model. 2.1. Photochemical processes: generation of H and OH The concentration of hydrogen atom in the atmosphere is negligibility small below a level of 10 km, because radiation is critical for the photolysis of atmospheric gases and the generation A), is completely absorbed by ozone in of O (l e wavelength < 2900 the stratosphere is situated between 10 km and 30 km (Okabe, 1978). Hydrogen atom escapes from Earth’s gravity into space, because of its light weight (Tiwary and Colls, 2010). Generation of hydrogen atom is caused by photolysis of the following compounds: methane (SO4), ammonia (NH3), molecular hydrogen (O2), and formaldehyde (OSOP), hydrogen sulfide (H2S) and water (O2P). The total concentration of these molecules in the atmosphere constitutes w1019e1020 m3. We shall consider the reactions generating hydrogen atom only, and the conditions of their behavior (Okabe, 1978).
Initial processes of methane photolysis by radiation at
l e 1100e1600 A can be presented as: CH4 /CH3 þ H CH4 /CH2 þ H2 ; H2 /H þ H; CH4 /CH þ H2 þ H:
Three main initial processes for the photolysis of radiation in range of the near and vacuum ultraviolet for ammonia are:
NH3 /NH2 þ H at l< 2800 A
(1)
NH3 /NH þ H2 at l< 2240 A
(2)
NH3 /NH þ H þ H at l< 1470 A
(3)
Processes (1e3) are more probable for the dissociation at wavelength <2800 A. The main initial photochemical process for the formaldehyde photodissociation is:
HCHO/H þ HCO threshold wavelength le3500 A : Initial process for the hydrogen sulfide photodissociation, at a near UV e range, is:
H2 S/H þ SH at l< 3170 A: The main initial process for water photodissociation in range of wavelengths 1200e1900 A is:
H2 O/H þ OH at l< 1357; 2420 A:
(4)
Molecular hydrogen, nascent as a result of secondary, can dissociate in the atmosphere under the radiation act over the range 844.7e1108 A: H2 /H þ H. Concentration of hydroxyl strictly depends on solar radiation but will not exceed 106e107 cm3 at a release height (Rohrer and Berresheim, 2006). In the standard atmosphere OH is formed in the result of the reaction sequences:
O3 þ hn/O2 ð1 Dg Þ þ Oð1 DÞ at l< 320 nm; Oð1 DÞ þ H2 O/2OHðz5%Þ Oð1 DÞ þ M/OH þ Mðz95%; ground state transition Oð3 PÞ; N2 and O2 in the air; Oð3 PÞ then forms O3 Þ;
Fig. 1. The total energy distribution of electrons.
where M ¼ CH4, H2, N2, or O2. Notice that the reaction rate of OH radical formation by photolysis of O3 is fortunately restricted by small amounts of solar radiation <320 nm in the troposphere. Other sources of OH are: nitrous acid (HONO), hydrogen peroxide (H2O2), methane peroxide (CH3OOH), reaction nitric oxide (NO) and radical hydro peroxide (HO2), or reaction ethylene and ozone. As has been shown in Li et al. (2008) the major natural source of tropospheric hydroxyl part is the reaction NO*2 with water vapor. If the main part of NO*2 reacts with water vapor then the following processes of generation OH take place:
G. Kolotkov, S. Penin / Journal of Environmental Radioactivity 115 (2013) 69e72
NO2 þ hn/NO*2 at l< 4200 A; NO*2 þ M/NO2 þ M; where M ¼ N2, O2 or H2O
NO*2 þ H2 O/OH þ HONO: The HONO photolysis gives additional OH:
HONO þ hn/OH þ NO at l< 3900 A: On the basis of the considered reactions it is possible to conclude that the radiation with wavelengths from 844.7 A to 4200 A make the greatest contribution to the generation of hydrogen atom and hydroxyl. By the formula Ed ¼ hc/l (Okabe, 1978), we determine the dissociation energy lies in the range 2.95e14.68 eV. Thus the equilibrium concentration of atoms O and OH depends on the processes of generation and recombination. 3. Estimation of H and OH concentration in the emission plume region
dQn ¼
8e2 y2 =3c3 $neff dn; erg sec1
3.1. Photochemical processes: recombination of H and PO These estimates show that about 1015 atoms of hydrogen in one m per second are formed in the result of the decay of the listed above isotopes in the emission plume. Knowing the recombination rate of hydrogen atoms allows estimate the stationary concentration from the equation (Okabe, 1978): 3
1=2
NHðnonstatÞ =2k
;
OH þ CO/H þ CO2 recombine about 70%; k ¼ 1:5 1013 ðT=300Þ0:6 cm3 mol1 s1 ; HO2 þ NO/OH þ NO2
where e is the electron charge, C, c is the light speed, cm s1, y is the electron speed, neff ¼ Nystr is the effective frequency of collisions (N is the number of atoms in 1 cm3, str is the transport scattering cross-section, cm2). In order to find power Qn which the electron radiates in the interval of wavelengths dn it is necessary to sum dn over all collisions. Assuming the diffusion to be isotropic, the electron deceleration time w106 s and taking into account results presented in Kolotkov et al. (2006), after summation we obtain the amount of energy from 0.1 to 2$1012 erg cm3 emitted in the wavelength interval 844.7e4200 A.
NH ¼
process is the main mechanism of disappearance of hydrogen atoms under normal atmospheric conditions the equation (5) is true. In this case, the stationary concentration of O in the plume is w1014 m3. The hydroxyl radical, OH, is a significant chemical species of HOx family and plays key role in atmospheric chemistry. Extremely high reactivity of OH and strong dependence on time of day, latitude and humidity are part of the complexity in the precise definition of OH concentration (Rohrer and Berresheim, 2006; Li et al., 2008; Sedunov, 1991). The average background concentration is about 1012 atoms m3. We consider the bremsstrahlung of law-energetic electrons is the major mechanism of radiation effects on atmospheric constituents and in view of the generation of OH in the reaction (4), thus the generation rate is 1015 m3 s1. There are two main sink reactions of OH in the troposphere (Plane, 2009; Seinfeld and Pandis, 2006; Sander et al., 2011):
H þ O2 ðþMÞ/HO2 ðradical hydroperoxideÞ
For calculation of the energy radiated by an electron in the given interval of wavelengths, it is possible to apply classical electrodynamics which yields the result, quite fit for estimations. As collisions of electrons with atoms occurs rarely (in comparison with the frequency of the radiated electromagnetic wave), it is possible to consider the consecutive collisions as independent, and the energy radiated at many collisions is simply the sum of the energies radiated by the separate collisions. As the act of scattering occurs very quickly in comparison with the period of the field oscillation, it is possible to write down the formula for the quantity of the bremsstrahlung electron energy in the frequency interval dn per second (Zel’dovich and Raizer, 1966; Kolotkov et al., 2006):
71
(5)
where NH is the stationary concentration of hydrogen atoms, k is the recombination coefficient m3 molecule1 s1. From experimental data, it is known that the constant of recombination rate for neutral hydrogen atoms under standard conditions, about 1013e1014 m3 mol1 s1 (Okabe, 1978). If a recombination
(6)
It is necessary to note that reduction of OH in the first cycle.
OH þ CH4 /CH3 þ H2 O z30% OH reacts by this way; k ¼ 7 1015 cm3 mol1 s1 CH3 þ O2 ðþMÞ/CH3 O2 CH3 O2 þ NO/CH3 O þ NO2 CH3 O þ O2 /CH2 O þ HO2 ðformaldehydeÞ CH2 O þ hvðl < 338 nmÞ/HCO þ H H þ O2 /HO2 HCO þ O2 /CO þ HO2
(7)
Then 3 HO2 radicals react with NO and generate 3 OH / chain reactions: HO2 þ NO/OH þ NO2 . If the NO concentration is smaller than peroxides generation rate then scavenged by atmospheric water particles. As OH recombination rate is small compared with OH generation rate and the cycles reactions (6) and (7) lead to OH regeneration, then we could assume that hydroxyl concentration slightly increase. Thus, OH concentration is about 1015 m3.
4. Estimation of spontaneous radiation intensities from the plume emission Radiation intensity (line) is defined by radiative transition probability Ank and by the following formula: S ¼ EnkAnk, where E ¼ h$Dn (h e Planck’s constant, Dn e transition frequency). The energy of hyperfine splitting of the lowest orbital energy state of hydrogen atom is equal 9.412$1023 J for Dn ¼ 1420.4057517 MHz. The probability of spontaneous transition is w3$1015 s1. Thus the radiation power emitted by one atom is 2.824$1037 W. As the concentration of hydrogen atoms in one cubic meter of the emission plume is about 1014 atoms, then the power radiated in volume of 1 km3 at 1420 MHz frequency is about 1013 W. As mentioned before, the characteristic emissions of H and OH could be used for detection of an activity level of NPP plume. Beside of H emission could use emission of OH radicals at the frequencies: 1612, 1665, 1667 j 1721 MHz. The number of radio lines is explained by existence of nuclear spin of hydrogen atom. The summary table for 4 radio lines of OH present below (Haar and Pelling, 1974) (Table 1).
72
G. Kolotkov, S. Penin / Journal of Environmental Radioactivity 115 (2013) 69e72
7. Conclusion
Table 1 Pivot table of OH emission lines. Frequency (MHz)
Einstein coefficient A (1011 s1)
Energy of hyperfine splitting (1025 J)
Radiated power (1035 W)
1612.231 1665.40 1667.358 1720.533
1.289 7.103 7.698 0.940
10.7 11.0 11.0 11.4
1.3792 7.8133 8.4678 1.0716
It is thought that the fundamental frequencies of spontaneous transition are 1665e1667 MHz and the radiation power of emitted by hydroxyl molecule is about 1034 W. Thus the emission volume of 1 km3 radiates 2 1010 W at 1665e1667 MHz range. In work of Penin and Chistyakova (1997), the experimental data are presented which show the feasibility of detection of the radiation at 1420 MHz from the nuclear reprocessing plants at distances up to 30 km. Thus these intensities would be quite sufficient for detection of radionuclides release from NPP at the distance of several kilometers.
The radiant intensity at the frequencies of 1420 MHz and 1665e1667 MHz is enough for monitoring the amount of radionuclide released from NPP at the distance of 10 km and more from the source in real time. This weak electromagnetic radiation at the frequencies could be measured by a dual-channel 1.3e1.8 GHz radiometric complex. The design of the microwave radiometer is simplified as the hydrogen atom and hydroxyl spontaneously radiate in the same spectral range. Within the contract with TRIO Consulting Incorporation the development of the scheme and production of the full-function on-board dualchannel 1.3e1.8 GHz radiometric complex was performed.
Acknowledgments We appreciate invaluable comments made by Dr. S. C. Sheppard as well as anonymous reviewers.
5. Doppler spectral broadening for OH and H References It is well-known fact that there is the broadening of a spectral line of the emitting particle moving toward or away from observer. Such line broadening Dn (cm1) is defined by formula: Dn ¼ 7:16$107 $no $ðT=MÞ1=2 , where n0 is the wave number of central wavelength, T is the gas temperature in K, and M is the atomic mass. The Doppler width of the OH lines (1665e1667 MHz) at T ¼ 300 K is equal to 10.5$107 cm1 or 31.5 kHz. The Doppler width of the H line (1420 MHz) does not exceed of 150 kHz because the energy of translational motion of hydrogen atom <2 eV (Penin and Chistyakova, 1997). 6. Substantiation of use of 1420 and 1665e1667 MHz radiofrequencies The troposphere is practically transparent to the microwave radiation with these frequencies. The atmospheric attenuation is low at the microwave range from 1 to 10 GHz. The noise background is less than 1021 W m2 in this spectral range 1e10 GHz and the attenuation due to atmospheric absorption is less than 2 dB. The frequency bands 1400e1427 and 1660.5e1668.4 MHz are used for search for intentional emissions of extraterrestrial origin. That means any transmissions are not recommended according to the recommendation 702 of ITU (International Telecommunication Union) (ITU, 2008) and prohibited by countries all over the world: USA, Great Britain, Russia and etc.
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