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α-Particle track investigation of the Chernobyl Nuclear Power Plant accident region soil samples
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Radiation Measurements 36 (2003) 529 – 532 www.elsevier.com/locate/radmeas
-Particle track investigation of the Chernobyl Nuclear Power Plant accident region soil samples L.L. Kashkarova;∗ , G.V. Kalininaa , V.P. Perelyginb;1 a Vernadsky
Institute of Geochemistry and Analytical Chemistry RAS, Kosygin Street 19 Moscow 117975, Russia b Joint Institute for Nuclear Research, Joliot Curie, 8, Dubna 141980, Russia
Received 21 October 2002; received in revised form 11 February 2003; accepted 6 May 2003
Abstract Results of -particle track studies (Radiat. Meas. 25(1– 4) (1995) 413; Radionuclides and Heavy metals in Environment, Vol. 5, 2001, Kluwer Academic Publisher, Dordrecht) indicate that the surface (6 5 cm) layer of the soil in the Chernobyl Nuclear Power Plant (NPP) accident region consists of thinly dispersed radionuclides and highly-radioactive “hot” particles (HPs). The latter contain nearly 2/3rds of the total -activity of the contaminated soil. In the present report, the new results of continued HP -activity characteristics are presented. The chief attempt made was to investigate size–frequency vs. -activity distribution of HPs of size fraction 6 10–100 m. For the Hp-aggregates with ∼100–1000 m sizes, -radio-nuclide heterogeneity was established. This is probably the result of formation of HP-aggregates during the second stage of the NPP accident process: in these HPs the presence of not only U and >ssion products of “fuel” origin has been revealed, but also of terrestrial matter components. c 2003 Elsevier Ltd. All rights reserved. Keywords: Tracks; CZ plastic track detector; Highly-radioactive “hot” particles; Chernobyl accident region; Radio-nuclide soil contamination
1. Introduction
2. Experimental
The radioactive contaminated soil matter of the Chernobyl Nuclear Power Plant (NPP) area is due to the >nest aerosol HPs, containing very high concentrations of radio-nuclides. Detailed analysis of HP behaviour in natural environment matter and their speci>c radioactivity are of greatest importance for the quantitative estimation of real radiation conditions in the environment. Preliminary results (Kashkarov et al., 1995, 2001) signi>cantly complete our knowledge about the radio-nuclide contents, -activity of HPs and their soil-depth variations. However, statistically essential values and more precise estimations of the radioactive contamination in the Chernobyl region soil material need to be obtained.
Soil samples have been collected between 1986 and 1990 by GEOKHI RAS radio-chemical expeditions in the Chernobyl NPP region. Registration of HP -activity was carried out using a plastic nuclear track detector of the CZ type (Kashkarov et al., 1993), with registration eFectively ∼80% for isotropic -particle Hux. HP sizes were obtained by using simple measuring techniques (Kashkarov and Kalinina, 2002). In this method, the plate of the CZ-detector is irradiated with perpendicular oriented -particles, crossed through a micrometry collimator placed between the sample and track detectors.
∗ Corresponding author. Tel.: +7-96-522-1988; fax: +7-95-938-2054. E-mail address: [email protected] (L.L. Kashkarov). 1 Deceased.
3. Results and discussion Examples of the -track microphotograph, corresponding to some type of the HPs and the aggregates, are presented in Fig. 1.
c 2003 Elsevier Ltd. All rights reserved. 1350-4487/03/$ - see front matter doi:10.1016/S1350-4487(03)00199-9
530
L.L. Kashkarov et al. / Radiation Measurements 36 (2003) 529 – 532 90 80
Number of hot particles
70 60 50 40 30 20 10 0 1
10
Size, µm
100
1000
Fig. 2. Size-frequency distribution of HPs in the Pripyat-5 soil sample, Chernobyl NPP region.
Fig. 1. Microphotographs of -tracks due to HPs of diFerent sizes and -activities. Numbers 1– 4 correspond to four groups of HPs. Exposure time of the CZ-type plastic tracker detector in contact with the soil sample surface is equal to 3–56 days.
3.1. Size-frequency distribution Revising our earlier data on the HP size–frequency distribution gave analogous results. At least four HP-groups can be identi>ed on the histogram (see Fig. 2). The >rst group consists of the smallest (l 6 5 m) HPs with very high -activity with A 6 10 Bq/particle; the second group of HPs is characterized by 8 6 l 6 12 m and 1 6 A 6 5 Bq/particle; and the third and fourth groups are practically HP-aggregates of sizes: 40 6 l 6 80 and l 6 100 m, respectively, with A 6 1 Bq/particle. The (I-2) of the HP groups are subjected to the log-normal size–frequency relationship. This result can be an indicator of the major process of the formation of these HPs which was the high-temperature melting of the NPP active zone matter and subsequent fast cooling of the smallest primary individual micro-drops. Aggregates formation from this point of
Fig. 3. Variation of HP distribution with -activity as a function of the HPs size group 1– 4.
L.L. Kashkarov et al. / Radiation Measurements 36 (2003) 529 – 532
531
Table 1 Results of the total -track density measurements and presence of HPs of diFerent sizes in the searched soil samples from the Chernobyl NPP region No.
1 2 3
4
5
6
Sample
Bryansk, C9 Bryansk, M1 Pripyat, P-1 Pripyat, P-1 Pripyat, P-1 Pripyat, P-1 Pripyat, P-3 Pripyat, P-3 Pripyat, P-3 Pripyat, P-3 Pripyat, P-5 Pripyat, P-5 Pripyat, P-5 Pripyat, P-5 Pripyat, P-31 Pripyat, P-31 Pripyat, P-31 Pripyat, P-31
NTR
236 328 238
4.7 7.8 3.1
168
2.0
206
3.1
208
2.5
L1 ≈ 50 (m)
L2 ≈ 100 (m)
L3 ¿ 100 (m)
N
n
N
n
N
n
0 0 4 9 1 2 7 3 8 8 3 2 6 7 9 1 11 14
0 0 1.0 2.3 0.2 0.45 1.6 0.7 1.56 1.56 0.6 0.4 1.5 1.8 2.0 0.2 2.4 3.0
0 0 4 8 4 1 5 3 6 3 4 4 13 2 4 4 14 11
0 0 1.0 2.0 0.9 0.2 1.14 0.7 1.2 0.59 0.8 0.8 3.3 0.5 0.9 0.9 3.0 2.4
0 1 7 3 21 11 3 4 8 13 15 9 26 9 9 3 10 4
0 0.06 1.75 0.75 4.8 2.5 0.7 0.9 1.56 2.5 3.1 0.8 6.5 2.0 0.68 2.2 0.87
There are: NTR —total number of accounted tracks; —track density in units of tracks per cm2 ; N —common number of HPs, observed on the same surface of the sample; n—corresponding to N HPs soil surface density (per cm2 ).
view can be considered as the product of the continued stages when addition of non-radioactive soil matter was possible. 3.2. -Activity distribution of HPs The distributions of HPs and HP-aggregates on the total number of detected -tracks-per HP (that is evaluated by their speci>c -activities) have been measured. The results are given in Fig. 3. As is seen, the very high spread of track values is observed between the 1 and 3 HP groups: it is failed within the range ∼10–120 tracks per HP. SuMciently higher scattered track data ∼20–200 tracks per HP are observed for HP-aggregates (4). 3.3. -Activity contamination of soil matter Summarized -activity data of the soil samples from different positions of the Chernobyl Power Plant region are presented in Table 1. 4. Conclusions 1. The studied soil samples and HPs from the Chernobyl NPP region are characterized by a very wide range of -activity. 2. The size–frequency distribution for HPs with l 6 100 m, is characterized by the presence of three diFerent groups.
3.
4.
5. 6.
The >rst follows approximately a log-normal function and indicates the importance of the melting process in their formation. The sizes of the HP-aggregates fall within one order of l∼100–1000 m and are characterized by low radio-nuclide contamination. The high degree of heterogeneity in -track density distribution can be assumed as a result of the second stage of the NPP accident process: these HPs-aggregates indicated the presence of some terrestrial components. The predominant radioactive contamination of the surrounding environment for the most part is due to the smallest, HPs in the submicrometer range ∼10 m, having the highest (upto ∼10 Bq/particle) speci>c -activity. The average homogeneous -activity of the soil samples in the 30 km zone of the Chernobyl NPP falls inside the interval oF 10−3 –10−4 Bq=cm2 . Estimation of the contribution of HPs in the -radioactivity of soil matter was found to be nearly 2/3rd of the total detected in each sample.
References Kashkarov, L.L., Kalinina, G.V., 2002. The new simplest method of the high alpha-active hot particle parameters determination. Abstract B8/P, 21st ICNTS, India.
532
L.L. Kashkarov et al. / Radiation Measurements 36 (2003) 529 – 532
Kashkarov, L.L., Stovbun, S.V., Perelygin, V.P., 1993. Track parameters for accelerated Ne ions in the new CZ-type solid state track detector. Nucl. Tracks 22 (1– 4), 129–130. Kashkarov, L.L., Kalinina, G.V., Ivliev, A.I., Tchercezian, V.O., 1995. “Hot” particles in soil from Chernobyl AES region. Radiat. Meas. 25 (l– 4), 413–414. Kashkarov, L.L., Tchercezian, V.O., Kalinina, G.V., Ivliev, A.I., Shalaeva, T.V., Korovaikov, P.A., 2001. Chernobyl “hot”
particles: radionuclide composition and contribution in the total soil radioactivity. In: Frontasyeva, M.V., Perelygin, V.P., Vater, P. (Eds.), Radionuclides and Heavy Metals in Environment. NATO Science Series Vol. IV. Earth and Environmental Sciences. Vol. 5. Kluwer Academic Publisher, Dordrecht, pp. 43– 48.
Radiation Measurements 36 (2003) 529 – 532 www.elsevier.com/locate/radmeas
-Particle track investigation of the Chernobyl Nuclear Power Plant accident region soil samples L.L. Kashkarova;∗ , G.V. Kalininaa , V.P. Perelyginb;1 a Vernadsky
Institute of Geochemistry and Analytical Chemistry RAS, Kosygin Street 19 Moscow 117975, Russia b Joint Institute for Nuclear Research, Joliot Curie, 8, Dubna 141980, Russia
Received 21 October 2002; received in revised form 11 February 2003; accepted 6 May 2003
Abstract Results of -particle track studies (Radiat. Meas. 25(1– 4) (1995) 413; Radionuclides and Heavy metals in Environment, Vol. 5, 2001, Kluwer Academic Publisher, Dordrecht) indicate that the surface (6 5 cm) layer of the soil in the Chernobyl Nuclear Power Plant (NPP) accident region consists of thinly dispersed radionuclides and highly-radioactive “hot” particles (HPs). The latter contain nearly 2/3rds of the total -activity of the contaminated soil. In the present report, the new results of continued HP -activity characteristics are presented. The chief attempt made was to investigate size–frequency vs. -activity distribution of HPs of size fraction 6 10–100 m. For the Hp-aggregates with ∼100–1000 m sizes, -radio-nuclide heterogeneity was established. This is probably the result of formation of HP-aggregates during the second stage of the NPP accident process: in these HPs the presence of not only U and >ssion products of “fuel” origin has been revealed, but also of terrestrial matter components. c 2003 Elsevier Ltd. All rights reserved. Keywords: Tracks; CZ plastic track detector; Highly-radioactive “hot” particles; Chernobyl accident region; Radio-nuclide soil contamination
1. Introduction
2. Experimental
The radioactive contaminated soil matter of the Chernobyl Nuclear Power Plant (NPP) area is due to the >nest aerosol HPs, containing very high concentrations of radio-nuclides. Detailed analysis of HP behaviour in natural environment matter and their speci>c radioactivity are of greatest importance for the quantitative estimation of real radiation conditions in the environment. Preliminary results (Kashkarov et al., 1995, 2001) signi>cantly complete our knowledge about the radio-nuclide contents, -activity of HPs and their soil-depth variations. However, statistically essential values and more precise estimations of the radioactive contamination in the Chernobyl region soil material need to be obtained.
Soil samples have been collected between 1986 and 1990 by GEOKHI RAS radio-chemical expeditions in the Chernobyl NPP region. Registration of HP -activity was carried out using a plastic nuclear track detector of the CZ type (Kashkarov et al., 1993), with registration eFectively ∼80% for isotropic -particle Hux. HP sizes were obtained by using simple measuring techniques (Kashkarov and Kalinina, 2002). In this method, the plate of the CZ-detector is irradiated with perpendicular oriented -particles, crossed through a micrometry collimator placed between the sample and track detectors.
∗ Corresponding author. Tel.: +7-96-522-1988; fax: +7-95-938-2054. E-mail address: [email protected] (L.L. Kashkarov). 1 Deceased.
3. Results and discussion Examples of the -track microphotograph, corresponding to some type of the HPs and the aggregates, are presented in Fig. 1.
c 2003 Elsevier Ltd. All rights reserved. 1350-4487/03/$ - see front matter doi:10.1016/S1350-4487(03)00199-9
530
L.L. Kashkarov et al. / Radiation Measurements 36 (2003) 529 – 532 90 80
Number of hot particles
70 60 50 40 30 20 10 0 1
10
Size, µm
100
1000
Fig. 2. Size-frequency distribution of HPs in the Pripyat-5 soil sample, Chernobyl NPP region.
Fig. 1. Microphotographs of -tracks due to HPs of diFerent sizes and -activities. Numbers 1– 4 correspond to four groups of HPs. Exposure time of the CZ-type plastic tracker detector in contact with the soil sample surface is equal to 3–56 days.
3.1. Size-frequency distribution Revising our earlier data on the HP size–frequency distribution gave analogous results. At least four HP-groups can be identi>ed on the histogram (see Fig. 2). The >rst group consists of the smallest (l 6 5 m) HPs with very high -activity with A 6 10 Bq/particle; the second group of HPs is characterized by 8 6 l 6 12 m and 1 6 A 6 5 Bq/particle; and the third and fourth groups are practically HP-aggregates of sizes: 40 6 l 6 80 and l 6 100 m, respectively, with A 6 1 Bq/particle. The (I-2) of the HP groups are subjected to the log-normal size–frequency relationship. This result can be an indicator of the major process of the formation of these HPs which was the high-temperature melting of the NPP active zone matter and subsequent fast cooling of the smallest primary individual micro-drops. Aggregates formation from this point of
Fig. 3. Variation of HP distribution with -activity as a function of the HPs size group 1– 4.
L.L. Kashkarov et al. / Radiation Measurements 36 (2003) 529 – 532
531
Table 1 Results of the total -track density measurements and presence of HPs of diFerent sizes in the searched soil samples from the Chernobyl NPP region No.
1 2 3
4
5
6
Sample
Bryansk, C9 Bryansk, M1 Pripyat, P-1 Pripyat, P-1 Pripyat, P-1 Pripyat, P-1 Pripyat, P-3 Pripyat, P-3 Pripyat, P-3 Pripyat, P-3 Pripyat, P-5 Pripyat, P-5 Pripyat, P-5 Pripyat, P-5 Pripyat, P-31 Pripyat, P-31 Pripyat, P-31 Pripyat, P-31
NTR
236 328 238
4.7 7.8 3.1
168
2.0
206
3.1
208
2.5
L1 ≈ 50 (m)
L2 ≈ 100 (m)
L3 ¿ 100 (m)
N
n
N
n
N
n
0 0 4 9 1 2 7 3 8 8 3 2 6 7 9 1 11 14
0 0 1.0 2.3 0.2 0.45 1.6 0.7 1.56 1.56 0.6 0.4 1.5 1.8 2.0 0.2 2.4 3.0
0 0 4 8 4 1 5 3 6 3 4 4 13 2 4 4 14 11
0 0 1.0 2.0 0.9 0.2 1.14 0.7 1.2 0.59 0.8 0.8 3.3 0.5 0.9 0.9 3.0 2.4
0 1 7 3 21 11 3 4 8 13 15 9 26 9 9 3 10 4
0 0.06 1.75 0.75 4.8 2.5 0.7 0.9 1.56 2.5 3.1 0.8 6.5 2.0 0.68 2.2 0.87
There are: NTR —total number of accounted tracks; —track density in units of tracks per cm2 ; N —common number of HPs, observed on the same surface of the sample; n—corresponding to N HPs soil surface density (per cm2 ).
view can be considered as the product of the continued stages when addition of non-radioactive soil matter was possible. 3.2. -Activity distribution of HPs The distributions of HPs and HP-aggregates on the total number of detected -tracks-per HP (that is evaluated by their speci>c -activities) have been measured. The results are given in Fig. 3. As is seen, the very high spread of track values is observed between the 1 and 3 HP groups: it is failed within the range ∼10–120 tracks per HP. SuMciently higher scattered track data ∼20–200 tracks per HP are observed for HP-aggregates (4). 3.3. -Activity contamination of soil matter Summarized -activity data of the soil samples from different positions of the Chernobyl Power Plant region are presented in Table 1. 4. Conclusions 1. The studied soil samples and HPs from the Chernobyl NPP region are characterized by a very wide range of -activity. 2. The size–frequency distribution for HPs with l 6 100 m, is characterized by the presence of three diFerent groups.
3.
4.
5. 6.
The >rst follows approximately a log-normal function and indicates the importance of the melting process in their formation. The sizes of the HP-aggregates fall within one order of l∼100–1000 m and are characterized by low radio-nuclide contamination. The high degree of heterogeneity in -track density distribution can be assumed as a result of the second stage of the NPP accident process: these HPs-aggregates indicated the presence of some terrestrial components. The predominant radioactive contamination of the surrounding environment for the most part is due to the smallest, HPs in the submicrometer range ∼10 m, having the highest (upto ∼10 Bq/particle) speci>c -activity. The average homogeneous -activity of the soil samples in the 30 km zone of the Chernobyl NPP falls inside the interval oF 10−3 –10−4 Bq=cm2 . Estimation of the contribution of HPs in the -radioactivity of soil matter was found to be nearly 2/3rd of the total detected in each sample.
References Kashkarov, L.L., Kalinina, G.V., 2002. The new simplest method of the high alpha-active hot particle parameters determination. Abstract B8/P, 21st ICNTS, India.
532
L.L. Kashkarov et al. / Radiation Measurements 36 (2003) 529 – 532
Kashkarov, L.L., Stovbun, S.V., Perelygin, V.P., 1993. Track parameters for accelerated Ne ions in the new CZ-type solid state track detector. Nucl. Tracks 22 (1– 4), 129–130. Kashkarov, L.L., Kalinina, G.V., Ivliev, A.I., Tchercezian, V.O., 1995. “Hot” particles in soil from Chernobyl AES region. Radiat. Meas. 25 (l– 4), 413–414. Kashkarov, L.L., Tchercezian, V.O., Kalinina, G.V., Ivliev, A.I., Shalaeva, T.V., Korovaikov, P.A., 2001. Chernobyl “hot”
particles: radionuclide composition and contribution in the total soil radioactivity. In: Frontasyeva, M.V., Perelygin, V.P., Vater, P. (Eds.), Radionuclides and Heavy Metals in Environment. NATO Science Series Vol. IV. Earth and Environmental Sciences. Vol. 5. Kluwer Academic Publisher, Dordrecht, pp. 43– 48.