Overview about Fukushima Daiichi Nuclear Power Plant accident
The Fukushima Daiichi Nuclear Power Plant (FDNPP), operated by the Tokyo Electric Power Company (TEPCO), is situated in Okuma Town and Futaba Town in Fukushima Prefecture, northeast Honshu Island, Japan Covering approximately 3.5 million square meters near the Pacific Ocean, FDNPP consists of six BWR-type reactors with a total power generating capacity of 4,696 megawatts.
There are about 1,100 employees of TEPCO who work at FDNPP In addition, about 2,000 employees of TEPCO-associate companies or plant manufactures work at the power station 2)
On March 11, 2011, at 14:46, a 9.0 magnitude earthquake struck the Sanriku region of Japan, marking the strongest earthquake ever recorded in the country Approximately 50 minutes later, a massive tsunami hit the Tohoku region, impacting the Fukushima Daiichi Nuclear Power Plant (FDNPP) where around 750 TEPCO employees were present The earthquake disabled all off-line power supplies at the plant, and although the reactor's emergency safety system and standby power supply were activated to cool the reactor, the 15-meter tsunami damaged these emergency power supplies, including backup batteries Consequently, the reactor cooling system failed, leading to the evaporation of water in the reactor and a dangerous drop in water levels.
High-temperature steam interacted with the exposed fuel rods in the reactor, generating hydrogen gas This accumulation of hydrogen in the furnaces resulted in explosions in units 1, 3, and 4, which subsequently released radioactive materials into the environment.
Figure 1-1 The epicenter of Great East Japan Earthquake and position of nearby nuclear power plants 1)
Following the explosion at the Fukushima Daiichi Nuclear Power Plant (FDNPP), radioactive materials, primarily Cesium 137, Cesium 134, and Iodine 131, were dispersed to the Northwest due to various weather factors, including wind, terrain, rain, and snow The Nuclear and Industrial Safety Agency (NISA) of Japan reported significant total discharge amounts of these radioactive substances.
The air emissions from the Fukushima Daiichi Nuclear Power Plant (FDNPP) were estimated to contain approximately 1.6×10^5 TBq of Iodine-131 and 1.5×10^4 TBq of Cesium-137 In contrast, TEPCO reported higher figures, estimating 5×10^5 TBq for Iodine-131 and 1×10^4 TBq for Cesium-137.
Figure 1-2 Air dose rates map of 80km area from the FDNPP by time 3)
Soil property in Fukushima
In Japan, the soil composition consists of 36% Gray Lowland, 30% Gley, and 10% Andosol, as noted by T M Nakanishi Specifically, in the paddy fields of Fukushima Prefecture, the soil profile is comprised of 51% Gray Lowland soil, 17% Gley soil, and 10% Andosol This indicates a notable difference between the soil found in the mountainous areas of Fukushima and the national averages in Japan.
Fukushima's Brown Forest soil exhibits radioactive contamination levels that are 2.2 times higher than the national average in Japan, with Andosol proportions approximately 60% lower Despite this variance, both paddy and upland fields in Fukushima Prefecture show similar levels of radioactive contamination from the Fukushima Daiichi Nuclear Power Plant (FDNPP) In 2011, around 6% of the land in Fukushima was heavily polluted, registering over 5000 Bq/kg of Cesium-137, while 57% of the area had contamination levels below 100 Bq/kg This soil pollution primarily stems from radioactive materials released by FDNPP, which dispersed into the atmosphere due to wind.
Figure 1-3 Air dose rates at 1m above ground surface in Fukushima on April 29, 2011 6)
The Ministry of Environment Japan (MOE) reported that decontamination efforts initiated immediately after the accident successfully lowered air dose rates in farmland within the Special Decontamination Area by 58%, decreasing levels from 1.19 µSv/h to 0.5 µSv/h at a height of 1 meter above ground.
Purpose of the research
Following the FDNPP accident, significant amounts of 134 Cs and 137 Cs were released into the atmosphere, leading to contamination of land and rice fields In response to this disaster, efforts have been made since 2011 to cultivate global leaders equipped with interdisciplinary knowledge to effectively manage reconstruction and recovery activities in the wake of radiation emergencies.
Hiroshima University launched the Phoenix Leader Education Program for Renaissance from Radiation Disaster (PLEP), part of the Program for Leading Graduate School supported by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) As a PLEP student, I focused on the critical issue of radiation disaster recovery, particularly in Fukushima Prefecture, where food safety became a significant concern following the accident Contaminated rice was detected in Fukushima City, which formed the foundation of my doctoral dissertation Despite numerous studies on radioactive cesium contamination and its transfer from soil to rice in Fukushima's paddy fields post-FDNPP accident, further investigation is needed to understand the mechanisms of cesium uptake, its migration, and the influencing factors.
In 2013, seven investigations revealed elevated levels of radioactivity from 137 Cs and 134 Cs in rice sourced from a neighboring rice field This study focuses on assessing the contamination of radiocesium in both rice and the soil of paddy fields, examining the factors influencing this contamination and the transfer mechanisms of 137 Cs and 134 Cs into rice.
Literature review
Following the FDNPP accident, extensive research on cesium radiation was conducted T Saito et al (2012) demonstrated that potassium fertilizer can reduce radiocesium levels in rice, although discrepancies exist regarding the relationship between soil potassium concentration and cesium transfer to rice T M Nakanishi (2012) indicated that radioactive cesium accumulation in rice primarily results from the absorption of dissolved Cs ions rather than those adsorbed in soil Research by Y Ohmori et al (2014) revealed that Koshihikari rice, a popular cultivar in Japan, exhibited cesium concentrations nearly double the average of 85 other cultivars Additionally, Tsujimoto et al (2016) identified a correlation between soil grain size distribution and the transfer of radiocesium into rice Q H Fan et al (2014) concluded that cesium mobility in soil is significantly influenced by clay mineral expandability and natural organic matter H Lepage et al (2014) noted that radiocesium tends to concentrate in the upper layers (< 5 cm) of Andosols in both undisturbed and managed paddy fields within the main Fukushima contamination plume A study in Minami-Souma City, Fukushima, also assessed the Transfer Factor (TF) from soil to rice.
The study by T M Nakanishi (2018) revealed that Cesium 137 and Cesium 134 have a strong affinity for soil, with minimal downward migration of only 1–2 mm per year These isotopes do not easily dissolve in water from mountainous areas and are not readily absorbed by crop plants when adequate Potassium is present Additionally, the uptake of Cesium 137 and Cesium 134 by trees primarily occurs through the bark rather than the roots In terms of rice, the concentrations of these isotopes were relatively low, with values ranging from 0.019 to 0.026 in rice ears, while chaff, rice bran, brown rice, and polished rice showed higher levels of 0.049, 0.10–0.16, 0.013–0.017, and 0.005–0.013, respectively.
1 Nuclear Emergency Response Headquarters Government of Japan, Report of
Japanese Government to the IAEA Ministerial Conference on Nuclear Safety- The Accident at TEPCO's Fukushima Nuclear Power Stations, June 2011
The Final Report from the Investigation Committee on the Accident at the Fukushima Nuclear Power Stations, published by Tokyo Electric Power Company on July 23, 2012, provides a comprehensive analysis of the events leading to the disaster This report outlines the critical failures in safety protocols and emergency response that contributed to the nuclear accident It emphasizes the need for improved regulatory oversight and enhanced safety measures in nuclear power operations to prevent future incidents Access the full report for detailed findings and recommendations at the official website.
3 Nuclear Regulation Authority, Results of Airborne Monitoring in Fukushima
Prefecture and neighboring prefectures and the Thirteenth Airborne Monitoring in the 80km zone from them Fukushima Daiichi NPP, 8 March, 2019 https://radioactivity.nsr.go.jp/en/list/307/list-1.html
4 Nakanishi, T M., Agricultural aspects of radiocontamination induced by the
Fukushima nuclear accident — A survey of studies by the Univ of Tokyo
Agricultural Dept (2011–2016), Proceedings of the Japan Academy, Series B, Volume 94 Issue 1 (2018)
5 Ministry of the Environment of Japan, Environmental Remediation in Affected Areas in Japan, December, 2018 http://josen.env.go.jp/en/pdf/environmental_remediation_1812.pdf
6 The Extension Site of Distribution Map of Radiation Dose, http://ramap.jmc.or.jp/map/eng/
7 Matsuda, N and Nakashima, S., Radioactive Cesium in Water and Soil and Its Absorption by Rice Plant, Japanese Journal of Radiation Safety Management, 13, 89–91 (2014), (in Japanese)
A study by Saito et al (2012) explored the impact of potassium application on the root uptake of radiocaesium in rice The research was presented at the International Symposium on Environmental Monitoring and Dose Estimation following the Fukushima Daiichi Nuclear Power Station accident, highlighting the importance of understanding how potassium influences radiocaesium absorption in rice cultivation.
9 Nakanishi, M T., Kobayashi, I K and Tanoi, K., Radioactive caesium deposition on rice, wheat, peach tree and soil after nuclear accident in Fukushima, J Radioanal Nucl Chem., 296, 985–989 (2013)
10 Ohmori, Y., Inui, Y., Kajikawa, M., Nakata, A., et al., Difference in caesium accumulation among rice cultivars grown in the paddy field in Fukushima
Prefecture in 2011 and 2012, J Plant Res., 127, 57–66 (2014)
11 Tsujimoto, M., Miyashita, S., Nguyen, H T and Nakashima, S., A correlation between the transfer factor of radioactive caesium from soil into rice plants and the
10 grain size distribution of paddy soil in Fukushima, Radiation Safety Management,
In their 2014 study published in Geochimica et Cosmochimica Acta, Fan et al investigated how natural organic matter and the expandability of clay minerals influence the adsorption and mobility of caesium Using Extended X-ray Absorption Fine Structure (EXAFS) analysis, the researchers demonstrated that these factors significantly affect caesium behavior in the environment, highlighting their importance in understanding contaminant dynamics in soil and water systems.
13 Lepage, H., Evrard, O., Onda, Y., Lefèvre, I., Laceby, J P., and Ayrault, S.: Depth distribution of radiocesium in Fukushima paddy fields and implications for ongoing decontamination works, SOIL Discuss., 1, 401-428, https://doi.org/10.5194/soild-1- 401-2014, 2014
14 Endo, S., Kajimoto, T and Shizuma, K., Paddy-field contamination with 134 Cs and
137Cs due to Fukushima Daiichi Nuclear Power Plant accident and soil-to-rice transfer coefficients, J Environ Radioact., 116, 59–64 (2013).
Sampling and Method
Sampling
Samples were collected in Fukushima City, located approximately 60 km northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), on multiple dates: April 26, August 11, and September 25 in 2014; August 21 and October 31 in 2015; April 26 and August 2 in 2016; August 23 in 2017; and March 14 in 2018 The study area features paddy fields bordered by mountains to the east and the Abukuma River to the west, with irrigation supplied by a nearby pond and water from the river.
The samples were taken from 4 paddy fields which are marked as A, B, C and D
5 sample sites were designed in each field (Figure 2-1) Rice and soil samples were collected in each site
Paddy fields were actively cultivated for many years prior to the 2011 FDNPP incident However, since 2015, both Field A and Field B have remained uncultivated Soil samples from these fields were collected until 2018 to monitor the impact of fallow periods on soil characteristics and radiation levels.
Figure 2-2 Paddy field before and after harvest
Core soil sample was taken by using soil auger with inserting a 30cm PVC liner sampling tube (Figure 2-3 and Figure 2-4)
Figure 2-3 Soil auger and 30cm5cm PVC liner tube
Figure 2-4 Sampling in paddy field.
Sample preparation
Each 30 cm long core soil sample was cut in 5 cm segment (Figure 2-5), rice plant (Figure 2-6), from which mud was washed was divided into grain, stem and root parts (Figure 2-7) and all samples were dried at ambient temperature for 3 weeks Stem and root were cut to small pieces For radioactivity measurement, the samples were contained in U8 vessels
Figure 2-5 Drying and weighing soil samples
Figure 2-7 Rice sample in U8 container as rice grain (a), rice stem (b), and root (c)
We classified soil samples based on the geomaterial classification method outlined by the Japanese Geotechnical Society (JGS0051) The surface soil samples, taken from a depth of 0-5 cm, were sorted into five distinct categories using a sieving technique, as illustrated in Figure 2-10.
X < 75 àm as silt and clay,
75 àm < X < 250 àm as fine sand,
250 àm < X < 850 àm as medium sand,
850 àm < X < 2 mm as coarse sand, and 2 mm < X as gravel a b c
The soil larger than 2 mm was not used to measure 57 Fe Mӧssbauer spectra because its amount is little
To analyze the grain component of soil, a specific weight of the sample was sieved using mesh screens To improve the representativeness of the sampling point, the homogenization and quartering method was employed, ensuring that the subsample accurately reflected the soil's properties at the site The soil samples were then gently ground in a porcelain mortar to create smaller particles, and any debris, such as large organic matter and plastic, was removed Small organic materials, like root fragments, were eliminated using a plastic sheet The soil was evenly spread in a tray and divided into four parts, from which two opposite sections were selected for weighing and placed into stainless steel sieve meshes The samples were subsequently shaken for analysis.
2 hours (Figure 2-12) Then the categorized soil grain parts were weighed (Figure 2-13)
Figure 2-8 Grinding soil sample and taking out trash
Figure 2-9 Removing roots from soil sample
Figure 2-10 Stainless steel sieving meshes
Figure 2-11 Weighing soil sample for sieving
Radioactivity levels of 134 Cs, 137 Cs, and 40 K were assessed in an U8 container using a Ge semiconductor detector (GEM 30-70, ORTEC) Additionally, 57 Fe Mӧssbauer spectroscopy was conducted at room temperature with a 57 Co (Rh) radiation source in constant acceleration mode on a Wissel MB-500 Mӧssbauer parameters were determined through least-squares fitting to Lorentzian peaks, with calibration performed using the six lines of α-Fe, setting the center as zero isomer shift Consistent sample amounts and measurement conditions were maintained across samples to enable accurate comparison of absorption intensity.
Radioactivity calculation
In Figure 2-14, Figure 2-15 and Figure 2-16, the decay of Cesium 137, Cesium
Cesium-134, with a half-life of approximately 2 years, emits gamma energy at 605 KeV (97.6% emission) and 796 KeV (85.5% emission) In contrast, Cesium-137, which has a half-life of about 30 years, emits gamma energy at 662 KeV (85% emission), while Potassium-40, with a half-life of 1.25 billion years, emits at 1460 KeV (11% emission).
Figure 2-14 Decay scheme of Cesium 134 isotope
Figure 2-15 Decay scheme of Cesium 137 isotope
Figure 2-16 Decay scheme of Potasium 40 isotope
Figure 2-17 Spectrum of a sample which was measured in Ge-detector
When a radioactive material undergoes gamma decay, the total number of nuclei in sample N is,
Where N0 is the number of nuclei in sample at initial time,
The decay rate R is calculated as
𝑑𝑡 = 𝑁 0 𝑒 − 𝑡 Half-life 𝑇 1/2 = ln(2) / then = ln(2) /T 1/2
The radioactivity levels of isotopes 134 Cs, 137 Cs, and 40 K were assessed using a Ge semiconductor detector (GEM 30-70, ORTEC) Calibration for the measurements was conducted with the MX033U8PP source set from the Japan Radioisotope Association, ensuring accurate count efficiency for 134 Cs at 605 KeV.
134Cs (796 KeV) were interpolated from count efficiency of 137 Cs (662 KeV) and 54 Mn
(835 KeV) Simultaneously count efficiency of 40 K (1461 KeV) was extrapolated from
60Co of gamma energy of 1173 KeV and 1332 KeV
Appendix 1 is the measurement of MX033U8PP source set
Count efficiency CE is calculated as,
𝐴 × 𝐼 Where CPS is count per second on measurement day,
A is activity on measurement day,
Based on Count Efficiency values of standard source set, the efficiency of MX033U8PP source set in Ge-detector was drawn as Figure 2-18
Figure 2-18 Efficiency of MX033U8PP source set in Germanium detector
In the high-energy region depicted in Figure 2-18, there is a linear relationship between Count Efficiency (CE) and energy, specifically from 320 keV (151 Cr) to 1836 keV (88 Y) For ease of interpretation, Figure 2-19 presents a logarithmic graph illustrating this relationship, with additional data available in Appendix 2.
The linear regression equation for logCE with the logE variable corresponding to the sample’s thickness is described as follows:
For h=5mm, y = -0.9358x + 1.1427 (R² = 0.9951) hmm, y = -0.9008x + 0.9937 (R² = 0.995) h mm, y = -0.8739x + 0.8184 (R² = 0.9974) h0mm, y = -0.8489x + 0.6651 (R² = 0.9969)
Figure 2-19 Logarithmic scale of Count Efficiency versus Energy
Based on the relationship between Energy and Count Efficiency found above,
134Cs's Count Efficiency values at 605 KeV and 796 Kev, and 40 K's Count Efficiency at
1460 KeV energy are interpolated from the graph in the Figure 2-19 The data is showed in Appendix 4
In the case of various thicknesses of measurement sample, the relationship between Count Efficiency and Thickness of sample is built as shown in Figure 2-20 The regression equation is:
Figure 2-20 Relationship between Count Efficiency versus Thickness of standard samples
Radioactivity is calculated as follow:
Where CPS: count per second (count rate, is calculated as Net count/measurement live time),
CE: count efficiency, I: emission rate, m: weight of sample (g)
Radioactivity concentration at sampling day is calculated as:
Where tmeas: time of measurement,
When using a Germanium semiconductor detector to measure samples, background radioactivity from environmental sources, including building materials and airborne radon, can interfere with results To mitigate this issue, the Radioisotope Division at Hiroshima University employs a GEM 30-70 (ORTEC) Germanium semiconductor detector that is shielded with 10 cm of lead This effective shielding significantly reduces the background signal, enhancing measurement accuracy.
134Cs and 137 Cs radionuclides became insignificant 2) However the 40 K background should be deducted The background spectrum was shown in Figure 2-21 The value of
40K background measurement was written in Table 2-1
For deduction the background, the value of 40 K’s count rate (CPS) of sample was calculated as:
Figure 2-21 Background spectrum in Ge-detector
Live time Net err cps err
According to Iimoto Takeshi 3) the detection limit of Net count of the measurement nn is: n 𝑛 >𝐾
Whereas: nb: Count rate of the background measurement, tb: Time of the background measurement,
28 ts: Time of the sample measurement,
K: the number of times that the Net count exceeds the standard deviation, K equals 3 when the measurement is qualitative; K equals 10 when the measurement is quantitative
Transfer factor is defined as the radioactivity which transfers from soil to rice Transfer factor is calculated as followed:
1 Emma Popek, Sampling and Analysis of Environmental Chemical Pollutants
(Second Edition), Elsevier, 2018 (https://doi.org/10.1016/C2014-0-03819-1)
2 I Radulescu, A M Blebea-Apostu, R M Margineanu, N Mocanu, Background radiation reduction for a high-resolution gamma-ray spectrometer used for environmental radioactivity measurements, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 715, Pages 112-118, 1 July 2013
3 T Iimoto, Y Uwamino, T Kawano, Fundamental of radiation measurement, The Journal of the Japan Society of Plasma Science and Nuclear Fusion Research Vol
89, No.9, Pages 629-634, September 2013 (In Japanese)
Depth Distribution of Radioactive Cesium in Soil after Cultivation and the
Introduction
Radioactive cesium contamination in rice remains a significant issue in Fukushima, even over seven years after the Fukushima Dai-ichi Nuclear Power Plant disaster While the uptake mechanism of radioactive cesium by plants has been studied, ongoing investigations continue to shed light on this matter Although potassium has been shown to influence the absorption of radioactive cesium in rice plants, inconsistencies in the correlation indicate that additional factors may also play a role in this absorption process.
In 2013, contaminated rice was detected in paddy fields in Fukushima City, located about 60 km northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), as investigated by the Subcommittee Concerning Chemical Treatment of the Japanese Society of Radiation Safety Management Among four paddies labeled A through D, Field B exhibited contamination in rice ears, although the concentration of potassium-40 was low Previous research indicated that grain size distribution in paddy soil significantly influences the transfer factor of radioactive cesium to rice grains, with higher transfer factors observed in soils primarily composed of medium sand compared to silt and clay This study further examined the depth dependence of soil concentrations of radioactive cesium and its correlation with rice ear concentrations across the four paddies in 2014 and 2015, aiming to understand the characteristics of the paddy field that produced contaminated rice.
Materials and methods
Samples were collected from four paddy fields in Fukushima City, located approximately 60 km northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), on specific dates in 2014 and 2015 The fields were primarily irrigated from a nearby pond, with minimal contribution from the Abukuma River Soil and rice plant samples were taken from various locations within each field, with soil cores segmented for analysis All samples were dried for three weeks before being measured for radioactivity using a Ge semiconductor detector The radioactivity levels of Cesium-137, Cesium-134, and Potassium-40 were calculated based on specific gamma-ray emissions, and results were corrected to reflect the sampling day The average radioactivity for the soil was determined from five samples, while individual rice ear samples were analyzed for radioactivity in both years.
31 set (MX033U8PP, Japan Radioisotope Association) The count efficiency was calculated by logarithmic and logarithmic interpolation.
Results and discussion
On April 26th, 2014, the analysis of soil samples revealed that the concentration of Cesium 137 decreased with increasing depth, as illustrated in Figure 3-1 This trend was similarly observed in the concentration levels of Cesium 134, indicating a consistent pattern in the depth dependence of both isotopes across five sampling points in each field.
Figure 3-1 Depth dependence of Cesium 137 concentration for the soil obtained on
April 26th, 2014 The average value for the five points is compared
The ratio of radioactivity concentration between 134 Cs and 137 Cs was measured at 0.373, which closely aligns with the expected ratio of 0.376 on the sampling day This decline is attributed to the shorter half-life of 134 Cs compared to 137 Cs, considering that both isotopes were released in equal amounts from the FDNPP reactor In 2013, the fields were cultivated, ploughed, and irrigated prior to transplanting rice seedlings; however, the concentrations of 137 Cs and 134 Cs in the soils showed variability and depth dependency in 2014 It is anticipated that smaller particles, such as clay, play a role in this distribution.
Ra di oac ti vi ty Co n c e rn tra ti on / (Bq/ k g) 0
Depth 0～5 cm 5～10 cm 10～15 cm 15～20 cm 20～25 cm 25～30 cm
The presence of significant radioactive cesium levels in the soil is evident, with larger particles settling quickly while smaller particles, like clay, descend more slowly during sedimentation after ploughing and irrigation This mixing of soils leads to noticeable differences among Fields A, B, and C, as illustrated in Figure 3-1.
D The radioactivity of 137 Cs and 134 Cs for 0–5 cm depth was higher in Fields C and D than in Fields A and B, while the radioactivity for 5–10 cm was lower in Fields C and D than in Fields A and B Relatively higher radioactivity of 137 Cs and 134 Cs was found at greater depth in Fields A and B than in Fields C and D We have already reported the grain size distribution of the surface soil 9) Fields A and B had great abundance of medium sand than Fields C and D On the other hand, Fields A and B had less abundance of clay and silt than Fields C and D It is expected that the radioactive cesium penetrated more deeply in the soils having more medium sand If we compare the average concentration from 0 to 30 cm, the value becomes 647, 674, 708, and 602 Bq/kg for A, B, C, and D, respectively This might suggest that the radioactive cesium migrated from Fields A and B to Field C, while the radioactive cesium did not migrate much from Field C to D It is possible that the small particles moved through the ridge Such migration is still under study Figure 3-2 shows the depth dependence of 40 K con centration for the soil obtained on April 26th, 2014 Significant depth dependence was not observed, and the radioactivity concentration for Fields A and B was lower than that for Fields C and D
Figure 3-2 Depth dependence of 40 K concentration for the soil obtained on April 26th,
2014 The average value for the five points is compared
On September 25th, 2014, soil samples (0–5 cm depth) revealed that Fields C and D exhibited higher radioactivity concentrations of 134 Cs and 137 Cs compared to Fields A and B, with a concentration ratio of 0.335, closely aligning with the expected ratio of 0.331 While the differences in 40 K radioactivity concentrations among the fields were minimal, Field B maintained a notably low concentration Subsequent analyses on August 21st and October 30th, 2015, indicated a decreasing trend in the ratio of 134 Cs to 137 Cs over time, with 137 Cs levels on August 21st generally exceeding those from September 25th, 2014, except in Field C Additionally, a significant decline in radioactivity was observed from August 21st to October 30th, 2015, attributed to the heterogeneous distribution of radioactive cesium across the fields, even post-ploughing.
Table 3-1 Radioactivity concentration with standard deviation in soil (0–5 cm depth) obtained on September 25th, 2014
Table 3-2 Radioactivity concentration with standard deviation in soil (0–5 cm depth) obtained on August 21st, 2015
Table 3-3 Radioactivity concentration with standard deviation in soil (0–5 cm depth) obtained on October 30th, 2015
In 2014, 134Cs was detected in rice ears exclusively in Field B, with measurements of 6.5±0.9 Bq/kg for 137Cs and 2.5±0.7 Bq/kg for 134Cs, despite lower radioactivity levels of both isotopes in the surface soil of Field B compared to other fields This pattern aligns with findings from 2013, attributed to the lower potassium content and higher presence of middle sand in Field B A summary of the radioactivity levels in rice ears for 2015 is presented in Table 3-4.
2015, there were samples in site C-4 and D-4 (48.5±4.6 Bq/kg and 80.9±2.8 Bq/kg for
137Cs, and 13.1±3.2 Bq/kg and 19.1±2.0 Bq/kg for 134 Cs, respectively) which had much
In 2013 and 2014, rice ears from sites C and D exhibited no significant contamination, while sites C-1, C-3, D-1, D-2, and D-3 showed slight concentrations of 137 Cs, with D-4 recording 3 Bq/kg The radioactivity levels in these fields were higher than those found in Field B in 2014 Research indicates a correlation between the transfer factor of radioactive cesium from soil to rice plants and the grain size distribution of paddy soil in Fukushima, suggesting that an increase in medium sand content enhances this transfer It is hypothesized that the reduction of clay and silt in Fields C and D, particularly from C-4 to C-3 and D-4 to D-3, may be due to irrigation flow, which could explain the higher levels of radioactive cesium found in C-4 and D-4 in 2015 Additionally, the decrease in clay and silt at these points may not have been compensated by Fields A and B due to their fallowing, highlighting a need for further investigation into this phenomenon.
Table 3-4 Radioactivity concentration with standard deviation in rice ear obtained on
Conclusion
The study examined the distribution of radioactivity concentrations of 137 Cs, 134 Cs, and 40 K in soil at a research field in Fukushima City, focusing on depth and site location Findings revealed that the concentrations of 137 Cs and 134 Cs decreased from the surface to deeper layers, despite prior cultivation Variations were noted between Fields A, B and Fields C, D, with Field B showing the lowest surface radioactivity but still containing 137 Cs in rice ears in 2014 Additionally, unusually high radioactivity levels were recorded at sites C-4 and D-4 in 2015 The fallowing of Fields A and B may influence the uptake of radioactive cesium in Fields C and D, necessitating long-term monitoring to fully understand this effect Previous research indicates that factors like potassium concentration and soil grain size distribution play a role in contamination levels.
37 rice, however, our results suggest that dynamics of soil among the neighboring fields should be explored in future studies
1 White, P J and Broadley, M R., Mechanisms of caesium uptake by plants, Sci Ed.,
2 Endo, S., Kajimoto, T and Shizuma, K., Paddy-field contamination with 134 Cs and
137Cs due to Fukushima Daiichi Nuclear Power Plant accident and soil-torice transfer coefficients, J Environ Radioact., 116, 59–64 (2013)
3 Nakanishi, M T., Kobayashi, I K and Tanoi, K., Radioactive caesium deposition on rice, wheat, peach tree and soil after nuclear accident in Fukushima, J Radioanal Nucl Chem., 296, 985–989 (2013)
4 Ohmori, Y., Inui, Y., Kajikawa, M., Nakata, A., et al., Difference in caesium accumulation among rice cultivars grown in the paddy field in Fukushima
Prefecture in 2011 and 2012, J Plant Res., 127, 57–66 (2014)
5 Nihei, N., Tanoi, K and Nakanishi, M T., Inspections of radiocaesium concentration levels in rice from Fukushima Prefecture after the Fukushima Daiichi Nuclear Power Plant accident, Sci Rep., 5, 8653 (2015)
6 Saito, T., Ohkoshi, S., Fujimura, S., Iwabuchi, K., et al., Effect of potassium application on root uptake of radiocaesium in rice, Proceedings of Int Symp
Environmental Monitoring and Dose Estimation of Residents after Accident of TEPCOʼs Fukushima Daiichi Nuclear Power Stations Part 3–5, Kyoto Univ Res Reactor Inst., (2012)
7 Fan, Q H., Tanaka, M., Tanaka, K., Sakaguchi, A., et al., An EXAFS study on the effects of natural organic matter and the expandability of clay minerals on caesium adsorption and mobility, Geochim Cosmochim Acta, 135, 49–65 (2014)
8 Matsuda, N and Nakashima, S., Radioactive Caesium in Water and Soil and Its Absorption by Rice Plant, J Rad Safety Manage., 13, 89–91 (2014), in Japanese.
Study on paddy soil in Fukushima using Mӧssbauer spectroscopy
Introduction
Research on radioactive cesium uptake by plants has been ongoing since the Fukushima Daiichi Nuclear Power Plant disaster, yet the contamination of rice grains has received limited attention even eight years later Understanding how to suppress radioactive cesium uptake is crucial, particularly as potassium's role in this process has been identified, although some discrepancies exist Notably, radioactive contamination was detected in rice from a paddy field in Fukushima City, located about 60 km from the disaster site, with Field B showing higher cesium levels than the others The transfer factor of radioactive cesium from soil to rice varied among the fields, with Field B exhibiting lower potassium concentrations Soil size distribution and field management practices, such as fallowing, were found to influence cesium uptake This study aims to explore how oxidative and reductive atmospheres in these paddy fields affect soil characteristics, potassium solubility, and radioactive cesium absorption.
57Fe Mӧssbauer spectroscopy And we studied the role of soil size distribution from the point of iron amount
Experimental
Soil samples were dried at room temperature The 57 Fe Mӧssbauer spectra for the samples without sieving were measured from April to July, 2015 to know oxidation state
Soil samples were thoroughly dried and sieved according to the Japanese Geotechnical Society's classification method (JGS0051) for geomaterials The surface soil samples (0-5 cm) were categorized into five groups based on particle size: less than 75 µm, between 75 µm and 250 µm, between 250 µm and 850 µm, between 850 µm and 2 mm, and greater than 2 mm Soil larger than 2 mm was excluded from the 57 Fe Mӧssbauer spectra measurements due to its minimal quantity The spectra for the sieved samples were measured from April to August 2019 to assess the relative iron content based on soil size, ensuring consistent sample amounts and measurement conditions for accurate comparison of absorption intensity.
A 57Fe Mӧssbauer spectroscopic measurement was conducted at room temperature using a 57Co (Rh) radiation source in constant acceleration mode on a Wissel MB-500 spectrometer The Mӧssbauer parameters were determined through least-squares fitting to Lorentzian peaks, and the spectra were calibrated using the six lines of α-Fe, with the center defined as the zero isomer shift.
Results and discussion
Figure 4-1 shows the typical 57 Fe Mӧssbauer spectrum of the samples without sieving at room temperature at the velocity scale of ±14.2 mm/s
Figure 4-1 Typical 57 Fe Mӧssbauer spectrum at room temperature
The Mӧssbauer parameters presented in Table 4-1 indicate the presence of divalent iron (Fe 2+), trivalent iron (Fe 3+), and hematite (α-Fe2O3) in the spectrum A minor second magnetic component, likely magnetite (Fe3O4), was occasionally detected, attributed to trace soil attached to the magnet Notably, the sample from Field B exhibited a lower ratio of Fe 2+ compared to samples from Fields A, C, and D To validate this observation, spectra were measured at a velocity scale of ±4.4 mm/s at room temperature.
Table 4-1 Mӧssbauer parameters for the soil samples without sieving measured from
Sampling point a) / mms -1 Eq/ mms -1 / mms -1 H/ T Area ratio/ % Assignment
Re la ti ve Tra n smi ss ion
0.61±0.02 -0.61±0.03 0.21±0.06 46.4±0.10 2±1 magnetite a) Relative to iron foil
Figure 4-2 shows the ratio of Fe 2+ to the sum of both divalent and trivalent iron
The relative area of Fe 2+ was found to be slightly lower in Field B compared to Fields A, C, and D, suggesting that Fields A, C, and D exist in a relatively reductive atmosphere, whereas Field B is characterized by a more oxidative environment.
Figure 4-2 Ratio of Fe(II) to the sum of divalent and trivalent iron A-1 to D-3 show the sampling point
Fields A and B contain larger-sized soils, which are expected to facilitate the easier oxidation of iron In these fields, potassium is present in much greater abundance compared to trace amounts of radioactive cesium We hypothesize that the oxidative atmosphere may influence the soil characteristics, subsequently reducing potassium elution and impacting the absorption of radioactive cesium by plants As a result, radioactive cesium is more likely to dissolve in the soil water due to the competitive nature of potassium and cesium ions Conversely, Fields C and D consist of smaller-sized soils.
In smaller soils, iron is expected to be less prone to oxidation, while potassium ions adsorbed to the soil may dissolve in water under reductive conditions This reductive environment decreases cesium solubility due to competition with potassium ions Notably, Figure 4-2 illustrates a difference in the relative divalent iron ratio between Field A and Field B, despite both fields having larger soil sizes The water from Field A flows slowly into Field B, potentially allowing oxygen to dissolve during this transition, which could influence the oxidative conditions in Field B, a phenomenon that is still under investigation.
Figure 4-3 Change of 57 Fe Mӧssbauer absorption depending on the soil size in 2014
Figure 4-3 illustrates the variation in 57 Fe Mӧssbauer absorption based on soil size, with key parameters detailed in Table 4-2 The spectrum reveals the presence of Fe 2+, Fe 3+, and hematite, while the second magnetic splitting associated with magnetite, noted in Table 4-1, is absent Additionally, a relatively low ratio of divalent iron is observed in Field B.
Re la ti v e Tra n s mi tt a n c e
Velocity/ (mm/s) black: < 75 m blue: 75 m - 250 m green: 250 m - 850 m red: > 850 m
Re la ti v e Tra n s mi s s ion
Velocity/ (mm/s) black: < 75 m blue: 75 m - 250 m green: 250 m - 850 m red: > 850 m
Re la ti v e Tra n s mi s s ion
Velocity/ (mm/s) black: < 75 m blue: 75 m - 250 m green: 250 m - 850 m red: > 850 m
Re la ti v e Tra n s mi s s ion
Velocity/ (mm/s) black: < 75 m blue: 75 m - 250 m green: 250 m - 850 m red: > 850 m
45 in Table 4-1 and Figure 4-2 became vague Probably this was due to heat treatment and long storage of the soil sample at room temperature
Table 4-2 Mӧssbauer parameters for the soil samples based on soil size measured from
Sampling point Soil size a) /mm s -1 Eq/ mm s -
1.09±0.02 2.54±0.05 0.52±0.06 0 13±1 Fe 2+ a) Relative to iron foil
Figure 4-4 illustrates that the relative transmission for smaller-sized soils remains consistent across four fields, while significant differences are observed in larger-sized soils between Fields A, B and Fields C, D The minimum relative transmission, indicating maximum absorption, varies with soil size, showing a decrease in relative absorption as soil size increases For smaller soils, absorption rates are similar across all fields, but larger soils exhibit varying absorption rates, likely due to the higher iron content in Fields A and B compared to Fields C and D Smaller soils, rich in clay, strongly adsorb radioactive cesium, whereas cesium in larger soils is more easily desorbed and absorbed by rice plants The presence of iron may influence the desorption of radioactive cesium from larger soils, potentially acting as a catalyst in the process.
Figure 4-4 The change in the least relative transmission depending on soil size.
Conclusion
The oxidative/reductive atmosphere in the paddy field was investigated using
We conducted a study using 57Fe Mӧssbauer spectroscopy to analyze how the amount of iron varies with soil particle size Our findings suggest that an oxidative atmosphere influences soil characteristics and enhances the uptake of radioactive cesium by rice plants Additionally, the presence of iron in larger soil particles may play a significant role in the transfer of radioactive cesium from the soil to the rice plants.
1 Saito, T., Ohkoshi, S., Fujimura, S., Iwabuchi, K., et al., Effect of potassium application on root uptake of radiocaesium in rice, Proceedings of Int Symp
Environmental Monitoring and Dose Estimation of Residents after Accident of TEPCO’s Fukushima Daiichi Nuclear Power Stations Part 3–5, Kyoto Univ Res Reactor Inst., (2012)
2 Endo, S., Kajimoto, T and Shizuma, K., Paddy-field contamination with 134 Cs and
137Cs due to Fukushima Daiichi Nuclear Power Plant accident and soil-to-rice transfer coefficients, J Environ Radioact., 116, 59–64 (2013)
Re la ti ve Tra n smi tt an c e
3 Nakanishi, M T., Kobayashi, I K and Tanoi, K., Radioactive caesium deposition on rice, wheat, peach tree and soil after nuclear accident in Fukushima, J Radioanal Nucl Chem., 296, 985–989 (2013)
4 Matsuda, N and Nakashima, S., Radioactive Cesium in Water and Soil and Its Absorption by Rice Plant, Japanese J Rad Safety Manage., 13, 89–91 (2014), in Japanese
5 Tsujimoto, M., Miyashita, S., Nguyen, H T and Nakashima, S., A correlation between the transfer factor of radioactive caesium from soil into rice plants and the grain size distribution of paddy soil in Fukushima, Radiation Safety Management,
6 Nguyen Thanh Hai, Masaya Tsujimoto, Sunao Miyashita and Satoru Nakashima, Depth Distribution of Radioactive Cesium in Soil after Cultivation and the
Difference by Year of the Uptake of Radioactive Caesium in Rice in Fukushima Prefecture after the 2011 Nuclear Accident, Radioisotopes, 68, 1–6 (1019).
The changing in radioactivity by year
Introduction
The 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident led to the release of radioactive materials that contaminated the local soil While the government has undertaken decontamination efforts in agricultural and residential areas, residual radioactivity remains in the environment Two primary processes influence the levels of radioactivity in the soil: factors that can increase radioactivity include airborne deposits and water inflow from surrounding lands, while natural decay, absorption by plants and microorganisms, downward movement, and migration to adjacent areas help reduce radioactivity levels This dynamic is illustrated in Figure 5-1.
Figure 5-1 Processes that affect the amount of radioactivity in the soil
To comprehend the behavior of radioactive isotopes 134 Cs and 137 Cs in soil, we conducted a comprehensive analysis of cesium radioactivity variations across different soil layers This study focused on the influence of soil particle size in the topsoil of the research area, spanning from 2014 to 2018.
Vertical distribution of radioactivity in paddy field
The four plots, labeled A, B, C, and D, have been cultivated for an extended period prior to the 2011 FDNPP incident Irrigation for these rice fields is sourced from a nearby pond and the Abukuma River The fields are arranged in ascending elevation from Field A to Field D, resulting in a sequential flow of water and sediment Additionally, the presence of mountains to the east and south influences the radioactivity levels in the fields due to the inflow of water from these regions.
Figure 5-2, Figure 5-3 and Figure 5-4 show the vertical distribution of 134 Cs and
In 2014, a study on paddy fields revealed that radioactive cesium, particularly 134Cs and 137Cs, is primarily concentrated in the topsoil, with 134Cs in the top 0-5 cm accounting for 59% to 77% of the total radioactivity in 30 cm core samples, and 137Cs comprising 59% to 79% Notably, downstream fields C and D exhibited higher surface radiation levels compared to upstream fields A and B, with Field C recording the highest surface radiation values of 1201±8 Bq/kg for 134Cs and 3269±13 Bq/kg for 137Cs Additionally, the distribution of potassium within the paddy fields was found to be relatively homogeneous across different depths.
Figure 5-2 Vertical distribution of 134 Cs in paddy fields in 2014
Figure 5-3 Vertical distribution of 137 Cs in paddy fields in 2014
Figure 5-4 Vertical distribution of 40 K in paddy fields in 2014
Since 2015, fields A and B have remained uncultivated, while fields C and D have been cultivated regularly To assess the impact of fallowing on soil radioactivity concentration, we conducted ongoing soil sampling The depth distribution of isotopes 134 Cs and 137 Cs is illustrated in Figures 5-5, 5-6, and 5-7.
In 2018, a study in the area revealed a significant reduction in radioactivity over four years, particularly in the topsoil The levels of radioactive isotope 134Cs decreased by approximately 75%, from around 1025 Bq/kg to about 232 Bq/kg Similarly, 137Cs levels saw a decline of nearly 33%, dropping from approximately 2729 Bq/kg to around 2067 Bq/kg.
In 2014, a notable increase in radioactivity concentration was detected in the 5-10 cm soil layer, particularly in the fallow fields, Field A and Field B However, the levels of radioactive cesium in the topsoil of Field A and Field B remain lower compared to those found in Field C.
D It can be concluded that there is a migration of radioactivity into deep soil layers, especially in the fallow fields
Concerning to the concentration of 40 K in paddy fields in 2018, caused by fallowing and water erosion, in the 5cm top soil concentration of 40 K was lower than
2014 but the undisturbed deeper layer of soil had not changed
Figure 5-5 Vertical distribution of 134 Cs in paddy fields in 2018
Figure 5-6 Vertical distribution of 137 Cs in paddy fields in 2018
Figure 5-7 Vertical distribution of 40 K in paddy fields in 2018.
Changing in ratio 134 Cs / 137 Cs by year
An article of Y Nishizawa et al 1) (2015) indicated that the ratio of airbone 134 Cs and 137 Cs on March 15, 2011 near the study area of this study was 1.05
In the study area, the ratio of 134 Cs to 137 Cs in paddy soil was analyzed, revealing that the short half-life of 134 Cs, approximately 2 years, causes its levels to decline more rapidly than those of 137 Cs Consequently, this results in a decreasing ratio of 134 Cs to 137 Cs over time Table 5-1 presents the values of this ratio observed between 2014 and 2018 in the study area.
Figure 5-8 depicts the relationship of 134 Cs / 137 Cs ratio and time In 4 years, this ratio became to less than one halved
Table 5-1 Ratio of 134 Cs / 137 Cs from 2014 to 2018
Year 134 Cs (Bq/kg) 137 Cs (Bq/kg) 134 Cs / 137 Cs
Figure 5-8 Changing of ratio 134 Cs / 137 Cs from 2014 to 2018
Changing in radioactivity by size of grain soil
In order to understand the characteristics of radioactivity in soil of the paddy field of the study, the size distribution of surface soil was investigated
Particle size analysis was performed on the topsoil of paddy fields in the study area, focusing on the grain size composition of upstream (A and B) and downstream (C and D) rice fields in 2014 and 2018, as illustrated in Figures 5-9 through 5-12.
Until 2014, all rice fields were actively cultivated, leading to a limited presence of silt and clay particles in the soil due to their small size and lightweight nature, which allows them to easily wash away in water Consequently, soil samples primarily consist of fine sand, accounting for 35% in fields A and B and 46.4% in fields C and D, as well as medium sand, which makes up 37.8% in fields A and B and 32.7% in fields C and D.
In the measured results in 2018, because the upstream field was abandoned since
2015, the soil in this area is not disturbed by the plowing activity Therefore, the silt and clay content in Fields A and B increased (19.3%)
Figure 5-9 Percentage grain size in Field A and Field B in 2014
Figure 5-10 Percentage grain size in Field C and Field D in 2014
Figure 5-11 Percentage grain size in Field A and Field B in 2018
Figure 5-12 Percentage grain size in Field C and Field D in 2018
Most radioactive cesium is found in small soil particles, such as fine sand, silt, and clay In 2014, significant concentrations of cesium radioactivity were observed in these specific particle sizes.
Figure 5-13 Radiocesium by grain size in 2014
Figure 5-14 illustrates that downstream cultivated fields exhibit a significant accumulation of radiocesium, particularly in smaller particle sizes This phenomenon can be attributed to the presence of dissolved cesium ions in paddy water, which facilitates the formation of soil colloidal particles enriched with cesium Yoshimura et al (2016) further noted that the prolonged flooding of paddy fields after puddling leads to the preferential discharge of fine soil particles, which, upon settling, absorb radiocesium and subsequently accumulate in the downstream areas.
Figure 5-14 Radiocesium by grain size in 2018.
Mӧssbauer spectra for the samples obtained in 2018
The Figure 5-15 shows the change of 57 Fe Mӧssbauer absorption depending on the surface soil’s size of samples which were taken in 2018
The intensity changes observed in 2018 are comparable to those recorded in the soil of 2014, as illustrated in Figure 4-3 Notably, the intensity for soil particles larger than 850 micrometers (represented by the red line) shows that while Fields C and D maintained similar intensity levels to 2014, Fields A and B exhibited significantly higher intensity levels in comparison Additionally, there is a marked intensity difference between Fields A and B versus Fields C and D, which have been fallowing since then.
2015) become large by years It could be concluded that the fallowing made iron much accumulated in the soil larger than 850 micrometer
Figure 5-15 Mӧssbauer spectra for sampling sites in fields A, B, C, and D obtained in 2018
1 Nishizawa, Y., Yoshida, M., Sanada, Y.,Torii, T., Distribution of the 134 Cs/ 137 Cs ratio around the Fukushima Daiichi nuclear power plant using an unmanned helicopter radiation monitoring system, Journal of Nuclear Science and
2 Yoshimura, K., Onda, Y., Wakahara, T., Time Dependence of the 137 Cs
Concentration in Particles Discharged from Rice Paddies to Freshwater Bodies after the Fukushima Daiichi NPP Accident, Environmental Science & Technology, 50, 8, 4186-4193 (2016) https://doi.org/10.1021/acs.est.5b05513
General Conclusion
Nearly nine years have passed since the Fukushima Daiichi Nuclear Power Plant disaster, which involved an earthquake, tsunami, and radiation release Extensive scientific research has been conducted on this incident, enhancing our understanding of radioactive cesium pollution and its dissemination in soil and rice.
Between 2014 and 2018, ongoing research revealed significant radioactive pollution accumulation in rice fields due to the 2011 FDNPP accident Soil and rice samples collected from paddy fields, both pre- and post-disaster, indicated that radioactivity levels were highest in surface soil, decreasing with depth In 2014, the average radioactive cesium concentration in surface soil was 3754±7 Bq/kg, dropping to 2300±3 Bq/kg by 2018 Some survey sites exhibited unusually high cesium levels in certain years However, the radioactive cesium content in rice was relatively low, well below the Ministry of Health, Labor, and Welfare's provisional limit of 100 Bq/kg These findings highlight the effectiveness of measures taken to mitigate radioactive emissions from FDNPP and the ongoing decontamination efforts in the affected area.
Recent observations indicate a decline in surface soil radioactivity levels, accompanied by a shift of radioactive materials to deeper soil layers Additionally, the presence of fallow land has influenced the accumulation of radioactive cesium, as outlined in Notice No 0315 Article 1 by the Department of Food Safety, dated March 15, 2012.
The study of radioactive cesium (137 Cs) in soil reveals that its accumulation is influenced by the soil's oxidative/reductive atmosphere, which affects the dissolution of cesium ions from colloidal particles This oxidative environment facilitates the uptake of radioactive cesium by rice plants, while the presence of iron in larger soil particles may enhance the transfer of cesium to the rice Notably, higher penetration of 137 Cs was observed in fallowed fields compared to cultivated ones, particularly in soils with iron particles larger than 850 micrometers.
I would like to express my heartfelt gratitude to my supervisor, Professor Satoru Nakashima of Hiroshima University, for his patient guidance and unwavering support throughout my years of study I also extend my thanks to Assistant Professor Sunao Miyashita, Professor Tsutomu Mizuta, Professor Shinya Matsuura, and Professor Kiriko Sakata for their invaluable feedback, which significantly enhanced my work Additionally, I am grateful to my friend and colleague, Mr Masaya Tsujimoto, for his assistance in both my academic journey and daily life in Japan.
I sincerely thank The Phoenix Leader Education Program (Hiroshima Initiative) for their financial support of my studies, funded by Japan's Ministry of Education, Culture, Sports, Science and Technology, which plays a crucial role in addressing the impacts of radiation disasters.
The article discusses various types of errors related to measurements, including Bq error percentages, net count errors, and CPS errors It highlights the significance of understanding these errors to ensure accurate data interpretation and reliability in results The focus is on quantifying error rates, such as net error percentages and count errors, which are crucial for maintaining quality control in experimental setups.
The article discusses various error metrics, including Bq Error, Net Count Error, CPS Error, and CE Error, each represented as a percentage These metrics are crucial for evaluating the accuracy and reliability of data measurements in different contexts Understanding these error rates helps in identifying areas for improvement and ensuring data integrity.
The article discusses various types of errors in measurement, including Bq error percentages, net count errors, and CPS error percentages It emphasizes the significance of understanding these errors to ensure accurate data interpretation and analysis Additionally, it highlights the importance of monitoring error rates, such as net error and count error percentages, to maintain data integrity and reliability in scientific research.
The Bq error percentage recorded is 5.2%, with a net count error of 0.0015 and a corresponding net error percentage of 3.73% The CPS error stands at 0.95%, while the CEE error is at 0.69% Additional data includes a Cd-109 measurement of 2509.00 and a count of 20994.00, with respective errors of 130.47 and 200.06 The measurements were taken on August 1, 2016, at 12:00, providing essential insights into the accuracy and reliability of the data.
The data presents a detailed overview of error percentages across various metrics, including Bq Error and Net Count Error For instance, the Bq Error is recorded at 5.1%, with a corresponding Net Count Error of 0.0015% Additionally, the CPS Error stands at 3.73%, while the CEE Error is noted at 1.12% The values indicate significant precision in measurements, with specific readings such as 4081.75 for Net Count and 3564.90 for CPS Overall, the analysis highlights the importance of monitoring these errors to ensure data accuracy and reliability.
N et C ou nt C P S - R ea l C ou n t E ffe cie n cy ( C E )
C ou n t E ffe cie n cy ( C E ) C P S - R ea l L iv e T im e ( s)
N et C ou nt C P S - R ea l C ou n t E ffe cie n cy ( C E )
N et C ou nt C P S - R ea l C ou n t E ffe cie n cy ( C E )
N et C ou nt C P S - R ea l C ou n t E ffe cie n cy ( C E )
C o- 60 T 1/ 2 ( D ay s) λ t ( la ps ed t im e) E xp ( -λ *t ) S ta nda rd S ou rc e, on M ea su re m en t E m is sion R at e ( Ir) L iv e T im e ( s) C o- 57
The standard source of Co-57 is utilized for measuring radioactivity, which follows the exponential decay formula Exp(-λ*t), where λ represents the decay constant and t denotes the elapsed time.
R ad ioi sot op e E ɣ ( K eV ) S ta nda rd S ou rc e, R adi oa ct iv ity E m is sion R at e ( Ir) L iv e T im e ( s) C o- 57
The standard source of radioactivity is characterized by its emission rate (Ir) and half-life (T1/2 in days), which are crucial for accurate measurements The decay constant (λ) is determined by the relationship between elapsed time (t) and the exponential decay function, expressed as Exp(-λ*t) Understanding these parameters is essential for effective analysis and application in radiological measurements.
The half-life (T 1/2) of radioactive isotopes, such as Co-57, is measured in days and is crucial for understanding their decay rates The decay constant (λ) is related to the elapsed time (t) through the equation Exp(-λ * t), which helps in calculating the emission rate (Ir) of the standard source This knowledge is essential for accurate measurements in radiological applications.
The measurement of the MX033U8PP source set, conducted by the Japan Radioisotope Association, involves analyzing the radioactive properties of the Co-60 standard source The emission rate (Ir) is determined based on the half-life (T1/2) of the isotope, which is expressed in days, and the decay constant (λ) is calculated using the elapsed time (t) The exponential decay formula, Exp(-λ * t), is applied to assess the activity levels accurately.