Introduction

COVID-19 due to Coronavirus is distressing many countries and their territories around the world [1, 2]. This pandemic emerged during December 2019 from Wuhan city of China to other parts of the world [3]. In this problematic situation, every country is working on applying many strategies to prevent and control the spread of coronavirus among their people. Many countries already applied tremendous strategies, which include one of the dominant strategies is lockdown of state or country. The Indian government has also adopted this strategy and before applying lockdown, the prime minister of India has requested the Indian public to follow self-lockdown as called Janta Curfew for one day (22 March 2020), which was efficacious. The Indian government has declared a total of 21 days (from 24 March 2020 to 14 April 2020) as a lockdown, which extended three times from 15 April 2020 to 3 May 2020; 4 May 2020 to 17 May 2020 and 18 May 2020 to 31 May 2020 [4]. The annual effective dose of gamma radiation is the most important value to estimate the effect of gamma radiation on mankind, UNSCEAR was given the formula for calculation of these values and this formula is utilized around the world for estimation of AEDE values [5]. The annual effective dose is calculated by using indoor and outdoor gamma dose and based on many studies, indoor gamma dose rate values are usually higher than the outdoor gamma dose rate, except in a few countries or territories of the world [5, 6]. Lockdown situations where movement restricted will affect the AEDE values because, in this period, the public stays inside of the house instead of outside. Hence, the values of the annual gamma dose rate will change in the lockdown period. The intention of this study was to estimate the extra AEDE value of the natural background gamma dose rate during this lockdown period for adults, children and infants from areas (Balod, Durg and Bemetara) of the Chhattisgarh region.

Material and methodology

All researchers usually used the formulas for calculation of AEDE value, which were reported by UNSCEAR by applying the indoor and outdoor gamma dose rate, which was as [5, 7]:

$$AEDE\left( {indoor/outdoor} \right) = D\left( {indoor/outdoor} \right)~ \times T~ \times conversion\;coefficient~ \times occupancy\;factor$$
(1)

where D(indoor) = Indoor absorbed gamma dose rate (nGy/h). D(outdoor) = Outdoor absorbed gamma dose rate (nGy/h). T = Time conversion factor (hour into a year) (1 year = 8760 h).

The dose conversion coefficient value for an adult was 0.7 (UNSCEAR), and the values of the occupancy factor for outdoor and indoor were 0.2 and 0.8, respectively [5]. The conversion coefficient values for the children and infants were approximately 10 and 30% higher than those for adults [5]. The value of the total AEDE value was calculated by the accumulation of the AEDE values of indoor and outdoor gamma dose rates.

In India (including all states), 68 days set for lockdown means people of the country will be spending 1632 h inside of houses. It indicated that out of 8670 h in a year, people utilize 1632 h inside of houses. Moreover, the remaining hours of the year 7128 h can be utilized as the normal distribution of occupancy factors of 0.8 and 0.2 for indoor and outdoor. As of now (18 July 2020), the COVID-19 condition is still continuing [1, 4]. The lockdown of the few places of Chhattisgarh State might be increased by the central government of India or state government of Chhattisgarh. The Indian government has declared June and July month as unlock-1 and unlock-2 means all work will start slowly but still education or few other organizations such as schools, colleges closed.

Results and discussion

The annual effective dose values were already published by many researchers and in our previous studies [6,7,8,9]. Table 1 shows the calculation of extra annual effective dose values by using Balod, Durg and Bemetara districts indoor and outdoor gamma dose rate values [6,7,8,9]. In columns, D and E present the AEDE values of indoor and outdoor, respectively, by using the 7128 h after subtracting the 1632 h of lockdown (period of lockdown) [4]. The F column indicates the AEDE value during lockdown and the addition of D, E and F is the total AEDE value with 68 days of lockdown. Annual effective dose values were also calculated by using Eq. 1 with occupancy factors of 0.8 and 0.2 for indoor and outdoor respectively, and these values were subtracted from lockdown values to obtain the total extra dose, which can be received by people during the lockdown period, which was precisely the same as calculated. The same value can be calculated directly by using the following formula.

$$\begin{aligned} & Extra\;AEDE\;value\;during\;lockdown = D\left( {indoor - outdoor} \right) \times ~Time\;of\;lockdown \\ ~ & \quad \times \;conversion\;coefficient~ \times ~difference\;in\;occupancy\;factor \\ \end{aligned}$$
(2)
$$Extra\;AEDE\;value\;during\;lockdown\;for\;adult = \left[ {\left( {X \times 228} \right) + \left\{ {\left( { - 2.42} \right) \times e^{{ - 11}} } \right\}} \right]$$
(3)
$$Extra\;AEDE\;value\;during\;lockdown\;for\;children = \left[ {\left( {X \times 261} \right) + \left\{ {\left( { - 3.78} \right) \times e^{{ - 11}} } \right\}} \right]$$
(4)
$$Extra\;AEDE\;value\;during\;lockdown\;for\;infants = \left[ {\left( {X \times 294} \right) + \left\{ {\left( { - 3.02} \right) \times e^{{ - 11}} } \right\}} \right]$$
(5)

where X = difference between indoor and outdoor gamma dose rate.

The range of difference between indoor and outdoor gamma dose rates was found from − 20 to 124 nSv/h. These difference values were used to calculate the extra annual dose rate during the lockdown period for adults, children and infants. The resultant values showed a strong correlation between indoor and outdoor gamma dose rates. The relation between both can be calculated by using Eqs. 3, 4 and 5  for adults, children and infants, respectively. The relationship between extra gamma dose rate values during lockdown and differences in indoor-outdoor gamma dose rate are shown in Figs. 1, 2 and 3 for adults, children and infants, respectively. The extra dose rate ranged from − 4.57 to 28.33 µSv/y; − 5.22 to 32.38 µSv/y and − 5.88 to 36.43 µSv/y for adults, children and infants, respectively.

Table 1 Calculation of extra AEDE values during the lockdown period for adults, children and infants from Balod, Durg, Bemetara districts [6,7,8,9]
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Fig. 1
figure 1

Relationship between extra gamma dose rate values during lockdown and difference values of indoor–outdoor gamma dose rate for adults

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Fig. 2
figure 2

Relationship between extra gamma dose rate values during lockdown and difference values of indoor–outdoor gamma dose rate for children

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Fig. 3
figure 3

Relationship between extra gamma dose rate values during lockdown and difference values of indoor–outdoor gamma dose rate for infants

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Conclusions

  • It has been observed that the calculation of extra AEDE values through Eq. 2 is the same as calculated by using AEDE separately; hence, it is suitable for estimation of additional natural gamma dose rate values during lockdown situations.

  • This study will be helpful in calculating the extra annual effective dose value, and the mean values of extra AEDE for Balod, Durg and Beemetara districts of India were 10.66 µSv/y, 12.18 µSv/y and 13.70 µSv/y for adults, children and infants, respectively.

  • This study will be applicable in lockdown situations only, and formula (Eqs. 3, 4, 5) can be used for the estimation of extra AEDE values of natural gamma dose in many countries during 2020 due to COVID-19.

  • The value of AEDE due to lockdown have been obtained highest and lowest 28,332 nSv/y and − 4570 nSv/y respectively at area Bortara (Bemetara district) and Piparchhedi (Balod district).

  • During COVID-19, most of the people are inside the shelter, so the scenario of radiations upon outside and inside are drastically varied. Due to population, it varies somewhere low and high; however, geology and civil structure may be one cause of this variation.

  • The range of relative difference in lockdown versus non-lockdown AEDEs varies from − 0.46 to 2.24% (− 4570 to 28,332 nSv/y, absolute difference). The impact of lockdown appears inconsequential because the variability across the locations studied has a 48% relative difference in non-lockdown AEDE values (773,858–1,488,850 nSv/y) and lockdown AEDE values (780,484–1,502,787 nSv/y). In other words, while the lockdown produces a small difference in AEDE, the total effect is small compared to the variability in AEDE.

  • This study will be beneficial for mankind to predict the annual gamma dose rate during the pandemic situation.