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In order to grasp the radon concentration and γ-ray radiation level in a museum in Chengdu, and evaluate the radiation damage caused to the museum staff, the radon concentration and the instantaneous dose rate of gamma rays in the museum warehouse and exhibition room were monitored and estimated the annual effective dose caused by it. The results show that the radon concentration range in the museum is 24.12 - 78.9 Bq/m3, the average is 36.17 Bq/m3, far below China’s 400 Bq/m3 standard. The range of γ air absorbed dose rate is 7.1 - 13.6 × 10?8 Gy/h, the average is 10.8 × 10?8 Gy/h, it is the normal natural background range. The average annual effective dose of radon and its decay products was 8.68 × 10?3 - 2.84 × 10?2 mSv/a, the average annual effective dose of γ radiation was 0.100 - 0.192 mSv mSv/a, and the combined dose was 0.109 - 0.220 mSv/a, far less than 1 mSv/a standard.

In recent years, people have realized the health effects of long-term exposure to natural radiation [

γ radiation monitoring is based on the principle of distribution: The survey area is divided into proper size grids, and a monitoring point is selected in each grid. In the end, there were 30 points in the warehouse, 30 in the exhibition room and 30 in the yard, which made a total of 90 points. Radon gas distribution principle also uses the appropriate size grid to divide the survey area, taking one point in each grid. In the end, there were 6 locations in the warehouse and 6 exhibition rooms, with a total of 12 locations. The plan of the museum is shown in

According to the “Standard Measurement Methods of radon in Ambient Air (GB/T 14582-93)”, the sampling layout and solution requirements for indoor radon concentration measurement are as follows: 1) The sampling height is 0.8 - 1.5 m and the distance from the inner wall should not be less than 0.5 m; 2) Sampling work should be carried out normally under completely closed conditions, the outside doors and Windows must be closed, and the outside doors

should not be opened for more than a few minutes during normal access; 3) Internal and external air-conditioning systems such as ceiling fans and Windows must be stopped during sampling [

According to the “Specification for The Determination of Dose rate of Environmental Surface gamma RadiationGB14583-1993”, in this study, the γ air absorbed dose rate was measured by instantaneous measurement. The air dose rate of ambient gamma radiation at 1 m above the point was measured directly by the x-gamma dose rate meter. Each point is measured for 3 times, and the measurement time of each group of data is set at 270 s. If the data of the measurement point is abnormal, it can be measured for multiple times [

The radon concentration measuring instrument is fD-216 radon measuring instrument developed by Beijing Geological Research Institute of Nuclear Industry (Range of measurement: 3 - 100,000 Bq/m^{3}; Sensitivity: >1.5 Bq・m^{−3}/cp20m; Background: ≤0.5 cpm). Gamma dose rate was determined using the BH3103B portable X-gamma dose rate manufactured by Beijing Nuclear instrument Factory (Range of measurement: 1 - 10,000 × 10^{−8} Gy/h; Cosmic-ray response: ±15%; Long-term stability: ≤ 7%; calibration factor: 1.00).

The statistics of the measured data are shown in

The measured data are compared with the upper and lower limits of the anomaly, and the values beyond the range are eliminated.

1) It can be seen from

statistical magnitude | γ Air Absorbed Dose Rate (10^{−8} Gy/h) |
---|---|

The total number of measurements | 268 |

Mean value | 10.93 |

standard deviation | 1.63 |

Range | 13.6 - 7.1 |

Abnormal upper and lower limits* | 15.82, 6.04 |

*Note: Determination of upper and lower limits of anomaly (Refer to geochemical correlation methods, N ± 3δ distribution is recommended as the limit of high anomaly and low anomaly, respectively).

2) The content difference of different measurement points in the same measurement route is also very different, because of different geological structure, different ground materials, and different types of ore storage. The ground of some measurement points is concrete, while the ground of some measurement points is marble, and the ore type stored has a great impact on the measurement data.

The range of γ air absorbed dose rate is 7.1 - 13.6 × 10^{−8} Gy/h, the average is 10.8 × 10^{−8} Gy/h. Compare the results of this experiment with those of previous years: The range of γ air absorbed dose rate in Sichuan province in 1990 was 60.8 - 66.0 nGy/h, The average γ air absorbed dose rate of in China is 98.3 - 99.1 nGy/h [

The measurement results are shown in

It can be seen from ^{3}, the mean value is 36.17 Bq/m^{3}, it can be seen that the radon concentration in the museum is far lower than the Chinese standard of 400 Bq/m^{3}.

It can be seen from

The estimate can be made according to the following formula:

H e = D r ⋅ K ⋅ t (1)

where H_{e}: annual effective dose equivalent (mSv/a); D_{r}: γ Air Absorbed Dose Rate ( G y / h ); K: Ratio of effective dose equivalent rate to air absorbed dose rate, 0.7 Sv/Gy; t: Residence time in the environment, 2000 h.

According to the formula, the maximum, minimum and average of the measured air absorbed dose rate can be substituted into the formula, and the effective dose of external irradiation caused by γ radiation can be calculated, as shown in

For the estimation of internal exposure to radon, the formula for estimating the effective dose caused by radon in an equilibrium state is as follows:

H E = 1 .8 × 10 − 10 C R n ⋅ t (2)

where H_{e}: annual effective dose equivalent (mSv/a); 1.8 × 10^{−10} Sv/(Bq/(m^{3}・h)); C_{Rn}: Radon concentration (Bq/m^{3}); t: The time of exposure to radon is 2000 h according to the international standard.

According to the above formula, the maximum, minimum and average value of radon concentration obtained can be substituted into it, and the effective dose of internal exposure caused by radon can be calculated as shown in

In this survey, measurements were made of museum galleries, yard and warehouses.

The radon concentration in the museum ranged from 24.12 to 78.9 Bq/m^{3}, with an average of 36.17 Bq/m^{3}, it can be seen that the radon concentration in the museum is far lower than the Chinese standard of 400 Bq/m^{3}.

Statistical magnitude | Radon concentration (Bq/m^{3}) |
---|---|

The maximum | 78.90 |

The minimum value | 24.12 |

The average | 36.17 |

Statistic | Annual effective dose (Sv/a) |
---|---|

The maximum | 1.92 × 10^{−4} |

The minimum value | 1.00 × 10^{−4} |

The average | 1.53 × 10^{−4} |

Statistic | Annual effective dose (Sv/a) |
---|---|

The maximum | 2.84 × 10^{−5} |

The minimum value | 8.68 × 10^{−6} |

The average | 1.30 × 10^{−5} |

The range of γ air absorbed dose rate is 7.1 - 13.6 × 10^{−8} Gy/h, the average is 10.8 × 10^{−8} Gy/h. Compared the results of this experiment with those of previous years, the range of γ air absorbed dose rate in Sichuan province in 1990 was 60.8 - 66.0 nGy/h, the average γ air absorbed dose rate of in China was 98.3 - 99.1 nGy/h. Comparing the two data, it can be seen that the gamma radiation level rate in the museum is higher than that in Sichuan province and the whole country, which belongs to the normal natural low range.

The effective doses of external irradiation caused by gamma rays and internal irradiation caused by radon ranged from 0.100 to 0.192 mSv and 8.68 × 10^{−3} - 2.84 × 10^{−2} mSv, respectively. Therefore, the total annual effective dose range of radiation received by staff is 0.109 - 0.220 mSv, which is far less than the national standard of 1 mSv for public individuals.

In summary, the environmental radioactivity level of the museum is normal and will not cause any harm to the staff of the museum.

The authors declare no conflicts of interest regarding the publication of this paper.

Shao, Y., Hu, H. and Hu, S.J. (2020) Background Environmental Radiation in a Museum in Chengdu. Open Access Library Journal, 7: e6584. https://doi.org/10.4236/oalib.1106584