1. Estimation of the effects of a lead vest on dose reduction for NPP workers using Monte Carlo calculations
KIM JEONG-IN

2. Contents Introduction Materials and Methods Results and Discussion
Future Works
Conclusion

3. Introduction
In the field of medical diagnosis or treatments using radiations, lead vests or aprons are widely used to protect the patients from unwanted irradiation.
In nuclear power plants, it is recommended that the workers should wear a lead vest to reduce the dose for working in high radiation area.
Various models have been designed and changed for convenience and effectiveness for dose reduction

4. Introduction
Personal dosimeters like TLDs, Film badges have been used to estimate the doses of radiation workers
The dosimeters cannot give the absolute values
Measured values should be modified by comparing the reference conditions with conversion factors
In ICRP 74, These conversion factors are tabulated for various particles, energies and typical phantom geometries.

5. Introduction
The dose of a worker with a lead vest cannot be estimated directly from the personal dosimeter
Many trials using two or more dosimeters (located in/outside the shield, head and chest respectively) were done. But it still has limitations.
In the concepts of ALARA, conservative approach is not always the best choice.
Through this research, the personal doses with/without a lead vest and the effectiveness were evaluated by Monte Carlo methods

6. Materials & Methods [ lead vest ]
Used in KHNP nuclear site since 2004
Two front sides were folded
2.5cm*32cm*1.5mm lead plates were placed
About 9.3kg

7. Materials & Methods [ The phantom ]
MIRD-V
Simplified human body with critical organs
Front side : 3mm, back side : 1.5mm

8. Materials & Methods [ Monte Carlo Method ]
Most of the natural phenomena are random nature.
If we understand the underlying principles, we can simulate the process by Monte Carlo method
Utility of Monte Carlo technique
Sampling
Particle behavior (molecules, radiation)
Reactions
uncertainty

9. Materials & Methods [ Monte Carlo Method ]
Merits?
Can handle complicated 3-D geometries
Can visualize simulated particle behavior
Can give uncertainty estimates
Drawbacks
Long computing time (geometry tracking)
Limited number of detectors

10. Materials & Methods [ Monte Carlo Method ]
AP, PA, RLAT, LLAT
Parallel photon beam (0.2, 0.4, 0.6, , 1.2MeV)
MCNP-5 Monte Carlo transport code PA
LLAT
RLAT AP

11. Results [ AP ]

12. Results [ PA ]

13. Results [ RLAT ]

14. Results [ LLAT ]

15. Discussion
The results have some limitations to apply due to the differences between phantom and real body
In most cases, the lead vest decreases the organ doses about 30%.
For low energy (<400keV), the lead vest is very effective to reduce the dose but it is not so good for high energy photon shielding (less than 20%).
Both the shielding effect of lead vest and the delay of working time due to heavy clothing should be considered.

16. Discussion
For thyroids, the doses to high energy photons increased by 5% on the contrary
These results comes from scattered radiation (Build-up)

17. Future Works
Monte Carlo results are not always good answers. For verification, real measurements should be done and compared
For the optimal method of dose measurements using personal dosimeters and dose conversion factors from personal dosimeters

18. Future Works
Other type of phantom models should be used to calculate the dose.
More precise values and build up effects can be calculated.

19. Conclusion
Using Monte Carlo method, the effects of a lead vest on dose reduction for various irradiation geometries were examined.
In most cases, it had 30% dose reduction effect. But some problems should be considered were also found.
Real measurements and applications to advanced man-like mathematical phantoms are required.
This study may be applied to the better design of personal shielding and dose estimation procedures for practical use.

20. Thank you