Iranian Researcher Proposes Universal Radiation Protection System Hypothesis

Saturday, July 28, 2018 - 12:57

A faculty member of Department of Energy Engineering and Physics, Amirkabir University of Technology, has presented a universal radiation protection system hypothesis for a global, standardized system for the safety of the workers, the public, and the environment in the 21st century.

According to an ISCA report, Prof. Mehdi Sohrabi presented a new theory “Bridging the LNT and hormesis radiation protection models Proposed: A universal radiation protection system hypothesis for a global, standardized system for the safety of the workers, the public, and the environment in the 21st century” which its results published in Nuclear News Journal, June 2018.

As he explained in his research, over half a century ago, when he was in charge of health physics for the 5-MW research reactor at the University of Tehran, and later, as a dosimetry researcher at the Health Physics Research Reactor at Oak Ridge National Laboratory in the United States, a maximum permissible dose of 5 rem per year (rem/y) for ionizing radiation workers, as recommended by the International Commission on Radiation Protection (ICRP), was enforced.

The maximum permissible dose in 1991 was changed by the ICRP to dose limit, with a value for workers reduced from 50 to 20 millisieverts per year (mSv/y, or 2 rem/y) averaged over five years.

The 50 mSv/y is still practiced as the dose limit for workers in the United States and 1 mSv/y is the standard for the public from planned exposure situations where radiation protection can be planned in advance and are reasonably predictable.

The current ICRP radiation protection philosophy is based on the linear no-threshold (LNT) model, which indicates that no matter how small the radiation dose is, there is always a risk. On the other hand, a competing hormesis model indicates that low doses of radiation are beneficial and stimulate the activation of repair mechanisms that protect against disease.

Regardless of extensive studies on health effects, radiobiology, epidemiology, and genetics over decades, no convincing, supporting, and reproducible health risk data at low doses exist with good science to a point that is acceptable by all.

In addition, neither the LNT model nor the hormesis model includes the chronic natural background radiation doses in the health risk estimates. The United States, however, with an advanced regulatory infrastructure and a large advanced health physics community, has been debating the possibility of considering the hormesis model as an alternative in order to modify the dose limit to a higher value.

A decision on selecting either of the LNT and hormesis models is being seriously pursued by the Health Physics Society and many other governmental organizations in the United States such as the U. S. Environmental Protection Agency, such as the U.S. Nuclear Regulatory Commission, etc. particularly under the recent Presidential Executive Order 13777 of February 28 2018 on Enforcing the Regulatory Reform Agenda.

The universal radiation protection system (URPS) as proposed by me is hypothesized on a new philosophy, concept and methodology and applies a URPS model which would bridge the two models by integrating the doses a worker receives from nonoccupational exposures as a member of the public and from occupational exposures incurred during work, by applying a standardized integrated dose system.

This URPS model would also involve applying a fractionation correction factor, introduced for the first time in radiation protection, in order to take into account the actual duration an individual works and the doses received.

As the LNT and hormesis models are being debated internationally, the time seems ripe to revolutionize the current radiation protection philosophy by adapting the URPS hypothesis, such that a worker has the same risk limit within a new dose limit, no matter where he or she works or lives in the world.

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