Radiometriában mit jelent a WLM/év kifejezés?

Most nem fordítom le ha nem baj:

In the early days of uranium mining, a radon concentration of 100 pCi L-1 was adopted as a limit value. When it was realized that most of the lung dose came from the radon progeny (called daughters in those days), not the gas, a new limit value was introduced, the working level (WL). This was based on the energy that inhaled progeny would deposit in the lung.

In old uranium mines, the ventilation was often poor, and the radon progeny was close to equilibrium with the radon. The progeny in equilibrium with 100 pCi L-1 radon gas would release approximately 130,000 MeV alpha energy in decay, so the WL was defined as:

1 WL = 130,000 MeV alpha energy per litre air

= 20.8 microjoules (µJ) alpha energy per cubic meter (m3) air.

The nominal working hours per month for a miner at that time was 170, so the working level month (WLM) was introduced to simplify record keeping.

WLM = Working Level Month = 1 WL exposure for 170 hours.

1 WLM = 170 x 20.8 = 3.54 mJ h m-3

17,000 pCi h L-1 radon = 1 WLM

1 pCi h L-1 = 59 µWLM