1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: When does 226Ra become safe ?

  1. May 20, 2010 #1
    When does 226Ra become "safe"?

    Hi, I was working on an assignment which deals with radioactive decay.
    Half life of 226Ra is 1600 years (it varies from source to source, but this is the one I chose), and the equation I got for half-life is y=Ce^(-0.000433216988t), C being the initial value and y being amount left in grams, and t being the amount of time passed in years.

    When does 226Ra become "safe", where the radiation from it is no longer considered to the public? I know 226Ra is a toxic element, so I'm expecting pretty low...
    also, if possible, give the units in grams, like x micrograms per gram, not using other units like pCi/L.

  2. jcsd
  3. May 20, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Re: When does 226Ra become "safe"?

    Safe depends on the amount of radiation.
    When there is either a small enough total amount of the material, or it has decayed to a point where there is a small enough amount of the radioactive isotope left to meet the safety limits for your country.
    Generally with Radon the halflife isn't really a factor because new Radon is being produced from the Uranium in the native rock so there is a constant amount of radioactive Radon present.

    In mining there is a monthly safe limit - this assumes 160hours exposure (40hours/week * 4weeks) and is equal to roughly 3.5 mJhours/m^3 or a concentration of 250Bq/m^3

    Household exposure where you are exposed to the gas for >12hours a day and there is no monitoring would be higher, and so the safe limit in a home must be lower.
    Last edited: May 20, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook