Radiation Problem [10 points]?

Radioactive isotopes are often used for medical imaging. Technetium-99m 99Tc is a particularly popular isotope since it has a short half-life and is easy to make. (The "m" in technetium-99m just means that the nucleus is in a metastable, i.e., excited, state.) Also, 99mTc can be chemically bonded to a number of different compounds and cell types for imaging different parts of the body.

99m Tc has a half-life of 6.02 hours. It decays into 99 Tc by emitting a gamma ray, with energy 140 keV for this problem, assume that 99mTc is present in the body for 2 hours after being injected and then is immediately removed. This assumption is reasonable for certain techniques such as renal scans. (For others, a more complex model of technetium removal is needed.)

What is the number N(o) of 99 Tc atoms that must be present to have an activity of 15 mCi?

Thanks 😀

3 Answers

  • wow you look like a guy that is at my uni...

    ok what you do is convert the 15mCi into Bq as you already know 1 Ci = 3.70x10^10

    so you have 5.55*10^8bq which is your R_o

    then find t1/2

    = 6.02 *60*60 to get it into seconds = 21672 s

    N_o which is what your finding = t1/2 * R_o / 0.693


    gl with the rest

  • An interesting question;

    A Curie is defined as the amount of material in which 3.7 X 10^10 atoms transform per second.

    Thus the activity of 15mCi of "tec" would be 15/1000(3.7 x 10^10) = 5.55 x10^8 atoms present.

    Looks like your prepping for your CMNT exam. Good luck on that!.

    Here is a little "free clinical advise". There is a lot of tissue attenuation with Tc99m and the obese, particularly with skeletal imaging. So unless you want to end up skipping lunch, staying late or having your entire schedule disrupted, you "nuke" fat boy with the max permissible dose.

  • time spent in Houston = (sixty 5 - 30) = 35 years 35 years × 220mRem/twelve months = 7700 mRems time in trip = 13 × 3 = 39 days 39 days × 19mRem/day = 741 mRems entire radiation from time in Houston and trip = 8441 mRems time spent in Denver = 30 years 30 years × 383 mRem/twelve months = 11490 mRems entire lifetime exposure so some distance = 19.9 Rems, rounded to 10th of Rem

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