From key@physics.utoronto.ca Wed Apr 2 09:08:38 2008 Date: Wed, 02 Apr 2008 09:08:37 -0400 From: Tony Key To: Li He Cc: Tony Key Subject: Re: Phy138 Mastering Physics Practice Problem [ The following text is in the "windows-1252" character set. ] [ Your display is set for the "ISO-8859-1" character set. ] [ Some characters may be displayed incorrectly. ] HI Alex - thanks for your question. I haven't checked the numbers in your equations, but you are on the right track. Since we are asked for lambda_n and lambda_be, I'd rewrite the equations in terms of these two. Then I think the third equation you need is the value of N_0, the no. of radioactive nuclei that would have been injected at time =0 INTO THE sample volume. Since you know the no. injected into whole volume of blood at time=0 in terms of 25mCi and lambda_n, you find the no. in the sample by dividing this last no. by the volume of blood in the body, and multiplying by the known sample volume. Put that value of N_0 into your equations, and you have two equations in two unkowns - lambda_be and lambda_n. Let me know if that helps. TonyK Li He wrote: > Dear Professor Key. > > My name is Alex, and i'm a phy138 student. I have a question about the > current mastering physics assignment. Its Question #6, about the half > lives and about the counts. Its the problem that is just for practice > > I am stuck on this problem. The problem is, i am not sure what or where to > use the given activity of 25 mCi and also how does the total blood volume > and the sample volume come into play in solving this problem? > > The two equations i got, which i am pretty sure is wrong are > > 6760 = N_o exp ( - 26lamda_n - 24lamda_eff) > > which turns into > ln 6760 - ln N_0 = - 26 lamda_n - 24 lamda_eff > > and > > ln 3580 - ln N_0 = - 2 lamda_n - 48 lamda_eff > > > But i still have two unknowns so that doesnt' help me. I've tried the > hints but i am still stuck. Any advice would be appreciated. > > ------------------------------------------------------------------------ > Sign in to Windows Live Messenger, and enter for your chance to win $1000 > a day?today until May 12th. Visit SignInAndWIN.ca > [ Part 2, Text/X-VCARD (charset: UTF-8 "Internet-standard ] [ Unicode") (Name: "key.vcf") 9 lines. ] [ Unable to print this part. ]