These problems are due on Monday, Dec. 13 at midnight. The first six problems cover material that will be discussed in class on Tuesday, Dec. 7th.
The only issue I can see in advance is with #5 (SV8.29.54). In part (a), the question asks you to find the activity of milk due to potassium. Unstated is that you want to find the activity of 1 liter of milk.
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Prof. Stephens and Prof. Koch
I have been working on the chapter 29/30 hw and I have a concern. The WebAssign is apparently rounding off values such as neucleon masses and constants such as 1u = 931.494 Me/V. Due to this my calculations are coming out with far more accuracy than the WebAssign answer expects. By experimenting with my answers I founf that WebAssign expects an answer within about +/- 0.2 of mine. I believe that 931.494 is being rounded to 931.5 but I have no idea what is being used for nucleon masses and other constants. This was a problem for both questions 2 and 5 so far.
Is there anyway to tell us what values WebAssign is expecting us to use?
Thank you for your help,
Peter Davis
I think that WebAssign is satisfied with answers accurate to 1%. But for some problems, like these nucleon mass ones, you have to carry more precision in the calculations to obtain overall 1% accuracy. Masses in SV8 appendix B and 931.5 MeV/u should suffice.
I'm having problems with Q3.
I have a)Se 78, b)Pb 208, c)Au 197, d)Zn 64.
In a) and d) I get negative mass in difference (Mproton + Mneutron)- Melement.
In b) and c), the answers I get manually don't match the ones provided in the textbook's graph (p. 917)
Ex. b) Lead 208,
((126*1.008665)+(82*1.007825))-207.2 = 2.53344
then 2.53344*931.5=2359.89936/208=11.34567
BUT the correct answer is approx. 7.866
Am I doing anything wrong here?
thanks in advance.
The value 207.2 you used for Pb is for the natural mixture of all isotopes - called the chemical atomic mass in this table. You want the atomic mass of isotope 208, which is 207.976636. That's probably the problem you're having with the other ones as well.
For number 5 it is telling me I'm off by a number of ten.
part a) lambda = 1/717 e -17 (per second)
R= lambda N
N = [(.0117 x .002) / 40] x 6.022 e 23 = 3.523 e 17 atoms
R = 6.049 decays per second = 6.049 Bq
Is the / in your first equation a typo? I think your problem is that 0.0117 is not the same as 0.0117 percent.
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