Homework Help: Nuclear physics help

1. Jan 28, 2006

f4d_girl

The reaction 18(number of neturons + protons) O(oxygen) 8 (number of protons) (p,n) 18 F 9

requires an input of energy equal to 2.453 MeV. What is the mass of 18F9?

I tried to use Q-value equation, but it didn't work out at all

then i thought, since the enrgy is conserved, the kinetic energy equation might work

but it didn't again

Last edited: Jan 28, 2006
2. Jan 28, 2006

Astronuc

Staff Emeritus
So this is a binding energy type of problem.

18O + p -> 18F + n

And it requires an input of energy (endothermic) of 2.453MeV, in other words, the rest mass of the reactants is less than the rest mass of the products.

One could use an energy equivalent of the atomic mass unit (amu), and use amu's to solve the problem. Otherwise if the masses are in kg, and one uses mc2, then energy would need to be in Joules.

If the formula for the Q value is written in the conventional way,

Q = (mproducts - mreactants) c2 and Q < 0, for an endothermic reaction, and > 0 for exothermic reaction.

Try mass of 18O = 17.999161001 amu from http://wwwndc.tokai.jaeri.go.jp/cgi-bin/nuclinfo2004?8,18 [Broken]

mass of 1H = 1.00782503207 from http://wwwndc.tokai.jaeri.go.jp/cgi-bin/nuclinfo2004?1,1 [Broken]

or mass p = 1.00727644 amu (Dolan, Fusion Research, 1982)

mass n = 1.00866491574 http://wwwndc.tokai.jaeri.go.jp/cgi-bin/nuclinfo2004?0,1 [Broken]

http://wwwndc.tokai.jaeri.go.jp/cgi-bin/selchart2004?Z=O&A=18 [Broken]

Mass-energy equivalence: 1 amu = 931.481 MeV, so 2.453MeV = 0.002633 amu.

And 1 eV = 1.60219 x 10-19 J.

Last edited by a moderator: May 2, 2017