Finding kinetic energy and speed in beta decay with mass defect

[roy5995]

How do i calulate the kinetic energy and speed of a particle released form a beta decay reaction?

for example, if i have Na -> Mg + e (i can't type in the atomic masses and numbers)
Would i subtract the mass of Mg from Na ?
m=m_Na-m_Mg
=23.990961u-23.985042
=0.005937u

then multiply that mass by 931.5 (b/c 1u=931.4MeV)

E=0.005937*931.4
=5.5297MeV

^^^is that the kinetic energy, or is that the energy released? they are different right?
does finding the kinetic energy involve something with the masses of daughters and masses of parents?


Once i have found the correct energy would i just rearrange the equation E=1/2mv^2 to find the speed?




Also, is the mass of, for exapmle, oxygen is 15.003065u, what is that is kg?
what does u mean? and what is the mass of an electron in 'u'

 

[HallsofIvy]

You have caluculated the difference between the mass of Na and the mass of Mg but you still have the mass of the electron. If you add the mass of Mg to the mass of the electron what do you get? Is that the same as the mass of Na? If it is less, where do you think the extra mass went? (Hint: E= mc²!)


As far as "oxygen is 15.003065u" is concerned I have no idea what "u" is. My first thought was that is was really μ ("mu" for "micro-") but even that requires a base such as gram.

Are you really saying that none of this is in your textbook?

 

[himanshu121]

I believe u here is atomic mass unit which is defined as mass of one C-12 atom

 

[jamesrc]

Originally posted by himanshu121
I believe u here is atomic mass unit which is defined as mass of one C-12 atom

You mean 1/12 of the mass of one C-12 atom, right?