Nuclear Physics Chapter 25. 3 Li lithium 6.941 1 name symbol atomic number (# of p + ) average...
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Transcript of Nuclear Physics Chapter 25. 3 Li lithium 6.941 1 name symbol atomic number (# of p + ) average...
Nuclear Physics
Chapter 25
3Li
lithium6.941
1
namesymbolatomic number (# of p+)
average atomic masselectrons in outer energy level
Protons
positive charge
made of two up quarks and a down quark
Electric charge +2/3 e Electric charge -1/3 e
in the nucleus…
Neutrons
made of two down quarks and an up quark
Li 7
= proton
= neutron
number of nucleons(mass number)
Li 6an isotope of Li
mass number talks about 1 atomatomic mass is an average of all atoms
Mass is usually expressed in amu or u
1 amu = 1/12th the mass of a carbon 12 atom
1 amu = 1.66 x 10-27 kg = mass of p+ or n0
an n0 is actually about 5 x 10-4 u more massivean e- has a mass of about 5 x 10-4 u…hmmm
Mass can also be expressed in MeV/c2
rest energy (E0) = MeV
20
c
Em2
0 mcE
1 proton = 938.3 MeV/c2
Mega (1 x 106) electron volt (1.60 x 10-19 J)
Li73
mass number
atomic number(charge)
The electric force between protons is repulsive
)(2
21
r
qqkF celectric
In a nucleus, there must be a force stronger than the electric force holding the nucleus together
The Strong Force is the force that holds nucleons together.
It is independent of charge, it binds neutrons and protons.
It only works over very small distances (nuclear).
10-15 m rnucleus= (1.2x10-15 m )A1/3 where A is the atomic number
Stable “big” atoms have more neutrons than protons, because the electric force acts over greater distances.
Nucleons bound together in a nucleus have less mass (energy) than unbound nucleons
Ebind = mc2
binding energy is that energy that holds the nucleus together
mass defectthe difference in mass
Find the total binding energy of Al 27 if it has a mass of 26.981534 u. H 1 has a mass of 1.007825 u and the mass of a n0 is 1.008665 u. There are 931.50 MeV/u.
Al is atomic # 13, so it has 13(1.007825 u) of p+ and e-
Al has 14 n0 = 14(1.008665 u)
m = (13.101725 + 14.12131) u – 26.981534 u = .241501 ux 931.50 MeV/u = 225 MeV
= 13.101725 u.
= 14.12131 u
Nuclear Decay
Alpha Decay: an particle (He nucleus) escapes the strong force by quantum tunneling. The nucleus loses 2 p+ and 2 n0.
Pb21282 He4
220880Hg
Beta decay: the weak force causes an up quark to change into a down quark, or vice versa. This causes a proton to change into a neutron or vice versa.
epn 01
11
10
neutron proton electron-
antineutrino
enp 01
10
11
proton neutron positron+
neutrino
A thallium 208 nucleus emits a - particle (an electron). Write the equation.
Tl20881 e01
20882 Pb
Gamma Decay: a nucleon can be in an excited state, needing to get rid of energy to reach a stable energy level. The nucleon emits a photon, but the structure of the nucleus stays the same.
CC 146
146