Nuclear Physics

Vocabulary

alpha particle - positively charged particle consisting of two protons and two neutrons. (Helium nucleus)

atomic mass number (A) - the number of protons and neutrons in the nucleus of an atom.

atomic mass unit - the unit of mass equal to 1/12 the mass of a carbon-12 nucleus; the atomic mass rounded to the nearest whole number is called the mass number.

atomic number (Z) - the number of protons in the nucleus of an atom.beta particle - high speed electron emitted from a radioactive element

when a neutron. decays into a protonbinding energy - the nuclear energy that binds protons and neutrons in

the nucleus of the atom.element - a substance made of only one kind of atom.isotope - a form of an element which has a particular number of neutrons,

that is, has the same atomic number but a different mass number than the other elements which occupy the same place on the periodic table.

Vocabulary

mass defect - the mass equivalent of the binding energy in the nucleus of an atom by E = mc2

neutron - an electrically neutral subatomic particle found in the nucleus of an atom

nuclear reaction - any process in the nucleus of an atom that causes the number of protons and/or neutrons to change

nucleons - protons or neutronsstrong nuclear force - the force that binds protons and neutrons together

in the nucleus of an atomtransmutation - the changing of one element into another by a loss of gain

of one or more protons

Equations, symbols and units

E m c 2

Three units for mass :

1u1.661x10 27kg931.5MeVc 2

XAZ

where E = binding energy of the nucleusΔm = mass defect of the nucleusc = speed of light = 3 x 108 m/su = atomic mass unitX = element symbolA = atomic mass number (number of protons and neutrons)Z = atomic number (number of protons)

Find the number of protons, electrons and neutrons in a neutral atom of iron.

Fe5626

# protons

# protons + #neutrons

26 protons

30 neutrons

neutral → #protons = # electrons = 26

M2M1

Before After

M 5

M4

M3

Eo Ef=<Mo Mf=>

Eo = Ef + (Mo-Mf)c2

Eo = Ef + (Δm)c2

MASS is transferred to ENERGY

N147 p

ppppppn nn

nn

n n

N147

ppppppp

n nnn

nn n

Mass defect is responsible for the binding energy. Ebinding = (Δm)c2

Transmutation of nitrogen into carbon

714N0

1n 614C

Nuclide/particle Mass (u)

14.0031

neutron 1.008664

14.003241

proton 1.007825

14N

14C

Nuclear fusion – The joining of two small nuclei to form one big one.

Nuclear fission – Splitting a large nuclei to two smaller nuclei.

Binding energy per nucleon vs. mass number

Binding energyPer nucleon

(MeV)

Mass number

Fusion Examples:

Nuclide Mass (u)

1.007825

2.014101

3.016049

3.016029

4.002603

1.008664

1H

3He

3H

2H

4Hen10

12H1

3H 24He0

1n

12H1

2H 23He0

1n

12H1

2H 13H1

1p

12H2

3He 24He1

1p

Fission Example:

If splits into and , how many neutrons will be produced? Calculate the energy released in this reaction.

236U

100Mo

126Sn

Z symbol A Mass (u)

92 U 236 236.045563

42 Mo 100 99.907476

50 Sn 126 125.907653