1. Nuclear Physics
Chapter 29

2. Ernest Rutherford established the
existence of the nucleus through scattering experiments.
Nucleus -
(Nearly spherical, diameter
ranging from 2.6 x m to 16 x m.)
The atom is neutral so the positive charge of the nucleus is equal to the negative charge of the electrons. (If not equal, it is an ion.)
The mass of a carbon atom is the mass of 12 protons, not 6. To account for the excess mass in the nucleus, Rutherford postulated the existence of a neutral particle with the mass of a proton.

3. X Nuclear Notation A Z N (X = chemical symbol)
(mass number: # Nucleons=protons + neutrons) A X Z N
(# Neutrons - usually omitted)
(proton, or atomic number: # Protons – element species)
A: mass number, total of protons + neutrons
Z: proton number (aka atomic number), establishes the species of element in question
N: neutron number
(X = chemical symbol)

4. atoms whose nuclei have the same
III. Isotopes -
atoms whose nuclei have the same
# of protons but different # of neutrons.
A. Same electronic structure \ same
chemical properties.
B. Referred to by mass numbers (total # of nucleons)
i.e. carbon-12, carbon-13, carbon-14 12 6 C 13 6 C 14 6 C
C. Most elements have many isotopes that occur naturally.

5. IX. Total Binding Energy (Eb) -
the amount of
energy released when separate nucleons combine to form a nucleus.
(energy equivalent of mass defect)
Eb = (Dm)c2
=∆m (931.5MeV/1 u)
A. The mass of the nucleus is less than the
sum of its parts.
B. Mass Defect -
mass of the nucleus & the sum of its parts.
the difference between the

6. V. Nuclear Equations
A. The decay process is represented by a
nuclear equation
which is similar to a
chemical equation except it refers to nuclei.
B. Two Conservation Laws
apply to all
nuclear processes.
1. Conservation of Nucleons -
the total
# of nucleons (A) remains constant.
2. Conservation of Charge

7. 1. In 1899 Rutherford discovered that
uranium compounds emit 3 different types of radiation.
2. He separated them by their penetrating ability.
a. Alpha particles (a)
can be stopped by
a sheet of paper or a few cm of air.
(+)
b. Beta particles (b)
can be stopped by a
few mm of aluminum or a few m of air.
(-)
c. Gamma particles (g)
can be stopped by
several cm of lead.
(neutral)

8. VI. Types of Radiation
A. Alpha particles
are doubly (+) charged
particles that contain 2 protons & 2 neutrons.
(Emitted with a specific energy
that depends on the radioactive isotope.)
1. Identical to helium nucleus (4He) 2
2. Since it contains P+ & n, it must come
from the nucleus of an atom.

9. 92U 238 2He + 4 90Th 234 3. When an a particle is ejected, the
parent particle loses 2 p+,
so the
resulting daughter nucleus must be the nucleus of another element.
92U
238
2He + 4
90Th
234
Uranium isotope is transmuted to Thorium by a decay.

10. 90Th 234 91Pa 234 -1e B. Beta particles are high speed electrons and
emitted with a wide range of energies.
1. They are e- emitted by the nucleus.
2. The Mass # is unchanged since the mass
of an e- is a tiny fraction of the atomic mass.
3. The nucleus contains no e-,
so neutron in
nucleus decays into a proton & electron
(unseen neutrino accompanies b decay).
4. The # protons (Z) increases by one.
90Th
234
91Pa
234
-1e +
Thorium emits b particle & becomes protactinium isotope.

11. 1 1 0 0n 1p + -1e a. b- Decay involves the emission of an e-.
Isotopes decay by this method because they have too many neutrons compared to protons to be stable.
0n p e
(basic b- decay)
neutron proton electron

12. 1p 0n + +1e 1 1 0 8O7 15 +1e 7N8 15 b. b+ Decay (Positron Decay) -
too many protons compared to neutrons.
emission of a positron because there are
involves the
1p n e
(basic b+ decay)
proton neutron positron
8O7 15
+1e
7N8 15 +

13. C. Gamma Particles –
high energy photons
emitted with specific energy that depends on the radioactive isotope.
1. Redistribution of charge inside nucleus.
2. Emission of g ray by a nucleus
to the emission of a photon by a de-excited atom.
is analogous
(The nucleus is left in an excited state
after a previous radioactive decay.)

14. 3. Nuclei are thought of as having energy levels
like atomic electrons.
a. Nuclear energy levels are much farther apart
(keV or MeV as compared to a few eV).
b. Gamma rays are very energetic with
frequencies greater than those of X-rays & much shorter wavelengths.

15. 61 * 61 28Ni 28Ni + g nickel nickel gamma excited ray
61 *
nickel nickel gamma
excited ray
4. The * indicates that the nucleus is in an
excited state.
5. The de-excitation process results in the
emission of a gamma ray.
6. The daughter nucleus is simply the parent
nucleus with less energy.

16. unaffected by any external stimulus. A. Activity -
VII. Decay Rate -
unaffected by any external
stimulus.
A. Activity -
# of nuclear decays per second.
1. Decreases with time.
2. Each isotope has own rate of decrease. DN t
= -lN
(Minus indicates N is decreasing.)
3. l = decay constant
- different for
different isotopes
(>l = greater rate
of decay).

17. N = Noe-lt 4. The curve & N are said to decay exponentially
since the graph follows the exponential
function e-lt with time.
e ~ is the base of natural logarithms.
N = Noe-lt
No = initial # nuclei (t=0)
N = # of undecayed parent nuclei left

18. B. Half-life (t½) -
the time for half of the radioactive
sample to decay
(time corresponding to No/2).
N/No = 1/2
1. Decay rate of isotope is often expressed in
terms of its half-life rather than decay constant.
2. The # of decays/second or activity or
decay rate is decreased by half.
3. Decay rate is usually measured to determine
the half-life.

19. N = Noe-lt N/No = e-lt1/2 e-.693 ~ 1/2 t½ = .693/l
N = Noe-(.693t / t1/2)
C. One Curie (Ci)
= 3.70 x 1010 decays/s
(traditional unit).
D. The Becquerel (Bq) is the SI unit.
Bq = 1 decay/s
3.70 x 1010 Bq = 1 Ci