1. Dr. Kamal K. Ali
University of Baghdad
College of science
Geology
2nd year
Radioactivity & Isotopes geology
Lecture 1
• Atom stracture.
• Nuclides
• Elements , isobars, isotones, isotopes

2. Matter is made up of
very small particles
called atoms
• Each atom has a
very small and very
dense core called
nucleus.
• Most of the mass
of atom is contained
in the nucleus
• A proton has a unit positive charge.
• A neutron is an uncharged particle.
• An electron has a negative charge.

3. • The electrons move in orbits
around the nucleus.
• There are a lot of empty
spaces within atom • A
Atom nucleus consists of a number
of protons and neutrons.
• Protons and neutrons also
known as mass number
(nucleons).
Nucleus Z electrons
Z protons
Nucleus structure
A
Z
X A mass number (nucleons) = Z + N
N neutrons

4. Dimentions Diameter of Nucleus is
and range of 1.75 fm- 15 fm
fm=10-15m
Distance
1cm
100m
500m

5. Neutron slightly heavier than proton
Masses Mass n=1.67495x10-27 Kg
Mass p= 1.67265x10-27 kg
Mass p> mass e about 1836 times
Suppose the mass of the electron
1g…
… then the mass of the nucleus is
108 Tonnes

6. What is nuclide?
• A nuclide is an atom of a particular structure.
Each element has nucleus with a specific
number of protons.
A
• Nuclide notation
12
• Example 6C , ZX1
• Proton 1p , Neutron 0 n , electron -1e
1 0

7. Elements- Isotopes-Isobar
Number of p (Z) = atomic number. It
determines the chemical element.
Ex. Z=92 is Uranium, Z=90 is Thorium
Z= 86 Radium Z=27 Cobalt
Number of Neutron (N)
Mass number OR nucleon number(A)=Z+N
Number of electron=number of proton(It
impacts chemical reaction)

8. • Thommson,1914, Aston, 1919:
(There are different mass number(A) for a
given (Z) for an element. That is mean they
have different (N)……..THEY ARE ISOTOPES.
Isotopes: Greek phrase : isos topos meaning :
“The same place” isotopes of the same
elements occupy the same position in
periodic table.

9. Isotopes

11. Oxygen (3 isotopes)
17
Nucleon number = 17
Atomic number = 8
Nucleon number = 16
Atomic number = 8
Nucleon number = 18
Atomic number = 8

12. Hydrogen (3 isotopes)
Nucleon number = 2
Atomic number = 1
Nucleon number =1
Atomic number = 1
Nucleon number = 3
Atomic number = 1

13. • Isotopes either stable or
unstable(radioactive)
59
• Co : stable isotope;
60
• Co: radioactive(radioisotope)

14. Nuclides with same mass(nucleon)
numbers(A)but with slightly
different # of protons(Z).
87
• Ex: Rubidium 37Rb&Strontium38Sr.
87
12 12
• Carbon -12 6C and Boron-12 5B

17. 3 basic Location charge comments
particles
proton
neutron
Electron

18. Number of No. of No. of
Term (Z) (A) (N)
isotopes
isobars
isotones

22. • Isotopes either Stable or
Unstable(Radioactive)
59
• Co, H, H, O, O :
1 2 16 18
Stable Isotopes;
60
• Co, H,: Radioactive
3
(Radioisotope)

23. Radioactivity
• Radioactivity was discovered and studied by Henri
Becquerel and then Pierre and Marie Curie from 1896
to 1902.
• Radioactivity is the phenomenon by which certain
nuclei transform (transmute) spontaneously into
other nuclei and give off particles or radiation to
satisfy the laws of conservation of energy and mass.
• Proton is made of pieces called quarks(2up, 1down).
• When proton breaks apart it produces high energitic
pieces.
• So radioactivity is explosion of the nucleus of an
atom.

24. Radioactivity and Radiation
• When we have a radioactive nucleus exploding,
the pieces is going flying out with energy a
typically have 1 MeV. And some with 2MeV.,
WHILE IN CHEMICAL REACTION of hydrogen
and oxygen the energy product about 1 eV.
• This the dangerous of radioactivity and this is
the advantage of radioactivity.
• The pieces come out when a nucleus explode
we called them
radiation.(radioactivity=explosion,
Radiation=pieces come out).

25. Lecture 3: Mechanism of radioactive
decay and types of radiation
• Radioactive decay is a nuclear process and is
independent of chemical and physical states of
nuclide. It depends on the neutron/proton ratio
and on the mass-energy relationship of the
parent, daughter and emitted particles.
• For the nuclides of low atomic mass, the greatest
stability is achieved when the number of
neutrons and protons are approximately
equal(N=Z), but as atomic mass increase, the
neutron/proton ratio increase until N/Z=1.5

26. Lecture 2: Radioactivity and Stability
Elements for which Z is an
even number have far more
isotopes than elements for
which Z is an odd number.
Fluorine (Z=9), sodium
(Z=11), phosphorus (Z=15),
and scandium(Z=21) have
just a single isotope.
The distribution of natural stable isotopes in the neutron–proton
diagram. After N=20, the zone of stable nuclei moves away from the
diagonal for which the number of neutrons equals the number of
protons. For N>20, the number of neutrons then exceeds the number of
protons. This zone is called the valley of stability as it corresponds to a
minimum energy level of the nuclides.

27. Mechanism of radioactive ,Type of Radiation
4
1-Alpha particle (a helium nucleus 2He)
• For the nuclides of high atomic mass such as
U-238 are unstable. U-238 have 146
neutrons and 92 protons. So its nucleus
emits Alpha particles (α) to reach the
stability. Alpha particle is (two protons and
two neutrons) positive charge(+2). In this
case number of protons and neutrons in the
nucleus reduces by two for each. So it
becomes 90 proton and 144 neutron and the
new nuclide is Thorium-234. we can express
it as follow:
234
92U α + 90Th 2:146 2:92
238 4
2

28. Alpha particles
• The particles have large kinetic energies but
are rapidly slowed down by collisions with
other atomic nuclei. At thermal energies they
soon gain two orbital electrons and become
indistinguishable from other helium atoms.
• The average distance travelled in solid rock
before this occurs is measured in fractions of a
millimeter.

29. Beta-minus particle
• Alpha emission produces nucleus rich in neutrons and
deficient in protons and still unstable. So a neutron
disintegrates into a proton and an electron. The electron
expelled from the nucleus as a negative particles called Beta
particle(β-), They differ from other electrons only in having
higher kinetic energies. To satisfy the law of conservation of
energy and mass, it is assumed that the nucleus emits energy
particles has no mass nor charge called an antineutrino along
with the electron. The decay equation is written :
1 1
• 0n p + β- + v
1
• neutron -------------- proton + electron + antineutrino.
• So in Th-234 it decays to Pa-234 by emitting β- as follow:
234 234
90 Th 91 Pa + β- + v

30. Gamma ray
• In many cases the nuclide produced by beta
minus decay is left in an exited state, which
subsequently decay to the ground state nuclide
by release of energy. This may be lost as gamma
(γ) ray(electromagnetic ray) of discrete energy.
A A
z
P* z
P + e- (mission of photon)
• The metastable state or “ Isomers” of the
product nuclide are denoted by super fix ‘m’

31. Beta-plus and electron capture
• Nuclides deficient in neutrons e.g. K-38 may
decay by two different processes:
 positron emission
Electron capture.
Both processes yield a product nuclide that
isobar of the parent, by transformation of a
proton into neutron
1 1
p n + β+ + v
1 0
proton neutron + β+ + neutrino

32. Electron capture
• A nuclear proton is transform into a neutron by capture
of an orbital electron, usually from the inner shells.
1 1
p + e- n + β+ + v
1 0
Outer orbital electron falls into the vacancy produced by
electron capture, emitting a characteristic X-ray. The
product nucleus may be left in exited state, in which
case it decays to the ground state by gamma emission
(γ).
Gamma rays and X- rays are both electromagnetic rays ,
they are differ where they are produced.

34. Isotopes measurement
The Mass Spectrometer (MS)
• “There would be no isotope geology without MS”.
• The principle of MS.
 Atoms of the chemical element whose isotopic
composition is to be measured are ionized in a vacuum
chamber.
 The ions produced are accelerated by using a potential
difference of 3-20 kV.
 This produces a stream of ions , and so an electric
current.
 This electric current is passed through a magnetic field.

35. Isotopes measurement
The Mass Spectrometer (MS)
The magnetic field exert a force perpendicular
to the electric current and so bends the beam
of ions.
The lighter ions are deflected more than the
heavier ones and so the ions can be sorted
according to their mass.
So, the relative abundance of each isotope can
be measured from the relative values of the
electron currents produced by each stream of
ions separated out by this way.

36. The Mass Spectrometer (MS)
1. The source: 2. Magnet: It deviates the ions and
To generate ions from atoms. this deflection separates them by
To accelerate the ion by potential mass.
differences. 3. Collectors: collect and integrate
To shape the beam, through the ion charges so generating an
calibrated slits in the high electric current.
voltage plates. all of which are maintained under vacuum.

37. Short Quiz
• Decide which of these nuclei are stable or
unstable:
235 223 12 24
1. 92 U 2.88 Ra 3. C 4. Mg
6 12
128 22
5. 53 I 6. 10Ne

38. Isotopes measurement
The Mass Spectrometer (MS)
• Suppose atoms of the element in question
have been ionized. The ion acceleration is:
2
eV =1/2mν eV : electric energy
2
e:ion charge 1/2mν : kinetic energy
m: mass of the ion
ν: its speed…………….then
1/2
ν = (2eV/m)

39. The Mass Spectrometer (MS)
• Magnetic deflection is given by equating the
magnetic force Beν to centripetal acceleration
(ν2/R)multiplied by mass m, where B is the
magnetic field and R the radius of curvature of
the deflected path:
Beν=(ν2/R)m……where B=magnetic field
Note: when a charge particle moves through a
magnetic field: Magnetic force
 F= magetic field(B) X electical charge(e) X its
velocity(ν)………THEN:
νBeR= ν2m

40. The Mass Spectrometer (MS)
ν= BeR/m ….. Then
1/2
BeR/m= (2eV/m)
 B2 e2 R2/m2= 2eV/m …. B2 e2 R2m= m22eV
m/e= B2R2/2V
In which B in tesla, R in meters, m in atomic
mass, and V in Volts.
Atomic mass unit m= 1.6605402 X10-27 kg
Electron charge e = 1.60219 X10-19 coulombs

41. Exercises
• A mass spectrometer has a radius of 0.3m and
an acceleration voltage of 10 000 V. The
magnetic field is adjusted to the various
masses to be measured. Calculate the atomic
mass corresponding to a field of 0.5 T.
• Answer: Just apply the formula with suitable
units:
• m= (B2R2/20721V) X 1012 =
(0.5)2x(0.3)2x1012/20721x10000=108.58

42. Exercises
• If hydrogen ions (mass number=1) are
accelerated with a voltage of 10 kV, at what
speed are they emitted from the source?
1/2
• Answer Just apply the formula : ν = (2eV/m)
Atomic mass unit m= 1.6605402 X10-27 kg
Electron charge e = 1.60219 X10-19 coulombs
ν= (1.9272x1012)1/2 = 1388 km/s

43. Ionization techniques
1. Thermal-ionization mass
spectrometry.
2. Electronic bombardment.
3. Inductively coupled plasma mass
spectrometry(ICP-MS).
4. Ionic bombardment in secondary
ion mass spectrometry(SIMS)

44. Short Quiz
• Two of the isotopes of the element whose
atomic number is 10 have mass numbers of 20
and 22.
• Write the symbol of each isotope.
– How many protons does each of the isotopes
have?
– How many neutrons does the isotope with mass
number 20 have? How about for the other one?

45. R = Abundance of Heavy isotope (rare)/ abundance of light
isotope

46. sample standard
standard

49. 3
Tritium H
• Tritium H values reported as
3
absolute concentration called Tritium
Unit (TU), where on TU
corresponded to I tritium atom per
108 hydrogen atoms. Tritium values
may also be expressed in terms of
activity (pCi/l), where
1TU= 3.2 pCi= 7.2 dpm/l