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1. FUNDAMENTAL OF RADIOACTIVITY
Ravish Yadav

2. TOPICS
• RADIONUCLIDE
• PROPERTIES OF RADIONUCLIDE
• RADIOISOTOPE
• RADIOACTIVE DECAY
• HALF LIFE OF RADIOACTIVITY
• SPECIFIC ACTIVITY
• BECQUREL
• CURIE
• SIEVERT AND GRAY
• RADIONUCLIDE PURITY
• RADIOCHEMICAL PURITY
• COUNTING TECHNIQUES – GEIRGER –MULLER AND LIQUID
SCINTILLATION
• SAFETY ASPECTS

3. • The alpha particle is a helium nucleus; it consists of two protons and
two neutrons. It contains no electrons to balance the two positively
charged protons.
• Alpha particles are therefore positively charged particles moving at
high speeds.
• Beta particles are emitted by neutron rich unstable nuclei

7. Radionuclide
• It is a nuclide which is radioactive (i.e. radiation is emitted by the
spontaneous transformation of the nucleus) the transformation may
involve emission of charged particles ( alpha and beta) which may be
accompanied by the emission of gamma radiation.
• Isotopes are nuclides of the same element
• i.e. with same atomic number (A) but different no. of neutrons and
hence different mass number (Z).

8. Ideal properties of Radionuclide

9. • 1. A) Suitable half-life : i.e. a few hours, such that a reasonable dose can
be admin to the patient, counting can be done within an hour or so with
good counting statistics. Radioactivity will then decay away within a day
so that radiation dose to the patient is minimised.
• B) pure gamma emitter of suitable energy. Range 100-200 KeV is
optimal.
• C) radionuclide must be capable of being produced daily in hospital
pharmacy
• D) radionuclide must be capable of being converted to a range of
chemical entities for imaging a range of organs.
• 2. pharmaceutical properties : normal requirements for an injection
must be applied (eg : sterility, apyrogenicity, pH)
• 3. chemical properties : correct chemical form is required for targetting
the required organ.

10. Radioactive DECAY

11. RADIOACTIVE DECAY
• ALPHA particle decay: many isotopes of elements with high atomic
no. contain too many nuclear particles to be stable..hence to become
stable, the nucleus must eject some of these particles, and the
resulting spontaneous emission of 2 neutrons and 2 protons together
(ie HELIUM) is called alpha particle decay

12. Beta decay
• Types : negatron emission – converting neutron into a proton and
producing electron also to retain electroneutrality.
• Positron emission – here a proton is converted into a neutron with
production of electron to retain electroneutrality.
• Electron capture – nucleus captures electron leading to vacancy in
valence shell. Which is immediately filled with electron from next
shell. Energy liberated lies in the X ray region hence what is actuallly
measured for EC is emission of X rays

14. Gamma radiation - the alpha and beta particles leave
daughter nucleus in excited state, hence the nucleus
will lose its energy in the form of a short wavelength
radiation called GAMMA radiation

16. Half life of Radioactivity
• Defination: it is the time taken for the activity of the sample to be
reduced to half its initial value.
• That is : Ao to be reduced to Ao/2…. For Ao/2 to be further reduced
to Ao/4

17. GRAPHICAL PRESENTATION ( IT NEVER TOUCHES
THE X-AXIS SINCE MATTER DOESN’T GET
DESTROYED )

18. EXAMPLE
• Cal number of radioactive atoms remaining after 40 seconds for an
isotope of T 0.5= 10 sec. where initial no. of radioactive atoms = 1600
• To find : N Given: Ao = 1600
• Solution: after 10 sec, N=1600/2 =800
• after 20 sec, N=800/2 = 400
• after 30 sec, N=400/2 = 200
• after 40 sec, N=200/2 = 100
Hence,no. of radioactive atoms remaining after 40 sec = 100.

19. SPECIFIC ACTIVITY
• There are experimental difficulties of working with quantities like
0.000000000000001 g
• Hence in most experiments, active isotope is mixed with inactive
material which are called CARRIERS
• Sample of pure radioisotope, undiluted is called Carrier-FREE
• Sometimes this carrier is added deliberately for chemical manipulation.
Also it is difficult to obtain a carrier free preparation.
• It is necessary to define not just isolated conc of radioisotope, but its
total conc along with the carrier. This is called SPECIFIC ACTIVITY.
• Units : Bq mol-1 or Bq g-1 (solids) and Bg dm-3 (soln)

20. Becquerel and Curie
• Becquerel : it is defined as as the quantity of radioactive material in
which one nucleus decays per second.UNIT : per second or sec-1
• Curie : 1 Ci = 3.7 × 10 raised to 10 decays per second

22. Sievert and Gray
• Gray is defined as the generation of 1 J Kg-1. the unit of absorbed dose is
the Gray (Gy)
100 rad = 1 gray
• Siervert (sv) is defined as grays * RBE.
(RBE = relative biological effectiveness)
RBE = 10 for alpha particles ; 1 for beta and gamma

23. Relative biological effectiveness
• In radiobiology, the relative biological effectiveness (often
abbreviated as RBE) is the ratio of biological effectiveness of one type
of ionizing radiation relative to another, given the same amount of
absorbed energy. The RBE is an empirical value that varies depending
on the particles, energies involved, and which biological effects are
deemed relevant. It is a set of experimental measurements.
• In dosimetry (the practical attempt to apply RBE realistically and
uniformly to human and animal experience), the RBE is represented
in regulations by the radiation weighting factor (WR)

24. • Different types of radiation have different biological effectiveness
mainly because they transfer their energy to the tissue in different
ways.
• Photons and beta particles have a low linear energy transfer
coefficient, meaning that they ionize atoms in the tissue that are
spaced by several hundred nanometers (several tenths of a
micrometer) apart, along their path.
• In contrast, the much more massive alpha particles and neutrons
leave a denser trail of ionized atoms in their wake, spaced about one
tenth of a nanometer apart (i.e., less than one-thousandth of the
typical distance between ionizations for photons and beta particles).

26. Radionuclide purity
• This is defined as the percentage of total radioactivity due to the
specified radionuclide.
• Eg : Sodium iodide (I 125) should not have I 126 present to an
amount greater than 1%.
• The standard method of determining radionuclidic purity is by
gamma-spectroscopy, where gamma ray emissions can be used to
detect and quantify impurity levels.

27. Radiochemical purity
• This is defined as the amount of radioactivity in the specified chemical
form expressed as a percentage of total radioactivity.
• For eg : radiochemical impurity in sodium idoide ( I125) would be iodate
ion ( IO3-)
• Here radioactivity is associated with chemical form (iodate) which is
different from specified chemical form (iodide)
• Radiochemical purity can change with time due to radiation induced
decomposition where, H+ and OH- radicals produced attack radioactive
material, producing other chemical species.
• Radiochemical purity can be determinded by chemical separation
method and measurement of radioactivity in separated fracions.
• Methods : TLC, HPLC

28. Counting techniques
•Geiger muller
•Liquid scintillation