How to calibrate gamma rays

1. Presented by- KANGKAN DAS
Dr. B. BOROOAH CANCER
INSTITUTE (RCC), GUWAHATI a grant-in-aid Institute
of DEPERMENT OF ATOMIC ENERGY,GOVT.OF INDIA
and unit of Tata Memorial Centre , MUMBAI.

2. TABLE OF CONTAIN
Beam calibration in Co⁶⁰ gamma ray beam
- Aim of the experiment
- Equipment
- Dosimetry equipment
- Reference condition
- determination of absorbed dose under
reference condition
-Work sheet

3. AIM
 Output calibration of C0⁶⁰
with the help of using
IAEA TRS- 398 Protocol
is all procedures that
ensure consistency of
the medical prescription,
and safe fulfillment of
that prescription, as
regards the dose to the
target volume, together
with minimal dose to
normal tissue, minimal
exposure of personnel
and adequate patient
monitoring aimed at
determining the end

4. EQUIPMENT REQUREMENTS
WATER PHANTOM
IONIZATION CHAMBER
ELECTROMETER
BAROMETER
THERMOMETER
CONNECTING CABALE
SPRIT LEVEL

5. WATER PHANTOM
Water is recommended in
the IAEA Codes of Practice
TRS-398 as the
reference medium for
measurements of absorbed
dose for both photon and
electron beams and the
same is recommended in
this Code of Practice. The
phantom should extend to
at least 5 cm beyond all
four sides of the largest

6. field size employed at
the depth of
measurement. There
should also be a
margin of at least 5 g/
cm² beyond the
maximum depth of
measurement
in which case it should
extend to at least 10 g
cm-².
Extend 5cm – four sides
–field size – at depth of
measurement

7. IONIZATIN CHAMBER
The recommendations
regarding ionization
chambers given in Section
should be followed. Its size
0.6 cm³ Both cylindrical
and plane-parallel
ionization chambers are
recommended for use as
reference instruments for
the calibration of
COBALT⁶⁰ However, the

8. combined standard uncertainty in
Dw for plane parallel ionization
chambers will be slightly higher
than for cylindrical chambers due to
their higher uncertainty for pawl in
the 60Co reference beam quality .
with qualities at the reference depth
R res ≥ 0.5 g cm-2. Graphite walled
cylindrical chambers are preferable
to plastic walled chambers because
of their better long term stability
and smaller chamber to chamber
variations . The reference point for
these chambers is taken to be on the
central axis of the chamber at the
centre of the cavity volume; this
point is positioned at the reference
depth in the phantom.

9. PC ELECTROMETER
The Ultimate in Portable
Reference Dosimetry PC
Electrometer is a dual
channel reference class
electrometer for absolute
dose calibration. The system
is designed for accuracy and
convenience. It offers small
size (0.4 kg), near no warm-
up time (< 1 minute), and
complete operation through
USB, with no batteries or
external power connections.

10. Features and Benefits
• Reference class Dosimetry for
absolute dose calibration
• Two independent measurement
channels
• Lightweight and portable; only 0.4
kg
• USB powered — no batteries or
power cord
• Fully configurable and intuitive
software interface
• Interfaces directly with the Sun
Nuclear 1D SCANNER™
• Less than 1-minute warm-up time
• Single USB cable connection
• Fast 500 ms sampling interval
• Detector library

11. Barometer
A barometer is a scientific instrument
used in meteorology to
measure atmospheric pressure. Pressure
tendency can forecast short term changes
in the weather. Numerous measurements
of air pressure are used within surface
weather analysis to help find
surface troughs, high pressure systems
and frontal boundaries.
Barometers and pressure altimeters, (the
most basic and common type of
altimeter) are essentially the same
instrument, but used for different
purposes. An altimeter is intended to be
transported from place to place matching
the atmospheric pressure to the
corresponding altitude, while a
barometer is kept stationary and
measures subtle pressure changes caused
by weather. The main exception to this
is ships at sea, which can use a barometer
because their elevation does not change.

12. Thermo meter
Laboratory thermometers
are used to measure
temperatures or temperature
changes with a high degree
of precision. They are made
of metal or glass and
strengthened through
thermal tempering or
annealing.
The way a laboratory
thermometer works depends
upon its type. They are
generally a liquid-in-glass
device, a bimetallic strip, an
electronic thermistor
thermometer, or infrared
(IR) device.

13. Connecting wire
A wire is a single, usually cylindrical
flexible strand or rod of metal. Wires
are used to bear
mechanical loads or electricity and t
elecommunications signals . Wire is
commonly formed by drawing the
metal through a hole in a die or draw
plate. Wire gauges come in
various standard sizes, as expressed
in terms of a gauge number. Wire
comes in solid core, stranded, or
braided forms. Although usually
circular in cross-section, wire can be
made in square, hexagonal,
flattened rectangular, or other cross-
sections, either for decorative
purposes, or for technical purposes
such as high-efficiency voice
coils in loudspeakers. Edge-wound[1]
coil springs, such as the Slinky toy,
are made of special flattened wire.

14. Spirit level
A spirit level,
bubble level or simply
a level is an instrument
designed to indicate
whether a surface is
horizontal (level) or vertical
(plumb). ... These vials are
incompletely filled with a
liquid, usually a mercury
colored spirit or alcohol,
leaving a bubble in the tube.

15. Doesimetry equipment
Recommended reference instrument for calibration
-cylindrical and plane-parallel camber
In cylindrical – chamber axis at the centre of the cavity
volume
In plane-parallel- inner surface of the entrance window
at its centre .
 THE REFERENCE POINT SHOULD BE POSITIONED
AT THE REFERENCE DEPTH IN A WATER
PHANTOM

16. INFLUENCE Reference value or reference characteristics
Phantom material water
Cylindrical type Cylindrical or Plane-parallel
Measurement of zref
5g cm-² ( or 10g cm-²)
Reference point of
chamber
for cylindrical chambers, on the central axis at
the centre of the cavity volume.
For plane-parallel chambers, on the inner
surface of the window at its centre
Position of reference
point of chamber
for cylindrical and plane-parallel chambers, at
the measurement depth z ref
SSD or SCD 8o cm or 100 cm
Field size 10cm x 10cm²
REFERENCE CONDITIONS FOR THE DETERMINATION OF ABSORBED DOSE TO
WATER IN Co⁶⁰ GAMMA-RAY BEAMS

17. Determination of the absorbed dose to water
After the positioning of the chamber according to the reference conditions, the
absorbed dose to water is given by
Dw=MR ×NDW × KTP × KPOL × KS × KQQ0
PDD × (T +δt)
where MQ is the reading of the dosimeter incorporating the product ki of
correction factors for
influence quantities, and kQ,Qo is the correction factor which corrects for the
difference between the
reference beam quality Qo and the actual quality Q being used. This equation is
valid for all the
radiation fields for which the present Code of Practice applies.
DW,Q = DW , KQ, Q0 = KQ ( which has a value of unity)
and ND,W,Q0 = ND,W.

18. then we have,
DW = MQND,W.
Here,
MQ = corrected meter reading which includes kTP Kpol,
K sat where
KTP, which is the correction factor for temperature
and pressure given by,
KTP = (273.2 + T) Po/ (273.2 + To)P
To = 20oC ; Po = 760 mmHg

19. Kpol, which is the factor to correct the response of an
ionization chamber for the effect of change in polarity of
the polarizing voltage applied to the chamber given by
K pol = |M+| + |M-|/2M
M+ = meter reading for +300V
M - = meter reading for -300V

20. Ksat, factor to correct the response of an ionization chamber for
the lack of complete charge collection given by-
Ksat = (V1/V2)^2 – 1/ (V1/V2)^2 – (M1/M2)
V1 = voltage (+300V)
V2 = voltage (+150V)
M1 = meter reading for voltage V1(+300V)
M2 = meter reading for voltage V2(+150V)
The Ksat for a pulsed beam is given by,

21. Ksat = ao + a1(M1/M2) +a2(M1/M2)^2
Where a0, a1 and a2 are constants and the values
are-
2.303, -3.636 and 2.299 respectively.

22. Ks , Factor to correct the response of an ionization chamber for
the lack of complete charge collection (due to ion recombination).
KQ,Qo, Factor to correct for the difference between the response of an
ionization chamber in the reference beam quality Qo used for calibrating the
chamber and in the actual user beam quality, Q. The subscript Qo is omitted
when the reference quality is 60Co gamma radiation (i.e., the reduced notation
kQ always corresponds to the reference quality 60Co).
PDD , Percentage depth-dose.
MR is the dosimeter reading corrected for influence quantities, in order to
correspond to the
T exposure time
δ Time error
NDW Chamber calibration factor 5.377×10 ⁷

23. • Calibrations may be carried
out either directly against a
primary standard of absorbed
dose to water at
• a PSDL or, more commonly,
against a secondary standard
at an SSDL.
• It is assumed that the
absorbed dose to water, Dw,
is known at a depth of 5 g
cm-2 in a water phantom
• for 60Co gamma rays. This is
realized at the SSDL by
means of a calibrated cavity
ionization chamber,
• performing measurements in
a water phantom. The

24. • user chamber is placed with its reference point at
a
• depth of 5 g cm-2 in a water phantom and its
calibration factor ND,w is obtained from
ND,W = DW∕ M
• reference conditions for which the calibration
factor is valid. Reference conditions recommended
for
• the calibration of ionization chambers in C0⁶⁰

25. Worksheet

26. KTP= (1.027714 +T) × P
(1.027714 +T) Po
= (1.O27714+24.2°C) × 1013.2
(1.027714+20°C) 1000
= 1.199736405 × 1.0132
=1.21572926
MR= 73.46 nc
DW= 14.83×10¯⁹×100
56.50×1.007
= 14.83×10¯⁹ ×1.21557×5.37×10×100
56.5× 1.007
=81.43
56.89
= 1.4331 GY/Min
= 143.31 cGY/Min