This document discusses concepts and instruments used in dosimetry. It defines key terms like absorbed dose, exposure, and kerma. It explains dosimetry protocols like TG-51 and TRS-398 which provide standards for calibrating dosimeters. Common dosimeters discussed include ionization chambers like thimble chambers and parallel-plate chambers, as well as Geiger-Muller counters. Calibration of dosimeters involves various correction factors to account for influences like temperature, pressure and polarity.
Dosimetric Evaluation of High Energy Electron Beams Applied in RadiotherapyAYMAN G. STOHY
Electron-beam therapy: is used to treat superficial tumors at a standard 100 cm source-to-surface distance (SSD). Characteristics of electron beams from an Elekta PreciseTM linear accelerator are presented at a nominal SSD of 100 cm. However, certain clinical situations require the use of an extended SSD. The effects of extended source-to-surface distance (SSD) on the electron beam dose profiles were evaluated for various electron beam energies 6, 8, 10,12 and 15 MeV and the accuracy of various output correction methods was analyzed on an Elekta PreciseTM linear accelerator using a radiation field analyzer (RFA). Effective SSDs was evaluated for field sizes ranging from 6×6, 10×10, 14×14 and 20×20 cm2 for various energies.
Aim of the work
1.Investigate the physical properties of electron beams
at different beam energies.
2.Evaluate the accuracy of dose calculated by
Treatment Planning System (TPS) and measured for
different field configurations.
TISSUE PHANTOM RATIO - THE PHOTON BEAM QUALITY INDEXVictor Ekpo
TPR(20,10) is the recommended photon beam quality index by IAEA TRS-398 for megavoltage clinical photons generated by linear accelerators. This presentation goes through the basics of Tissue Phantom Ratio (TPR).
Dosimetric Evaluation of High Energy Electron Beams Applied in RadiotherapyAYMAN G. STOHY
Electron-beam therapy: is used to treat superficial tumors at a standard 100 cm source-to-surface distance (SSD). Characteristics of electron beams from an Elekta PreciseTM linear accelerator are presented at a nominal SSD of 100 cm. However, certain clinical situations require the use of an extended SSD. The effects of extended source-to-surface distance (SSD) on the electron beam dose profiles were evaluated for various electron beam energies 6, 8, 10,12 and 15 MeV and the accuracy of various output correction methods was analyzed on an Elekta PreciseTM linear accelerator using a radiation field analyzer (RFA). Effective SSDs was evaluated for field sizes ranging from 6×6, 10×10, 14×14 and 20×20 cm2 for various energies.
Aim of the work
1.Investigate the physical properties of electron beams
at different beam energies.
2.Evaluate the accuracy of dose calculated by
Treatment Planning System (TPS) and measured for
different field configurations.
TISSUE PHANTOM RATIO - THE PHOTON BEAM QUALITY INDEXVictor Ekpo
TPR(20,10) is the recommended photon beam quality index by IAEA TRS-398 for megavoltage clinical photons generated by linear accelerators. This presentation goes through the basics of Tissue Phantom Ratio (TPR).
In 2000 IAEA published another International Code of Practice.
“Absorbed Dose Determination in External Beam Radiotherapy” (Technical Report Series No. 398)
Recommending procedures to obtain the absorbed dose in water from measurements made with an ionisation chamber in external beam radiotherapy (EBRT).
In 2000 IAEA published another International Code of Practice.
“Absorbed Dose Determination in External Beam Radiotherapy” (Technical Report Series No. 398)
Recommending procedures to obtain the absorbed dose in water from measurements made with an ionisation chamber in external beam radiotherapy (EBRT).
Seminar on Uv Visible spectroscopy by Amogh G VAmoghGV
PPT of seminar on UV Visible spectroscopy, electronic transitions, Instrumentation of Double beam spectrophotometers, Advantages of Double beam over single beam, Beer Lamberts law derivation
Measurement of energy loss of light ions using silicon surface barrier detectoreSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Antenna chamber EMC chamber design guidelines...EMC test equipment for EMC compliance relevant standards ....antenna chamber design guidelines absorbers design development and test procedures
Global launch of the Healthy Ageing and Prevention Index 2nd wave – alongside...ILC- UK
The Healthy Ageing and Prevention Index is an online tool created by ILC that ranks countries on six metrics including, life span, health span, work span, income, environmental performance, and happiness. The Index helps us understand how well countries have adapted to longevity and inform decision makers on what must be done to maximise the economic benefits that comes with living well for longer.
Alongside the 77th World Health Assembly in Geneva on 28 May 2024, we launched the second version of our Index, allowing us to track progress and give new insights into what needs to be done to keep populations healthier for longer.
The speakers included:
Professor Orazio Schillaci, Minister of Health, Italy
Dr Hans Groth, Chairman of the Board, World Demographic & Ageing Forum
Professor Ilona Kickbusch, Founder and Chair, Global Health Centre, Geneva Graduate Institute and co-chair, World Health Summit Council
Dr Natasha Azzopardi Muscat, Director, Country Health Policies and Systems Division, World Health Organisation EURO
Dr Marta Lomazzi, Executive Manager, World Federation of Public Health Associations
Dr Shyam Bishen, Head, Centre for Health and Healthcare and Member of the Executive Committee, World Economic Forum
Dr Karin Tegmark Wisell, Director General, Public Health Agency of Sweden
The dimensions of healthcare quality refer to various attributes or aspects that define the standard of healthcare services. These dimensions are used to evaluate, measure, and improve the quality of care provided to patients. A comprehensive understanding of these dimensions ensures that healthcare systems can address various aspects of patient care effectively and holistically. Dimensions of Healthcare Quality and Performance of care include the following; Appropriateness, Availability, Competence, Continuity, Effectiveness, Efficiency, Efficacy, Prevention, Respect and Care, Safety as well as Timeliness.
QA Paediatric dentistry department, Hospital Melaka 2020Azreen Aj
QA study - To improve the 6th monthly recall rate post-comprehensive dental treatment under general anaesthesia in paediatric dentistry department, Hospital Melaka
Antibiotic Stewardship by Anushri Srivastava.pptxAnushriSrivastav
Stewardship is the act of taking good care of something.
Antimicrobial stewardship is a coordinated program that promotes the appropriate use of antimicrobials (including antibiotics), improves patient outcomes, reduces microbial resistance, and decreases the spread of infections caused by multidrug-resistant organisms.
WHO launched the Global Antimicrobial Resistance and Use Surveillance System (GLASS) in 2015 to fill knowledge gaps and inform strategies at all levels.
ACCORDING TO apic.org,
Antimicrobial stewardship is a coordinated program that promotes the appropriate use of antimicrobials (including antibiotics), improves patient outcomes, reduces microbial resistance, and decreases the spread of infections caused by multidrug-resistant organisms.
ACCORDING TO pewtrusts.org,
Antibiotic stewardship refers to efforts in doctors’ offices, hospitals, long term care facilities, and other health care settings to ensure that antibiotics are used only when necessary and appropriate
According to WHO,
Antimicrobial stewardship is a systematic approach to educate and support health care professionals to follow evidence-based guidelines for prescribing and administering antimicrobials
In 1996, John McGowan and Dale Gerding first applied the term antimicrobial stewardship, where they suggested a causal association between antimicrobial agent use and resistance. They also focused on the urgency of large-scale controlled trials of antimicrobial-use regulation employing sophisticated epidemiologic methods, molecular typing, and precise resistance mechanism analysis.
Antimicrobial Stewardship(AMS) refers to the optimal selection, dosing, and duration of antimicrobial treatment resulting in the best clinical outcome with minimal side effects to the patients and minimal impact on subsequent resistance.
According to the 2019 report, in the US, more than 2.8 million antibiotic-resistant infections occur each year, and more than 35000 people die. In addition to this, it also mentioned that 223,900 cases of Clostridoides difficile occurred in 2017, of which 12800 people died. The report did not include viruses or parasites
VISION
Being proactive
Supporting optimal animal and human health
Exploring ways to reduce overall use of antimicrobials
Using the drugs that prevent and treat disease by killing microscopic organisms in a responsible way
GOAL
to prevent the generation and spread of antimicrobial resistance (AMR). Doing so will preserve the effectiveness of these drugs in animals and humans for years to come.
being to preserve human and animal health and the effectiveness of antimicrobial medications.
to implement a multidisciplinary approach in assembling a stewardship team to include an infectious disease physician, a clinical pharmacist with infectious diseases training, infection preventionist, and a close collaboration with the staff in the clinical microbiology laboratory
to prevent antimicrobial overuse, misuse and abuse.
to minimize the developme
We understand the unique challenges pickleball players face and are committed to helping you stay healthy and active. In this presentation, we’ll explore the three most common pickleball injuries and provide strategies for prevention and treatment.
Leading the Way in Nephrology: Dr. David Greene's Work with Stem Cells for Ki...Dr. David Greene Arizona
As we watch Dr. Greene's continued efforts and research in Arizona, it's clear that stem cell therapy holds a promising key to unlocking new doors in the treatment of kidney disease. With each study and trial, we step closer to a world where kidney disease is no longer a life sentence but a treatable condition, thanks to pioneers like Dr. David Greene.
CRISPR-Cas9, a revolutionary gene-editing tool, holds immense potential to reshape medicine, agriculture, and our understanding of life. But like any powerful tool, it comes with ethical considerations.
Unveiling CRISPR: This naturally occurring bacterial defense system (crRNA & Cas9 protein) fights viruses. Scientists repurposed it for precise gene editing (correction, deletion, insertion) by targeting specific DNA sequences.
The Promise: CRISPR offers exciting possibilities:
Gene Therapy: Correcting genetic diseases like cystic fibrosis.
Agriculture: Engineering crops resistant to pests and harsh environments.
Research: Studying gene function to unlock new knowledge.
The Peril: Ethical concerns demand attention:
Off-target Effects: Unintended DNA edits can have unforeseen consequences.
Eugenics: Misusing CRISPR for designer babies raises social and ethical questions.
Equity: High costs could limit access to this potentially life-saving technology.
The Path Forward: Responsible development is crucial:
International Collaboration: Clear guidelines are needed for research and human trials.
Public Education: Open discussions ensure informed decisions about CRISPR.
Prioritize Safety and Ethics: Safety and ethical principles must be paramount.
CRISPR offers a powerful tool for a better future, but responsible development and addressing ethical concerns are essential. By prioritizing safety, fostering open dialogue, and ensuring equitable access, we can harness CRISPR's power for the benefit of all. (2998 characters)
Defecation
Normal defecation begins with movement in the left colon, moving stool toward the anus. When stool reaches the rectum, the distention causes relaxation of the internal sphincter and an awareness of the need to defecate. At the time of defecation, the external sphincter relaxes, and abdominal muscles contract, increasing intrarectal pressure and forcing the stool out
The Valsalva maneuver exerts pressure to expel faeces through a voluntary contraction of the abdominal muscles while maintaining forced expiration against a closed airway. Patients with cardiovascular disease, glaucoma, increased intracranial pressure, or a new surgical wound are at greater risk for cardiac dysrhythmias and elevated blood pressure with the Valsalva maneuver and need to avoid straining to pass the stool.
Normal defecation is painless, resulting in passage of soft, formed stool
CONSTIPATION
Constipation is a symptom, not a disease. Improper diet, reduced fluid intake, lack of exercise, and certain medications can cause constipation. For example, patients receiving opiates for pain after surgery often require a stool softener or laxative to prevent constipation. The signs of constipation include infrequent bowel movements (less than every 3 days), difficulty passing stools, excessive straining, inability to defecate at will, and hard feaces
IMPACTION
Fecal impaction results from unrelieved constipation. It is a collection of hardened feces wedged in the rectum that a person cannot expel. In cases of severe impaction the mass extends up into the sigmoid colon.
DIARRHEA
Diarrhea is an increase in the number of stools and the passage of liquid, unformed feces. It is associated with disorders affecting digestion, absorption, and secretion in the GI tract. Intestinal contents pass through the small and large intestine too quickly to allow for the usual absorption of fluid and nutrients. Irritation within the colon results in increased mucus secretion. As a result, feces become watery, and the patient is unable to control the urge to defecate. Normally an anal bag is safe and effective in long-term treatment of patients with fecal incontinence at home, in hospice, or in the hospital. Fecal incontinence is expensive and a potentially dangerous condition in terms of contamination and risk of skin ulceration
HEMORRHOIDS
Hemorrhoids are dilated, engorged veins in the lining of the rectum. They are either external or internal.
FLATULENCE
As gas accumulates in the lumen of the intestines, the bowel wall stretches and distends (flatulence). It is a common cause of abdominal fullness, pain, and cramping. Normally intestinal gas escapes through the mouth (belching) or the anus (passing of flatus)
FECAL INCONTINENCE
Fecal incontinence is the inability to control passage of feces and gas from the anus. Incontinence harms a patient’s body image
PREPARATION AND GIVING OF LAXATIVESACCORDING TO POTTER AND PERRY,
An enema is the instillation of a solution into the rectum and sig
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India Clinical Trials Market: Industry Size and Growth Trends [2030] Analyzed...Kumar Satyam
According to TechSci Research report, "India Clinical Trials Market- By Region, Competition, Forecast & Opportunities, 2030F," the India Clinical Trials Market was valued at USD 2.05 billion in 2024 and is projected to grow at a compound annual growth rate (CAGR) of 8.64% through 2030. The market is driven by a variety of factors, making India an attractive destination for pharmaceutical companies and researchers. India's vast and diverse patient population, cost-effective operational environment, and a large pool of skilled medical professionals contribute significantly to the market's growth. Additionally, increasing government support in streamlining regulations and the growing prevalence of lifestyle diseases further propel the clinical trials market.
Growing Prevalence of Lifestyle Diseases
The rising incidence of lifestyle diseases such as diabetes, cardiovascular diseases, and cancer is a major trend driving the clinical trials market in India. These conditions necessitate the development and testing of new treatment methods, creating a robust demand for clinical trials. The increasing burden of these diseases highlights the need for innovative therapies and underscores the importance of India as a key player in global clinical research.
2. DOSIMETRY
Deals with the measurement of the absorbed dose or dose rate
resulting from the interaction of ionizing radiation with matter.
It also refers to the determination of radiologically relevant quantities
such as:
Exposure
Kerma
Fluence etc.
3. DOSIMETRY CONCEPTS
AAPM (American Association of Physicists in
Medicine)
Task Group-21 (1983)
TG-51 (1999)
IAEA (International Atomic Energy Agency)
Technical Report Series -277(1997)
TRS-398 (2000)
4. TG -51
The TG-51 protocol is based on “absorbed dose to water” calibration.
Conceptually easier to understand and simpler to implement
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5. TG-51
Suitable nominal energy
• photon beams: 60Co-50MV
• electron beams: 4-50MeV
Ion chambers calibrated
• in terms of absorbed dose to water in a 60Co beam.
Purpose
• to ensure uniformity of reference dosimetry in external
beam radiation therapy with high-energy photons and
electrons.
6. General Formalism
In a Co-60 beam:
In any other photon beam:
(only cylindrical chamber allowed at present)
In any electron beam:
(both cylindrical and parallel-plate chambers allowed)
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Polarity corrections, Ppol :
Electrometer correction factor, Pelec
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8. Temperature Pressure Correction:
Standard environmental condition:
To=22oC
Po=101.33 kPa
humidity between 20%~80% (variation 0.15%)
PTP corrects charge or meter readings to standard environmental condition.
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9. Corrections for ion-chamber collection inefficiency, Pion :
if Pion 1.05, another ion chamber should be used
Voltages should not be increased above normal operating voltages. (~300V
or less)
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10. Point of Measurement &
Effective Point of Measurement
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rcav
r
Photon: r = 0.6 rcav
electron: r = 0.5 rcav
11. Beam Quality Specification (Photons)
For this protocol, the photon beam quality is specified by %dd(10)x, the
percent depth-dose at 10 cm depth in water due to the photon component
only, that is, excluding contaminated electrons.
For low energy photons (<10 MV with %dd(10) < 75%)
%dd(10)x = %dd(10) (contaminated electron is negligible)
For high energy photons (>10 MV with 75%<%dd(10)<89%)
%dd(10)x 1.267%dd(10) – 20.0
A more accurate method requires the use of a 1-mm thick lead foil placed
about 50 cm from the surface. (505cm or 301cm)
%dd(10)x = [0.8905+0.00150%dd(10)pb] %dd(10)pb
[foil at 50 cm, %dd(10)pb>73%]
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12. Beam Quality Specification (electrons)
Percent depth ionization to be measured at SSD = 100 cm for field size 1010 cm2
(or 2020 cm2 for E>20 MeV).
Parallel-plate chamber: measured curve II.
Cylindrical chamber: measured curve I,
needs to be shifted by 0.5 rcav to get curve II.
Curve II is the percent ionization curve.
R50 = 1.029I50 – 0.06 (cm) for 2I50 10 cm
R50 = 1.059I50 – 0.37 (cm) for I50 >10 cm
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14. Photon Beam Dosimetry
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15. Electron Beam Dosimetry
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absorbed dose to water chamber calibration factor
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16. TRS - 398
This protocols use different beam-
quality index TPR20,10 .
To be specified as TPR20,10 = ratio
of dose at isocenter with 20cm
attenuation to the same with
10cm attenuation.
SAD set up
Field size = (10x10)cm
17. Absorbed Dose
The energy absorbed per unit mass of any material
D = dE/dm
where dE is the mean energy imparted by ionizing radiation
of mass dm.
Old unit rad (radiation absorbed dose)
1 rad = 10 -2 J/Kg = 1cGy
SI unit of absorbed dose is Gray
1Gy = 1 J/Kg
18. Kerma
Kinetic energy released in the medium per unit mass.
K = dEtr /dm
dEtr is the sum of the initial kinetic energies of all the charged
particles liberated by uncharged particles in a material of
mass dm.
Unit = J/Kg
K= K col+ K rad
KERMA is used as an approximation to absorbed dose
when radiative losses are negligible.
19. Exposure
Measure of ionization produced in air by photons.
X = dQ/dm
dQ is the absolute value of the total charge of the ions of one
sign produced in air when all the electrons liberated by
photons in air of mass dm are completely stopped in air.
SI Unit = C/Kg Special Unit = Roentgen(R)
1R = 2.58 x 10 -4
20. Relating Absorbed Dose to Exposure
CPE
Dair = (Kc) air = X * (W/e)air
J/Kg J/Kg C/Kg 33.97 J/C
Dair = (Kc) air = 0.876 X
rad rad R
21. DOSIMETERS
A dosimeter can be defined generally as any device that is capable of
providing a reading r that is a measure of the absorbed dose D, deposited
in its sensitive volume V by ionizing radiation.
Dosimeter is a device that measures directly or indirectly
• Absorbed dose
• Exposure
• Kerma
• Equivalent dose
• Or other related quantities.
22. Dosimeters Divided Into Two:
Absolute dosimeters
here the dose is determined without reference to another
dosimeter.
Eg: free air ionization chamber, specially designed spherical
chambers of known volume, calorimeter, Fricke dosimeter .
Secondary dosimeters
these dosimeters requires calibration against a primary
standard.
Eg: thimble chambers, plane parallel ion chambers , TLD’s ,
Diodes and Films.
23. IONIZATION CHAMBERS
The ion chamber consists of a cylindrical
chamber containing air at atmospheric
pressure.
A moderate voltage (100 volts) is applied
between two electrodes, the anode and
cathode.
The interaction of radiation in a gas
results in the production of ion pairs
consisting of a negative ion (electron)
and a positive ion.
The negative ions are attracted to the
positive electrode (anode) and the
positive ions to the negative electrode
(cathode).
24. This flow of ions produces a small
electric current which is a measure of
the radiation dose rate, ie , ionisation
produced per second.
The current produced in the ion
chamber is very small ( ~ 10-12amps)
and therefore very sensitive
amplification electronics is required
making this type of monitor very
expensive.
25. Free Air Ionization Chamber
The free-air, or standard, ionization
chamber is an instrument used in the
measurement of the roentgen
according to its definition.
An x-ray beam, originating from a
focal spot S, is defined by the
diaphragm D, and passes centrally
between a pair of parallel plates.
A high-voltage is applied between
the plates to collect ions produced in
the air between the plates.
The ionization is measured for a
length L defined by the limiting lines
of force to the edges of the collection
plate C.
26. Free Air Ionization Chamber
Free-air ionization chambers are too delicate and bulky for routine use.
Their main function is in the standardizing laboratories where they can
be used to calibrate field instruments such as a thimble chamber.
27. THIMBLE CHAMBERS
It works based on the Bragg –Gray Cavity theory
A spherical volume of air is shown with an air cavity
at the center.
This sphere of air is irradiated uniformly with a
photon beam.
And the distance between the outer sphere and the
inner cavity is equal to the maximum range of
electrons generated in air.
Then the number of electrons entering the cavity is
the same as that leaving the cavity, ie, electronic
equilibrium exists.
If the air wall is compressed into a solid shell, we get
a thimble chamber. Then the thicknesses required for
the thimble chamber are considerably reduced
Air cavity
Air shell
Solid Air Shell
Air Cavity
28. THIMBLE CHAMBERS
The wall is shaped like a sewing thimble—hence the name.
The inner surface of the thimble wall is coated by a special material to make it
electrically conducting. This forms one electrode.
The other electrode is a rod of low-atomic-number material such as graphite or
aluminum held in the center of the thimble but electrically insulated from it.
A suitable voltage is applied between the two electrodes to collect the ions
produced in the air cavity.
The system as a whole behaves like a free-air chamber.
Most commonly used wall materials are made either of graphite (carbon), Bakelite,
or a plastic coated on the inside by a conducting layer of graphite or of a
conducting mixture of Bakelite and graphite.
29. FARMER CHAMBER
The thimble wall is made of pure graphite and the central electrode is of pure
aluminum.
The insulator consists of polytrichlorofluorethylene.
The collecting volume of the chamber is nominally 0.6 cm3.
The thimble is at ground potential and the guard is kept at the same potential as
the collector.
Most often the collector is operated with a positive voltage to collect negative
charge, although either polarity should collect the same magnitude of ionization
charge if the chamber is designed with minimal polarity effects
30. FARMER CHAMBER
Cylindrical (thimble) ionization chamber
– Most popular design
– Independent of radial beam direction
– Typical volume between
0.05 -1.00 cm3
– Typical radius ~2-7 mm
– Length~ 4-25 mm
– Thin walls: ~0.1 g/cm2
– Used for: electron, photon, proton or ion beams.
The guard electrode serves two different purposes:
One is to prevent leakage current from the high-voltage electrode
(the collector)
and the other is to define the ion-collecting volume.
31. The Extrapolation Chamber
(variable volume)
• Extrapolation chambers are parallel-plate
chambers with a variable electrode
separation.
• They can be used in absolute radiation
dosimetry (when embedded into a tissue
equivalent phantom).
• Cavity perturbation for electrons can be
eliminated by:
– Making measurements as a function of the
cavity thickness
– Extrapolating electrode separation to zero.
• Using this chamber, the cavity
perturbation for parallel plate chambers
of finite thickness can be estimated.
32. PARALLEL PLATE CHAMBERS
Parallel Plate/Plane parallel chamber is recommended for:
– Dosimetry of electron beams with energies below 10 MeV.
– Depth dose measurements in photon and electron beams.
– Surface dose measurements of photon beams.
Depth dose measurements in the build-up region of megavoltage
photon beams.
33. PLANE PARALLEL CHAMBERS
They have a fixed electrode spacing (1-
2mm).
Sensitive volume = 0.35 cm3
In a plane-parallel ion chamber, the plane-
collecting electrode is surrounded by a wide
margin of guard ring to prevent undue
curvature of the electric field over the
collector.
In such a chamber, when graphite coatings
are used as collecting surfaces on an
insulator, the collector can be separated
from the guard ring by a scratch through
the graphite coating.
34. GIEGER MULLER COUNTER
If the voltage in an ionisation system is
increased beyond a certain point, an effect
known as gas amplification occurs.
The negative ions are now accelerated
towards the anode and are of sufficient
energy to cause further ionisation themselves
before reaching the anode.
If the voltage is increased further, the gas
amplification or avalanche effect is so great
that a single ionising particle produces a large
pulse of current.
The size of the pulse is the same regardless of
the energy of the incident radiation.
35. GIEGER MULLER COUNTER
The Geiger counter is normally constructed in a
tubular form with the metal outer casing acting as the
cathode and a thin wire running through the centre
acting as the anode.
There is a thin end window usually constructed of
mica to allow soft beta particles to enter.
Inside the tube the counter gas (normally 90% argon
and 10% methane) is held at less than 1 atmosphere.
The methane is there as a quenching agent to “mop”
up the positive ions which would otherwise strike the
cathode, releasing further electrons which would
cause the counter to go into continuous discharge.
Modern counters now use halogen as a quenching
agent as methane has a finite lifetime and halogen
does not.
36. GM COUNTER
Area Gamma Monitor GA-720
Useful for monitoring Gamma dose
rate levels in working areas of
radioisotope laboratories, in oncology
departments near cobalt therapy
machines or Brachytherapy machines
or at other similar medical systems &
also in a medical cyclotron facility, or
at other medical & industrial
radiological installations.
Radiation detected: X-rays and Gamma
Radiation.
Range : 0.1mR/hr - 100mR/hr
37. GM COUNTER
Contamination Monitot: CM710P
Radiation Detected : Beta and
Gamma
Radiation Detector : Halogen
quenched G.M. Detector a. Pan
Cake - LND7311
Doserate: (0 - 200) mR/hr of
Gamma for End Window
Operating voltage: +900V
38. SOLID STATE DOSIMETERS
The term solid state detectors refers to
certain classes of crystalline substances
which exhibit measurable effects when
exposed to ionising radiation.
In these substances electrons exist
discrete energy bands separated by
forbidden bands.
The highest energy band in which
electrons normally exist is the valence
band.
The transfer of energy from a photon or
charged particle to a valence may raise it
to through the forbidden band into the
exciton band or the conduction band.
39. SOLID STATE DOSIMETERS
The vacancy left behind by the electron is known as a hole .
The three states shown above may be permanent or only exist for a short
time depending on the material and temperature.
In returning to the valence band the difference in energy is emitted as
fluorescent radiation, normally a light photon.
40. Thermo Luminescent Dosimeters
These detectors utilise the electron
trapping process.
One of the most common materials is
lithium fluoride and dysprosium doped
calcium sulphate(CaSo4:Dy ) which is
selected because after irradiation
electrons in the crystal matrix are raised
to a metastable excited state.
Under normal temperatures these
electrons remain in this state, but heating
the material to over 3000C releases them
from the traps and they rapidly return to
the valence band with the emission of a
light photon.
41. BARC TLD
There are 3 disc in TLD
1st disc consist of Al and Cu
combination filter window, which cut
of the beta radiation and gives the TL
due to the X and Gamma radiation.
2nd disc consist of the plastic window
which cut of the soft beta radiations
and records X-rays, Gamma rays and
hard Beta radiations.
3rd disc has no filter records all the
radiation.
It can measure doses ranging from
100 µSv to 10 Sv
42. ALBEDO DOSIMETER
This dosimeters are sensitive for the neutrons which are scattered back from the
body.
Since the human body consists of hydrogen atoms, a significant fraction of fast and
intermediate neutrons are slowed down to epithermal energies and back scattered.
These back scattered neutrons are called Albedo neutrons which interact with TL
material.
Neutron detector mechanism involves an Li-6 (n, ) H3 reaction. The alpha and
triton are absorbed by the LiF detector with a deposition of energy that can be
detected by common TLD read out technique.
Natural lithium TLD’s are sensitive to thermal neutrons and the sensitivity can be
increased by making the TLD out of lithium enriched with Li6
Li6 and Li7 enriched TLD’ s are used in pairs because to subtract gamma rays. ie,
TLD-600 response to both gamma and neutron radiation and the other TLD-700
respond only to gamma radiation. So the difference
in reading give the neutron dose.
43. SCINTILLATION DETECTOR
Fluorescent radiation emitted when an electron returns from an excited state to the
valence band.
Most monitors use sodium iodide (NaI) as the scintillator as it only takes about 1 s for
the electron to return to the valence band.
The absorption of 1 MeV gamma photon results in about 10,000 excitations and the
same number of photons of light.
These scintillations are detected by the front face of a photomultiplier tube via optical
coupling between the light tight can surrounding the NaI and the photo-cathode of the
PM tube.
The photo-cathode detects these very faint light signals and converts them into
electrical pulses.
44. CONTAMINATION MONITOR
Worked with unsealed radioactive materials
generates potential contamination of
surfaces.
Surface contaminations are measured as
activity per unit area [Bq/cm²] for specified
Radionuclides.
Surface contaminations are monitored
using a variety of methods and instruments.
Surface contamination detector using
scintillation theory
45. RADIOGRAPHIC FILM
A radiographic film consists of a transparent film base (cellulose acetate or
polyester resin) coated with an emulsion containing very small crystals of
silver bromide.
When the film is exposed to ionizing radiation or visible light, a chemical
change takes place within the exposed crystals to form what is referred to as
a latent image.
When the film is developed, the affected crystals are reduced to small grains
of metallic silver.
The film is then fixed. The unaffected granules are removed by the fixing
solution, leaving a clear film in their place.
The metallic silver, which is not affected by the fixer, causes darkening of the
film. Thus, the degree of blackening of an area of the film depends on the
amount of free silver deposited and, consequently, on the radiation energy
absorbed.
46. RADIOGRAPHIC FILM
The degree of blackening of the film is
measured by determining optical
density with a densitometer.
The optical density, OD, is defined as:
log Io/It
where I0 is the amount of light
collected without film and It is the
amount of light transmitted
through the film.
A plot of net optical density as a
function of radiation exposure or
dose is termed the sensitometric
curve or H-D curve.
Eg: Kodak EDR-2 and Kodak RPM-2
47. RADIOGRAPHIC FILM
Film suffers from several potential errors such as :
changes in processing conditions,
interfilm emulsion differences
artifacts caused by air pockets adjacent to the film.
For these reasons, absolute dosimetry with film is impractical.
However, it is very useful for checking
radiation fields
light-field coincidence
field flatness
Symmetry
and obtaining quick qualitative patterns of a radiation distribution.
In the megavoltage range of photon energies, however, film has been
used to measure isodose curves with acceptable accuracy (±3%)
48. RADIOCHROMIC FILM
The use of Radiochromic films for radiation dosimetry has been evolving since
the 1960s.
With the recent improvement in technology associated with the production
of these films, their use has become increasingly popular, especially in
brachytherapy dosimetry.
Major advantages of Radiochromic film dosimeters include:
tissue equivalence
high spatial resolution
large dynamic range (10-2-106 Gy)
relatively low spectral sensitivity variation (or energy dependence)
insensitivity to visible light
and no need for chemical processing(self developing).
49. RADIOCHROMIC FILM
Radiochromic film consists of an ultrathin (7- to 23-µm thick) colorless
radiosensitive leuco dye bonded onto a 100-µm thick mylar base.
Other varieties include thin layers of radiosensitive dye sandwiched between
two pieces of polyester base .
Polyester layer
Radiosensitive layer/
Active layer
28 µm
120 µm
120 µm
Gafchromic EBT3 Film
layer arrangement
50. Nuclear Track emulsion Type A (NTA)
Kodak Film
Used for neutron dosimetry.
The film consists of fine grain nuclear emulsions of thickness 30 micron coated
on one side of cellulose acetate base. It is wrapped in light tight black paper.
Fast neutron undergo elastic scattering with hydrogen nuclei, which take
place in the emulsion itself or in the cellular acetate base or in the packaging
of the emulsion, in the film holder and for high energy neutron in the body of
the person who is wearing the badge.
Recoil protons are produced which are recorded as photographic tracks in the
emulsion.
The length of the track depends upon the proton energy.
Recognition of tracks are possible only from neutron energy 0.5MeV
(threshold energy) and Above. And the tracks are counted on a microscope
after film processing.
Greatest disadvantage of the NTA film is the fading. And there is a threshold
neutron energy.