Radiobiology 7م

Prof.Dr.Tarek Elnimr L 7 Presented to the Biology Departments in Faculty of Sciences on February 15 , 2009

Bremsstrahlung Radiation

Energy is lost by the incoming charged particle through a radiative mechanism Beta Particle - Bremsstrahlung Photon + + Nucleus

X-Ray Machine Components

High Voltage Power Supply Tungsten Filament Target Glass Envelope Tube Housing Cathode Anode Current

X-Ray Machine Basics

kVp - how penetrating the X-rays are

Mammography - 20 - 30 kVp

Dental - 70 - 90 kVp

Chest - 110 - 120 kVp

mA - how much radiation is produced

Time - how long the machine is on

Combination of the above determines exposure

X-Ray Production Electron X-Ray Target Nucleus Tungsten Cathode (-) Anode (+) X-Rays

Radiation Detection Gas Filled Detectors Air or Other Gas Incident Ionizing Radiation Electrical Current Measuring Device + - Cathode - Anode + + + + - - - + - Voltage Source

Radiation Detection Scintillation Detectors Incident Ionizing Radiation Sodium-Iodide Crystal Photocathode Optical Window - Pulse Measuring Device Light Photon Photomultiplier Tube Dynode Anode

Bremsstrahlung Radiation Incident Electron (E 1 ) X-ray Photons Energy = (E 1 - E 2 ) Deflected Electron (E 2 ) (E 1 > E 2 )

X-ray Tube

Target

made of high atomic number material with good thermal properties, typically tungsten (W)

approx. 1%

of energy forms

x-rays, rest as

heat

anode rotates

to increase heat

loading capacity

Production of X-rays

2 types of interaction of e - with target

Bremsstrahlung (braking radiation)

e - passes close to the nucleus (+ ive charged) of the target material

electrostatic interaction causes the e - to bend form its path

energy given off as x-rays

Gamma Interactions

Gamma interactions differ from charged particle Interactions

Interactions called "cataclysmic" - infrequent but when they occur lot of energy transferred

Three possibilities:

May pass through - no interaction

May interact, lose energy & change direction (Compton effect)

May transfer all its energy & disappear (photoelectric effect)

Compton Effect

An incident photon interacts with an orbital electron to produce a recoil electron and a scattered photon of energy less than the incident photon Before interaction After interaction - - - Incoming photon Collides with electron - - - - Electron is ejected from atom - Scattered Photon

Interaction of Radiation

with Matter

Radiation deposits small amounts of energy, or "heat" in matter

alters atoms

changes molecules

damage cells & DNA

similar effects may occur from chemicals

Much of the resulting damage is from the production of ion pairs

Radiation Protection Concepts

Time

Distance

Shielding

Risk/Benefit

ALARA

Shielding

Radiation Protection Basics

Time: minimize the time that you are in contact with radioactive material to reduce exposure

Distance: keep your distance. If you double the distance the exposure rate drops by factor of 4

Shielding:

Lead, water, or concrete for gamma & X-ray

Thick plastic (lucite) for betas

Protective clothing: protects against contamination only - keeps radioactive material off skin and clothes

Time

Accumulated time from external radiation exposure is directly proportional to the amount of time spent in the area

Distance

The radiation field is inversely proportional to the square of the distance from the source

Shielding

The amount of shielding required depends on the type of radiation, the activity present and the dose rate acceptable outside the shielding material

< 2.5 uSv/hr

Required Personal Protective Equipment (PPE)

Personnel Monitoring

Workplace Monitoring

Safe Work Habits

Proper Lab Bench Set Up

A proper lab bench including:

survey meter

whole body shield

spill trays

waste container

labeling

etc.,

Use of high activity sealed sources to examine structural components such as beams or pipes

Radiological Hazards

Total Effective Dose

Equivalent, (TEDE)

Used to combine internal and external doses

Puts all dose on the same risk base comparison, whether from external or internal sources.

TEDE = CEDE + DDE

All units are in rems or Sieverts (Sv)

All regulatory dose limits are based on controlling the TEDE

External Radiation

Inverse Square Law

Radiation levels decrease as the inverse square of the distance (i.e. move back by a factor of two, radiation levels drop to one fourth)

Applies to point sources (distance greater than 5 times the maximum source dimension)

where I = Intensity (exposure rate) at position 1 and 2 and R = distance from source for position 1 and 2 Position 1 Position 2 (mrem/hr) (mrem/hr) Source 2 2 2 2 1 1 R I R I  R 1 R 2 I 2 I 1

Gamma Ray Constant

Gamma Ray Constant to determine exposure rate

 (mSv/hr)/MBq at 1 meter

Hint: multiply (mSv/hr)/MBq by 3.7

to get (mrem/hr)/uCi

Exposure Rate Calculation, X (mrem/hr) at one meter:

X = 

Where, A = Activity (  Ci)

 Gamma Ray Constant(mSv/hr)/Mbq

3.7 is the conversion factor

Sample Calculation

5 Curie Cs-137 Source

Calculate Exposure Rate at 1 meter

 = 1.032 E-4 mSv/hr/MBq @ 1 meter

X = 1.032 E-4 * 3.7 * 5 Ci * 1000 mCi/Ci * 1000 uCi/mCi

X = 1909 mrem/hour

X = 1.91 rem/hour

Gamma Ray Shielding

Effectiveness increases with thickness, d (cm)

Variation with material, (1/cm)

attenuation coefficients µ

High Z material more effective

Water - Iron - Lead

good - better - best

Shielding Beta Emitters

Low energy betas (H-3, C-14, S-35) need no shielding for typical quantities at Clarkson

Higher energy beta emitters (P-32) should be shielded

Beta shielding must be low Z material (Lucite, Plexiglas, etc.)

High Z materials, like lead, can actually generate radiation in the form of Bremsstrahlung X-rays

Bremsstrahlung from 1 Ci of P-32 solution in glass bottle is ~1 mR/hr at 1 meter

Contamination and

Internal Hazards

Units of Measure

activity/area (dpm/100 square cm)

Fixed vs Removable

Internal Hazards and Entry Routes

Ingestion

Inhalation - Re-suspension

Skin absorption

Wound Entry

Protective Clothing

Can be a very effective means of preventing skin, eyes, & clothing from becoming contaminated

Gloves (may want double layer)

Lab Coat

Eyewear to prevent splashes and provide shielding for high energy beta emitters

Closed toe footwear

It is much easier to remove contaminated clothing than to decontaminate your skin!

Contamination Control

Watch out where you put your “hot” hands during an experiment

Monitor yourself and your work area frequently for radioactivity (gloves, hands, feet, etc.)

Use most sensitive scale on meter (X0.1 or X1)

Have meter out and handy

Make sure to wash your hands frequently and after finishing an experiment

Don’t bring radioactive material to lunch or to your home!

Monitor your work area before and after an experiment

Avoid Ingesting

Radioactive Material

Don’t bring hands or objects near your mouth during an experiment

Eating, drinking, smoking, applying cosmetics are strictly prohibited in radioisotope use areas

Never mouth pipette

Never store personal food items in refrigerators or freezers used for radioactive material or other hazardous material storage

Avoid Inhaling

Radioactive Material

Make sure you have proper ventilation for your experiments

When using volatile materials such as Iodine-125 and some Sulfur-35 compounds, be sure to use a fume hood that has been inspected and certified for proper airflow

DACs & ALIs

DAC: Derived Air Concentration, an airborne concentration of of radioactive material which if inhaled for 2000 hrs per year will result in 5 rem CEDE or 50 rem CDE.

Units are uCi/cc

Each DAC-hour gives 2.5 mrem of dose.

ALI: Annual Limit on Intake, A quantity of radioactive material, which if inhaled or ingested, would result in the applicable annual dose limit.

1 ALI = 5 rem (CEDE) or 50 rem (CDE)

ALI and DAC Values listed for each nuclide in NHRCR (He-P 4090)

External vs Internal Dose

TEDE: Total Effective Dose Equivalent

TEDE = DDE + CEDE

Total Dose = External Dose + Internal Dose

1 rem internal (CEDE) same as 1 rem external (DDE)

Internal dose is protracted over several years but calculated over 50 years and assigned in the year of intake

Radiation Detection

Use of Survey Instruments

Check Physical Condition

Cables, Connections, Damage

Check for Current Calibration (License Requirement)

Battery Check

Zero Check

Response check prior to use

Select Proper Scale

Response Time (Fast or Slow?)

Audio (On or Off)

U. S. Nuclear Regulatory Commission

Regulates the nuclear industry pursuant to the Atomic Energy Act

Regulatory guides published to describe methods for complying with regulations

Agreement States

Some states have entered into an agreement with the NRC to regulate by-product material (and small quantities of source and special nuclear material)

Currently, 30 states are agreement states including New York

Regulatory Agencies

Ordering & Receipt of Radioactive Materials

Only RSO is authorized to order radioactive material

Use the Radionuclide Purchase Request Form

Complete form and fax to RSO at 268-7118

Be sure to state any special ordering instructions (preferred delivery date, fresh batch, etc.)

Packages are received by RSO, checked for contamination, logged in, and delivered to the lab on the same day as receipt

Posting & Labeling Notices

Labels

All containers (unless exempt) must be labeled

With “Caution – Radioactive Material”

Should include radionuclide, quantity, date,

initials, radiation levels, etc.

Posting

New York Notice to Employees form

Caution Radioactive Materials or X-Rays

Employee Rights

and Responsibilities

Right to report any radiation protection problem to state without repercussions

Responsibility to comply with the Radiation Protection Program and the RSO's instructions pertaining to radiation protection

Right to request inspection

in writing

grounds for notice

signed

Responsibility to cooperate with NY State inspectors during inspections and RSO during internal lab audits

Security

Licensed RAM must be secured against unauthorized removal at all times

Must maintain constant surveillance for any radioactive material outside a restricted area

Lock labs containing radioactive material if last one out - even if it’s “just for a minute”

Challenge all unknown individuals with “May I help you?”

OK to ask for ID

Report to supervisor if suspicious

Annual Dose from

Background Radiation

Total US average dose equivalent = 360 mrem/year Total exposure Man-made sources Radon Internal 11% Cosmic 8% Terrestrial 6% Man-Made 18% 55.0% Medical X-Rays Nuclear Medicine 4% Consumer Products 3% Other 1% 11

Exposure, X

A measure of the ionization produced by

X or Gamma Radiation in air

Unit of exposure is the Roentgen

X = Q (charge) M (mass of air)

Absorbed Dose, D

Absorbed Dose (or Radiation Dose) is equivalent to the energy absorbed from any type of radiation per unit mass of the absorber

Unit of Absorbed Dose is the rad

1 rad = 100 ergs/g = 0.01 joules/Kg

In SI notation, 1 gray = 100 rads

Dose Equivalent, H

One unit of dose equivalent is that amount of any type of radiation which, when absorbed in a biological system, results in the same biological effect as one unit of low LET radiation

The product of the absorbed dose, D , and the Quality Factor , Q

H = D Q

Units of Dose Equivalent

Human dose measured in rem or millirem

1000 mrem = 1 rem

1 rem poses equal risk for any ionizing radiation

internal or external

alpha, beta, gamma, x-ray, or neutron

In SI units 1 sievert (Sv) = 100 rem

External radiation exposure measured by dosimetry

Internal radiation exposure measured using bioassay sample analysis

Quality Factors for Different Radiations

Quality Factor X and Gamma Rays Electrons and Muons Neutrons < 10 kev >10kev to 100 Kev > 100 kev to 2 Mev >2 Mev Protons > 30 Mev Alpha Particles 1 1 5 10 20 10 10 20

Annual Dose from

Background Electromagnetic Radiation

Total Egyp average dose equivalent = 360 mrem/year Total exposure Man-made sources Radon Internal 11% Cosmic 8% Terrestrial 6% Man-Made 18% 55.0% Medical X-Rays Nuclear Medicine 4% Consumer Products 3% Other 1% 11

Annual Dose from

Background Radiation

Total US average dose equivalent = 360 mrem/year Total exposure Man-made sources Radon Internal 11% Cosmic 8% Terrestrial 6% Man-Made 18% 55.0% Medical X-Rays Nuclear Medicine 4% Consumer Products 3% Other 1% 11

Exposure, X

A measure of the ionization produced by

X or Gamma Radiation in air

Unit of exposure is the Roentgen

X = Q (charge) M (mass of air)

Absorbed Dose, D

Absorbed Dose (or Radiation Dose) is equivalent to the energy absorbed from any type of radiation per unit mass of the absorber

Unit of Absorbed Dose is the rad

1 rad = 100 ergs/g = 0.01 joules/Kg

In SI notation, 1 gray = 100 rads

Dose Equivalent, H

One unit of dose equivalent is that amount of any type of radiation which, when absorbed in a biological system, results in the same biological effect as one unit of low LET radiation

The product of the absorbed dose, D , and the Quality Factor , Q

H = D Q

Units of Dose Equivalent

Human dose measured in rem or millirem

1000 mrem = 1 rem

1 rem poses equal risk for any ionizing radiation

internal or external

alpha, beta, gamma, x-ray, or neutron

In SI units 1 sievert (Sv) = 100 rem

External radiation exposure measured by dosimetry

Internal radiation exposure measured using bioassay sample analysis

Quality Factors for Different Radiations

Quality Factor X and Gamma Rays Electrons and Muons Neutrons < 10 kev >10kev to 100 Kev > 100 kev to 2 Mev >2 Mev Protons > 30 Mev Alpha Particles 1 1 5 10 20 10 10 20

N(t 0 ), A (t 0 ) are the initial number of radionuclides and initial activity, respectively. The half life t 1/2 of a radionuclide is the time by which the number of radionuclides has reduced to 50%. This shows a direct correlation between half life and decay constant for each radionuclide. The lifetime r of a nucleus is defined by: Quite often the expression “lifetime” can be found for radionuclides. This means that after a period corresponding to the “lifetime”  of a radioactive nucleus the initial abundance has decreased to 36.8% of its initial value, of a nucleus can be found!

Unit for exposure E is the Roentgen [R] which is defined by the ionization between EM-radiation and air. 1 Roentgen is the amount of EM-radiation which produces in 1 gram of air 2.58  10 -7 C at normal temperature (22°C) and pressure (760 Torr) conditions. Dosimetry Units Due to the interaction between radiation and material ionization occurs in the radiated material! (Energy transfer from the high energetic radiation photons or particles to atomic electrons.) The ionization can be used as measure for the amount of exposure which the material had to radiation. 1 R = 2.58  10 -4 C/kg

When interacting with matter EM-radiation shows particle like behavior. The 'particles' are called photons. The energy of the photon and the frequency  (or wavelength  ) of the EM-radiation are determined by the Planck constant h: h=6.62 -34 J  s = 4.12  10 -21 MeV  s The photon energy for X-rays and  -rays is in the eV to MeV range.

X-rays originate either from characteristic deexcitation processes in the atoms (K  , K  transitions) (Characteristic X-rays). The photon energy corresponds to the difference in binding energy of the electrons in the excited levels to the K-level.

X-rays also originate from energy loss of high energy charged particles (e.g. electrons) due to interaction with the atomic nucleus ( bremsstrahlung )

The exposure rate ER (= ionization/time) can be related to the activity A of a source (in units mCi) via : F is the exposure constant in units [ (R  cm 2 ) / (h  mCi) ] , and d is the distance between source and material in units [cm]. The exposure constant is characteristical for the radiation source:

The absorbed dose D of radiation in any kind of material depends on the typical ionization energy of the particular material. The absorbed dose is defined in terms of the absorbed radiation energy per mass W 1P . It therefore clearly depends on the energy loss behavior of the various kinds of radiation. The unit for the absorbed dose is : 1 Gray = 1Gy = 1 J/kg = 10 4 erg/kg = 100 rad The average ionization energy for air is W 1P  34 eV/ion. With 1 eV = 1.6022  10 -19 J and the charge per ion is 1.6  10 -19 , this yields for the absorbed dose in air D for 1 R exposure of EM radiation: D = 1 R • 34 J/C = 2.58  10 -4 C/kg  34 J/C = 8.8  10 -3 J/kg = 8.8  10 -3 Gy = 0.88 rad

The average ionization energy depends critically on the material.

There is an empirical relation between the amount of ionization in air and the absorbed dose for a given photon energy and absorber (body tissue). The absorbed dose in rads per roentgen of exposure is known as the roentgen-to-rad conversion factor C C is approximately equal to one for soft body tissue in the energy range of diagnostic radiology. The increase for bone material is due to higher photoelectric absorption cross section for low energy photons.

Dose (rad) = Exposure (R) x R to Rad Conversion factor

Exposure, exposure rate and absorbed dose are independent of the nature of radiation. Biological damage depends mainly on the energy loss of the radiation to the body material. These energy losses differ considerably for the various kinds of radiation. To assess the biological effects of the different kind of radiations better, as new empirical unit the dose equivalent H is introduced: DOSE EQUIVALENT with the quality factor Q which depends strongly on the ionization power of the various kinds of radiation per path length. In first approximation Q  Z of radiation particles, Q(  , X,  )  1. As higher Q as higher the damage the radiation does!

EFFECTIVE DOSE The various body organs have different response to radiation. To determine the specific sensitivity to radiation exposure a tissue specific organ weighting factor w T has been established to assign a particular organ or tissue T a certain exposure risk. The given weighting factors in the table imply for example that an equivalent dose of 1 mSv to the lung entails the same probability of damaging effects as an equivalent dose to the liver of (0.12/0.05)  1 mSv = 2.4 mSv The sum of the products of the equivalent dose to the organ H T and the weighting factor w T for each organ irradiated is called the effective dose H  : Like H T , H  is expressed in units Sv or rem!.

or Natural Decay Law The rate of the decay process is determined by the activity A (number of decay processes per second) of the radioactive sample. The activity is proportional to the number of radioactive nuclei (radionuclide)  is the decay constant! Differential equation for N(t) can be solved

Thank You