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Transcript of 2/14/2016 L10,L11 and L12 1 PRINCE SATTAM BIN ABDUL AZIZ UNIVERSITY COLLEGE OF PHARMACY Nuclear...
05/04/2305/04/23 L10,L11 and L12L10,L11 and L12 11
PRINCE SATTAM BIN ABDUL AZIZ UNIVERSITYCOLLEGE OF PHARMACY
Nuclear PharmacyNuclear Pharmacy((PHT 433PHT 433 ) )
Dr. Shahid JamilDr. Shahid Jamil
The roentgen is the amount of x or γ radiation that produces
ionization of one electrostatic unit of either positive or negative
charge per cubic centimeter of air at 0C and 760 mmHg (STP).
Since 1 cm3 air weighs 0.001293 g at STP and a charge of
either sign carries 1.6 × 10-19 Coulomb (C) or 4.8 × 10-10
electrostatic units, it can be shown that
1R = 2.58 × 10-4 C/KgIt should be noted that the roentgen applies only to air and to x
or γ radiations. Due to practical limitations of the measuring
instruments, the R unit is applicable only to photons of less
than 3 MeV energy
1. The exposure dose1. The exposure dose (rontgen).(rontgen).
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b- Dose units b- Dose units
The unit of absorption dose.The absorbed dose of any ionizing radiation is the energy imparted to matter per unit mass of irradiated material.1 rad is that quantity of radiation which delivers 100 ergs per gm of matter.Absorbed dose (rads) = Exposure dose (Roentgens) X (C.F.)C.F. = Conversion factor depending on the density of the absorbing body and type of radiation.
2- The Radiation Absorbed Dose (RAD)2- The Radiation Absorbed Dose (RAD)
EnergyEnergyMevMevC.F. inC.F. inWaterWaterBoneBoneMuscleMuscle
Soft X raysSoft X rays0.050.050.8920.8920.3580.3580.9200.920Medium X raysMedium X rays0.50.50.9650.9650.9250.9250.9570.957γγ rays (from Corays (from Co6060))110.9650.9650.9190.9190.9570.957
The unit of absorption dose.The absorbed dose of any ionizing radiation is the energy imparted to matter per unit mass of irradiated material.1 rad is that quantity of radiation which delivers 100 ergs per gm of matter.Absorbed dose (rads) = Exposure dose (Roentgens) X (C.F.)C.F. = Conversion factor depending on the density of the absorbing body and type of radiation.
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The Rem is used to express human biological doses The Rem is used to express human biological doses as a result of exposure to one or several types of as a result of exposure to one or several types of ionizing radiations.ionizing radiations.Thus it is defined as: That dose of radiation which Thus it is defined as: That dose of radiation which produces in man the effects of 1 rad.produces in man the effects of 1 rad.
3. The Roentgen Equivalent Man (REM)3. The Roentgen Equivalent Man (REM)
Dose equivalent H (rems) = absorbed dose (rads) X (Q.F.) X (D.F.)Dose equivalent H (rems) = absorbed dose (rads) X (Q.F.) X (D.F.)
Q.F. = Quality Factor.Q.F. = Quality Factor.D.F. = Distribution factor depends on the energy D.F. = Distribution factor depends on the energy produced produced and angle of incidence.and angle of incidence.Both Q.F. and D.F. could be replaced by RBE Both Q.F. and D.F. could be replaced by RBE
(Relative Biological Effectiveness) = 1 for (Relative Biological Effectiveness) = 1 for γγ, X and , X and ββ
radiation and equal to 10 for radiation and equal to 10 for αα particles, protons and particles, protons and fast neutrons.fast neutrons.
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The primary event producing injury in a cell is the
production of ionization.
Excitation plays a small part, since radiations which
cause excitation without ionization, as UV, are less
effective in cell damage.
The dose of radiation which kills a cell may cause
ionization in only one molecule in 108.
THE BIOLOGICAL EFFECTS OF RADIATIONMechanism of Injury
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Direct radiation effects
Result from an ionization or
excitation within a biologically
functional molecule.
The occurrence of an ion cluster
within such a molecule releases
sufficient energy that terminate
biological function of the cell.
There are several theories concerning the mechanism
by which damage arises. but the damage results
from a mixture of direct and indirect effects.
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All nuclear disintegrations result directly or indirectly in production of fast-moving , charged particles. As these charged particles pass through matter they collide with atoms in their path and share their energies with the planetary electrons. Some of the latter may acquire sufficient energy to tear themselves away from the atom. Thus, a track of negative electrons and positively charged molecule together with its separated electron is called an ion pair and the "tearing-away" process is known as ionization.
1. Ionization
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Sometimes, when radiations react with matter,
ionization does not take place.
Instead, the atoms simply acquire extra energy from
the particles and assume an excited state, a process
known as excitation.
This excess energy may be discharged in several
ways, one which is the emission of light.
Alpha and beta particles cause ionization and
excitation directly.
2. Excitation
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Gamma radiation, because it is
without mass or charge, reacts
much less strongly with matter.
However, it does interact with
some of the planetary electrons
and these escape, often with high
energy, causing the above effects.
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Ionization and excitation of molecules in the body cause abnormal chemical reactions. For example, essential enzymes are inactivated, proteins are coagulated, nucleic acids in the genetic apparatus are damaged, and histamine- like substances are produced. These primary effects lead to the familiar signs of radiation damage.
Biological Effects:
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Indirect radiation Effects It result from the radiolysis of intracellular water (80 %) of most cells, and of any extracellular water which may be present. The principal effects are oxidativethat oxidations may result from reactions with the hydroxyl, hydroperoxy free radicals, hydrogen peroxide and the hydrogen radicals, which is responsible for destructive effects of radiation.As oxygen enhances radiation damage thus substances which protect against radiation are reducing agents (e.g. cysteamine, cysteine, glutathione).
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Reactions in the radiolysis of water (free radicals underlined)05/04/2305/04/23 1212L10,L11 and L12L10,L11 and L12
The free radicals •OH and •H may reacts
•OH + •OH H2O2
•H + •H H2
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Radiation Effects on the Human BodyThe effects of radiation on the entire organism depends on the proportion irradiated, Most severe with whole body exposure and least if only a small mass of insensitive tissue such as the hands is exposed.The degree of damage is influenced by the radiation intensity and the exposure time. In general, a number of small doses spread over several week does less damage than the same amount of radiation in one dose. However, this does not apply to the reproductive cells of the testes and ovaries, that the effect on which is cumulative.
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Short term effects.(prompt effect)Immediately appeared effect Whole body doses of about 25 rem would produce a transient change in the leucocyte count. Increasing the dose would result in increasing severity, 100 rem causing moderate illness (diarrhea, vomiting) in about 10 per cent of subjects, and severe illness in about1 per cent, the syndrome is known as radiation sickness. The median lethal dose (LD50) for death in 30 days is about 400 rem and with a dose of 600 rem there would be few survivors. Death from doses of this magnitude is usually the result of gut damage and a loss of resistance to disease. So that infections due to the intestinal microflors proceed.
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Some degree of protection against radiation sickness is afforded by the presence of reducing chemicals (cysteamine, glutathione) and by shielding certain important tissues such as the spleen and the bone marrow.
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Long term effects.
The results of long term exposure include permanent skin damage, bone necrosis and increased incidence of anemia, leukaemia, cataract and carcinomata. The human embryo is very sensitive and doses as small as 25 rem may lead to sever abnormalities.
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This was observed in early workers with X-rays who received very large doses over a prolonged period. A short exposure to intense radiation produces erythema. Longer exposure can cause brittleness and dryness (due to destruction of the sebaceous glands), loss of hair (due to damage to the hair follicle) and, if the dose is very large, burns. The latter heal very slowly and occasionally become malignant.
1- Skin Damage
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2. Somatic effectsThis may become evident from about two months to many years after exposure.They include cataract, severe anaemias, leukaemia, and cancer.Cancer tends to occur in tissues severely damaged by radiation. The latent period is very long and often exceeds twenty years.
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3. Genetic effectsRadiation has two effects on reproductive cells.
It can damage the chromosomes and increase the
frequency of gene mutation.
The former is not very important because it is
caused only by long exposure to low intensity X- and
gamma - rays.
Because damage to genetic material is cumulative
and irreversible, long exposure at low intensity
effects the mutation rate as much as an equivalent
dose of high intensity, i.e. there is no safe threshold
dose.
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The mutations will be hereditary by future
generations and most are harmful.
Consequently, it is not the exposed person who is at
special risk but, rather, future generations and,
through these, the whole population.
Thus it is important that radiation exposure should
be minimized during the early years.
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4- The effect on the rate of cell
divisionAll cells are susceptible to radiation damage depends
on the rate of cell division.
Thus tissues increase in resistance in the following
order: lymphocytes, erythrocytes, germinal
epithelium, intestinal epithelium, skin, internal
organs, brain, muscle, nerve.
This indicates that an important part of the damage
must be to the nuclear apparatus due to interference
with nucleic acid synthesis with the production of
abnormal chromosomes.
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Since any defect would result in imperfect
replication, that the effect of which would be
multiplied at each cell division, thus the greater the
rate of cell division the greater being the observed
damage. The effects in radiosensitive tissues (gonads, gut) commence at doses of about 10 rem and are severe at 100 rem. In liver and muscle, which are relatively radioresistant, doses greater than 1000 rem are needed to produce effects.
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Man is continually exposed to external and internal
radiations of natural origin (background radiation)
Exposure to RadiationRadiation from natural sources.
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(a) The earth's crust contains radioactive minerals
and therefore, man made structures of brick and
material expose to measurable amounts of
radiation.
(b) Cosmic (outer space) rays from outer space
(c) The atmosphere contains minute amounts of
radon and thorn, gaseous decay products of
radium and thorium.
(d) Radioactive constituents of the human body,
e.g.: 40K, 14C, and 226 Ra.
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The Gonads Dose Of Radiation From Natural Sources
SourcesSourcesDose Dose (mrads/wk)(mrads/wk)
Earth's crustEarth's crust
Cosmic radiationCosmic radiation
AtmosphereAtmosphere
Body constituentsBody constituents
i.e. the yearly dose is i.e. the yearly dose is
1-31-3
0.5 0.5
0.050.05
2-42-4
0.1-0.2 rads0.1-0.2 rads05/04/2305/04/23 2626L10,L11 and L12L10,L11 and L12
Radiation from other sourcesMan also receives radiation from the accessories of
civilization.
Sources of such radiation include natural
background,
X-ray examination, Fall-out from test explosions
and industrial exposure.
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THE CONTROL OF RADIATION EXPOSURE
Maximum Permissible Doses
(MPD)One maximum permissible dose is that dose which,
received in a certain defined period and repeated
regularly and is not expected to cause appreciable
bodily harm.
Doses resulting from medical procedures are
excluded since they are regarded as necessary and
beneficial. 05/04/2305/04/23 2828L10,L11 and L12L10,L11 and L12
The relationship governing the total permissible
cumulative
dose results
in an average dose rate of 5 rems per year for
persons engaged in radiation work from the age of 18
years.
It is assumed that there is no occupational exposure
to radiation permitted at age less 18 years.
Lower limits of permissible dose are set for the
general population, amounting to an addition equal to
the natural background dose, and for groups exposed
occasionally, such as laboratory maintenance workers.
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Organ of interestOrgan of interestMaximum Maximum permissiblpermissible dose e dose (rems) Per (rems) Per yearyear
External radiationExternal radiationGonads, blood-forming organs and the lens ofGonads, blood-forming organs and the lens ofthe eyethe eye
55
Weakly penetrating radiation:Weakly penetrating radiation:to the skin (except the hands, forearms, feetto the skin (except the hands, forearms, feetand ankles)and ankles)
3030
to the hands, forearms, feet and anklesto the hands, forearms, feet and ankles7575Internal radiationInternal radiationLimited exposure of internal organs resulting Limited exposure of internal organs resulting from from uptake (other than the thyroid, gonads and uptake (other than the thyroid, gonads and blood-blood-forming organs)forming organs)
1515
Whole body exposure resulting from Whole body exposure resulting from generalized uptakegeneralized uptake55
Maximum Permissible Dose For Radiation Workers
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This is an average dose rate.
The total permissible cumulative dose is given by:
Where N is the age in years, and not More than 60
rem may be accumulated by 30 age of years.
5)N- 18 (rems
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RadioprotectionDose rates at working positions
should always be measured.
The effect of distanceThe effect of distance
γγ-dose rates-dose ratesββ-dose rates-dose rates..
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The effect of distanceRadiations are emitted from a source in all directions so with a point source in a non-absorbing medium
where d is the distance from the source.
For γ-radiation air is almost a non-absorbing
medium. With β--particles there is considerable air absorption and external dose rates are not usually a problem.
dose rate α 1 /d2
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point source of that nuclide and have units of rongtens per millicurie hour at 1 cm. This is the most accurate basis for calculating the
dose at any distance from γ-emitting source
γ-dose rates The specific γ-ray constant (k-factor) is the dose rate
produced by the γ-radiation from a radionuclide at a distance of 1 cm from a 1 mCi
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β-dose rates.The whole body dose rates due to β--particles is not considered since the particles have a limited finite range and can be stopped completely by simple shielding. But some parts of the body, as the hands and forearms, may be exposed. For a point source of β—emitter, the exposure dose is given by :
where C is the source strength in curies.
Dose rate at 10 cm = 3100 C rads per hour in tissue
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The effect of β--energy is negligible.
It should be noted that β--particle doses to the hands
may be very large, and the handling of an unshielded
1 mCi source of 32P would give a dose to the hands of
about 3 rems per hour, assuming an average
distance of 10 cm.
This would result in the accumulation of one year's
maximum permissible dose in 25 h.
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From the inverse square law and the
appreciable air absorption of β--
particles, that doses may be reduced
by working at a sufficient distance
from a source with small amounts of
radioactivity.
With larger amounts of activity
shielding is necessary.
Shielding materials may consist of
lead, iron or concrete
Shielding
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Shielding against β--particles.
The maximum range of 2 MeV β--particles in air is
about
7.5 m.
But in denser materials the ranges are much less, the
range in Perspex is about 8.5 mm, thus 1 cm of
Perspex will give effective protection against β—
particles that a Perspex screen can be used as the
simplest method of shielding.
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Shielding against γ-particles.
The extent to which the intensity of a beam of γ-radiation is reduced by a barrier depends on the radiation energy and the atomic number and thickness of the barrier material. The tenth thickness of an absorber is that thickness required to reduce the intensity of radiation to one-tenth of its initial value.A greater thicknesses are required to reduce doses by the first factor of 10 than are needed for subsequent factors of 10.
e.g. for 60Co (mean γ- energy 1.25 MeV) the thickness of lead required to attenuate the dose by a factor of 1000 is approximately (4.4+3.6+3.6) cm = 11.6 cm.
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The calculation of the dose rates, which arise
due to the presence of radionuclides in the
tissues (internal radiation), is required only for
patients receiving diagnostic or therapeutic
doses of radionuclides or in the case of
accidental ingestion by radiation workers.
Estimation of Internal Dose Rates
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Factors influence such calculations
are:
(1)The rate of turnover of the element in the
body. The effective half life (Teff) is derived
from the actual half-life of the radionuclide
(T½) and the biological half- life (Tb), which
defines the turnover rate
Teff = T1/2 x Tb / (T1/2+Tb)
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(2) The degree of
absorption by the body
and of selective
localization within
particular organs and the
nature of the organ.(3) The energy and quality of the radiation, the
energy of α - and β- particles being absorbed
wholly within a small volume; whereas only a
part of the emitted γ-radiation is absorbed
within the body.
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RADIATION CONTROLSRADIATION CONTROLSA. Basic Control Methods for External RadiationA. Basic Control Methods for External Radiation
ALARA (As low as ALARA (As low as reasonable attainable) reasonable attainable) principlesprinciples Decrease Time
Increase Distance Increase Shielding
B. MonitoringB. Monitoring oPersonnel monitoringPersonnel monitoringoLaboratory monitoringLaboratory monitoring oBiological monitoringBiological monitoring
. .Basic Control Methods for External RadiationBasic Control Methods for External Radiation(ALARA)(ALARA)
TimeTime: Minimize time of exposure to minimize total : Minimize time of exposure to minimize total dose. Rotate employees to restrict individual dosedose. Rotate employees to restrict individual dose . .
DistanceDistance: Maximize distance to source to : Maximize distance to source to maximize attenuation in air. The effect of distance maximize attenuation in air. The effect of distance can be estimated from equationscan be estimated from equations..
ShieldingShielding: Minimize exposure by placing absorbing : Minimize exposure by placing absorbing shield between worker and sourceshield between worker and source . .
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