Secure Order Radiation Detectors Contact

   Test Source
   Battery Box
   Coincidence Box
   GMI Interface
   Air Sampler
Users Group
Raspberry Pi
Random Numbers
Safety Uses
Radiation Info
Rad Map
Secure Order

Assorted Facts

By George W. Dowell

2.54 cm = 1 inch. 30.4 cm = 1 foot. 2.83E4 cc = 1cubic foot.
The atom is the smallest part of an element that can be
separated by chemical reaction.
Atomic number is the number of protons. This is known as the
Z number.
Atomic mass number is the sum of the number of protons
and neutrons in the nucleus. This is known as the A number.
Protons and Neutrons are called Nucleons.
One atomic mass unit (AMU) is equal to 1/12 the mass of a
carbon-12 nucleus. (1.6604E-24 g.) (Also called a Dalton.)
Radioactivity is the process by which the nucleus of unstable
nuclides disintegrates with the resulting emission of nuclear
radiation. Becquerel discovered radiation.
Half-Life is the term in which half of the atoms of a particular
radioactive substance decay to another nuclear form, or element.
Ionization is the general process of producing Ions by the
passage of high energy particles.
Chronic radiation exposures are those involving continuous
or repeated exposures over a relatively long time interval.
Acute radiation exposures are involving relatively large doses
in a short time.
Somatic effects refer to the individual that received the exposure.
Isotopic abundance is the amount of the isotope (percentage)
present in a normal natural mixture of the element.
Isotopes are defined as atoms with the same atomic number
(Z) but different atomic mass number (A).
Linear Attenuation Coefficient: " A fraction decrease in energy
through absorption of material inverse of the mean free path".
This is the name that describes the number of interactions
per unit length.
The unit for energy in nuclear reactions is the electron volt (ev),
which is the amount of energy gained by an electron when
accelerated through a potential difference of one volt.1 Mev
is 1E6 ev.
A Curie is 3.7E10 dps (one dps is equal to one Becquerel) or
2.22E12 dpm. A Pico Curie is 2.22 dpm
The Roentgen is a measure of Exposure of air to gamma and
x-rays. The energy absorbed by one gram of air exposed to
one Roentgen of gamma rays is 87 ergs. There is no SI
The RAD is used as a unit of measurement for the energy
deposited by any radiation in any material. 1 Rad = 100 ergs/gm
any radiation in any material. 100 Rad = 1 Gray.
REM is Dose Equivalent resulting from any type of radiation
exposure. Rem is the unit of measure for internal exposure.
REM Dose = RAD Dose x Quality Factor. 100 Rem = 1 Sievert.
Quality Factor is used to convert Absorbed Dose (RAD) to
Biological Effect (REM). QF: Gamma = 1, Beta = 1, Thermal
Neutron = 2 (NEU) to 3 (DOE), Fast Neutron = 10, Alpha = 20,
Proton = 10.
The new 10 CFR 20 and 10 CFR 835 is based on ICRP #26.
A major change in dose limits between the old and revised
10 CFR 20 is that the old limits are based on calendar quarter
time period and the revised limits are based on an annual
time period.
An individual must be supplied with a personnel monitoring
device if entering the restricted area and will receive or is
likely to receive an exposure in excess of 10% of the (federal)
limit. A minor will be allowed 10% of an adults limit per year.
When entering a high radiation area, you need personnel
monitoring devices.
TODE, Dose limit for the extremities as per 10 CFR 20 is 50
DDE, deep dose equivalent, is dose to the whole body (WB)
from 'external' radiation exposure.
TEDE, total effective dose equivalent, is the sum of all internal
and external dose.
CDE is the dose equivalent from Internal exposure to an
individual organ or tissue, as calculated over a 50 year period
after the exposure. CEDE equates risk from organ to risk from
whole body dose.
WF, weighting factor, is the equivalent whole body exposure
from exposure of all organs due to radioactive material intake.
According to the ICRP "ALI" stands for Annual Limit on Intake.
1 ALI = 2000 DAC Hrs = 5 Rem.
The annual PSE limit for TEDE is 5 Rem. PSE = Planed special
exposure. The NRC must be notified prior to any PSE.
A radiation area is posted at 5 mr/hr @ 30 cm.
The revised 10 CFR 20 specifies that radiation levels be
measured at 30 cm.
Black lettering is now ok for Radiation signs.

-- The nucleus carries a positive charge.
-- Protons and Neutrons are collectively known as "Nucleons".
-- The diameter of the nucleus is relatively small compared to the diameter
of the atom.
-- Electrons carry a negative charge.
-- Electrons, protons, and neutrons ARE NOT all about the same size.
-- The nucleus contains 99.9% of the mass of the atom and about 10E-10 of
the volume.
-- The number of orbital electrons is equal to the number of protons in
electrically neutral atoms.
-- A Proton is an elementary particle that is identical with the nucleus of
a Hydrogen atom and carries a positive charge.
-- C0-60: The element is Cobalt, with 60 nucleons, 27 protons, 33 neutrons.
-- An atom of a Carbon-12 has six protons, and six neutrons. If a Carbon-12
atom and an alpha particle were fused together, an Oxygen-16 isotope would
-- 95Am-241 has 95 protons and 146 neutrons.
-- 38Sr-90 decays by emission to Y-90. You would add 1 to the number of
protons, so the scientific nomenclature of the daughter is 39Y-90
-- The highest to lowest relative penetration of 1 MeV Alpha, Beta, and
Gamma rays is: Gamma, Beta, Alpha.
-- Charged particles interact with matter by Excitation and Ionization.
-- Ionizing radiation interacts with the orbital electrons of an atom and
creates two particles of opposite charge, these particles are called ion
-- The primary mechanisms whereby charged particles lose energy in
transversing materials are ionization and excitation affecting the
electronic structure of the material atoms.
-- Alpha Particles (a) are Helium Nuclei emitted from the nucleus of an
unstable atom.
-- The interaction between alpha particles and atoms is most through
columbic. (electrostatic)
-- A 7 Mev Alpha particle travels in air 2 inches.
-- The range of beta particles in air depends on the energy of the particle.
-- The range of 1Mev beta particle in air is about 10 ft. (12ft actual per
-- A beta particle can be either a positively or negatively charged
-- The electron has a negative electrostatic charge, and is equal in charge
intensity to the proton. It's mass is 1/1838 that of a proton.
-- A beta particle is an electron (1/1838 mass of a proton) emitted from the
nucleus of a radioactive isotope.
-- Bremsstrahlung radiation is originated by a high energy beta particle as
it decelerates near a heavy nucleus.
-- The secondary radiation produced when beta particles are stopped by
shielding is bremsstrahlung.
-- The difference between X-rays and gamma photons of the same energy is
their origins.
-- Nuclear radiation refers to the emanation of the energetic particles
and/or the electromagnetic wave from the nucleus of the atom.
-- Atomic radiation refers to electromagnetic waves emitted from the
electron shell.
-- A single quanta of electromagnetic energy is called a photon.
-- Gamma photons originate in the nucleus of the atom.
-- After undergoing Compton Scattering, a gamma photon is deflected off at
an angle with reduced energy.
-- Pair Production is when a high energy photon enters the vicinity of an
atoms nucleus, the photon energy is converted into an electron-positron
pair. (1.022MeV.)
-- Pair production is when a high energy photon (more than 1.022 Mev) enters
the vicinity of an atom's nucleus, the photon energy is converted into an
electron-positron pair.
-- X-rays come from electromagnetic ionizing radiation emitted by an orbital
electron as it moves from the L shell to the K shell (changing energy
-- X-ray radiation refers to electromagnetic waves associated with
electronic energy transition. (electron cloud)
-- During photoelectric effect, a gamma photon gives up all of its energy to
orbital electrons.
-- The photon (gamma) interaction where a portion of the photons kinetic
energy is transferred to an atom's orbital electron is called Compton
-- The minimum energy photon in theory for a pair production is 1.022 Mev,
however, this type of interaction in not observed for photons having
energies less than about 2.5 Mev.
-- Neutrons can cause ionization indirectly by knocking charged particles
out of the nucleus. (Protons out of H-1)
-- A Neutron has no charge.
-- Fast Neutrons are the most severe external radiation hazard.
-- H-1 (Hydrogen) has the most effect on the thermalization of fast neutrons
as far as biological chemicals.
-- In soft tissue, fast neutrons lose 80% to 90% of their energy by
interacting with hydrogen.
-- The chief difference between fast and slow neutrons is their (kinetic)
--- Elastic scattering slows down neutrons because it causes a neutron to
lose kinetic energy without exciting the target nucleus.
-- After an inelastic scattering process, the excited nucleus will emit a
gamma photon.
-- A neutron is absorbed and a gamma is released, is the best description of
the method of inelastic scattering pertaining to neutrons.
-- Beta decay process: During radioactive decay, a nucleus emits an
electrically charged particle equal in mass to an electron.

Part Three: Detectors and Meters

-- (MDC) Minimum detectable counts is the smallest number of sample counts
that are statistically greater than the background counts and are a result
of radioactivity in the sample.
-- (MDA) Minimum detectable activity is the minimum activity present in a
sample that may be detected by a particular instrument.
-- The purpose of the chi-squared test is to ensure that the instrument's
results lie within a normal Gaussian Distribution.
-- Pulse height determines which source it is. Alpha pulses are the highest.
-- You don't check the desiccant for a initial check on instruments prior to
use, or the beta shield calibration (duh).
-- The following checks are made on a survey instrument prior to use: check
the instrument for date calibrated (calibration expiration date), proper
battery condition, and a response check.
-- The principal that explains the operation of most radiation detection
instruments is the radiation causes ionization in the detector which is
converted into a meter reading.
-- Radiation is not measured directly, but is measured instead by its effect
on the detector walls or the material within the detector.
-- In a gas filled detector, radiation ionizes the fill gas releasing
electrons that are attracted to the positively charged anode and measured by
the electrical circuitry.
-- The ratio of intensity measured by the detector (intensity of the primary
beam and scatter radiation) to the calculated actual intensity is the
buildup factor.

-- The type of gas used would affect the sensitivity of an ion chamber
detector because some gases ionize more easily than others.
-- An ion chamber produces output based on the ions produced in the wall of
the chamber.
-- In the ionization chamber, the detector output is approximately equal to
the amount of primary ionization produced in the gas.
-- An ion chamber survey instrument is used to ascertain the amount of
exposure personnel would receive as it accounts for all the ionization
events occurring.
-- The instrument used for the best tissue equivalent dose rate is the ion

-- The Dead Time for GM detectors is the period in which a second pulse will
not be detected.
-- Unless some type of quenching gas is used, a Geiger-Mueller detector will
re-trigger its avalanche because of electrons released while the positive
ions interact with the outer wall.
-- When compared to ion chambers, proportional counters and fission
chambers, the Geiger-Mueller detectors are the most sensitive to low level
gamma fields, but not more accurate.
-- In the Geiger-Mueller detector the output pulse is approximately
independent of the type and energy of the radiation entering the detector.

-- Proportional counters operate at higher voltages than ionization
chambers. (RIPLGC)
-- A proportional counter system can tell the difference between alpha and
beta radiation because the size of the pulse caused by the alpha interaction
will be much higher than the pulse caused by the beta interaction.
-- The main advantage of using a proportional counter is it is able to
differentiate between different types of radiation.

-- The function of the Photo Cathode in a photo-multiplier (PM) tube is to
release electrons when it is struck by light emitted from scintillation.
-- In a scintillation detector, the photomultiplier tube converts and
amplifies the electrons freed by ionization in the scintillation crystal to
a larger light output.
-- In general, scintillation detectors are more sensitive then gas-filled
detectors for gamma radiation because they contain material with a higher
density for gamma's to interact. They are often used for counting
measurements in laboratories.
-- Surface medium for scintillators, alpha is zinc sulfide (ZnS), beta is
anthracene, and gamma is sodium iodine (NaI).

-- The GeLi is a Semi Conductor Detection System. The middle section is
composed of germanium and lithium mixture. Pure germanium is on one side of
the mixture and pure lithium on the other side. When a gamma enters the
center region of the crystal it undergoes an interaction that frees an
electron from one of the atoms in the crystal. When this happens, a vacancy,
or hole is left in the inner electron shell around the nucleus.
-- The center region is the part of the semiconductor crystal that is
sensitive to ionizing radiation.
-- When a gamma ray is detected by a semi-conductor crystal a flow of free
electrons is initiated toward the positive end of the crystal.
-- For a semiconductor material to detect radiation, the voltage applied to
the detector must be large enough to separate the positive charges from the
negative charges to form a depletion region.
-- In Germanium crystal detectors, the flow of free electrons towards the
positive electrode and the apparent movement of holes toward the negative
electrode create a current flow in the circuit.
-- A whole body counter is for measuring internal gamma emitters.
-- In-vivo or whole body counting, determines the amount of a radionuclide
deposited in an individual by liquid or solid crystal scintillation

-- It is important to add moderating materials to shield for a fast neutron
source since the absorption cross section for most elements increases as the
velocity or energy of the neutron decreases.
-- A good thermal neutron absorber used in the portable detectors is
-- The neutron interaction used in portable survey instrumentation is
neutron capture with the emission of a charged particle.
-- Neutron detectors are easy to design because there are a large number of
materials with large cross sections for absorption.
-- Paraffin is used to attenuate fast neutrons.

-- Individual dosimeter placement could be described as an error associated
with relating a dosimeter reading to an actual dose.
-- Beta and gamma exposure is determined in a Beta-Gamma Radiation field
using film/TLD dosimetry by subtracting the closed window (shielded) film
reading from the open window (unshielded) film/TLD reading.
-- Finger rings don't have a need for neutron sensitivity.
-- Minute by minute update on exposure is not an error or problem in
relating TLD readings to the actual dose received by the body.
-- A TLD's disadvantage is that it is expensive to use.

-- Recognize the Decay Formula and the Decay Constant. (l) ln2/t1/2.
-- In an atom prior to Beta Minus Decay, there will be excess neutrons in
the atoms nucleus.
-- Materials with a low Atomic Number (such as water, plastic, and paraffin)
are used in making neutron shields because their atomic size allow for
greater transfer of the neutrons energy per collision.
-- Shallow dose equivalent applies to the external exposure of the skin or
an extremity and is taken as a dose equivalent at a tissue depth of 0.007cm
averaged over an area of 1 cm2.
-- Using the assumption that 2" of lead equals one tenth thickness, the
amount of shielding required to reduce a Cs-137 gamma beam of 100 mr/hr
intensity to 1 mr/hr would be 4". (1/100)
-- The mathematical expression which expresses the relationship between the
radioactive decay constant and the half-life of an isotope is, T 1/2 = ln2/
Decay constant.
-- The decay process emitting an alpha particle can be described as when a
positively charged particle with a mass equal to a Helium nucleus is emitted
from a nucleus during radioactive decay.
-- To determine shielding, build up factors is not a valid reason to perform
a radiation survey.
-- If you shield a beta source with a higher atomic number shielding
material, you will create more X-rays. (Bremsstrahlung).
-- Shielding material with a high atomic number attenuates radiation more
effectively than a lower atomic number material because, more electrons are
available for interactions.
-- The decay constant and the half-life are constants for a given
-- The effective half-life formula is Teff = (TR x TB) + (TR + TB). The
result will always be shorter than the shortest half-life.
-- Beta shielding is better accomplished by aluminum than lead due to the
production of Bremsstrahlung radiation.
-- The actual decrease in the intensity of a beam of gamma rays passing
through a wall is less than the theoretical decrease because some gamma
interactions result in other gamma rays of lower energy being given off,
this is called buildup.
-- The shielding half value thickness for 1 Mev gamma of: lead is 0.5
inches, concrete is 4 inches, and water is 8 inches. The shielding tenth
value thickness for 1 Mev gamma of: lead is 1.5 inches, concrete is 12
inches, and water is 24 inches. The shielding half value thickness for 6 Mev
gamma of: lead is 0.7 inches, steel/iron is 1.3 inches, concrete is 8
inches, and water is 16 inches. The shielding tenth value thickness for 6
Mev gamma of: lead is 2 inches, steel/iron is 4 inches, concrete is 24
inches, and water is 48 inches.
-- For lines and equipment containing reactor water, or primary steam with
hold-up times of less than five minutes, you would use 6 Mev gamma 1/10
shielding (lead 2", water 48").

Thinking of buying a surplus CDV-700 or 715 detector? Be sure to read our report first.