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Lesson one keep in mind that requirements and standards might have changed since the information hasn't been updated since 10/28/17. But regardless the information should give you a valuable look at the job of a radiation protection technician or nuclear technician and let you get some practice in. You can click this link to move onto the next lesson.
This procedure provides basic instructions to operate
common instruments used for radiation and contamination surveys. General descriptions, operating
characteristics and limitations of these instruments are provided as
attachments.
1.2
Scope and Applicability
This procedure provides guidance for the selection and
operation of portable instruments that measure gamma, beta, alpha and neutron
radiation. If supplemental personnel are
expected to operate instruments beyond the scope of this procedure, additional
training may be required consistent with the site training and qualification
program.
This procedure will be used to train supplemental
radiological protection technicians.
Current revisions are maintained on the INPO website.
Terms, acronyms, and definitions are provided in
NISP-RP-13, Radiological Protection
Glossary.
Clarifying notes for requirements and process steps
are provided in Section 4.0 using superscript numbers in the preceding sections.
2.1
Ensure that selected survey instruments
are appropriate and calibrated to detect the types of radiation present in the
work area.
2.1.1
Ensure that instruments used to measure
radioactivity count rate have a scale that reads in units of counts per minute
(cpm) or a multiple of this unit.
2.1.2
Ensure that instruments used to measure
gamma dose rate have a scale that reads in units of mR/hr or mrem/hr or a
multiple of these units.
2.1.3
Refer to Attachment 1, “General Radiation
Detector Types and Uses” for general information on instrument types and use.
2.1.4
Refer to Attachment 2, “Typical Portable
Radiation Detection Systems in Use at Nuclear Power Stations” to obtain
specific information about standard portable detection systems.
2.1.5
Read all tags and labels on an instrument
to determine if the use of a scale is restricted.
2.2
When using an instrument model for the
first time, review the applicable manufacturer technical or operational manual,
or operating procedure to understand the data display, control adjustments, and
limits.
2.3
Ensure the instrument is turned on prior
to entering an area to survey. Zero the instrument, if applicable, prior to
entering the radiation field.
2.4
Prevent contamination of an instrument by
avoiding contact with contaminated surfaces or bagging the instrument prior to
use in a contaminated area.
2.5
Prevent damage to thin window detectors by
avoiding contact with small, sharp objects.
2.6
Apply appropriate correction factors as
provided by site procedures.
2.7
When using an instrument with an internal
detector, use case markings to align the detector with radiation sources.
2.8
When using an instrument with an analog
meter, allow the meter to recover/stabilize from inertial effects on the
needle.
2.9
If the instrument has a scale adjustment,
set the instrument on a scale appropriate for the expected dose rates prior to exposing the instrument to the radiation field.
2.9.1
Adjust scales with the objective to obtain
a stabilized reading between 10% and 90% of the scale.
2.9.2
Allow the meter to stabilize after
switching scales due to the potential for electronic noise to cause a temporary
meter deflection.
2.9.3
If radiation levels are < 10% of the
lowest scale, consider the radiation levels to be lower than the minimum
sensitivity of the instrument and therefore a meter with a more appropriate
range meter scale should be used
2.9.4
Prevent instrument damage by avoiding
exposure to excessive heat, moisture, and radiation fields that are
significantly above full- scale of the instrument.
3.1
Perform Pre-Use Instrument Inspections and
Checks.
3.2
Inspect instruments for physical damage
prior to and during use.
3.2.1
Ensure all cables are connected securely;
verify no spikes or erratic results are displayed when moving cables.
3.2.2
Ensure switches and knobs can be operated without
restriction.
3.2.3
If using a scintillation detector, turn
the instrument on and check for punctures in the detector window by exposing
the detector to a light source. An increase in the background count rate may be
indicative of a punctured window.
3.2.4
If damage is suspected, tag the instrument
out of service and contact appropriate site instrument coordinator or
supervisor.
3.3
Ensure the instrument has a calibration
sticker affixed and that the calibration due date is in the future.
3.4
If the instrument has a Battery Check
mode, perform a battery check and ensure that the reading is within the
specified range.
3.5
When inspecting an instrument with an
analog or digital meter:
3.5.1
Ensure a source check per the required
frequency has been performed on the scales expected to be used.
3.5.2
When performing source checks, use the
identified source.
3.6
If the site uses an instrument
accountability system, sign instruments out and in as appropriate.
3.7
Operate an Ion Chamber Survey Instrument
3.7.1
Determine the gamma dose rate by holding
the instrument in a steady position with the window closed and allowing the
readout to stabilize.
3.7.2
Determine the beta dose rate by obtaining
open window and closed window readings with the instrument in the same
position. Apply the following
calculation:
|
where: |
|
|
WO= |
Window Open |
|
WC= |
Window Closed |
|
CFβ= |
Beta Correction Factor (provided on an
instrument label or in site procedures)
|
3.7.4
Apply correction factors as provided by
site procedures as needed to convert readings to dpm/100 cm2 (e.g.
75,000 dpm/mR per hour of Cs-137).
3.8
Operate a GM Survey Instrument
3.8.1
Determine the gamma dose rate by holding
the instrument in a steady position and allowing the display to stabilize.
a.
If the detector has a beta window, ensure
the window is closed during gamma measurement.
3.8.2
Exercise caution if a reading is off-scale
high or low due to the potential for over-ranging conditions that may damage
the instrument.
a.
Remove the instrument from the radiation
field and/or change scales to prevent over-ranging conditions.
3.9
Operate a Count Rate Meter with a GM
Frisker Probe
3.9.1
Turn on the count rate meter and allow
approximately 10 seconds for an analog count rate meter to stabilize.
3.9.2
Estimate background by setting the range
switch on the lowest range with an on-scale reading and setting the response
time to the slowest setting, if adjustable.
3.9.3
Determine the count rate by multiplying
the value indicated on the meter by the scale factor shown on the range
selector switch.
3.9.4
Frisk surfaces as instructed in
NISP-RP-02, Radiation and Contamination
Surveys.
3.9.5
Convert count rate readings (CPM) to disintegration
rate (DPM) as follows:
a.
For pancake GM detectors, multiply the CPM
meter reading by 10 or as directed by RP supervision.
3.9.6
Press the reset button to clear alarms as
needed.
3.10
Operate a Count Rate Meter with an Alpha,
Beta, or Dual Scintillation Probe
3.10.1
Turn on the count rate meter and allow
approximately 10 seconds for an analog count rate meter to stabilize
3.10.2
For instruments with multiple channels for
alpha, beta, or dual response, ensure the instrument is set to appropriate mode
corresponding to the probe being used.
3.10.3
Maintain the protective cover over the
detector when not in use to prevent puncturing the thin film window.
3.10.4
Estimate background radiation level by
setting the range switch on the lowest range that provides an on-scale reading.
a.
When using a dual scintillation probe for
both alpha and beta readings, ensure that separate background readings are
measured.
3.10.5
Determine the count rate by multiplying
the value indicated on the meter by the scale factor shown on the range
selector switch.
a.
Some digital instruments may automatically
switch ranges and directly show the corresponding cpm values.
3.10.6
Frisk surfaces as instructed in
NISP-RP-02, Radiation and Contamination
Surveys.
3.10.7
Convert count rate readings (CPM) to
disintegration rate (DPM) as follows:
a.
Multiplying
the meter reading by the factor labeled on the instrument or as provided by RP
supervision.
b.
When using a dual alpha and beta
scintillation probe, ensure that the appropriate factors are applied to alpha
and beta readings.
3.11
Operate a Neutron Rem-meter
3.11.1
Turn on the analog neutron rem-meter and
allow approximately 10 seconds for the meter to stabilize.
3.11.2
Determine the neutron dose rate by holding
the instrument in a steady position allowing the readout to stabilize.
3.11.3
If required by site procedures, apply correction
factors to meter results to get corrected readings.
4.0
Clarifying Notes
4.1 Some
digital instruments
automatically switch ranges and
directly display cpm
values without the need for applying multiplication factors.
5.1
NISP-RP-02, Radiation and Contamination Surveys
Attachment 1: General Radiation Detector Types and Uses
General Types of Radiation Detectors
There are
several types of radiation detectors used in the nuclear industry, some of the
more common detector types are listed below along with general information on
detector type, their operation, and use.
Gas-filled Detectors
All gas-filled detectors require a voltage be applied
between a center anode and the detector chamber (cathode). As a radiation particle or photon enters the
chamber, it ionizes gas atoms creating positive ions and free electrons which
are captured by the positive charge on the anode and negative charge on the
cathode. The collection of these ions and electrons creates a pulse which is
sensed and converted by the instrument’s electronic circuitry to provide an
accurate display of the measured contamination or radiation fields depending on
the type of instrument. By varying the voltage on the chamber, three useful
types of gas-filled detectors can be created; Geiger-Mueller (GM) detectors,
proportional counters, and ionization chambers.
The gas inside the detectors can vary depending on
design and use. Certain gas-filled
detectors operate on normal air while others use specialty gas.
GM detectors have a relatively high voltage
(approximately 1000 - 1400 volts) applied to the chamber and as such, every
particle or photon entering the chamber creates enough secondary ionizations
that the entire chamber is ionized producing one large pulse.
Proportional
counters have less typically more voltage applied than GM
detectors (approximately 300 –800 volts) which can vary depending on its
use. Because the voltage is typically
more, proportional detectors can be set up to produce pulses that are
proportional to the energy of the incident radiation and therefore can be used
to differentiate between alpha and beta particles. Common hand-held
proportional detectors include both gas-flow and sealed chambers. Gas-flow proportional detectors require a
constant flow of gas through the chamber in order to operate.
Ionization
chambers
require varying amount of voltage (approximately 50 - 300 volts) and are
designed to produce outputs which are relative to the incident energy of the
photons or particles and thus can be calibrated to be relatively energy
independent.
Ionization chambers are one of the preferred detectors
for measuring gamma dose rates because they can measure deep dose equivalent
and tend to be accurate over a wide range of gamma energies. Ionization chambers
have varying responses to neutron radiation due to recoil protons
Scintillation Detectors
Certain crystals, plastics, liquids and other
materials will “scintillate”, or give off visible light, when they absorb
ionizing radiation. The amount of light
emitted is proportional to the amount and energy of ionizing radiation that
they absorb. When coupled with a photomultiplier tube or photo cathode (devices
which convert visible light into electronic pulses) these materials make very
useful radiation detectors.
Scintillation detectors are widely used to detect alpha, beta, and gamma
radiation and can be used to measure gamma dose rate and contamination.
Because the properties of certain materials allow them
to absorb radiation differently, certain scintillation detectors are more
useful than others for specific radiation types. There are many types of scintillation
materials and detectors, but the common ones used for hand-held applications in
the nuclear power industry are:
Zinc
Sulfide (ZnS) Detectors are
generally used to measure alpha contamination.
A thin layer of ZnS effectively absorbs the energy from alpha particles
and produces light but the ZnS layer does not have the characteristics to
efficiently absorb beta particles or photons.
ZnS detectors are excellent detectors for detecting low levels of alpha
particles because of their inherently low response to background.
Plastic
Scintillator Detectors
are typically used to detect beta and gamma radiation. Thin
layers of plastic scintillators are very effective in measuring beta particles
and very low energy photons, such as those emitted from Iodine-125. Thin plastic scintillators are too thick to
produce light from alpha particles and are not large enough to absorb gamma
rays of moderate energy and thus are very good beta detectors.
Thick plastic scintillators absorb
moderate to higher energy photons effectively and can be used for measuring
gamma dose rate and gamma rays from contamination but are too thick to effectively
absorb alpha or beta particles and covert them to measurable light. Plastic scintillator detectors are very
popular because plastic can be molded in a variety of configurations to provide
specialty application. Thick plastic scintillation detectors are often used in
vehicle monitors, tool monitors, and some hand-held instruments, such as
micro-rem meters.
Sodium Iodide
Detectors (NaI)
Sodium Iodide (NaI) crystals are
used in a variety of applications and are very effective in detecting gamma
photons. Thick NaI detectors are very
sensitive to gamma radiation and can be used for gamma monitoring and gamma
spectroscopy. Detectors with thin NaI
crystals can be effectively used to measure lower energy photons and are mostly
used in medical applications.
Cesium Iodide
Detectors (CsI)
Cesium Iodide (CsI) crystals are
used in some portable detectors for measuring gamma radiation. Handheld systems
with CsI detectors are also used to perform gamma spectroscopy and can be used
for underwater applications.
Dual Scintillation
Detectors
Some detector probes contain a
combination of scintillation material allowing them to detect more than one
type of radiation simultaneously. Common
types of dual scintillation probes contain a thin plastic scintillator with a
coating of ZnS. These probes are
effective in surveying for both alpha and beta particles at the same time and
if used with the appropriate electronics, can provide a separate readout for
alpha and beta count rate.
Semi-Conductor
Detectors
Semi-conductor detectors (sometimes referred to as
“solid-state” detectors) have properties midway between a good conductor and a
good insulator and can act much like an ionization chamber. Common materials
used to make semi-conductor detectors includes Germanium and Silicon. Germanium detectors are often used for gamma
spectroscopy and laboratory applications; however, Silicon has been widely used
to make portable detection systems including alarming dosimeters, air monitors,
and some area monitors.
Attachment 2: Typical Portable Detection Systems in Use at
Nuclear Power Stations
|
Manufacturer |
Model(s) |
Detector Type |
Typical Use |
Typical Range |
Notes and Special Considerations |
Image |
|
Ludlum |
12-4 |
Internal He3 Proportional Counter |
General area neutron dose rate surveys |
4 Ranges 0 to 10,000 rem/hr |
·
Instrument provides gamma background rejection up
to 12 R/hr. |
 |
|
Ludlum |
14-C |
Internal GM Probe for dose rate monitoring External Pancake GM Detector for count rate
monitoring |
Internal probe can be used for dose rate
monitoring External Pancake probe used for beta
contamination monitoring |
Internal
Probe: 5
Ranges 0 to 2
R/hr External
Probe: 4
Ranges 0 to
660K cpm |
·
Ensure that the selector switch is set to the
correct detector (i.e. internal vs. external) to ensure proper result. |
 |
|
Ludlum |
177 |
Beta + Gamma |
GM |
0 cpm - 500k
cpm |
·
Meter face can have both mR/hr and cpm
readouts. User must be aware of the
probe and calibration and use proper scale |
 |
|
Ludlum |
3 |
External Pancake GM Detector for
count rate monitoring |
External Pancake probe used for
beta contamination monitoring |
External Probe: 4 Ranges 0 to 500K cpm |
·
Meter face can have both mR/hr and cpm
readouts. User must be aware of the
probe and calibration and use proper scale |
 |
|
Ludlum |
3 |
Gamma |
GM |
0 - 200 mR/hr
|
·
Meter face can have both mR/hr and cpm
readouts. User must be aware of the probe
and calibration and use proper scale |
 |
|
Ludlum |
9-7 |
Beta + Gamma |
Ion Chamber,
2 detectors |
LOW:
0.001 – 1.99 R/hr MID:0.1
- 199.9 R/hr HIGH:0.01-
19.9 KR/hr |
·
Can be used with low, mid, and high range probes ·
Digital readout ·
Similar controls to RO-7 |
 |
|
Mirion |
AMP-50/100/200 |
Internal Energy Compensated GM Tube |
Remote area monitor or underwater detector |
AMP-50: 10uR/hr
to 4 R/hr AMP-100: 0.5
mR/hr to 1,000 mR/hr AMP-200: 0.5
R/hr to 10,000 R/hr |
·
Cables can be up to 350’ long ·
Unit can be used with WRM wireless transmitters |
 |
|
Mirion |
Ram Gam-1 |
Internal energy compensated GM
tube |
General area and contact gamma dose rate surveys. Often used for shipping surveys since it
can get close to packages for contact readings. |
0.05mR/hr to 999mR/hr |
·
Digitial Instrument |
 |
|
Mirion |
RDS-30 |
Internal energy compensated GM
tube |
General area and contact gamma
dose rate surveys. Often used for
shipping surveys since it can get close to packages for contact readings. |
1 uRem/hr to 10 Rem/hr |
·
Digital instrument ·
Needs factory software to calibrate |
 |
|
Mirion |
RDS-31 |
Internal energy compensated GM
tube |
General area and contact gamma
dose rate surveys. Often used for
shipping surveys since it can get close to packages for contact readings. |
1 uRem/hr to 10 Rem/hr |
·
Digital instrument ·
Needs factory software to calibrate |
 |
|
Mirion |
Telepole |
2 Internal energy compensated GM
tubes 1 high range, 1 low range |
General-area and contact gamma dose rate surveys. Can be used for shipping surveys since it
can get close to packages for contact readings |
0.05 mR/hr to 1000 R/hr |
Pole extends 11’ |
 |
|
Thermo Eberline |
6112B Teletector |
2 internal GM Detectors for Low and High Range |
General-area and contact gamma dose rate surveys |
5 Ranges 0.1 mR/hr to 1000R/hr |
·
Detectors extend to approximately 13’ |
 |
|
Thermo Eberline |
E-140 |
External GM probe |
General area and contact gamma dose rate
surveys. Often used for shipping
surveys since it can get close to packages for contact readings. |
0 to 200 mR/hr when calibrated to dose rate |
·
Meter face has both mR/hr and cpm readouts. User must be aware of the probe and
calibration and use proper scale. |
 |
|
Thermo
Eberline (formally
Bicron) |
Microrem |
Gamma + X-Ray
|
TEP
Scintillator |
5 Ranges 0 - 200
mRem/hr |
·
Tissue equivalent and flatter energy response
than Ludlum Micro-R |
 |
|
Thermo Eberline |
RM-14 |
External Pancake GM Detector for count rate monitoring |
External Pancake probe used for beta contamination monitoring |
External Probe: 3 Ranges 0 to 500K cpm |
·
Can be used with both a GM pancake probe or with
an end-window GM probe in a fixed counting holder |
 |
|
Thermo Eberline |
RO 2/2A |
Internal Ion Chamber |
General-area gamma and beta dose rate surveys |
RO-2: 4
Ranges 0.1
mR/hr to 5 R/hr RO-2A 4
Ranges 1
mR/hr to 50 R/hr |
·
Has two battery checks for each of the two
batteries ·
Significant changes in atmospheric pressure or
temperature can affect reading and require re-calibration |
 |
|
Thermo Eberline |
RO 20 |
Internal Ion Chamber |
General-area gamma and beta dose rate surveys |
5 Ranges 0.1 mR/hr to 50 R/hr |
·
Updated model of the RO-2 which includes the
additional RO-2A range |
 |
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