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Chapter 10

HRHuman ResourcesTD Training & Development

¾ Contamination Surveys

¾ Contamination Monitoring

H-201 - Health Physics Technology - Slide 1 - Objectives

¾ Review the 10 CFR Part 20 requirements for surveys

¾ Discuss the purpose of performing surveys.

¾ Distinguish between surveys and monitoring.

¾ Discuss why there can be differences between licensee and NRC survey results.

H-201 - Health Physics Technology - Slide 2 - Objectives

¾ Describe the different types of contamination likely to be encountered ¾ Explain how the extent and magnitude of the contamination can be evaluated ¾ Describe the techniques used in performing contamination surveys ¾ Calculate the contamination levels present given relevant parameters

H-201 - Health Physics Technology - Slide 3 - Part 20 - Surveys

Subpart F--Surveys and Monitoring

Sec. 20.1501 General.

(a) Each licensee shall make or cause to be made, surveys that-- (1) May be necessary for the licensee to comply with the regulations in this part; and (2) Are reasonable under the circumstances to evaluate-- (i) The magnitude and extent of levels; and (ii) Concentrations or quantities of radioactive material; and (iii)The potential radiological . (b) The licensee shall ensure that instruments and equipment used for quantitative radiation measurements (e.g., dose rate and effluent monitoring) are calibrated periodically for the radiation measured. H-201 - Health Physics Technology - Slide 4 - Radiation Surveys vs. Contamination Surveys

H-201 - Health Physics Technology - Slide 5 - Radiation Level Monitoring From a

Ionization chamber: GM detector:

Measures mR/hr which May measure cpm is what we want but we want mR/hr

H-201 - Health Physics Technology - Slide 6 - Surface Contamination

¾ Non-fixed (removable) – means radioactive contamination that can be removed from a surface during normal conditions

¾ Fixed – means radioactive contamination that cannot be removed from a surface during normal conditions

- 49 CFR 173.403 definitions for transport

H-201 - Health Physics Technology - Slide 7 - Point vs Dispersed Source

¾ For a point source, the measured value will decrease as the is moved farther from the source due to inverse square for photons

¾ For charged particles, measurement is dependent on range of the particles

H-201 - Health Physics Technology - Slide 8 - Point vs Dispersed Source

For a dispersed source, the measured value will greatly depend on the geometry. The closer the survey meter is to the source, the more accurate the measurement will be relative to the actual amount of contamination present since only the photons or particles directly under the probe will be detected. As the probe is raised above the surface, the range of the particles becomes a factor as well as the “crosstalk” between particles outside the “footprint” of the probe which are counted and those within the “footprint” which escape. H-201 - Health Physics Technology - Slide 9 - Calculating dpm

cpm = Total Efficiency * dpm

where total efficiency is composed of the following:

IE = intrinsic efficiency of instrument (counts/hit) GE = geometric efficiency (hits/particle emitted) Y = yield of (particles emitted/disintegration)

(a “hit” implies that a photon or particle enters the detector but it may or may not result in a “count”)

H-201 - Health Physics Technology - Slide 10 - Intrinsic Efficiency (IE)

c c 1 x = min sec area of detector (cm2)

c 1 h x = cm2 - sec c 2 IE cm -sec h

This can be converted to mR/hr by using the photon fluence graph on page Misc-40 which tells us how many photons per cm2 per sec equals one R/hr.

H-201 - Health Physics Technology - Slide 11 - Factors for Calculating cpm from dpm

c = IE x GE x Y x d m m

where:

IE = intrinsic efficiency of instrument (counts/hit) GE = geometric efficiency (hits/particle emitted) Y = yield of radionuclide (particles emitted/disintegration)

(a “hit” implies that a photon or particle enters the detector but it may or may not result in a “count”)

H-201 - Health Physics Technology - Slide 12 - Factors for Calculating cpm from dpm

c = c x h x p x d m h p d m

For the general case of several different types of :

c = {(IE x GE x Y ) + (IE x GE x Y ) + …} x d m 1 1 1 2 2 2 m

H-201 - Health Physics Technology - Slide 13 - Factors for Calculating dpm from cpm

For the simple case of c 1 d one type of radiation: x = m (IE x GE x Y) m where:

IE = intrinsic efficiency of instrument (counts/hit) GE = geometric efficiency (hits/particle emitted) Y = yield of radionuclide (particles emitted/ disintegration)

H-201 - Health Physics Technology - Slide 14 - Factors for Calculating dpm from cpm

c 1d x=c h p m xx m h p d

d d c 1 = c m x c m x=c m d

For the general case of several different types of radiations: c 1 d x m = m {(IE1 x GE1 x Y1) + (IE2 x GE2 x Y2) + …}

H-201 - Health Physics Technology - Slide 15 - Geometric Efficiency (Ideal)

2B or 4B

GE = h/p If the instrument is placed on top of the However, if the detector source (e.g., a surrounds the source portable survey (e.g., a “well counter”), instrument), then the then the GE = 0.5 h/p or less. GE = 1 h/p or less.

H-201 - Health Physics Technology - Slide 16 - Example from Vendor Brochure

“Beta Efficiency = 35% as a percent of 2B emission rate”

The detector “counts” 35% of all the particles emitted in the upward direction so its intrinsic efficiency is 35% (i.e., it counts 35 out of every 100 particles that hit the detector). Since only 50% of the particles are emitted upwards (geometry), the detector “counts” only about 17.5% of ALL the particles emitted from the source.

H-201 - Health Physics Technology - Slide 17 - Example from Vendor Brochure

“Beta Efficiency = 35% as a percent of 2B emission rate”

c h p c 0.35 x 0.5 x 1 = total efficiency = 0.175 h p d d

Remember, if your ultimate goal is to detect the amount of surface contamination (:Ci or dpm), then you MUST be able to account for ALL of the particles emitted so you can get the number of disintegrations.

H-201 - Health Physics Technology - Slide 18 - Geometry (Real)

If the detector is not in contact with the source (i.e., it is not as close as possible to the source), then some of the particles travelling upwards may not hit the detector. In that case, the GE has two components:

h h u GE = = x p u p where u/p is the fraction of the particles emitted upwards (normally 0.5 for ideal situation) and h/u is the fraction of the upward particles that actually hit the detector which could be any fraction from 1 to 0 depending on how close or far the detector is from the source.

H-201 - Health Physics Technology - Slide 19 - Geometry

h h u GE = = x p u p

For example, if an alpha detector is placed on the source the GE would equal 0.5 (u/p = 0.5 and h/u =1). But if the same detector were raised about 2 inches, the GE would equal 0. Even though u/p would still be 0.5, h/u would be 0 since none of the upward particles would reach the detector.

H-201 - Health Physics Technology - Slide 20 - Problem 10-1

A radiation safety technician, carrying a survey meter with a beta/gamma GM pancake probe, enters an unoccupied laboratory where 125I iodinations are performed to conduct a routine weekly survey. When the technician moves the probe into the hood, the instrument goes off scale on the lowest scale. What could be causing this and what should be done?

H-201 - Health Physics Technology - Slide 21 - Problem 10.2

A technician enters a laboratory where small sources of americium are used for research. The technician is carrying a ZnS alpha scintillation survey meter. The technician scans the counter top with negative results. The technician then stoops down to check the floor and notices that the instrument registers a positive result whenever it crosses a seam between floor tiles. What could this mean?

H-201 - Health Physics Technology - Slide 22 - Problem 10.3

An individual is drawing a dose of 99mTc from a vial. The individual is wearing gloves and the syringe is shielded. After drawing the dose and administering it to a patient in a dosing room, the technician removes the gloves and discards them in radioactive trash. The technician then proceeds to an imaging room where another patient is just completing a scan. When the technician moves his/her arm under the camera to adjust something, the imaging screen up like a Christmas tree. What could this mean?

H-201 - Health Physics Technology - Slide 23 - Problem 10.4

The surface contamination limits listed in USNRC Regulatory Guides are given in terms of dpm per 100 cm2. You are performing a surface contamination survey using an alpha probe which has a scale calibrated in cpm. The sensitive area of the probe is 60 cm2. Brieflyyp explain what you would do to make your measurement(s) consistent with the limits.

H-201 - Health Physics Technology - Slide 24 - Problem 10.5

A technician uses a GM pancake probe to monitor a tabletop for beta/gamma surface contamination. The probe has a sensitive area of 15 cm2. The technician surveys an area measuring about 400 cm2 and obtains an average reading of 2,300 cpm. The background is 100 cpm. The instrument has a total efficiency (intrinsic and geometric) of 10%. What is the contamination level in terms of dpm per 100 cm2?

H-201 - Health Physics Technology - Slide 25 -

Although these helpful hints refer to the old NRC Reg Guide 10.8 and a previous version of 10 CFR Part 35, they still illustrate the conceptft of cond ucti ng surveys at varying frequencies depending on the level of .

Problem 10.6

There is an 131I spill at a nuclear pharmacy. The spill area measures about 3 m in diameter. The count rate using a GM pancake probe is 1 x 107 cpm with a 20% intrinsic efficiency, i.e., 2 out of every 10 betas hitting the detector are counted (assume the gamma efficiency is very small compared to the beta efficiency). The probe face area is 50 cm2. What is the estimated dose rate to the gonads about 1 meter above the ground?

H-201 - Health Physics Technology - Slide 30 - Problem 10.7

You are using an air with the beta window open. You are measuring a relatively high dose rate. You close the beta window. The dose rate is reduced by ½. What does this mean?

H-201 - Health Physics Technology - Slide 31 - Problem 10.8

You have performed a survey of the surface of the exterior wall of a shielded exposure room. All of your measurements were less than 1 mrem/hr. As you walk away from the wall you note that the exposure rate appears to be increasing to about 3 mrem/hr. How do you explain this?

H-201 - Health Physics Technology - Slide 32 - Problem 10.9

An NRC inspector, using an air ionization chamber, measures 40 mR hr-1 at a rope barrier set up by a radiographer. The area outside the rope barrier is designated an unrestricted area. Do you concur with this designation? Briefly explain why or why not .

H-201 - Health Physics Technology - Slide 33 - END OF CHAPTER 10

H-201 - Health Physics Technology - Slide 34 -