Identifying unknown isotopes using the sam 935 surveillance and measurement system
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Identifying Unknown Isotopes Using the SAM-935 Surveillance and Measurement System. V11 Firmware Revision . Overview. Why I.D. Unknown Radioisotope Instrument Operating Principle Instrument Set-up Startup/Calibration Monitoring and “Capture” Sampling Interpreting Results

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Identifying unknown isotopes using the sam 935 surveillance and measurement system

Identifying Unknown Isotopes Using the SAM-935 Surveillance and Measurement System

V11 Firmware Revision


Overview
Overview and Measurement System

  • Why I.D. Unknown Radioisotope

  • Instrument Operating Principle

  • Instrument Set-up

  • Startup/Calibration

  • Monitoring and “Capture” Sampling

  • Interpreting Results

  • Hands-on Scenario


Overview1
Overview and Measurement System

  • SAM 935 is a complex instrument that has many capabilities, including some that overlap our other radiation detection equipment

  • Our primary use of the 935, however, will be to determine the isotope(s) of an unknown source

  • ADM-300, Innovision 450P, TLDs, etc better for our other needs – so we will not focus on 935 capabilities outside of identifying unknown


Why i d unknown radioisotope
Why I.D. Unknown Radioisotope and Measurement System

  • Understand potential contamination concern

    • I-131 ½ life = 7 days . . . gone in months

    • Ra-226 ½ life = 1600 years . . . here for awhile

  • Understand potential source of material

    • I-131 probably medical dose

    • Cs-137 probably industrial

    • Pu-239 probably needs FBI involvement . . .

  • Basic info needed for disposition/disposal


Instrument operating principle
Instrument Operating Principle and Measurement System

Many radioactive materials give off electromagnetic

radiation in the form of gamma or x-rays


477 KeV Gamma

Be-7

1.37 MeV Gamma

197 KeV Gamma

O-19


722 KeV Gamma

Zr-95

765 KeV Gamma

Nb-95

Mo-95


765 KeV Gamma

(from Zr-95)

722 KeV Gamma

(from daughter Nb-95)

Zr-95


100 KeV x-ray

722 KeV Gamma

255 KeV Gamma

50 KeV Gamma

3 MeV Gamma

765 KeV Gamma

722 KeV Gamma

Zr-95


# hits at each

energy level

Energy level of the

individual gamma/x-rays

hitting the probe


  • Compares peaks to a library of radioactive materials and their peaks

Peaks


Instrument set up
Instrument Set-up of gamma/x-rays associated with a particular isotope (or decay chain “family”)

Probe “Window”

On/Off Switch

External “2 x 2” Probe

Power Cord

LCD Display Screen

SAM-935

Our version has no internal detectors (other model 935s might)


Instrument set up1
Instrument Set-up of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • “2 X 2” External probe has a sodium iodide detector near the front end

  • Probe body is resin that absorbs low energy gamma/x-ray

  • Front face of probe is thin plastic “window”

  • Want the “window” facing the material you are trying to identify

“2 x 2” detector

inside probe

Probe “Window”

is face of tube


Instrument set up2
Instrument Set-up of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • If your SAM has an External Sodium Iodide probe, lining up the red dots on the cable/plug while power is off.

  • Plug in power cord (or operate off battery up to 8hrs).

  • Turn the 935 on - first screen should be:

  • Allow 935 to warm up (typically 30 seconds)

Verify battery “good”

If battery “low”,

operate with power

cord and recharge

asap

Contrast

Bklight

OK

Wait


Calibration background
Calibration + Background of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • When first turned on, the 935 will self-test and auto-calibrate. This is a good time to take a new background (start of every new survey location)

  • Press F3 to start calibration or F2 to cancel and go straight to Background. Press F2 to start collection

15-Mar-04

22:37:51

Auto calibration

is required.

Perform calibration now?

Util

Adjust

F2

F3

F2


Dose rate mode
Dose Rate Mode of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Most days, 935 will go directly into Dose Rate mode:

  • Each time the instrument power is cycled or the temperature shifts +/- 5 degrees, the instrument will automatically calibrate. ( for example, going from inside to outside, etc)


Dose rate mode1
Dose Rate Mode of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • 935 starts in this mode, showing the “full” dose rate of everything it sees from background sources

  • First step -- see what your background “full” level is without input from any sources

  • Keep probe away from sources (including your check sources) and see background range (typically 1-10 uR/hr)

Trigger list

being used

Dose rate of

everything 935

is detecting

Total dose

recorded this

“alarm” cycle

Srch On

Monitor

Calib

Capture


Surveillance monitoring
Surveillance/Monitoring of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Move the 2 x 2 probe window as close as possible to the source you want to identify (remember inverse square law)

  • When 935 finds peaks above background it associates with a particular isotope in the trigger list, it lists the isotope and the estimated dose rate that isotope contributes to “full”

  • 935 will also list “unknown” if it sees peaks it does not associated with isotope in library


Surveillance monitoring1
Surveillance/Monitoring of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Isotopes w/steady reading are possibly a good detection

  • Transient/flickering means not a good match

  • Surveillance/monitoring only tentative i.d. -- follow with a “ID” sample

Dose rate of

everything 935

is detecting

“IND” = typical industrial source

Trigger list

being used

Dose rate of

specific

isotopes

Typ Source Abv:

IND = Industrial

NRM = Natural

MED = Medical

SNM = Weapon


Capture with id
Capture with ID of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • The “capture” function collects data over a longer period of time to get better spectrum for library comparison

  • Default capture time is 1 minute (vs. 1 sec for surv/mtr)

  • Place probe window near source and press F3 to start an ID from surveillance/monitor mode

F3


Identify
Identify of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • The 935 will collect data over the acquisition period, showing a real-time spectrograph

  • When finished, “ID” will end in an “MCA report”

  • Use arrow buttons to scroll down report

MCA REPORT15-Mar-04

22:37:51

MCA REPORT

Report scroll bar

DATE: 15-Mar-2004 22:30

EN CAL DATE: 15-Mar-2004 07:03

BKG DATE: 15-Mar-2004 07:04

ELAPSED LT 59

USE F2 OR F3 TO PRINT REPORT

Use arrow buttons

to scroll down/up

report

Return

P-Full

P-Short


Mca report
MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Scroll down report to table with energies where gamma/x-ray counts were found significantly above background

  • Isotopes are listed next to an energy line the 935 associated with an isotope definition in the library

  • The uncertainty (“UNC”) should be lower than 11% for a “good” identification and lower uncertainty is better

MCA REPORT15-Mar-04

22:37:51

Not a good i.d.

Uncertainty too high

ENERGY NET UNC NUCLIDE

(keV) (CPM) (%%)

16.5 551.28 +- 9.32

125.8 293.15 +- 43.3 Co57

430.2 2309.2 +- 5.35

659.7 33763 +- 0.58 Cs137

Report scroll bar

Good i.d.

Low uncertainty

USE F2 OR F3 TO PRINT REPORT

Use arrow buttons

to scroll down/up

report

Return

P-Full

P-Short


Mca report1
MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Scroll down further to see isotopes “found”

  • “Cor” correlation is how well the 935 thinks it matched the energies it found to the library energies for the isotope

  • Correlation may be high even for bad i.d. (uncertainty high)

  • Shows how many energies are identified in library for isotope and lists the ones found

MCA REPORT15-Mar-04

22:37:51

This report saying both Co57 and Cs137 were found,

but we know Co57

uncertainty was too high

Correlation for

each isotope “found”

1/1 Lib Lines for Co57; Cor = 0.80

LINE PEAK NET CPM

123.7 126.9 293

1/1 Lib Lines for Cs137; Cor = 0.80

LINE PEAK NET CPM

661.7 659.8 33762

USE F2 OR F3 TO PRINT REPORT

Return

P-Full

P-Short


Mca report2
MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Scroll down further to see all the isotopes on your trigger list that were “not found”

MCA REPORT15-Mar-04

22:37:51

NUCLIDES NOT PRESENT

1/2 Lib Lines for Cd109; Cor = 0.50

1/6 Lib Lines for Eu152; Cor = 0.05

0/3 Lib Lines for Ra226; Cor = 0.00

USE F2 OR F3 TO PRINT REPORT

Return

P-Full

P-Short


Mca report3
MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Scroll down further to see the energy levels where significant gamma/x-ray counts were seen, but not associated with an isotope on your trigger list

  • So where the heck did those unassociated gamma/x-rays come from? Bremstrallung? Compton?

MCA REPORT15-Mar-04

22:37:51

LINES NOT ASSOC WITH NUCLIDES

Energy Net CPM Eff Corrected

16.5 551.3 551275.6 C

199.3 3020.5 80284.9 C

430.1 2309.2 134990.8 C

USE F2 OR F3 TO PRINT REPORT

Return

P-Full

P-Short


Check background vs peaks
Check Background vs Peaks of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • From MCA report, press F1 “Return” once, “UTIL” button twice, and then F1 ”Wide” to view the capture spectrum

  • Move vertical cursor by using arrow buttons

  • EN = the energy line being looked at , CNTS = the counts at that energy

Vertical cursor on energy line being looked at

MCA DISPLAY15-Mar-04

Alarm 17 22:37:51

CH=22 EN=48keV CNTS=1225

Normal

Log

Strip


Check background vs peaks1
Check Background vs Peaks of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • Verify the peaks in your spectrum are at least 20 times higher than the “background hump” (using the “counts”)

  • If peaks are not 20 times higher than background, the identification may not be solid – get health physicist support to look at spectrum in detail

  • Exit MCA Display by pressing “Util” twice, then F1 “Exit” to return to surveillance/monitoring

Good

Poor

Peak

Peak

Bkg

Bkg


Interpreting mca report
Interpreting MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • False positive: just because MCA report lists an isotope as found with low uncertainty, is it really there?

  • Possible misidentification:

    • Co-57 . . . often mis-identified because its primary energy falls in typical “background” area

    • If the “real” isotope is not enabled in library, isotopes with similar energy line(s) may get mis-identified

    • Shielded sources - Compton scattering can create gamma with “random” lower energy levels, increasing the “background hump”


Interpreting mca report1
Interpreting MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • False negative: just because MCA report does not list an isotope as found, is it confirmed not present?

    • The “unknown” isotope may not be “enabled” in library?

    • Did you run “capture” long enough: if unknown is “screaming”, probably seeing enough gamma/x-ray, but if not very “hot” may take longer to get enough counts – adjust capture time

    • Isotope may have gamma/x-ray energies outside 935 range

      (13 Kev – 3 MeV) or not emit gamma/x-ray

    • Shielding may absorb the low energy lines of an isotope needed to match library definition

  • If there is strong activity/strong peaks with no identification, a health physicist can interpret spectrum


Interpreting mca report2
Interpreting MCA Report of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • So when can you be confident?

    • Good calibration and background

    • Activity at least 10 times “Full” background

    • MCA report identification with uncertainty less than 11% and does not have a ? next to the isotope.

    • “Peaks” at least 20 times greater than “background hump”

  • Still good to send spectrum for health physics confirmation


Adjusting for longer id
Adjusting for Longer ID of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • If 1 minute capture does not clearly identify unknown, may need to adjust to a longer capture to get even better data set

  • Re-run capture and see if longer time has identified isotope


Changing between trigger lists
Changing Between Trigger Lists of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • The 935 can only look for 20 isotopes at one time in surveillance/monitor mode, so we build several trigger lists

  • To change to an alternate trigger list (A, B, or C)

    • Press Util button, scroll to trigger list of choice and press enter

    • Press F1 “Return” 3 times to return to Dose Rate Screen

Note trigger

list being used

Srch On

Monitor

Calib

Capture


Sending mca report spectrum
Sending MCA Report/Spectrum of gamma/x-rays associated with a particular isotope (or decay chain “family”)

  • This slide waiting for software and RS-232 cable

  • Explain how to save a capture MCA report/spectrum and send by email to AFIOH HP support.

  • Questions?Truly unknown radiation source? Call DOE RAP team in your region


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