1. Interesting findings of a
comparison of Real Time versus
Passive Radon Thoron Monitoring
In a Rare Earth Mine
Masood A Inayat
RSO, Molycorp Inc.
July 14, 2015

2. Radon Thoron Monitoring

3. Objectives
 Impact of Passive monitoring in accurately
determining exposures
 Impact of single anomalous event on passive
monitoring
 Weighted averaging in real time versus linear
averaging in passive monitoring
 Radon Thoron ratio accuracy in real time monitoring
versus passive monitoring
 Timely results with ability to mitigate in real time
monitoring versus passive monitoring

4. Traditional approach passive monitoring
Track Etch Detectors

5. Radon only
Type DNRM (Radon Only)
Filter makes the short lived thoron (55
second half life) to decay before entering
the detector

6. Radon plus thoron
Type DNRF (Radon + Thoron)
No filter allows both radon & thoron to
enter the detector

7. Operation principle
Inside both Type DNRM & DNRF detectors
is a piece of film that records the impacts
(tracks) of alpha particles produced by
the decay of radon/thoron and their
decay by-products. These detectors are
also knows as Alpha track or track etch
detectors.

8. Continuous real time monitoring
Alphaguard Continuous Real Time
Radon Thoron monitor

9. Comparison Alpha Track (Passive) Alphaguard (Active)
Low Per Unit Cost Yes No
Accuracy Somewhat Yes
Reliability Somewhat Yes
Timeliness No Yes
Comparison
DNRF OR DNRM $15-$20 each X # of units deployed
location X Monitoring Time frames (monthly quarterly etc.)
2013 54 units monthly exchange 54 X 12 X15= $9720
Currently 14 units quarterly exchange 14 X 4 X 20 = $1120
Alphaguard $12000-15000 per unit

10. Passive Vs. Real Time
A rare earth mine expansion perspective

11. Existing facilities for passive monitoring
quarterly exchange
Legacy facilities monitored on quarterly exchange basis
CHP Fenceline Fenceline #1
Fenceline #2 Fenceline #3
Didymium Packaging Lanthanum Packaging

12. 2013 Existing Facilities Rn+Tn data comparison of real
time versus passive monitoring shows consistent high
results for real time monitoring as compared to passive
monitoring
0
1
2
3
4
5
6
7
8
CHP Area Didy Room Fenceline #1 Fenceline #2 Fenceline #3 Lanthanum
Packaging
2013 Real Time Vs Passive Existing
Facilities Comparison
Real Time Rn+Tn Passive Rn+Tn
0
1
2
3
4
5
6
7
8
CHP Area Didy Room Fenceline #1 Fenceline #2 Fenceline #3 Lanthanum
Packaging
2013 Real Time Vs Passive Existing
Facilities Comparison
Real Time Rn+Tn Passive Rn+Tn

13. 2013 Radon Only real time versus passive data shows
relatively similar average radon concentrations although
the difference is observed in different areas
0
0.1
0.2
0.3
0.4
0.5
0.6
CHP Area Didy Room Fenceline #1 Fenceline #2 Fenceline #3 Lanthanum
Packaging
2013 Real Time Vs Passive Existing
Facilities Comparison
Real Time Rn Passive Rn
0
0.1
0.2
0.3
0.4
0.5
0.6
CHP Area Didy Room Fenceline #1 Fenceline #2 Fenceline #3 Lanthanum
Packaging
2013 Real Time Vs Passive Existing
Facilities Comparison
Real Time Rn Passive Rn

14. 2013 Thoron only real time versus passive data showing
higher thoron concentrations for real time than passive
monitoring.
0
1
2
3
4
5
6
7
8
CHP Area Didy Room Fenceline #1 Fenceline #2 Fenceline #3 Lanthanum
Packaging
Real Time Tn Passive Tn
0
1
2
3
4
5
6
7
8
CHP Area Didy Room Fenceline #1 Fenceline #2 Fenceline #3 Lanthanum
Packaging
Real Time Tn Passive Tn

15. New facilities online in 2013
With addition of new facilities beginning in 2013
a monthly radon thoron passive monitoring
regime was put in place for the above listed
facilities

16. New facilities for passive monitoring
monthly exchange
New facilities monitored on monthly exchange basis
PASTE TAIL OUTDOOR PASTE TAIL DEPOSITORY CRACK 1A LEVEL 3 CRUSHER
PASTE TAIL INDOOR NW FENCE LINE CRACK 1A LEVEL 1 NEW MILL
NE FENCE LINE SXH&I CHP INSIDE P16 FENCE LINE
SX-D MINE PIT CHP CERIUM CHLOR ALKALI

17. 2013 average Radon + Thoron results are showing
higher results throughout the year during the new
facilities construction
0
0.5
1
1.5
2
2.5
3
3.5
4
RadonThoronConc.pCi/litre
Passive Radon Thoron (DNRF) Monitoring Locations
2013 Passive Radon + Thoron (DNRF) Yearly Weighted
Average Monthly Exchange
2013 Passive Radon + Thoron (DNRF) Yearly Weighted Average Monthly
Exchange
0
0.5
1
1.5
2
2.5
3
3.5
Rn+TnConc.pCi/liter
Monitoring Locations
Average Rn+Tn

18. Note the average passive radon levels are
consistently1pCi/liter or higher throughout
2013 as the construction of the new facilities
was progressing
0
0.5
1
1.5
2
2.5
3
3.5
RnConc.pCi/liter
Monitoring Locations
Average Radon Only
0
0.5
1
1.5
2
2.5
3
3.5
2013 Passive Radon (DNRM) Yearly
Weighted Average Monthly Exchange
Average Radon Only

19. Note with the exception of crusher and mine pit
Thoron levels are either low or non existent
throughout new construction areas during 2013.
Thoron levels in these two locations are
somewhat higher as Radon levels
0
0.5
1
1.5
2
2.5
3
3.5
2013 Passive Thoron (DNRF-DNRM)
Yearly Weighted Average Monthly
Exchange
Average Thoron Only
0
0.5
1
1.5
2
2.5
3
3.5
TnConc.pCi/liter
Monitoring Locations
Average Thoron Only

20. Conclusions
While new facilities were being constructed monthly exchange
monitoring was carried out in 2013 to study the impact. The results
painted an unexpected picture as inferred below:
1) Average Radon concentration values in areas where ore
processing and beneficiation activities were not taking place were
showing higher than normal radon levels
2) Areas where ore processing and beneficiation activities were
taking place were showing almost similar results
3) Radon numbers were showing higher but thoron numbers did not go
up higher relatively
4) There was a need to find a common source impacting radon levels
site wide irrespective of ore processing and beneficiation activities
5) Was it a leak in the old P-16 tailings dam due to heavy earth
moving and construction equipment moving activity
6) Was it related to dust control process
7) Any other potential cause?

21. All 7 Fenceline PASSIVE RADON (DNRM) locations are
reported as “LESS THAN INDICATED VALUE”

22. 2014 Real Time Vs. Passive Radon Comparison
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Fenceline #1 Fenceline #2 Fenceline #3 CHP
Fenceline
NW
Fenceline
NE Fenceline P-16
Fenceline
2014 Real Time Vs. Passive Radon
Comparison
2014 Real Time Rn 2014 Passive Rn
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Fenceline #1 Fenceline #2 Fenceline #3 CHP
Fenceline
NW Fenceline NE Fenceline P-16
Fenceline
2014 Real Time Vs. Passive Radon
Comparison
2014 Real Time Rn 2014 Passive Rn
2014 Passive fenceline monitors show a consistent “LESS THAN DETECTED
VALUE” of 0.33pCi/liter of Radon concentration at all locations versus a
variable and higher radon concentration for real time monitoring.

23. All 7 Fenceline PASSIVE THORON (DNRF
- DNRM) locations are reported
Locations 2014 Passive Rn 2014 Passive Tn 2014 Passive Rn+Tn
Fenceline #1 0.33 0.13 0.45
Fenceline #2 0.33 0.53 0.85
Fenceline #3 0.33 0.60 0.93
CHP Fenceline 0.33 1.03 1.35
NW Fenceline 0.33 0.35 0.68
NE Fenceline 0.33 0.23 0.55
P-16 Fenceline 0.33 1.10 1.43

24. Alphaguard 2014 Fencelines Real Time
Radon Thoron Monitoring Averages
Locations 2014 Real Time Rn 2014 Real Time Tn 2014 Real Time Rn+Tn
Fenceline #1 0.54 0.48 1.02
Fenceline #2 0.27 6.78 7.05
Fenceline #3 0.56 2.48 3.04
CHP Fenceline 0.45 1.33 1.78
NW Fenceline 0.45 2.6 3.05
NE Fenceline 0.4 1.22 1.62
P-16 Fenceline 0.67 2.85 3.52

25. 2014 Real Time Vs. Passive Thoron Comparison
0
1
2
3
4
5
6
7
8
Fenceline #1 Fenceline #2 Fenceline #3 CHP
Fenceline
NW Fenceline NE Fenceline P-16
Fenceline
2014 Real Time Vs. Passive Thoron
Comparison
2014 Real Time Tn 2014 Passive Tn
0
1
2
3
4
5
6
7
8
Fenceline #1 Fenceline #2 Fenceline #3 CHP
Fenceline
NW Fenceline NE Fenceline P-16
Fenceline
2014 Real Time Vs. Passive Thoron
Comparison
2014 Real Time Tn 2014 Passive Tn
2014 Passive fenceline monitors show a consistent lower Thoron concentration at all locations
versus a higher thoron concentration for real time monitoring.

26. All 7 Fenceline PASSIVE RADON + THORON (DNRF)
locations are reported

27. 2014 Real Time Vs. Passive Radon+Thoron Comparison
0
1
2
3
4
5
6
7
8
Fenceline #1 Fenceline #2 Fenceline #3 CHP
Fenceline
NW Fenceline NE Fenceline P-16
Fenceline
2014 Real Time Vs. Passive Radon+Thoron
Comparison
2014 Real Time Rn+Tn 2014 Passive Rn+Tn
0
1
2
3
4
5
6
7
8
Fenceline #1 Fenceline #2 Fenceline #3 CHP
Fenceline
NW Fenceline NE Fenceline P-16
Fenceline
2014 Real Time Vs. Radon+Thoron
Comparison
2014 Real Time Rn+Tn 2014 Passive Rn+Tn
2014 Passive fenceline monitors show a consistent lower Radon+Thoron concentration at all
locations versus a higher radon+thoron concentration for real time monitoring.

28. Discussion
Ore @Mountain Pass contains an average of 0.005% Uranium and 0.02% Thorium
content therefore:
1. Thorium content is almost 4 times higher than Uranium content
2. Uranium is the parent for Ra-226 the precursor for Rn-222
3. Thorium is parent for Ra-228 the precursor for Rn-220
4. Therefore the Rn-220 average concentration should be about a factor of 4 higher
than Rn-222
5. Passive monitoring does not support this ratio whereas real time monitoring does
6. Passive monitoring shows lower exposures with radon thoron combined than with
radon alone
7. Passive monitoring may report higher than actual exposure for Radon
8. Passive monitoring may report lower than actual exposure for Thoron
9. Significance of Radon is important but significance of Thoron cannot be ignored
either
10.In case of passive monitoring once a high exposure event has been recorded
that affects the average for that time frame irrespective of the lows for that period
11.Real Time monitoring measures actual lows and highs of exposures and weighted
averages are determined.

29. What Lies Ahead
1) Passive monitoring has been in use and is relied
upon mostly due to its lesser cost
2) Long term real time results need to be acquired and
data comparisons made
3) Real time monitoring shows several promising
aspects such as immediate results, thereby helping
provide opportunity to mitigate in a timely manner
4) Work areas where occupational workers are present
should be relied upon with real time monitors as the
circumstances and environment tends to change
much more rapidly
5) Perimeters and fencelines can still me monitored
using passive techniques as such areas are
relatively less disturbed

30. Detailed Info
For more info on DNRM and DNRF monitors
http://www.Landauer.com
For more info on Alphaguard monitors
http://www.saphymo.com

31. Contact
Masood A Inayat
Molycorp Inc.,
67750 Bailey Road
Mountain Pass, CA 92366
1-760-856-7661 Direct
1-702-280-6023 Cell
1-760-856-5610 Fax
http://www.Molycorp.com
Masood.Inayat@Molycorp.com Email.