Regulatory Guide 5.27
| ML003740050 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1974 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-5.27 | |
| Download: ML003740050 (12) | |
June 1974 U.S. ATOMIC ENERGY COMMISSION
REGULATORY GUIDE
DIRECTORATE OF REGULATORY STANDARDS
REGULATORY GUIDE 5.27 SPECIAL NUCLEAR MATERIAL DOORWAY MONITORS
A. INTRODUCTION
Paragraph (b), "Exit Requirement," of § 73.60, "Ad ditional Requirements for the Physical Protection of Special Nuclear Material at Fixed Sites," of 10 CFR Part
73, "Physical Protection of Plants and Materials,"
requires that individuals exiting from material access areas be searched for concealed special nuclear material (SNM). This guide describes means acceptable to the Regulatory staff for employing SNM doorway monitors to comply with that requirement.
B. DISCUSSION
Special nuclear material doorway monitors provide an efficient, sensitive, and reasonably unobtrusive means of searching individuals exiting from a material access area for concealed SNM. With proper installation and opera tion, gram quantities or less of SNM can be detected with a high level of reliability while maintaining a low false alarm rate.
I. Theory of Operation The doorway monitor is composed of a detector unit(s), associated electronics, and alarm logic. The detector unit(s) is sensitive to the radiations which emanate from the SNM and responds to these radiations (usually gamma rays) by generating current pulses. These pulses are amplified, filtered, and fed to alarm logic v'hich interprets the number (or rate) of pulses in some period of time, for example, one second. The alarm logic may be either a digital or analog system; in either case, if the number (or rate) of pulses exceeds a set level, an alarm condition ensues.
2. General Characteristics Typically, the detectors of a doorway monitor are NaI(Tl) scintillators or solid or liquid organic scintilla tors. Geiger-Mueller detectors have also been used in this application, although the lower intrinsic efficiency of these detectors renders them less suitable than scintilla tion detectors.
Detectors are arranged such that a detection area is defined by a plane perpendicular to the line of passage of individuals through the doorway monitor. Various arrangements of the detectors are possible; however, specific placement of detectors is usually dictated by the need to eliminate dead spots.
Some commercially available doorway monitors are equipped with an automatic background updating system. The automatic background updating system periodically monitors and averages the background. A
doorway monitor equipped with an automatic back ground updating system is also provided with a treadle pad or beam-break system to indicate that the sensitive area is occupied. When the sensitive area is occupied, the radiation level detected by the doorway monitor is compared with the mean backgroun
d. If the level is
"significantly" greater than the mean background, an alarm condition ensues. Significance is usually deter mined by comparing the radiation level when the sensitive area is occupied with the mean background plus some multiple of the square root of the mean back ground*
- The square root of the mean of a Poisson-distributed quantity is the unbiased estimate of the standard deviation of that quantity.
USAEC REGULATORY GUIDES
Copies of published guides may be obtained by request indicating the divisions desired to the US. Atomic Energy Commission, Washington, D.C. 20545, Regulatory Guides are issued to describe and make available to the public Attention: Director of Regulatory Standards. Comments and suggestions for methods acceptable to the AEC Regulatory staff of implementing sPecific parts of improvements in these guides ae encouraged and should be sent to the Secretary the Commission's regulations, to delineate techniques .ned by the staff in of the Commission, US. Atomic Energy Commission, Washington, D.C. 20545, evaluating specific problems or postulated accidents, or to provide guidance to Attention: Chief, Public Proceedings Staff.
applicants. Regulatory Guides are not substitutes for regulations and compliance with them is not required. Methods and solutions different from those set out in The guides ae issued in the following ten broad divisions:
the guides will be acceptable if they provide a basis for the findings requisite to the imuance or ontinuance of a permit or license by the Commission.
1. Power Reactors
6. Products
2. Reaseerd enid Test Reactors
7. Transportation
3. Fuels and Materials Facilities
8. Occupational Health Published guidas will be revised periodically, as appropriate, to accommodate
4. Environmental and Siting
9. Antitrust Review comments amd to refloct new informeaion or experience.
5. Materials and Plant Protection
1
0. General
Thus the condition for an alarm can be written as G > B + n, where B is the mean background, G is the radiation level with the sensitive area occupied, and n is a multiplier, usually an integer between 4 and 10.* The value of n directly affects the false alarm rate, and the combination of B and n affect the sensitivity.
Although the automatic background updating system allows unattended use of the doorway monitor, for technical reasons, the system may be less effective in certain situations. Techniques to prevent this are des cribed in the Regulatory Position.
Doorway monitors not equipped with an automatic background updating system either must rely on the inherent sensitivity of the instrument and low back ground variation to ensure that concealed SNM will be detected or must be attended so that a measurement of background can be taken immediately prior to use and the alarm level set to maintain the desired sensitivity to concealed SNM. As with the doorway monitor equipped with an automatic background updating system, a doorway monitor not so equipped compares the activity with the detection area occupied with some set value, usually the measurement of background taken just prior to use. In any case, the expression above can be used as a condition of alarm by replacing B + nr'Wwith the set level.
Whether or not a doorway monitor is equipped with an automatic background updating system, high back ground activity will decrease sensitivity. Measuring activ ity for longer periods will somewhat compensate for high background; however, longer measurement periods will make use of the doorway monitor less convenient.
C. REGULATORY POSITION
1. Minimum Qualifications for SNM Doorway Monitors
a. General
(1) SNM Doorway monitors should be used in conjunction with a metal detector and should be installed in a passageway (see Regulatory Guide 5.7,
"Control of Personnel Access to Protected Areas, Vital
- Note that, in general, for a count rate system, the condition for afarm should be modified to account for the response time of the instrument as follows:
G > B + n1]0l - e-t/7)
where t is the counting time and r is the time constant of the instrument. If, as should be the case, t/,r > 5 the added factor is essentially unity.
Areas, and Material Access Areas,") in such a manner that objects cannot be passed over, around, or under the detection area.
. (2) The detector elements should be designed and positioned so that detection sensitivity is as uniform as possible over the detection area; in no case should any areas where SNM is not detectible be permitted.
(3) Power, sensitivity, and other controls of the doorway monitor should be tamper-safed when unat tended.
(4) Signal lines connecting alarm relays to the alarm monitor should be supervised.
(5) Some doorway monitors may require an indi vidual to occupy the detection area for a specified time, longer than a normal walking pace would provide. If this is the case, the doorway monitor should be provided with a treadle pad and a "clock" device to assure that the detection area is occupied for the requisite time. An aural and visual indication should be given if an individual being searched does not occupy the area sufficiently long.
b. System Specification
(1) Plutonium-239. A doorway monitor used to detect plutonium should be capable of detecting a minimum of 0.5 gram of plutonium-239 encased in a minimum of 3 mm of brass at a 90% confidence limit.
The false alarm rate should be less than 0.1% (Appendix C).
(2) Uranium-233. A doorway monitor used to detect uranium-233 should be capable of detecting within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of purification* a minimum of 1 gram of uranium-233 containing between 7 and 10 ppm of uranium-232 encased in a minimum of 3 mm of brass at a 90% confidence limit. The false alarm rate should be less than 0.1% (Appendix C).
(3) Uranium-235. A doorway monitor used to detect uranium-235 should be capable of detecting a minimum of 3 grams of uranium-235 contained in uranium enriched to 20% or more in the uranium-235 isotope encased in a minimum of 3 mm of brass at a 50%
confidence limit. The false alarm rate should be less than
0.1% (Appendix C).
2. Use of Doorway Monitors In general, doorway monitors should be used in locations of minimum background and minimum back ground fluctation. If circumstances dictate use of a doorway monitor in an area of high background, sufficient shielding should be provided to maintain necessary sensitivity.
a. Attended Doorway Monitor
(1) If the doorway monitor is attended during use, it need not be equipped with an automatic
- Purification means removal of all decay products.
5.27-2
background updating system, although such capability is preferred.
(2) Prior to each use* of a doorway monitor not equipped with an automatic background updating system, a measurement of background should be taken, and the alarm threshold should be set to the proper value listed in Table I for the measured background and the proper n value as determined in Appendix B. Each individual to be checked should, in turn, enter the detection area and be required to remain sufficiently long for the device to operate properly. During use, the background should be checked and the alarm threshold reset at least each 15 minutes.
(3) With the individual being checked in the detection area, an alarm should sound if the activity in the detection area exceeds the alarm threshold T, as such a situation would indicate the presence of SNM.
(4) The doorway monitor should be equipped with a high-background alarm which will sound if the measurement of background exceeds the appropriate maximum permissible background level listed in Table II
as determined in Appendix C. The doorway monitor should not be used during such periods of high back ground.
b. Unattended Doorway Monitor
(1) If the doorway monitor is unattended, an automatic background update system should be incor porated into the doorway monitor electronics and alarm logic. The control circuitry, if possible, should be located at the central alarm station (or other monitoring point).
(2) Door interlocks and closed-circuit TV in combination with beam breaks, motion detectors, and/
or treadle pads, should be employed to:
(a) Indicate to the person manning the central alarm station that an individual has entered the secure access passageway and/or is approaching the doorway monitor, (b) Allow observation of the individual ap proaching the doorway monitor, (c) Preclude a slow approach to the sensitive area of the doorway monitor, and
- By use is meant an individual or several individuals, each, in turn, being checked for SNM by the doorway monitor. The maximum period between threshold sets while the doorway monitor is in use is determined by the stability of local background and may necessarily be more frequent than every
15 minutes.
(d) Activate the electronics and alarm logic when an individual is within the detection area and initiate operation of the doorway monitor.
(3) An alarm should sound in the central alarm station if, when occupied, the activity in the detection area exceeds the internally set threshold level (the mean background plus some multiple times the square root of the mean background), as such a situation would indicate the presence of SNM upon the individual being checked.
(4) The doorway monitor should be equipped with a high-background alarm which will sound if the average background at the location of the doorway monitor exceeds the appropriate maximum permissible background level listed in Table II as determined in Appendix C. The doorway monitor should not be used during such periods of high background. Other moni tored exits should be used.
3. Testing and Calibration a. Testing Doorway monitors should be tested by passing an appropriate source of the amount and isotope specified in Regulatory Position C.l.b. through the doorway monitor no less frequently than once per day.* In addition, a functional performance test should be carried out at least once per week. An acceptable functional performance test procedure is discussed in Appendix A
of this guide b. Calibration Doorway monitors should be calibrated with a source of the amount, configuration, and variety of SNM
to be detected (e.g., 0.5 gram Pu in 3 mm of brass).
Calibration should be carried out according to a proce dure such as that in Appendix B.
c. Operating Instructions Operating instructions should be posted near the doorway monitor,* if attended, or at the monitoring point if the doorway monitor is unattended. The instructions should clearly indicate the procedure for use of the doorway monitor and the procedure for setting thresholds, if appropriate. In addition, the operating instructions should indicate what corrective action is to be taken and who is to be notified in the event of a malfunction.
- Doorway monitors used to search for concealed U-233 should be tested according to §6 of Appendix A.
5.27-3
TABLE I
ALARM THRESHOLD
T
B
n=
4
5
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420
440
460
480
500
520
540
560
580
600
620
640
660
680
700
720
740
760
780
800
820
840
860
880
900
920
940
960
980
6
140
164
.187
211
234
257
279
302
324
347
369
392
414
436
458
480
502
524
546
568
589
611
633
655
676
698
720
741
763
784
806
827
849
870
892
913
935
956
977
999
1020
1041
1063
1084
1105
5.27-4
7
8
150
175
199
223
247
271
294
317
341
364
387
409
432
455
477
500
522
545
567
590
612
634
656
678
700
722
744
766
788
810
832
854
876
898
920
941
963
985
1007
1028
1050
1072
1093
1115
1137
160
186
211
236
260
285
309
333
357
380
404
427
451
474
497
520
543
566
589
611
634
657
679
702
724
747
769
792
814
836
859
881
903
925
948
970
992
1014
1036
1058
1080
1102
1124
1146
1168
170
197
223
249
274
299
324
348
373
397
421
445
469
493
516
540
563
587
610
633
657
680
703
726
749
771
794
817
840
863
885
908
930
953
975
998
1020
1043
1065
1088
1110
1132
1155
1177
1199
180
208
235
261
287
313
339
364
389
414
439
463
488
512
536
560
584
608
632
655
679
702
726
749
773
796
819
842
866
889
912
935
958
981
1003
1026
1049
1072
1095
1117
1140
1163
1185
1208
1230
9
190
219
246
274
301
327
353
379
405
431
456
481
506
531
555
580
604
629
653
677
701
725
749
773
797
820
844
868
891
915
938
961
985
1008
1031
1055
1078
1101
1124
1147
1170
1193
1216
1239
1262
10
200
230
258
286
314
341
368
395
421
447
473
499
524
550
575
600
625
650
674
699
724
748
772
797
821
845
869
893
917
941
965
988
1012
1036
1059
1083
1106
1130
1153
1177
1200
1223
1247
1270
1293
TABLE I (Cont'd)
ALARM THRESHOLD
T
B
n =
4
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
4200
4400
4600
4800
5000
5200
5400
5600
5800
6000
6200
6400
6600
6800
7000
7200
7400
7600
7800
8000
8200
8400
8600
8800
9000
9200
9400
9600
9800
1126
1339
1550
1760
1970
2179
2388
2596
2804
3012
3219
3426
3633
3840
4047
4253
4459
4665
4871
5077
5283
5483
5694
5899
6105
6310
6515
6720
6925
7130
7335
7539
7744
7949
8153
8358
8562
8767
8971
9175
9379
9584
9788
9992
10196
5
1158
1373
1587
1800
2012
2224
2435
2645
2855
3065
3274
3483
3692
3900
4108
4316
4524
4732
4939
5146
5354
5561
5767
5974
6181
6387
6594
6800
7006
7212
7418
7624
7830
8036
8242
8447
8653
8858
9064
9269
9474
9680
9885
10090
10295
5.27-5
9
6
1190
1408
1624
1840
2055
2268
2481
2694
2906
3117
3329
3539
3750
3960
4170
4379
4589
4798
5007
5216
5424
5633
5841
6049
6257
6465
6672
6880
7087
7295
7502
7709
7916
8123
8330
8537
8743
8950
9156
9363
9569
9775
9932
10188
10394
7
1221
1442
1662
1880
2097
2313
2528
2743
2957
3170
3383
3596
3808
4020
4232
4443
4654
4864
5075
5285
5495
5705
5914
6124
6333
6542
6751
6960
7169
7377
7586
7794
8002
8210
8418
8626
8834
9042
9249
9457
9664
9871
10079
10286
10493
8
1253
1477
1699
1920
2139
2358
2575
2792
3008
3223
3438
3653
3866
4080
4293
4506
4718
4931
5143
5354
5566
5777
5988
6199
6409
6620
6830
7040
7250
7460
7669
7879
8088
8297
8507
8716
8924
9133
9342
9550
9759
9967
10176
10384
10592
1285
1512
1737
1960
2182
2402
2622
2841
3059
3276
3493
3709
3925
4140
4355
4569
4783
4997
5210
5424
5636
5849
6061
6273
6485
6697
6909
7120
7331
7542
7753
7964
8174
8385
8595
8805
9015
9225
9435
9644
9854
10063
10273
10482
10691
1316
1546
1774
2000
2224
2447
2669
289C
3110
3329
3548
3766
3983
4200
4416
4632
4848
5063
5278
5493
5707
5921
6135
6348
6562
6775
6987
7200
7412
7625
7837
8049
8260
8472
8683
8894
9106
9317
9527
9738
9949
10159
10370
10580
10790
TABLE II
MAXIMUM PERMISSIBL
E. BACKGROUND
a = 0,
Pa = 50%
B
n=
4
100
120
140
160
180.
200
220
240
260
280
300
320
340
360
380
400
420
440
460
480
500
520
540
560
580
600
620
640
660
680
700
720
740
760
780
800
820
840
860
880
900
920
940
960
980
5
67
83
100
117
134
151
168
186
203
221
238
256
274
292
310
328
346
364
382
400
418
436
455
473
491
510
528
546
565
583
602
620
639
657
676
695
713
732
750
769
788
806
825
844
863 G
61
76
92
108
124
141
157
174
191
208
225
242
259
277
294
312
329
347
365
382
400
418
436
454
471
489
507
525
543
562
580
598
616
634
652
671
689
707
725
744
762
780
799
817
835
6
55
70
85
100
116
131
147
163
180
196
213
229
246
263
280
297
314
331
348
365
383
400
417
435
452
470
488
505
523
541
558
576
594
612
629
647
665
683
701
719
737
755
773
791
809
5.27-6
7
50
64
78
93
107
123
138
153
169
185
201
217
233
249
266
282
299
316
332
349
366
383
400
417
434
451
468
486
503
520
538
555
573
590
607
625
643
660
678
695
713
731
748
766
784
9
10
8
46
59
72
86
100
114
129
144
159
174
190
205
221
237
253
269
285
301
317
334
350
367
383
400
417
433
450
467
484
501
518
535
552
569
586
603
621
638
655
673
690
707
725
742
760
42
54
67
80
93
107
121
135
150
165
179
194
210
225
240
256
272
287
303
319
335
351
367
384
400
416
433
449
466
482
499
516
532
549
566
583
600
617
633
650
667
685
702
719
736
38
50
62
74
87
100
113
127
141
155
170
184
199
214
229
244
259
274
290
305
321
337
352
368
384
400
416
432
448
464
481
497
513
530
546
563
579
596
613
629
646
663
679
696
713
TABLE II
(Cont'd)
MAXIMUM PERMISSIBL
E. BACKGROUND
B
G
n =
4
1000
1200
1400
1600
1000
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
4200
4400
4600
4800
5000
5200
5400
5600
5800
6000
6200
6400
6600
6800
7000
7200
7400
7600
7800
8000
8200
8400
8600
8800
9000
9200
9400
9600
9800
881
1069
1258
1448
1638
1829
2020
2212
2404
2596
2789
29S2
3175
3368
3561
3755
3949
4143
4337
4531
4725
4919
5114
5309
5503
5698
5893
6088
6283
6478
6673
6868
7064
7259
7455
7650
7846
8041
8237
8433
8628
8824
9020
9216
9412
5
854
1039
1225
1412
1600
1789
1978
2167
2357
2548
2738
2929
3121
3312
3504
3696
3888
4081
4273
4466
4659
4852
5045
5238
5432
5625'
5819
6012
6206
6400
6594
6788
6982
7176
7371
7565
7760
7954
8149
8343
8538
8733
8928
9122
9317 a -'0,
Pa = 50Z
6
827
1009
1193
1377
1563
1749
1936
2124
2312
2500
2689
2878
3068
3258
3448
3638
3829
4020
4211
4402
4593
4785
4977
5169
5361
5553
5745
5938
6130
6323
6516
6709
6902
7095
7288
7481
7674
7868
8061
8255
8449
8642
8836
9030
9224
7
802
981
1161
1343
1527
1710
1895
2081
2267
2453
2640
2828
3016
3204
3392
3581
3770
3960
4149
4339
4529
4719
4910
5100
5291
5482
5673
5864
6055
6247
6438
6630
6822
7014
7206
7398
7590
7782
7975
8167
8360
8553
8745
8938
9131
8
777
953
1131
1310
1491
1673
1855
2039
2223
2407
2593
2778
2964
3151
3338
3525
3713
3900
4088
4277
4465
4654
4843
5032
5222
5411
5601
5791
5981
6172
6362
6552
6743
6934
7125
7316
7507
7698
7889
8081
8272
8464
8656
8348
9039
5.27-7
9
753
926
1101
1278
1457
1636
1816
199D
2180
2363
2546
2730
2914
3099
3284
3470
3656
3842
4029
4216
4403
4590
4778
4966
5154
5342
5531
5719
5908
60'97
6286
6476
6665
6855
7045
7234
7425
7615
7805
7995
8186
8376
8567
8758
8949
10
730
900
1073
1247
1423
1600
1778
1958
2138
2318
2500
2682
2865
3048
3232
3416
3600
3785
3970
4155
4341
4527
4713
4900
5087
5274
5461
5648
5836
6024
6212
6400
6588
6777
6965
7154
7343
7532
7721
7911
8100
8290
8479
8669
8859
TABLE II
(Cont'd)
MAXIMUM PERMISSIBL
E. BACKGROUND
B
G
n
4
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420
440
460
480
500
520
540
560
580
600
620
640
660
680
700
720
740
760
780
800
820
840
860
880
900
920
940
960
980
57
72
87
103
119
135
151
168
185
201
218
235
252
270
287
304
322
339
357
374
392
409
427
445
463
480
498
516
534
552
570
588
606
624
642
660
679
697
715
733
751
770
788
806
824
5
51
65
80
95
110
126
141
157
173
189
206
222
239
255
272
289
306
323
340
357
374
391
409
426
443
461
478
496
513
531
549
566
584
602
619
637
655
673
690
708
726
744
762
780
798
6
46
59
73
87
102
117
132
147
163
178
194
210
226
242
258
275
291
308
324
341
357
374
391
408
425
442
459
476
493
511
528
545
562
580
597
614
632
649
667
684
702
720
737
755
773 S= 1.3, Pa = 90%
7
42
54
67
81
95
109
123
138
153
168
183
198
214
229
245
261
277
293
309
325
342
358
374
391
407
424
441
457
474
491
508
525
542
559
576
593
610
627
644
661
679
696
713
731
748
9
8
38
49
62
75
88
101
115
129
143
158
172
187
202
217
233
248
263
279
295
311
326
342
358
374
391
407
423
439
456
472
489
505
522
539
555
572
589
605
622
639
656
673
690
707
724
5.27-8
34
45
57
69
81
94
107
121
135
149
163
177
191
206
221
236
251
266
281
297
312
327
343
359
375
390
406
422
438
454
470
487
503
519
535
552
568
585
601
618
634
651
668
684
701
10
31
41
52
64
76 FS
100
113
127
1L0
154
167
181
196
210
224
22S
254
268
283
298
313
329
344
359
375
390
406
421
437
453
469
485
500
516
532
549
565
581
597
613
630
646
662
679
TABLE II
(Cont'd)
MAXIMUM PERMISSIBL
E. BACKGROUND
G
n=
4
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
4200
4400
4600
4800
5000
5200
5400
5600
5S00
6000
6200
6400
6600
6800
7000
7200
7400
7600
7800
8000
8200
8400
8600
8800
9000
9200
9400
9600
98-00
843
1027
1212
1398
1536
1773
1962
2151
2340
2530
2720
2911
3101
3292
3484
3675
3867
4059
4251
4443
4636
4828
5021
5214
5407
5600
5793
5987
6180
6373
6567
6761 r9955
7148
7342
7536
7731
7925
8119
3313
8508
8702
8897
9091
9286
5
816
997
1180
1363 it48
1734
1920
2107
2294
2482
2670
2859
3048
3238
3427
3617
3807
3998
4188
4379
4570
4761
4953
5144
5336
5528
5720
5912
6104
6296
6488
6681
6874
7066
7259
7452
7645
7838
8031
8225
8418
8611
8805
8998
9192
6
790
968
1148
1329
1512
1695
1879
2064
2249
2435
2622
2808
2996
3183
3371
3560
3748
3937
4126
4316
4505
4695
4885
5075
5266
5456
5647
5S38
6029
6220
6411
6602
6794
6985
7177
7369
7561
7753
7945
8137
8329
8521
8714
8906
9099
5.27-9 a = 1.3, P= = 90%
7
765
940
1117
1296
1476
1657
1839
2022
2205
2389
2574
2759
2944
3130
3317
3503
3691
3878
4066
4253
4442
4630
4819
5007
5196
5386
5575
5765
5954
6144
6334
6524
6715
6905
7096
7286
7477
7668
7859
8050
8241
8433
8624
8815
9007
8
741
913
1088
1264
1441
1620
1800
1980
2162
2344
2527
2710
2894
3078
3263
3448
3634
3319
4006
4192
4379
4566
4753
4940
5128
5316
5504
5692
5831
6070
6258
6447
6636
6826
7015
7205
7394
7584
7774
7964
8154
8345
8535
8725
8916
9
718
887
1059
1232
1407
1584
1761
1940
2119
2300
2481
2662
2844
3027
3210
3393
3577
3762
3946
4131
4317
4502
4688
4874
5061
5247
5434
5621
580G
5996
6184
6371
6559
6747
6936
7124
7313
7501
7690
7879
8063
8257
8447
8636
8826
10
695
861
1030
1201
1374
1548
1724
1900
2078
2256
2435
2615
2795
2976
3158
3340
3522
3705
3888
4072
4256
4440
4624
4809:
4994
5180
5365
5551
5737
5923
6110
6296
6483
6670
6857
7044
7232
7419
7607
7795
7983
8171
8360
8548
8737
APPENDIX A
PROCEDURE FOR TESTING SNM DOORWAY MONITORS
FOR
FUNCTIONAL PERFORMANCE
Doorway monitors should be tested by employing a test source of the same isotope of SNM the doorway monitor is used to detect as follows:
1. With the detection area unoccupied, measure and record background.
2. Determine alarm threshold T from Table I (see Appendix B).
3. Place a test source in the detection area of the doorway monitor. The test source should be such that the activity in the detection area slightly exceeds the T
level.* The doorway monitor should go into an alarm condition if operating properly.
4. Remove test source to its original location and measure background once again. If the measurement of
- The test source may be improvised by partially shielding the calibration source.
background taken immediately after the test varies by more than 2vN
from the background taken before the test, the test should be repeated, for such a difference indicates nonrandom fluctuations of the background or equipment malfunction. The probability of such an occurrence due to the randomness of the background is less than 8%.
5. A calibration source (Appendix B) should be carried repeatedly to various places within the detection area of the doorway monitor in simulation of actual use to verify that the SNM can be detected everywhere within the detection area and to assure proper operation of treadle pads, beam-break, or similar devices if the doorway monitor is so equipped.
6. Doorway monitors used to search for concealed uranium-233 should be tested with each uranium purification run, but no more frequently than daily. The test source should be freshly purified uranium-233 (within four hours of removal of decay products).
5.27-10
APPENDIX B
PROCEDURE FOR DETERMINING MAXIMUM PERMISSIBL
E. BACKGROUND
Background should be measured over several work shifts to determine the setpoints for alarm threshold (with or without automatic background updating) to assure that normal operation will be minimally affected by alarms due to high background.
The doorway monitor should be calibrated with the amount of the appropriate isotope specified in Regula tory Positions C.l.b(1), (2), or (3) of this guide (e.g., 0.5 gram plutonium-239 in 3 mm of brass).
The calibration procedure described below is essen tially a means of determining maximum permissible background for effective operation of the doorway monitor.
1. Place a calibration source variously about the detec tion area and take readings to determine the least sensitive point. This location of minimum sensitivity should be maintained as the calibration point.
2. Measure background over several workshifts to deter mine the periods of high background and the range of background. A minimum of 20 measurements should be taken. The variance of the background is given by N
Var B N*-
1 (Bi-B)2
(1)
where N is the number of measurements, B is the mean of the background measurements, and Bi is the ith background measurement.
3. With the calibration source at the calibration point, the mean gross counts G should be determined during a period of high background to establish the upper operating range of the doorway monitor. Table II lists various maximum permissible background levels for a given value of G for values of the parameters n and a.
During periods when the background exceeds the value found from Table II, the sensitivity of the doorway monitor will generally be below that specified as minimum in Regulatory Position C.l.b of this guide.
The parameter n is a function of the background variation and the permissible false alarm rate and is calculated from n >3.1 (var B) 1/2
(2)
Generally, n is taken as an integer. If n satisfies the above expression, the expected false alarm rate (Appen dix C) due to background fluctuations should be less than 0.1%. Larger values of n will decrease the expected false alarm rate; however, the maximum allowable background for a given G will also decrease.
4. For doorway monitors equipped with automatic background updating systems, the alarm threshold is Counts > B + nVii,
(3)
where n should be derived from expression (2), and the instrument set accordingly.
5. The high-background alarm should be set at the B
value given in Table II for the measured G and calculated n values.
6. For doorway monitors not equipped with an auto matic background update, the value of n determined above should be employed in the use of the doorway monitor according to Regulatory Position C.2.a.
- The false alarm rate is estimated by the probability that an observation of a quantity distributed normally about some value X will exceed X by n(Std. deviation of X). The factor 3.1 limits the false alarm rate to 0.1%, while the factor (Var B/B) 1/2 compensates for observed deviations in the background distribution from Poisson.
5.27-11
APPENDIX C
DETECTION CONFIDENCE LIMITS, THRESHOLDS,
AND MAXIMUM PERMISSIBL
E. BACKGROUND
With a calibration source at the calibration point, the condition for an alarm is, in general, g> T = B + m/Va' B
(1)
where g is a single measurement of G (the mean radiation level with the source), B is the mean back ground, and m is some multiplier. The detection confidence limit is the probability that with the calibra iton source at the calibration point, any single determin ation of G will exceed a threshold T, i.e., the above inequality will be satisfied. For any given probability Pa.,
there exists a value a such that g > G-
(2)
with a probability of Pa, where g is any single measure ment of the quantity G. Hence the condition for a detection confidence limit of Pais G - &
_-r*-G > T = B + m,,/'r B.
(3)
For a given value of G, solving (3) gives the maximum permissible B at which the doorway monitor will detect the source with a confidence Pr- For Pa = 90%, a = 1.3, and for Pa = 50%, a = 0.
The condition for a false alarm* is written as b = B + j a-'"B> T
(4)
where b is a single measurement without the source and
0 is a number corresponding to a false alarm probability P
p. For P
= 0.1%, 0 = 3.1. Hence the necessary condition for maintaining a false alarm rate below Pp is b = B +
-"B
< B + m ar.
(5)
However, the doorway monitor actually compares b with B + ni, hence the condition on n becomes orV
< rn'VaTr
= nvff
(6)
or n>0 ( Va B ) 1/2
(7)
In Table I threshold values of T were determined by substituting equation (6) into equation (3):
T = B + nv'r The values of B in Table II were then calculated for a = 1.3 and a = 0 from equation (3) assuming that, for the determination of G, the background should be reasonably stable and therefore \\/Var G -\\
- False alarm means an alarm condition generated by statistical fluctuations in the background radiation or by instabilities of the electronics which appear as background fluctuations when the detection area is occupied.
5.27-12