Special Procedure 6

 Requirements for Inventory Records (Top)

 
Inventory records must be kept for all unsealed radioactive material at Cornell University.  The key components of the inventory system at Cornell are provided below.
 
  • EHS assigns a Vial ID number to each vial of radioactive material upon receipt.  The Vial ID number is indicated on the inventory sheet for that vial.  (Recording the Vial ID number from the inventory sheet onto the vial is recommended for easier identification.)
  • ​The inventory sheets are the primary record for all radioactive materials received, used and disposed of at Cornell. Detailed recording of all the inventory information on this form is required.
  • Entries on inventory sheets for decay calculations, waste activities and inventory balances are required for waste pickups.  At the time of a waste pickup, EHS will pick up the original inventory sheets for which no radioactive material remains in the lab.  Photocopies of the inventory sheets for vials being partially disposed, i.e. some activity from that vial remains in the lab, will also be picked up by EHS at the time of a waste pick up.
  • Dispensing and waste disposition are required inventory sheet entries for each use of radioactive material.
  • Every calendar quarter, an “Inventory Verification Report”, listing the current on-hand inventory, will be sent to the permit holder by EHS.  The permit holder must perform a physical inventory, including verification that the inventory sheet and remaining radioactive material for each vial is present.
  • For transfers of material to a different permit holder, entries are required on inventory sheets for decay calculations, transferred activity and the current inventory balance.  Prior to the transfer, a new vial ID number must be obtained from EHS for that material.
  • The 3-year storage requirement for “zeroed out” inventory records will be maintained by EHS.
Physical Inventory:

Every calendar quarter, the permit holder will receive an “Inventory Verification Report” from EHS.  Listed in the report are all stock vials in the lab, activity (decayed to the report date) and the sum of the last six months of waste removals from each vial.  The physical inventory includes locating the inventory record for each stock and locating each stock vial that has not been disposed into waste.  (If the stock vial has been disposed into waste, the disposal must be indicated on the inventory sheet.)  When the inventory sheet and stock are accounted for, place a check next to that record on the "Inventory Verification Report" under the "Inventoried" column.  If a stock is missing or other discrepancies are found, contact EHS and record the discrepancy in the "Discrepancies" section near the bottom of the report.  Lastly, the report must be signed by the permit holder and returned to EHS within 15 days of the report date.

Waste Pickups:

In order to maintain a consistent, campus-wide, radioactive materials inventory record, the activity of each isotope stock vial for which waste is being removed must be decay-corrected to the date of the waste pickup[1]  Each time waste is scheduled to be removed, the amount to be removed must be indicated on the individual inventory sheets for each stock.  The waste disposal record must be entered on the inventory sheet prior to the waste pickup.  Waste removal slips must reflect with reasonable accuracy the waste activity decay corrected to the removal date.  Inventory sheets "zeroed out" by the waste pickup and photocopies of the remaining sheets, which are not "zeroed out", will be collected by EHS at the time the waste is collected.

Transfers:

Transfers of radioactive material to a different permit holder requires authorization from EHS.  The authorization may be a one-time approval or may be a standing condition listed on the respective permits.  Each time a transfer is proposed, the permit holder transferring the material must contact EHS for approval and/or a new vial ID number for the transfer.  When contacting EHS, have the following information available.

  • (Stock) Vial ID number
  • Isotope
  • Proposed transfer date
  • Activity decayed to the transfer date
  • Permit holder receiving the transfer

The original inventory sheet must include a record of the transfer, including decay to the date of the transfer, the activity transferred, the name of the permit holder receiving the material and the updated inventory balance.  Generate a new inventory sheet for the transferred material by completing the header information on a new form.  A blank inventory sheet is attached for your convenience.  The permit holder receiving the material must record the receipt of the transfer on the first line of the new sheet, including the permit holder the material was received from, the stock balance and the inventory balance.

Decay Calculations:

Three methods for calculating decay are described.

  • Method 1 employs the Excel spreadsheet described in Special Procedure 13.  The spreadsheet will calculate decay and the activities of waste being picked up.
  • Method 2 is using the standard decay equations.
  • Method 3 is using pre-calculated decay factors given in Table 2 on page 5.

[Note that methods 2 and 3 provide the amount of material that has decayed not the amount that is remaining.  The amount of decay can then be subtracted from the inventory balance to reflect the current activity remaining in the lab.]

Method 1: The Excel Spreadsheet

The spreadsheet described in Special Procedure 13, "Instructions for Using Excel Waste Disposition and decay Calculation Sheet", is designed to easily calculate activities of waste being picked up from each stock vial and decay to the date of waste pick up.  It is designed for labs that keep track of stock balance in volume and waste disposition in percentage.  This method is highly recommended.  It is also a time saver!  See Special Procedure 13 for actual instructions.

  Click on the Excel spreadsheet for waste and decay calculations to download the file. 

Table 1: Half-lives for Selected Isotopes

Isotope
Half-life
Isotope
Half-life
Isotope
Half-life
110mAg
249.85 days
59Fe
44.63 days
32P
14.29 days
76As
1.097 days
153Gd
241.6 days
33P
25.4 days
77As
1.617 days
159Gd
0.773 days
203Pb
2.167 days
133Ba
10.5 years
3H
12.28 years
210Pb
22.26 years
14C
5730 years
181Hf
42.39 days
86Rb
18.66 days
45Ca
162.7 days
125I
60.14 days
35S
87.44 days
47Ca
4.536 days
131I
8.04 days
46Sc
83.8 days
109Cd
464 days
111In
2.83 days
75Se
119.78 days
141Ce
32.5 days
114In
49.51 days
153Sm
1.946 days
36Cl
301,000 years
40K
1.277 x 109 years
113Sn
115.1 days
57Co
270.9 days
42K
0.515 days
85Sr
64.84 days
58Co
70.8 days
28Mg
0.871 days
99Tc
213,000 years
60Co
5.271 years
54Mn
312.7 days
99mTc
0.251 days
51Cr
27.704 days
22Na
2.602 years
44Ti
47.3 years
137Cs
30.17 years
24Na
0.625 days
88Y
106.6 days
154Eu
8.8 years
63Ni
100.1 years
65Zn
244.4 days
55Fe
2.7 years
 
 
 
 

 

Method 2: Equations
Direct decay calculation can be obtained by either of the two equations listed below.  Pay special attention to the units for each variable to obtain the amount of decay in millicuries. 

    D = A0 · (1 - e-(ln 2 / HL) · t)  or  D = A0 · (1 - 0.5(t / HL))

 Where:   D   =  Activity which has decayed in mCi      

               A0  =    Last decay-corrected stock activity balance in mCi

·   =    Indicates multiplication

HL  =    Half-life for that isotope (See Table 1 for the correct value for each isotope.) [2]
t    =    Amount of time that has elapsed since the last decay correction.  (Be sure that the time is in the same units as the half-life for that isotope.)
 
Method 3: Pre-calculated Decay Factors
This method only accounts for decay for up to 31 days.  If using this method for calculating decay for longer periods,
the method will need to be repeated for each month that has elapsed since the last decay correction.  The decay factors
listed in Table 2  on page 5 indicate the fraction of activity that has decayed for the most common isotopes used
at Cornell University. To determine decay using these factors, perform the following steps:
  1. Determine the number of days since the last decay correction.
  2. Refer to Table 2 on page 5 entitled "Decay Chart".[3]
  3. Locate the column for the isotope for which the decay is being calculated.
  4. Locate the decay factor for that isotope for the number of days determined in step "a" of this method.
  5. Multiply this decay factor by the most recent decay-corrected inventory balance. 

Related Information:

  • Table 3 "Activity Remaining Chart" [4] may be used to determine current activity by following the same steps outlined above in method 3, but substituting Table 3 values for Table 2 values.  The product from step "e" represents the current activity, i.e. inventory balance for that stock.  The inventory balance may also be obtained by subtracting the decay result from the previous inventory balance.
  • For detailed instruction on how to keep inventory records, take the EHS Advanced Record Keeper Training offered on CU Learn.

Table 2: Decay Chart (1 - e-((ln 2 / HL) · t) 

Number of Days
32P
35S
33P
125I
3H
45Ca
47Ca
51Cr
131I
86Rb
1
0.047
0.008
0.027
0.011
0.000
0.004
0.142
0.025
0.083
0.036
2
0.092
0.016
0.053
0.023
0.000
0.008
0.263
0.049
0.158
0.072
3
0.135
0.024
0.079
0.034
0.000
0.013
0.368
0.072
0.228
0.105
4
0.176
0.031
0.103
0.045
0.001
0.017
0.457
0.095
0.292
0.138
5
0.215
0.039
0.128
0.056
0.001
0.021
0.534
0.118
0.350
0.170
6
0.253
0.046
0.151
0.067
0.001
0.025
0.600
0.139
0.404
0.200
7
0.288
0.054
0.174
0.078
0.001
0.029
0.657
0.161
0.453
0.229
8
0.322
0.061
0.196
0.088
0.001
0.034
0.706
0.181
0.498
0.257
9
0.354
0.069
0.218
0.099
0.001
0.038
0.747
0.202
0.540
0.284
10
0.384
0.076
0.239
0.109
0.002
0.042
0.783
0.221
0.578
0.310
11
0.413
0.084
0.259
0.119
0.002
0.046
0.814
0.241
0.613
0.335
12
0.441
0.091
0.279
0.129
0.002
0.050
0.840
0.259
0.645
0.360
13
0.468
0.098
0.299
0.139
0.002
0.054
0.863
0.278
0.674
0.383
14
0.493
0.105
0.318
0.149
0.002
0.058
0.882
0.296
0.701
0.406
15
0.517
0.112
0.336
0.159
0.002
0.062
0.899
0.313
0.726
0.427
16
0.540
0.119
0.354
0.168
0.002
0.066
0.913
0.330
0.748
0.448
17
0.562
0.126
0.371
0.178
0.003
0.070
0.926
0.346
0.769
0.468
18
0.582
0.133
0.388
0.187
0.003
0.074
0.936
0.363
0.788
0.488
19
0.602
0.140
0.405
0.197
0.003
0.078
0.945
0.378
0.806
0.506
20
0.621
0.147
0.421
0.206
0.003
0.082
0.953
0.394
0.822
0.524
21
0.639
0.153
0.436
0.215
0.003
0.086
0.960
0.409
0.836
0.542
22
0.656
0.160
0.451
0.224
0.003
0.089
0.965
0.423
0.850
0.558
23
0.672
0.167
0.466
0.233
0.004
0.093
0.970
0.438
0.862
0.574
24
0.688
0.173
0.481
0.242
0.004
0.097
0.974
0.451
0.874
0.590
25
0.703
0.180
0.495
0.250
0.004
0.101
0.978
0.465
0.884
0.605
26
0.717
0.186
0.508
0.259
0.004
0.105
0.981
0.478
0.894
0.619
27
0.730
0.193
0.521
0.267
0.004
0.109
0.984
0.491
0.902
0.633
28
0.743
0.199
0.534
0.276
0.004
0.112
0.986
0.504
0.911
0.647
29
0.755
0.205
0.547
0.284
0.004
0.116
0.988
0.516
0.918
0.659
30
0.767
0.212
0.559
0.292
0.005
0.120
0.990
0.528
0.925
0.672
31
0.778
0.218
0.571
0.300
0.005
0.124
0.991
0.540
0.931
0.684

 

Table 3: Activity Remaining Chart  (1 - e-((ln 2 / HL) · t) 

 

Number of Days
32P
35S
33P
125I
3H
45Ca
47Ca
51Cr
131I
86Rb
1
0.953
0.992
0.973
0.989
1.000
0.996
0.858
0.975
0.917
0.964
2
0.908
0.984
0.947
0.977
1.000
0.992
0.737
0.951
0.842
0.928
3
0.865
0.976
0.921
0.966
1.000
0.987
0.632
0.928
0.772
0.895
4
0.824
0.969
0.897
0.955
0.999
0.983
0.543
0.905
0.708
0.862
5
0.785
0.961
0.872
0.944
0.999
0.979
0.466
0.882
0.650
0.830
6
0.747
0.954
0.849
0.933
0.999
0.975
0.400
0.861
0.596
0.800
7
0.712
0.946
0.826
0.922
0.999
0.971
0.343
0.839
0.547
0.771
8
0.678
0.939
0.804
0.912
0.999
0.966
0.294
0.819
0.502
0.743
9
0.646
0.931
0.782
0.901
0.999
0.962
0.253
0.798
0.460
0.716
10
0.616
0.924
0.761
0.891
0.998
0.958
0.217
0.779
0.422
0.690
11
0.587
0.916
0.741
0.881
0.998
0.954
0.186
0.759
0.387
0.665
12
0.559
0.909
0.721
0.871
0.998
0.950
0.160
0.741
0.355
0.640
13
0.532
0.902
0.701
0.861
0.998
0.946
0.137
0.722
0.326
0.617
14
0.507
0.895
0.682
0.851
0.998
0.942
0.118
0.704
0.299
0.594
15
0.483
0.888
0.664
0.841
0.998
0.938
0.101
0.687
0.274
0.573
16
0.460
0.881
0.646
0.832
0.998
0.934
0.087
0.670
0.252
0.552
17
0.438
0.874
0.629
0.822
0.997
0.930
0.074
0.654
0.231
0.532
18
0.418
0.867
0.612
0.813
0.997
0.926
0.064
0.637
0.212
0.512
19
0.398
0.860
0.595
0.803
0.997
0.922
0.055
0.622
0.194
0.494
20
0.379
0.853
0.579
0.794
0.997
0.918
0.047
0.606
0.178
0.476
21
0.361
0.847
0.564
0.785
0.997
0.914
0.040
0.591
0.164
0.458
22
0.344
0.840
0.549
0.776
0.997
0.911
0.035
0.577
0.150
0.442
23
0.328
0.833
0.534
0.767
0.996
0.907
0.030
0.562
0.138
0.426
24
0.312
0.827
0.519
0.758
0.996
0.903
0.026
0.549
0.126
0.410
25
0.297
0.820
0.505
0.750
0.996
0.899
0.022
0.535
0.116
0.395
26
0.283
0.814
0.492
0.741
0.996
0.895
0.019
0.522
0.106
0.381
27
0.270
0.807
0.479
0.733
0.996
0.891
0.016
0.509
0.098
0.367
28
0.257
0.801
0.466
0.724
0.996
0.888
0.014
0.496
0.089
0.353
29
0.245
0.795
0.453
0.716
0.996
0.884
0.012
0.484
0.082
0.341
30
0.233
0.788
0.441
0.708
0.995
0.880
0.010
0.472
0.075
0.328
31
0.222
0.782
0.429
0.700
0.995
0.876
0.009
0.460
0.069
0.316

 

Inventory Sheet

[1Isotopes with half-lives of greater than 101 years do not require decay calculations.

[2] If using this method, the half-lives listed in Table 1 on page 3 of this procedure must be used. This keeps all of the decay data consistent with EHS and other permit holders.  If the isotope of interest is not listed, contact EHS for the appropriate value.

[3] The "Decay Chart" is the calculated value of (1 - e-(ln 2 / HL) · t), where HL and t are the same as described above under Method 1.

[4] The "Activity Remaining Chart" is the calculated value of (e-(ln 2 / HL) · t), where HL and t are the same as described above under Method 2.

 

 

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