Possible Erratum, Si[32] half-life, NIST activation calculator

[pkienzle]

Error reported by user:

While using the NIST Neutron activation calculator ( https://www.ncnr.nist.gov/resources/activation/ ) to model the residual activity of a hypothetical silicon sample irradiated by thermal neutrons, I noted that the calculator states the half-life of the Si[32] isotope as one-hundred (100) years (highlighted in the activation table below.) This 100y half-life for Si[32] Beta- emission is likely incorrectly low. Recent literature half-lives for the decay of Si[32] to P[32] by Beta- emission are 172+/-4 years or 163+/-6 years. Please see the references below the table and in the attached paper. Using a 100-year half-life could tend to predict a higher activity and a shorter safe quenching time than would physically be the case for a given amount of transmuted Si[32] material.

Example NCNR Activation Calculation
Activation of Si after 10 hrs at 2.00e+14 n/cm2/s
Estimated activation only. All samples must be evaluated by NIST Health Physics to determine if and how the sample can be removed from the NCNR.
Sample in beam: 840.000 g of Si
Rabbit system: Cd ratio = 0, thermal/fast ratio = 100
Time to decay below 5.0000e-4 μCi is 60.5 yrs.

Activity (μCi)>5.0000e-4 μCi

element	reaction	product	half life	0 hrs	1 hr	24 hrs	15 days	1 yrs
Si-28	n,p	Al-28	2.25 m	5.7644e+6	5.4111e-2	1.2634e-186	0.0000e+0	0.0000e+0
Si-29	n,p	Al-29	6.5 m	1.4531e+5	2.4185e+2	2.9687e-62	0.0000e+0	0.0000e+0
Si-30	act	Si-31	2.62 h	2.8088e+8	2.1558e+8	4.9089e+5	1.2179e-33	0.0000e+0
Si-30	2n	Si-32	100 y	7.6036e-4	7.6036e-4	7.6034e-4	7.6014e-4	7.5510e-4
Si-30	n,a	Mg-27	9.458 m	4.3795e+3	5.3919e+1	6.4416e-43	0.0000e+0	0.0000e+0
			total activity	2.8679e+8	2.1558e+8	4.9089e+5	7.6014e-4	7.5510e-4

References:

1. Alburger et al. at Brookhaven (1986) provided a fitted figure of 172(4) years for the Si[32] half-life, abstract below; paper attached. Table 2 lists experimental half-life values.
   D.E. Alburger, G. Harbottle, E.F. Norton, “Half-life of 32Si” Earth and Planetary Science Letters, Volume 78, Issues 2–3,1986, Pages 168-176, ISSN 0012-821X doi:10.1016/0012-821X(86)90058-0
   Abstract: Beta rays from a 32Si-32P source, produced in 1968–1969 via the 30Si(t,p)32Si reaction using a Van de Graaff beam at Et = 3.4 MeV, were counted with an end-window gas-flow proportional counter system including an automatic precision sample changer. Comparison counts were taken on the β rays from a 36Cl source. Measurements beginning February, 1982 were made at approximately 4-week intervals, each consisting of a total of 40 hours of counting on each sample. The decay rate was determined from the32Si/36Cl ratio of counts. Small periodic annual deviations of the data points from an exponential decay curve were observed, but are of uncertain origin and had no significant effect on the result. Based on the analysis of 53 points taken in 48 months, the value T1/2 = 172(4) yr is adopted for the half-life of 32Si. This result is substantially greater than two previously reported measurements of 108(18) yr and 101(18) yr but is lower than values based on geophysical evidence.

2. [South] Korea Atomic Energy Research Institute, citing NUDAT information from 1999: https://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Si32 (Si[32] T½ = 172 years)

3. NNDC Brookhaven, Si[32] T½ = 163+/-6 years (NUDAT 3.0 published 2023) standard_booklet.pdf

4. NIH PubChem: Silicon, isotope of mass 32 | Si | CID 6335897 - PubChem [updated 2025-09-20, Si[32] T½ = 172 years]]

[pkienzle]

PubChem also gives 157 ± 7 years here. This is traceable to NuBASE2020.

Trying to chase down the values for NuDAT, I did a search in the ENSDF database for 32P, selected "32SI B- DECAY (157 Y)" and got the value of 157 years referenced in NuBASE2020. I don't understand why the NuDAT value is inconsistent with ENSDF when it claims here that it is using ENSDF values for half-life unless replaced by a value from the experimental unevaluated nuclear data list. Searching 32S and 32P in XUNDL does not give newer values for T1/2

My inclination is to use the NuBASE values, which are pulled from the same source as the isotope mass values that I'm using in the rest of periodictable, and are consistent with the ENSDF dataset that NuDAT claims to use. The corresponding PR should update all values to use the same table. However, I will need to first verify that there are not regulatory reasons to prefer the current data values, and possibly support two sets of values within the program.

5. F.G. Kondev et al 2021 Chinese Phys. C 45 030001 doi:10.1088/1674-1137/abddae

[pkienzle]

I did a comparison between activation.dat and the NUBASE2020 half-lives.

The following isomers are coded differently. Mostly a few 'm' isomers should have been 'm2':

                code_override = {
                    "Pb-204m": 2,
                    "Ir-194m": 2,
                    "Ta-182m+": 2,
                    "Lu-177m*": 3,  # 177Lup in NUBASE
                    "Eu-152m2+": 5,  # 152Eur in NUBASE
                    "Sb-122m+": 3,  # 122Sbp in NUBASE
                    "Ag-110m*": 2,
                    "Pd-109m+": 2,
                    "Pd-107m+": 2,
                    "Kr-83m": 2,
                    "Ge-73m": 2,
                    "Sc-46m+": 2,
                }

The following is listed as stable in NUBASE but not the activation calculator:

Te-122 => Te-123: T1/2 = 12 Ty != stbl

Of the 377 isotopes processed by the activation calculator, 179 of them differ in half-life by more than 0.5%

Here are a list of isotopes whose half-life values in the activation calculator differ from NUBASE2020 by more than 5%:

Be-9   => Be-10    :  15% ΔT½ (1.6 My != 1.387 My ± 0.9%)
Si-30  => Si-32    :  36% ΔT½ (100 y != 157 y ± 4.5%)
Cl-37  => Cl-38m+  :  39% ΔT½ (1 s != 715 ms ± 0.4%)
Ca-40  => Ca-41    :  30% ΔT½ (130 ky != 99.4 ky ± 1.5%)
Ni-58  => Ni-59    :   7% ΔT½ (75 ky != 81 ky ± 6.2%)
Zn-64  => Zn-65    :   8% ΔT½ (265 d != 243.94 d ± 0.0%)
Zn-70  => Zn-71m   :   5% ΔT½ (3.9 h != 4.148 h ± 0.3%)
Ga-71  => Ga-72m+  :   9% ΔT½ (0.036 s != 39.68 ms ± 0.3%)
Ge-72  => Ge-73m   :   6% ΔT½ (0.53 s != 499 ms ± 2.2%)
Ge-74  => Zn-71ms  :   5% ΔT½ (3.9 h != 4.148 h ± 0.3%)
Se-78  => Se-79    :  80% ΔT½ (65 ky != 327 ky ± 8.6%)
Kr-80  => Kr-81    :   8% ΔT½ (0.21 My != 229 ky ± 4.8%)
Zr-92  => Zr-93    :   6% ΔT½ (1.5 My != 1.61 My ± 3.1%)
Nb-93  => Nb-92    :   6% ΔT½ (37 My != 34.7 My ± 6.9%)
Nb-93  => Nb-93m   :   9% ΔT½ (14.6 y != 16.12 y ± 0.7%)
Mo-92  => Mo-93    :  12% ΔT½ (3500 y != 4.0 ky ± 20.0%)
Ru-96  => Tc-97    :  38% ΔT½ (2.6 My != 4.21 My ± 3.8%)
Pd-110 => Pd-111t  :   6% ΔT½ (22 m != 23.56 m ± 0.4%)
Ag-107 => Ag-108m* :  71% ΔT½ (127 y != 439 y ± 2.1%)
Cd-112 => Cd-113m  :   5% ΔT½ (14.6 y != 13.89 y ± 0.8%)
Cd-112 => Cd-113   :  11% ΔT½ (9000 Ty != 8.04 Py ± 0.6%)
Sn-112 => Sn-113m+ :   6% ΔT½ (20 m != 21.4 m ± 1.9%)
Sn-118 => Sn-119m  :  16% ΔT½ (245 d != 293.1 d ± 0.2%)
Sn-120 => Sn-121m  :  25% ΔT½ (55 y != 43.9 y ± 1.1%)
Sn-124 => Sn-126   :  56% ΔT½ (100 ky != 230 ky ± 6.1%)
Te-120 => Te-121m* :   6% ΔT½ (154 d != 164.7 d ± 0.3%)
Te-120 => Te-121   :  12% ΔT½ (16.8 d != 19.31 d ± 0.4%)
Te-130 => Te-131m  :   7% ΔT½ (30 h != 32.48 h ± 0.3%)
Xe-126 => Xe-127m+ :   8% ΔT½ (75 s != 69.2 s ± 1.3%)
Xe-132 => Xe-133   :   9% ΔT½ (5.72 d != 5.2474 d ± 0.0%)
Cs-133 => Cs-135   : 125% ΔT½ (3 My != 1.33 My ± 14.3%)
Sm-154 => Sm-155   :   5% ΔT½ (23.5 m != 22.18 m ± 0.3%)
Eu-151 => Eu-152t  :   6% ΔT½ (12.7 y != 13.517 y ± 0.0%)
Dy-156 => Tb-157   : 111% ΔT½ (150 y != 71 y ± 9.9%)
Dy-164 => Dy-165m  :   8% ΔT½ (1.15 m != 1.257 m ± 0.5%)
Ho-165 => Ho-166m  :   5% ΔT½ (1200 y != 1.1326 ky ± 0.3%)
Lu-175 => Lu-176   :  10% ΔT½ (33 Gy != 37.01 Gy ± 0.5%)
Lu-176 => Lu-177m* :  28% ΔT½ (115 d != 160.4 d ± 0.2%)
Hf-177 => Hf-178m  :   7% ΔT½ (4.3 s != 4.0 s ± 5.0%)
Re-185 => Re-184   :   7% ΔT½ (38 d != 35.4 d ± 2.0%)
Os-190 => Os-191m+ :  14% ΔT½ (15 h != 13.10 h ± 0.4%)
Os-192 => Os-193   :   5% ΔT½ (31.5 h != 29.830 h ± 0.1%)
Pt-190 => Pt-191   :   6% ΔT½ (3 d != 2.83 d ± 0.7%)
Pt-196 => Pt-197m+ :   5% ΔT½ (1.5 h != 95.41 m ± 0.2%)
Pt-196 => Pt-197   :   9% ΔT½ (18 h != 19.8915 h ± 0.0%)
Hg-204 => Hg-205   :   7% ΔT½ (5.5 m != 5.14 m ± 1.8%)
Pb-204 => Pb-205   :  17% ΔT½ (14 My != 17.0 My ± 5.3%)
Bi-209 => Bi-210ms :  15% ΔT½ (3.5 My != 3.04 My ± 2.0%)

Processed with nubase.py using nubase_4.mas20 from ANL here.