150Nd activation decay chain incorrectly handled.

[pkienzle]

The 150Nd activation chain is not handled correctly:

150Nd (n,y) 151Nd (β⁻ 12m) 151Pm (β⁻ 28.4h) 151Sm (β⁻ 90y) 151Eu

The 151Pm halflife is instead treated as if it were 151Nd:

150Nd (n,y) 151Nd (β⁻ 12m) 151Pm (β⁻ 12m) 151Sm (β⁻ 90y) 151Eu

Use the multistage Bateman equation (wikipedia) to check the 151Pm activation levels and compare it to the two-stage calculation shown below.

With 10 g of Nd at natural abundance exposed for 10 h it appears that decay time will be dominated by 147Pm, so even an underestimate of the intermediate 151Pm levels should not be too concerning.

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Activation of Nd after 10 hrs at 1.00e+8 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: 10.000 g of Nd
Time to decay below 5.0000e-4 μCi is 11.5 yrs.

Isotope	reaction	daughter	halflife	0 hr	1 hr	24 hr	15 days	7.8 y
Nd-146	act	Nd-147t	10.98 d	6.9608e-1	6.9425e-1	6.5350e-1	2.7003e-1	6.1453e-79
Nd-146	b	Pm-147	2.6234 y	1.0535e-4	1.2630e-4	5.9308e-4	4.9559e-3	1.0423e-3
Nd-148	act	Nd-149t	1.728 h	1.5441e+1	1.0339e+1	1.0179e-3	2.9792e-62	0.0000e+0
Nd-148	b	Pm-149	53.08 h	1.4703e+0	1.6162e+0	1.4545e+0	1.8080e-2	0.0000e+0
Nd-150	act	Nd-151t	12.44 m	7.2916e+0	2.5758e-1	1.0397e-34	0.0000e+0	0.0000e+0
Nd-150	b	Pm-151	28.40 h	1.5371e+0	1.5505e+0	8.8553e-1	2.4306e-4	0.0000e+0
Nd-150	b	Sm-151	94.6 y	5.9131e-5	5.9502e-5	5.9515e-5	5.9498e-5	5.6212e-5
Total				2.6437e+1	1.4458e+1	2.9952e+0	2.9337e-1	1.0986e-3

b reaction activity is slightly underestimated; it does not include decay of transients after removal from beam.

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[pkienzle]

I verified that the activity in 151Pr at t=0 translates into activity in 151Sm scaled by the ratio of the half-lives (29,180) after 284 hrs (10 half-lives for 99.9% decay). The 151Nd activity is lost.

This may be the incorrect calculation. Because the half life of 151Nd was used in calculating the initial 151Sm activity, it may be that all of the activity stored in the 151Pr transient has already been added into 151Sm at t=0. It may be more correct to use the 151Nd activity and half-life when calculating the delayed beta increase. Even better, we could subtract the 151Pr scaled activity from 151Sm at t=0, and let it build up during post-irradiation decay.