152m2-Eu -> 152-Eu -> 152-Gd daughter products not accumulated

[pkienzle]

The decay chain for isomer 152m2+Eu is not properly calculated.

This may not be a significant problem since the activation levels for 152m2 are several orders of magnitude down from the other neutron capture branches. Also, the original source comments included the following comment:

The "+" in indicates radioactive daughter production already included in daughter listing several parent t1/2's required to acheive calculated daughter activity. All activations are assigned at end of irradiation. In most cases the added activity to the daughter is small.

That is, the 152Gd buildup from the 152m2Eu path may already be accounted for with a slightly increased cross section for 151Eu (n,γ) 152Eu. We haven't verified or updated the capture cross-section values from the original neutron activation tables in Schleien (1998).

Neutron activation of 151Eu produces 152Eu, 152m1Eu and 152m2Eu

Using the IAEA chart of the nuclides (https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html):

152m2Eu -> 152Eu IT 100% 96(1) m

152m1Eu -> 152Gd β– 73(3)% 9.3116(13) h
152m1Eu -> 152Sm ec β+ 27(3)% 9.3116(13) h

152Eu -> 152Gd β– 27.92(13)% 13.517(14) y
152Eu -> 152Sm ec β+ 72.08(13)% 13.517(14) y

152Gd -> 148Sm α 100% 1.08(8)e14 y

148Sm -> 144Nd α 100% 7(2)e15 y

144Nd -> 140Ce α 100% 2.29(15)e15 y

The β– decays for 152Eu and 152m1Eu in the activation data tables have the appropriate "b mode" decay lines following them, covering the buildup of 152Gd. However the 152m2Eu entry does not. Further complicating the issue is that 152m2Eu is a three-stage decay, but the activation table only includes two-stage decay calculations (for exposure; for post-exposure decay we only warn that it isn't calculated).

The 148Sm and 140Nd daughters in the 152Gd decay chain are also ignored. See here: https://periodictable.com/Isotopes/063.152/index2.html

[1] Shleien, B., Slaback, L.A., Birky, B.K. (1998). Handbook of health physics and radiological health. Williams & Wilkins, Baltimore..

[pkienzle]

Note also that the Eu-152m1 line is not highlighted as part of the b-mode decay because the isomer is not tagged as transient. We could rename it Eu-152m1t in the database, or alternatively use its position as one before the b-mode line to indicate that it should be tagged.