Tin-126: Information from Answers.com

Long-lived
fission products
Prop: Unit:	t^½ Ma	Yield %	Q * KeV	βγ *
⁹⁹Tc	.211	6.1385	294	β
¹²⁶Sn	.230	.1084	4050	βγ
⁷⁹Se	.295	.0447	151	β
⁹³Zr	1.53	5.4575	91	βγ
¹³⁵Cs	2.3	6.9110	269	β
¹⁰⁷Pd	6.5	1.2499	33	β
¹²⁹I	15.7	.8410	194	βγ

Tin-126 is a radioisotope of tin and one of only 7 long-lived fission products. While tin-126's halflife of 230,000 years translates to a low specific activity that limits its radioactive hazard, its shortlived decay product, antimony-126, emits high-energy gamma radiation, making external exposure to tin-126 a potential concern.

¹²⁶Sn is in the middle of the mass range for fission products. Thermal reactors, which make up almost all current nuclear power plants, produce it at a very low yield (such as 0.0236% or 0.06%), since slow neutrons almost always fission ²³⁵U or ²³⁹Pu into unequal halves. Fast fission in a fast reactor or nuclear weapon, or fission of some heavy minor actinides like californium, will produce it at higher yields.

Actinides				Halflife	Fission products
²⁴⁴Cm	²⁴¹Pu ^f	²⁵⁰Cf	²⁴³Cm^f	10–30 y	¹³⁷Cs	⁹⁰Sr	⁸⁵Kr
²³²U ^f		²³⁸Pu	f is for fissile	69–90 y			¹⁵¹Sm nc➔
	²⁴⁹Cf ^f	²⁴²Am^f	f is for fissile	141–351	No fission product has halflife 10² to 2×10⁵ years
	²⁴¹Am		²⁵¹Cf ^f	431–898
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm	²⁴³Am	5–7 ky
4n	²⁴⁵Cm^f	²⁵⁰Cm	²³⁹Pu ^f	8–24 ky
	²³³U ^f	²³⁰Th	²³¹Pa	32–160
		²³⁴U	4n+3	211–290	⁹⁹Tc		¹²⁶Sn	⁷⁹Se
²⁴⁸Cm		²⁴²Pu		340–373	Long-lived fission products
	²³⁷Np	4n+2		1–2 my	⁹³Zr	¹³⁵Cs nc➔
²³⁶U	4n+1		²⁴⁷Cm^f	6–23		¹⁰⁷Pd	¹²⁹I
²⁴⁴Pu				80 my	>7%	>5%	>1%	>.1%
²³²Th		²³⁸U	²³⁵U ^f	.7–12by	fission product yield

References