Berkelium

Berkelium, Bk, is the name of element 97. It has the highest atomic number of any element for which fission is not significant.

Wikipedia has an article which provides a lot of information about the element.  This article will focus on things Wikipedia does not stress: formation and the element's natural presence on earth..

²⁴⁹Bk and heavier isotopes form in supernovae and neutron star mergers via rapid neutron capture followed by chains of beta decays. All are short-lived, but ²⁴⁹Bk may be present in young supernova or kilonova (neutron star merger) remnants. It will likely participate in dust formation..

On earth, neutrons from ²³⁸U spontaneous fission drive a slow process of neutron capture followed by beta decay followed by another capture. This process builds from ²³⁸U itself, and produces the isotopes ²⁴⁹Bk and heavier.

Its longest-lived isotope, ²⁴⁷Bk, has a half-life of 1380 yr, but does not form in quantity.

NUCLEAR PROPERTIES

INFORMATION SOURCES

Japan Atomic Energy Agency (JAEA) maintains an on-line chart of nuclides which includes decay properties of many predicted nuclides⁽¹⁾ - unlike charts published by Korea Atomic Energy Research Institute (KAERI) or the (U.S.) National Nuclear Data Center (NNDC). This chart gives separate numerical values for partial half-lives against fission, beta emission (both b^- and b⁺), and alpha emission. This reference provides the most focused look at the most significant predicted Bk isotopes. Other references used are cited.

PREDICTED AND OBSERVED PROPERTIES

Isotopes from the neutron dripline down to ²⁵⁴Bk are predicted to decay primarily by beta emission. Half lives are predicted to increase, as A declines, from around 0.001 sec at the dripline to 1 min at ²⁵⁷Bk and peaking around 20 min at ²⁵⁵Bk.

Beta decay is observed to continue down to ²⁴⁹Bk. Fission is negligible and alpha decay is a very minor branch. Half-lives increase to 1 hr at ²⁵¹Bk, to 3 hr at ²⁵⁰Bk, and 330 days at ²⁴⁹Bk.

²⁴⁸Bk has an isomer, ^248mBk, which beta decays. It is possible that neutron capture by ²⁴⁷Bk may produce this isomer. The ground state decays by alpha emission with a 300 yr half-life. It has not been observed to fission.

²⁴⁷Bk has a half-life of 1380 yr and nearly always alpha-decays. It is by a wide margin the most long-lived isotope of Bk.

Positive beta decay sets in at ²⁴⁶Bk. Half-lives drop from a few hours to seconds by ²³³Bk, the lightest reported isotope.

Ref 1 predicts isotopes as light as ²²⁴Bk. Ref 3 predicts isotopes with half-lives > 10^-09 sec down to ²¹⁹Bk. All these predicted isotopes are short lived, with half-lives under 0.001 sec. That they are possible at all indicates stabilization by the N = 126 neutron shell closure.

OCCURRENCE

FORMATION

a) Outside Earth

It appears likely that Bk isotopes from the neutron dripline down to ²⁴⁹Bk can form, with the possible exception of ²⁵²Bk. (²⁵²Cm is not predicted to have a beta-decay branch, but there may be a weak beta-decay branch. See "Californium", this wiki.)

Half-lives of isotopes that can form range from 0.001 sec near the neutron dripline to an hour at ²⁵¹Bk, then to 3 hrs at ²⁵⁰Bk, and 330 +/- 4 days at ²⁴⁹Bk.

²⁴⁸Bk and lighter isotopes are blocked from forming via rapid neutron capture & beta decay⁽⁴⁾, significantly by lack of a beta-decay branch in isotopes between ²⁴⁸Cm to ²⁴⁴Cm and presence of positive beta decay at ²⁴³Cm.

Berkelium's longest-lived isotope, ²⁴⁷Bk cannot form in quantity either because all neutron-capture / beta-decay processes (r-process, s-process, or reactor irradiation) are blocked by ²⁴⁷Cm which does not beta decay. Alpha bombardment of ²⁴³Am does produce some ²⁴⁷Bk both in the laboratory and "in the wild" (including earth's upper atmosphere), but quantities are minute.

Both high-A nuclides ejected during a neutron star merger and rapid neutron capture contribute to the production of those Bk isotopes which can form. Slow neutron capture can also contribute to the amount of Bk produced, but does not produce any isotopes not formed by rapid capture.

b) On Earth

While Bk is produced in some quantity in neutron star mergers and supernovae, those nuclides will decay quickly. After a short time, the only Bk remaining in a body will be what is produced continuously by slow neutron capture. Spontaneous fission of ²³⁸U produces free neutrons. This small flux of neutrons will produce a small amount of ²⁴⁹Bk and ²⁵⁰Bk. The short half-life of ²⁵⁰Bk means that, for all practical purposes, heavier isotopes don't form. Concentration of Bk will be many orders of magnitude smaller than uranium concentration; so only geologically-active rocky bodies like the earth, which can concentrate uranium, will contain potentially-detectable quantities of Bk.

PERSISTENCE

The amount of Bk produced during a supernova, neutron star merger, or comparable event will only be a few orders of magnitude less than the amount of uranium produced. Most of it decays until it either vanishes or comes into equilibrium with the continuous, slow production resulting from ²³⁸U fission.

²⁴⁹Bk, with its half-life close to a year may persist, in principle, over 150 years after the supernova, neutron star merger, or other event which led to its formation. The amount will be negligible for most of that time. It will persist long enough to exist in potentially detectable amounts in very young supernova or kilonova remnants.

²⁴⁹Bk persists long enough to participate in dust formation.

Slow neutron capture in rocky bodies active enough to concentrate uranium can produce ²⁴⁹Bk and heavier Bk isotopes. This production continues as long as U remains.

ATOMIC PROPERTIES

Wikipedia's article "Berkelium" addresses the element's atomic properties and chemistry in some detail. Chemistry of Bk is not quite limited to the laboratory.

REFERENCES

1. "Chart of the Nuclides, 2014", Japan Atomic Energy Agency; website available using "chart of nuclides" and "JAEA" as internet search terms.

2. "Nuclear Properties for Astrophysical Applications"; P. Moller & J. R. Nix; Los Alamos National Laboratory website; search by "LANL, T2", then "Nuclear Properties for Astrophysical Applications".

3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011.

4. "Isotopes of Californium", Wikipedia article.

9-Period Periodic Table of Elements
1	1 H																																																																	2 He
2	3 Li	4 Be																																																																	5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg																																																																	13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca																																																																	21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr																																																																	39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba																																																					57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb	71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra																																																					89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No	103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Cn	113 Nh	114 Fl	115 Mc	116 Lv	117 Ts	118 Og
8	119 Uue	120 Ubn																															121 Ubu	122 Ubb	123 Ubt	124 Ubq	125 Ubp	126 Ubh	127 Ubs	128 Ubo	129 Ube	130 Utn	131 Utu	132 Utb	133 Utt	134 Utq	135 Utp	136 Uth	137 Uts	138 Uto	139 Ute	140 Uqn	141 Uqu	142 Uqb	143 Uqt	144 Uqq	145 Uqp	146 Uqh	147 Uqs	148 Uqo	149 Uqe	150 Upn	151 Upu	152 Upb	153 Upt	154 Upq	155 Upp	156 Uph	157 Ups	158 Upo	159 Upe	160 Uhn	161 Uhu	162 Uhb	163 Uht	164 Uhq	165 Uhp	166 Uhh	167 Uhs	168 Uho	169 Uhe	170 Usn	171 Usu	172 Usb
9	173 Ust	174 Usq
Alkali metal Alkaline earth metal Lanthanide Actinide Superactinide Transition metal Post-transition metal Metalloid Other nonmetal Halogen Noble gas predicted predicted predicted predicted predicted predicted predicted predicted predicted

(11-23-20)