Mendelevium

Mendelevium, Md, is the name of element 101. It is the last element for which peak stability probably occurs in observed isotopes, though predicted isotopes are expected to persist longer after an initial formative event. Wikipedia has an article which provides a lot of information about the element.  This article will focus on things Wikipedia does not stress: heavy isotopes and formation.

Half-lives of Md isotopes range up to 58 days for ²⁵⁸Md. However, this isotope can only be synthesized. Among isotopes which can form, ²⁶¹Md is predicted to be most stable with a half-life near 8 days. It is expected to persist long enough to become part of supernova or kilonova remnants. Other isotopes are all shorter-lived.

A good deal of is known about the chemistry of Md, both theoretically and experimentally. We also can produce atoms at a rate high enough to be described as "production" in Wikipedia.

File:Md.jpg

The isotope ²⁶⁰Md has an odd number of both protons and neutrons, which implies it is highly resistant to fission; yet fission is its most common decay mode. It also decays by both beta and positron emission,which implies that the isotope is in the band where the most stable isotopes of Md are to be found. It also has an alpha-decay branch, making it one of the small number of nuclides which decay by all four principal modes.

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 Md isotopes.

An independent resource is provided by the U.S.'s Los Alamos National Laboratory (LANL) in interactive tables of contains tabulated partial half-life data for alpha and beta decay⁽²⁾ for numerous nuclides. The great weakness of this source is that it does not consider fission.

A third source describes decay properties of a large number of nuclides⁽³⁾. Half-life data in this source are presented via color, which makes specifying a value within an order of magnitude difficult. In addition, only the dominant decay mode is reported. Charts on pp 11 - 13 are the most valuable part of the document.

PREDICTED PROPERTIES

Isotopes from the neutron dripline down to ²⁷¹Md are predicted to decay primarily by beta emission. Half lives increase, as A declines, from around 0.001 sec at the dripline to 10 sec near ²⁷⁵Md and peaking around 1600 sec at ²⁷³Md. Isotopes at the light end of this band are likely to decay by a mixture of beta emission and fission.

Between ²⁷⁰Md and ²⁶⁶Md, odd-A (even-N) isotopes are predicted to decay principally by fission, with some beta emission. Even-A isotopes in this range are predicted to decay mainly by beta emission, with some loss to fission. Half-lives are under 1000 sec.

²⁶⁵Md is predicted to decay by an almost even split of beta emission and fission. It is also predicted to have a weak alpha-emission branch . Its half-life, as predicted by Ref. 2, may be as great as 10⁰⁵ sec. That seems anomalously high. 10⁰⁴ is more in line with ²⁶³Md's 12000 sec.

²⁶⁴Md to ²⁶²Md is predicted to be a set of 99% or better beta emitting isotopes, with weak alpha and fission branches. Peak half-life is predicted to be under 4 hrs at ³⁶³Md and under 1 hr for the others.

²⁶¹Md is predicted to decay mainly (0.99 per unit) by alpha emission, It it not predicted to have a beta-decay branch. Its half-life is predicted to be less than 10 days.

²⁶⁰Md, and all lighter isotopes down to A in the mid 240s, have been observed. ²⁶⁰Md is consistent with other even-A (odd-N) isotope half-lives reported, as is ²⁵⁹Md Both indicate that predicted partial fission half-lives in the ²⁶⁹Md to ²⁶¹Md range may be too long.

Isotopes of Md have been predicted or observed down to ²³⁶Md. Between ²³⁵Md and ²³⁰Md, there is a gap containing nuclides with half-lives in the 10^-14 - 10^-09 sec range or nuclear drops too short-lived to qualify as nuclides. Decay by fission is to be expected.

Ref. 3 predicts that a set of isotopes with N near 126, ²²⁹Md to ²²²Md, will have half-lives exceeding 10^-09 sec. All are short lived, with half-lives under 0.001 sec. ²²⁷Md (for which N = 126) is predicted to decay mainly by alpha emission. The other are predicted to decay either by fission or proton emission.

OCCURRENCE

FORMATION

It appears likely that Md isotopes from the neutron dripline down to ²⁶⁹Md can form. Some losses due to fission in beta-decay chains leading to Md is likely, but are not expected to be severe.

It appears likely that ²⁶⁸Md cannot form, due to lack of a beta decay branch in ²⁶⁸Fm.

Although fission reduces the amount which can form, it appears to be possible that ²⁶⁷Md through ²⁶³Md can form.

²⁶²Md cannot form because ²⁶²Fm does not have a beta-decay branch.

It is likely that ²⁶¹Md can form.

²⁶⁰Md to ²⁵⁸Md cannot form due to rapid fission in ²⁶⁰Fm to ²⁵⁸Fm. It is unlikely that lighter isotopes can form.

Both neutron star mergers and supernovae contribute to the production of those Md isotopes which can form. Slow neutron capture cannot produce any isotopes of Md.

PERSISTENCE

The longest-lived Md isotopes, ²⁶⁰Md and ²⁵⁸Md, cannot form. Of those which can form, ²⁶¹Md is longest-lived with a half-life up to 10 days. It can, in theory, persist for close to 4.5 yr after a supernova, neutron star merger, or similar event which led to its formation. ²⁶³Md and ²⁶⁵Md may persist for up to a year after events leading up to their formation.

Several Md isotopes survive long enough to be incorporated into the diffuse remnants of supernovae or kilonovae (neutron star mergers). ²⁶¹Md may persist long enough to be incorporated into dust. The amounts of Md involved, however, are likely to be too small to detect.

ATOMIC PROPERTIES

Wikipedia's article "Mendelevium" addresses the element's atomic properties and chemistry in some detail. Aside from dust formation in very young supernova or kilonova remnants, the chemistry of Md occurs solely in 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 Mendelevium", 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

(11-18-20)