Английская Википедия:Isotopes of livermorium

Содержание

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Шаблон:Short description Шаблон:Infobox livermorium isotopes Livermorium (₁₁₆Lv) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁹³Lv in 2000. There are five known radioisotopes, with mass numbers 288 and 290–293, as well as a few suggestive indications of a possible heavier isotope ²⁹⁴Lv. The longest-lived known isotope is ²⁹³Lv with a half-life of 70 ms.

List of isotopes

Шаблон:Isotopes table |- | ²⁸⁸Lv | style="text-align:right" | 116 | style="text-align:right" | 172 | | <1 ms | α | ²⁸⁴Fl | 0+ |- | ²⁹⁰Lv | style="text-align:right" | 116 | style="text-align:right" | 174 | 290.19864(59)# | Шаблон:Val | α | ²⁸⁶Fl | 0+ |- | ²⁹¹Lv | style="text-align:right" | 116 | style="text-align:right" | 175 | 291.20101(67)# | Шаблон:Val | α | ²⁸⁷Fl | |- | ²⁹²Lv | style="text-align:right" | 116 | style="text-align:right" | 176 | 292.20197(82)# | Шаблон:Val | α | ²⁸⁸Fl | 0+ |- | ²⁹³Lv | style="text-align:right" | 116 | style="text-align:right" | 177 | 293.20458(55)# | Шаблон:Val | α | ²⁸⁹Fl | |- | ^293mLv | colspan="3" style="text-indent:2em" | 720(290)# keV | Шаблон:Val | α | | |- | ²⁹⁴Lv | style="text-align:right" | 116 | style="text-align:right" | 178 | | 54 ms# | α ? | ²⁹⁰Fl | 0+ Шаблон:Isotopes table/footer

Nucleosynthesis

Target-projectile combinations leading to Z=116 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 116.

Target	Projectile	CN	Attempt result
208Pb	82Se	290Lv	Шаблон:No
238U	54Cr	292Lv	Шаблон:Yes
244Pu	50Ti	294Lv	Шаблон:Unk
250Cm	48Ca	298Lv	Шаблон:Unk
248Cm	48Ca	296Lv	Шаблон:Yes
246Cm	48Ca	294Lv	Шаблон:Unk
245Cm	48Ca	293Lv	Шаблон:Yes
243Cm	48Ca	291Lv	Шаблон:Unk
248Cm	44Ca	292Lv	Шаблон:Unk
251Cf	40Ar	291Lv	Шаблон:Unk

Cold fusion

²⁰⁸Pb(⁸²Se,xn)^290−xLv

In 1995, the team at GSI attempted the synthesis of ²⁹⁰Lv as a radiative capture (x=0) product. No atoms were detected during a six-week experimental run, reaching a cross section limit of 3 pb.

Hot fusion

This section deals with the synthesis of nuclei of livermorium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40–50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3–5 neutrons. Fusion reactions utilizing ⁴⁸Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30–35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.

²³⁸U(⁵⁴Cr,xn)^292−xLv (x=4)

There are sketchy indications that this reaction was attempted by the team at GSI in 2006. There are no published results on the outcome, presumably indicating that no atoms were detected. This is expected from a study of the systematics of cross sections for ²³⁸U targets.

In 2023, this reaction was studied again at the JINR's Superheavy Element Factory in Dubna, in preparation for a future synthesis attempt of element 120 using ⁵⁴Cr projectiles. One atom of ²⁸⁸Lv was reported; it underwent alpha decay with a lifetime of less than 1 millisecond. Further analysis of the reaction and its cross section are underway.

²⁴⁸Cm(⁴⁸Ca,xn)^296−xLv (x=2?,3,4,5?)

The first attempt to synthesise livermorium was performed in 1977 by Ken Hulet and his team at the Lawrence Livermore National Laboratory (LLNL). They were unable to detect any atoms of livermorium. Yuri Oganessian and his team at the Flerov Laboratory of Nuclear Reactions (FLNR) subsequently attempted the reaction in 1978 and met failure. In 1985, a joint experiment between Berkeley and Peter Armbruster's team at GSI, the result was again negative with a calculated cross-section limit of 10–100 pb.

In 2000, Russian scientists at Dubna finally succeeded in detecting a single atom of livermorium, assigned to the isotope ²⁹²Lv. In 2001, they repeated the reaction and formed a further 2 atoms in a confirmation of their discovery experiment. A third atom was tentatively assigned to ²⁹³Lv on the basis of a missed parental alpha decay. In April 2004, the team ran the experiment again at higher energy and were able to detect a new decay chain, assigned to ²⁹²Lv. On this basis, the original data were reassigned to ²⁹³Lv. The tentative chain is therefore possibly associated with a rare decay branch of this isotope or an isomer, ^293mLv; given the possible reassignment of its daughter to ²⁹⁰Fl instead of ²⁸⁹Fl, it could also conceivably be ²⁹⁴Lv, although all these assignments are tentative and need confirmation in future experiments aimed at the 2n channel. In this reaction, two additional atoms of ²⁹³Lv were detected.

In 2007, in a GSI-SHIP experiment, besides four ²⁹²Lv chains and one ²⁹³Lv chain, another chain was observed, initially not assigned but later shown to be ²⁹¹Lv. However, it is unclear whether it comes from the ²⁴⁸Cm(⁴⁸Ca,5n) reaction or from a reaction with a lighter curium isotope (present in the target as an admixture), such as ²⁴⁶Cm(⁴⁸Ca,3n).

In an experiment run at the GSI during June–July 2010, scientists detected six atoms of livermorium; two atoms of ²⁹³Lv and four atoms of ²⁹²Lv. They were able to confirm both the decay data and cross sections for the fusion reaction.

A 2016 experiment at RIKEN aimed at studying the ⁴⁸Ca+²⁴⁸Cm reaction seemingly detected one atom that may be assigned to ²⁹⁴Lv alpha decaying to ²⁹⁰Fl and ²⁸⁶Cn, which underwent spontaneous fission; however, the first alpha from the livermorium nuclide produced was missed.

²⁴⁵Cm(⁴⁸Ca,xn)^293−xLv (x=2,3)

In order to assist in the assignment of isotope mass numbers for livermorium, in March–May 2003 the Dubna team bombarded a ²⁴⁵Cm target with ⁴⁸Ca ions. They were able to observe two new isotopes, assigned to ²⁹¹Lv and ²⁹⁰Lv. This experiment was successfully repeated in February–March 2005 where 10 atoms were created with identical decay data to those reported in the 2003 experiment.

As a decay product

Livermorium has also been observed in the decay of oganesson. In October 2006 it was announced that three atoms of oganesson had been detected by the bombardment of californium-249 with calcium-48 ions, which then rapidly decayed into livermorium.

The observation of the daughter ²⁹⁰Lv allowed the assignment of the parent to ²⁹⁴Og and proved the synthesis of oganesson.

Fission of compound nuclei with Z=116

Several experiments have been performed between 2000 and 2006 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nuclei ^296,294,290Lv. Four nuclear reactions have been used, namely ²⁴⁸Cm+⁴⁸Ca, ²⁴⁶Cm+⁴⁸Ca, ²⁴⁴Pu+⁵⁰Ti, and ²³²Th+⁵⁸Fe. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as ¹³²Sn (Z = 50, N = 82). It was also found that the yield for the fusion-fission pathway was similar between ⁴⁸Ca and ⁵⁸Fe projectiles, indicating a possible future use of ⁵⁸Fe projectiles in superheavy element formation. In addition, in comparative experiments synthesizing ²⁹⁴Lv using ⁴⁸Ca and ⁵⁰Ti projectiles, the yield from fusion-fission was roughly three times smaller for ⁵⁰Ti, also suggesting a future use in SHE production.

Retracted isotopes

²⁸⁹Lv

In 1999, researchers at Lawrence Berkeley National Laboratory announced the synthesis of ²⁹³Og (see oganesson), in a paper published in Physical Review Letters. The claimed isotope ²⁸⁹Lv decayed by 11.63 MeV alpha emission with a half-life of 0.64 ms. The following year, they published a retraction after other researchers were unable to duplicate the results. In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by the principal author Victor Ninov. As such, this isotope of livermorium is currently unknown.

Chronology of isotope discovery

Isotope	Year discovered	Discovery reaction
288Lv	2023	238U(54Cr,4n)
290Lv	2002	249Cf(48Ca,3n)
291Lv	2003	245Cm(48Ca,2n)
292Lv	2004	248Cm(48Ca,4n)
293Lv	2000	248Cm(48Ca,3n)
294Lv ??	2016	248Cm(48Ca,2n) ?

Yields of isotopes

Hot fusion

The table below provides cross-sections and excitation energies for hot fusion reactions producing livermorium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile	Target	CN	2n	3n	4n	5n
48Ca	248Cm	296Lv		1.1 pb, 38.9 MeV	3.3 pb, 38.9 MeV
48Ca	245Cm	293Lv	0.9 pb, 33.0 MeV	3.7 pb, 37.9 MeV

Theoretical calculations

Decay characteristics

Theoretical calculation in a quantum tunneling model supports the experimental data relating to the synthesis of ²⁹³Lv and ²⁹²Lv.

Evaporation residue cross sections

The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.

DNS = Di-nuclear system; σ = cross section

Target	Projectile	CN	Channel (product)	σmax	Model	Ref
208Pb	82Se	290Lv	1n (289Lv)	0.1 pb	DNS
208Pb	79Se	287Lv	1n (286Lv)	0.5 pb	DNS
238U	54Cr	292Lv	2n (290Lv)	0.1 pb	DNS
250Cm	48Ca	298Lv	4n (294Lv)	5 pb	DNS
248Cm	48Ca	296Lv	4n (292Lv)	2 pb	DNS
247Cm	48Ca	295Lv	3n (292Lv)	3 pb	DNS
245Cm	48Ca	293Lv	3n (290Lv)	1.5 pb	DNS
243Cm	48Ca	291Lv	3n (288Lv)	1.53 pb	DNS
248Cm	44Ca	292Lv	4n (288Lv)	0.43 pb	DNS