spore: profile
id: samarium
spore_version: 0.2
family: rare-earth-metals
name: Samarium
abbreviation: Sm
role: neutron absorber and samarium-cobalt magnet metal
category: metals
type: heavy-metals
summary: |
  Samarium is a silver-white rare-earth metal, element 62, with atomic weight 150.36. Its solid density is about 7.5 g/cm3 and it melts at 1072 °C. It is made by reducing its oxide with barium or lanthanum. Its samarium-cobalt alloys keep a useful remanence at 300 °C in NASA tests. Natural samarium and its isotope Sm-149 capture thermal neutrons strongly, which is why the oxide is used in some reactor control rods. Massive metal tarnishes in air, but the metal ignites in air at 150 °C as a CRC figure, and it reacts with water to release hydrogen.
best_for: Neutron capture in reactor control (Sm-149 thermal capture cross section 40,140 barns), and as the rare-earth part of high-temperature samarium-cobalt magnets
weakest_at: 'Reactive metal: tarnishes in moist air, ignites in air as powder or chips at 150 °C, and releases flammable hydrogen on contact with water (PubChem, HSDB)'
identity:
  formula: Sm (element, atomic number 62); natural samarium is a mix of seven isotopes
  cas: 7440-19-9
  source: pubchem-sm
  where: Names and Identifiers, CAS entry; Record Description gives atomic number 62 and atomic weight 150.36
tags:
  applications:
    - mechanisms
    - radiation-shielding
properties:
  - benchmark: density
    label: Density of solid
    value: 7353
    unit: kg/m3
    scope: material
    conditions:
      basis: density of the solid as printed by WebElements
      temperature: not stated
    method: Value printed in the Density properties section of the WebElements physical-properties page
    status: ground
    source: webelements-physics
    where: Physical properties, Density properties (Density of solid)
  - benchmark: density
    label: Density at 25 °C
    value: 7.52
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
      unit_in_source: 7.52 g cu cm at 25 °C (the unit is garbled in the source)
    method: Value printed in the PubChem Density entry; the source's second value (7.536 at 25 °C) is not used
    status: ground
    source: pubchem-sm
    where: Chemical and Physical Properties > Experimental Properties > Density
  - benchmark: melting_point
    value: 1072
    unit: °C
    scope: material
    conditions:
      form: pure element
    method: Value printed in the PubChem Melting Point entry; WebElements prints 1345 K [1072 °C] on its main page
    status: ground
    source: pubchem-sm
    where: Chemical and Physical Properties > Melting Point
  - benchmark: boiling_point
    value: 1794
    unit: °C
    scope: material
    conditions:
      form: pure element
      pressure: not stated
    method: First boiling-point value printed in the PubChem Boiling Point entry
    status: ground
    note: WebElements main page prints 2076 K [1803 °C]; the two sources differ by 9 °C and are both recorded here as printed.
    source: pubchem-sm
    where: Chemical and Physical Properties > Boiling Point (first value)
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 50
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed in the Elastic properties section of WebElements
    status: ground
    source: webelements-physics
    where: Physical properties, Elastic properties (Young's modulus)
  - benchmark: shear_modulus
    label: Rigidity modulus
    value: 20
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed in the Elastic properties section of WebElements (labelled rigidity modulus)
    status: ground
    source: webelements-physics
    where: Physical properties, Elastic properties (Rigidity modulus)
  - benchmark: bulk_modulus
    value: 38
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed in the Elastic properties section of WebElements
    status: ground
    source: webelements-physics
    where: Physical properties, Elastic properties (Bulk modulus)
  - benchmark: poissons_ratio
    value: 0.27
    unit: '-'
    scope: material
    conditions:
      temperature: not stated
    method: Value printed as "0.27 (no units)" in the Elastic properties section of WebElements
    status: ground
    source: webelements-physics
    where: Physical properties, Elastic properties (Poisson's ratio)
  - benchmark: electrical_resistivity
    value: 94
    unit: µΩ cm
    scope: material
    conditions:
      unit_in_source: 94 × 10-8 Ω m
      temperature: not stated
    method: Printed as 94 × 10-8 Ω m. One µΩ cm equals 1e-8 Ω m, so the number is unchanged and only the unit is re-expressed.
    status: ground
    source: webelements-physics
    where: Physical properties, Electrical properties (Electrical resistivity)
  - benchmark: thermal_conductivity
    value: 13
    unit: W m-1 K-1
    scope: material
    conditions:
      temperature: not stated
    method: Value printed in the Heat and conduction section of WebElements
    status: ground
    source: webelements-physics
    where: Physical properties, Heat and conduction (Thermal conductivity)
  - benchmark: cte
    label: Coefficient of linear thermal expansion
    value: 12.7
    unit: ppm/K
    scope: material
    conditions:
      unit_in_source: 12.7 × 10-6 K-1
      temperature: not stated
    method: Value printed as 12.7 × 10-6 K-1 in the Heat and conduction section of WebElements. The unit 10-6 K-1 is ppm/K, so the number is unchanged.
    status: ground
    source: webelements-physics
    where: Physical properties, Heat and conduction (Coefficient of linear thermal expansion)
  - benchmark: thermal_neutron_capture_cross_section
    label: Thermal neutron capture cross section, Sm-149
    value: 40140
    unit: barns
    scope: material
    conditions:
      isotope: Sm-149
      energy: thermal neutrons
      uncertainty: ±600 barns
      table_heading: Cross section (barns)
    method: Value printed in Table 2 of the 1986 Livermore report on samarium and promethium neutron capture cross sections
    status: ground
    source: unt-sm-neutron
    where: Table 2, Thermal neutron capture cross sections of some samarium isotopes (row Sm-149)
  - benchmark: thermal_neutron_capture_cross_section
    label: Thermal neutron capture cross section, natural samarium
    value: 5670
    unit: barns
    scope: material
    conditions:
      isotope: elemental Sm (natural isotopic mix)
      energy: thermal neutrons
      uncertainty: ±100 barns
    method: Value printed in Table 2 of the same report, row Elemental Sm
    status: ground
    source: unt-sm-neutron
    where: Table 2, Thermal neutron capture cross sections of some samarium isotopes (row Elemental Sm)
  - benchmark: thermal_neutron_capture_cross_section
    label: Thermal neutron capture cross section, Sm-150
    value: 104
    unit: barns
    scope: material
    conditions:
      isotope: Sm-150
      energy: thermal neutrons
      uncertainty: ±4 barns
    method: Value printed in Table 2 of the same report, row Sm-150
    status: ground
    source: unt-sm-neutron
    where: Table 2, Thermal neutron capture cross sections of some samarium isotopes (row Sm-150)
  - benchmark: ignition_temperature_in_air
    label: Ignition temperature in air (metal)
    value: 150
    unit: °C
    scope: material
    conditions:
      form: metal, as printed for samarium (the data text does not name the form)
    method: Value printed in the PubChem Other Experimental Properties entry, which cites the CRC Handbook 2007
    status: ground
    note: Not a canonical property name, so it is kept as a snake_case benchmark.
    source: pubchem-sm
    where: Chemical and Physical Properties > Other Experimental Properties (CRC Handbook 2007, p. 4-31 as cited)
corrosion:
  - environment: Dry air at room temperature
    headline: Samarium metal reacts with dry air only slowly at room temperature.
    effect: The HSDB record for samarium metal says it reacts at room temperature with oxygen or dry air relatively slowly, and the reaction is rapid in moist air. Massive metal tarnishes on exposure to air (Haz-Map, via PubChem).
    rating: moderate
    conditions:
      exposure: room temperature, dry air; exposure time not stated
    source: pubchem-sm
    where: Toxicity > Ecological Information > Environmental Abiotic Degradation (HSDB); Physical Description (Haz-Map)
  - environment: Moist air
    headline: In moist air samarium corrodes quickly.
    effect: The HSDB record says the reaction with moist air is rapid, compared with dry air. The record gives no rate or time, and the coating that forms is not described.
    rating: severe
    conditions:
      exposure: moist air; humidity and time not stated
    source: pubchem-sm
    where: Toxicity > Ecological Information > Environmental Abiotic Degradation (HSDB)
  - environment: Air at elevated temperature
    headline: Samarium ignites in air at 150 °C.
    effect: The metal ignites in air at elevated temperatures, and the CRC Handbook figure of 150 °C is repeated in PubChem. Powder and chips are flammable in air and can catch fire from a flame or by spontaneous reaction with oxidisers (HSDB fire potential entry).
    rating: severe
    conditions:
      form: metal; powder and chips are the most reactive forms in the HSDB entries
    source: pubchem-sm
    where: Other Experimental Properties (150 °C); Safety and Hazards > Hazards Identification > Fire Potential (HSDB)
  - environment: Water and dilute mineral acids
    headline: Water releases flammable hydrogen; dilute acids dissolve samarium quickly.
    effect: The HSDB record says powder reacts with water to produce flammable and explosive hydrogen, and that the vapour-air mixture is explosive at high temperatures. The same record says dilute mineral acids dissolve samarium rapidly, forming samarium(III) ions.
    rating: severe
    conditions:
      form: powder (water reaction); acids not specified beyond dilute mineral acids
    source: pubchem-sm
    where: Safety and Hazards > Safety and Hazard Properties > Explosive Limits (HSDB); Environmental Abiotic Degradation (HSDB)
risks:
  hazards:
    - text: The aggregated ECHA notifications in PubChem carry H228 (flammable solid) for 91% of reports and H261 (in contact with water releases flammable gas) for 94.1%. PubChem also records that 2.4% of 255 reports (6 of 255) say it does not meet GHS hazard criteria.
      ghs:
        - H228
        - H261
      source: pubchem-sm
      where: Safety and Hazards > Hazards Identification > GHS Classification (ECHA C&L Inventory, aggregated)
    - text: The HSDB toxicity summary says samarium metal may be harmful if absorbed through the skin, swallowed or inhaled. It gives no quantitative toxicity values for the metal.
      ghs: []
      source: hsdb-sm
      where: Toxicity > Toxicological Information > Toxicity Summary
  failure_risks:
    - mode: Ignition of powder, chips or dust in air
      trigger: Heating in air, a flame or spark, or static charge during handling (HSDB gives keep away from heat, sparks and open flames)
      consequence: Fine metal burns; the metal ignites in air at 150 °C. Extinguish with dry sand or dry powder, not with water or halocarbon agents.
      severity: moderate
      source: hsdb-sm
      where: Safety and Hazards > Hazards Identification > Fire Potential (HSDB); Accidental Release Measures > Preventive Measures (HSDB)
    - mode: Hydrogen release on contact with water or moisture
      trigger: Contact with water, including firefighting water, or prolonged exposure to moist air
      consequence: Powder reacts with water to form flammable and explosive hydrogen; vapour-air mixtures are explosive at high temperatures.
      severity: high
      source: pubchem-sm
      where: Safety and Hazards > Stability and Reactivity > Hazardous Reactivities (HSDB)
  side_effects: []
  handling:
    - text: Keep the container tightly closed in a dry, well-ventilated place and store under inert gas, because samarium is air and moisture sensitive.
      source: hsdb-sm
      where: Safety and Hazards > Handling and Storage > Storage Conditions (HSDB, chip form)
    - text: Avoid dust formation and provide exhaust ventilation where dust forms; keep away from heat, sparks and open flames, and prevent electrostatic charge build-up.
      source: hsdb-sm
      where: Safety and Hazards > Accidental Release Measures > Preventive Measures (HSDB)
    - text: For fires, use sand or dry powder agents designed for metal powder fires, approved class D extinguishers, dry sand, dry ground limestone or dry clay. Do not use water or halocarbon extinguishers.
      source: hsdb-sm
      where: Safety and Hazards > Fire Fighting > Fire Fighting Procedures (HSDB)
    - text: The HSDB text, which reproduces a supplier safety data sheet, says to handle a spill as a radioactive spill. Space Mushroom did not verify this against isotope data, so treat it as the supplier's instruction.
      source: hsdb-sm
      where: Safety and Hazards > Accidental Release Measures > Cleanup Methods (HSDB)
  mitigations:
    - text: Handle the metal under inert gas and protect it from moisture; the HSDB preventive measures say this directly.
      source: hsdb-sm
      where: Safety and Hazards > Accidental Release Measures > Preventive Measures (HSDB)
uses:
  - application: mechanisms
    device: Magnetically suspended reaction wheel assembly (attitude-control actuator), built around samarium-cobalt magnets (ground development, not flown)
    example: Air Force Materials Laboratory funded a programme from May 1976 to June 1980 to set up samarium-cobalt magnet manufacturing and demonstrate the magnets in a space application. The wheel requirements came from the bias wheel of the DSP satellite, and the author reports success on both counts.
    source: ntrs-smco-wheel-1985
    where: Introduction, first page
  - application: radiation-shielding
    device: Neutron absorber, including the oxide used in some reactor control rods
    example: Table 2 of the 1986 Livermore report gives thermal capture cross sections of 5670 barns for natural samarium and 40,140 barns for Sm-149. PubChem records that the oxide is used in the control rods of some nuclear reactors.
    source: unt-sm-neutron
    where: Table 2 (thermal capture cross sections); PubChem Record Description
  - application: mechanisms
    device: Samarium-cobalt permanent magnets for high-temperature devices (the samarium-cobalt alloy, not the pure metal)
    example: NASA Lewis measured demagnetization resistance of samarium-cobalt magnets from 23 to 300 °C. The report says temperatures above 250 °C are being investigated for magnets in linear alternators for long-term space missions, and that traveling wave tubes are another expected use.
    source: ntrs-smco-tp3119
    where: Summary and introduction, first pages (NASA Technical Paper 3119)
supply:
  - subject: Samarium (as part of rare earths)
    abundance: 6000 ppb by weight in crustal rocks, as printed by WebElements
    producers:
      - country: China
        share_percent: 69.2
        year: 2025
      - country: United States
        share_percent: 13.1
        year: 2025
      - country: Australia
        share_percent: 7.4
        year: 2025
      - country: Burma
        share_percent: 5.6
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (Samarium is one of the 15 rare-earth entries)
        listed: true
    recycling: 'USGS: limited quantities of rare earths are recovered from batteries, permanent magnets and fluorescent lamps. USGS does not give a samarium-specific figure.'
    substitutes: []
    source: usgs-mcs2026-ree
    where: 'World Mine Production table, 2025 column (shares calculated by Space Mushroom against the 390,000 t world total; Burma''s figure is an estimate by USGS, footnote 12); Reserves: China 44,000,000 tons, world more than 75,000,000 tons; Recycling. Critical list: USGS critical minerals page.'
media: []
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Rare Earths'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
  - title: 'PubChem: Samarium (CID 23951), chemical and physical properties, safety and hazards'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Samarium
    year: 2026
  - title: Hazardous Substances Data Bank (HSDB) record for samarium, via PubChem
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/source/hsdb/7863
    year: 2026
  - title: NIST Atomic Weights and Isotopic Compositions for All Elements (samarium row)
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Sm&all=all&ascii=html
    year: 2026
  - title: 'WebElements: Samarium, physical properties'
    type: database
    url: https://www.webelements.com/samarium/physics.html
    year: 2026
  - title: A Preliminary Evaluation of Neutron Capture Cross Sections for Sm and Pm Isotopes (Lawrence Livermore, DE86 008148)
    type: report
    url: https://digital.library.unt.edu/ark:/67531/metadc1097317/m2/1/high_res_d/5872583.pdf
    year: 1986
  - title: 'NASA NTRS 19850005561: Magnetically Suspended Reaction Wheel Assembly'
    type: report
    url: https://ntrs.nasa.gov/citations/19850005561
    year: 1985
  - title: 'NASA Technical Paper 3119: 23 to 300 °C Demagnetization Resistance of Samarium-Cobalt Permanent Magnets'
    type: report
    url: https://ntrs.nasa.gov/citations/19920002034
    year: 1991
gaps:
  - No flight, vacuum, radiation or thermal-vacuum result for samarium metal was found. The reaction-wheel and TWT material is ground development on samarium-cobalt magnets, not the metal.
  - USGS reports rare earths in aggregate. No samarium-specific production figure was found, so the producer shares are for all rare earths.
  - The EU critical raw materials page names only light and heavy rare-earth groups and does not say which elements they contain, so samarium's EU status was not confirmed and no EU entry is given.
  - Speed of sound (2130 m/s) and Vickers and Brinell hardness (412 and 441 MN/m2) were printed by WebElements but have no canonical name, so they are left out.
  - The LANL periodic-table page could not be fetched from this environment; its values were not used.
  - Radioactivity of natural samarium (Sm-147) was not read in a source, so no half-life or activity is given.
  - No substitute for samarium in magnets or neutron absorbers was read in a source.
  - Only one supplier safety data sheet, reproduced in HSDB, and the PubChem GHS summary were read. No manufacturer SDS was fetched.
  - No alloy designations are given. This profile covers the element only; samarium-cobalt alloy grades are not described.
  - Side effects of neutron capture (transmutation products and their decay) were not read in a source, so side_effects is empty.
  - No photograph or diagram with a verified licence was fetched, so media is empty.
sources:
  pubchem-sm:
    title: PubChem compound record, Samarium (CID 23951)
    id: CID 23951; CAS 7440-19-9
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23951/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  hsdb-sm:
    title: Hazardous Substances Data Bank record for samarium, via PubChem (HSDB 7863)
    id: HSDB 7863
    url: https://pubchem.ncbi.nlm.nih.gov/source/hsdb/7863
    year: 2026
    kind: database
    license: public domain (NLM)
  usgs-mcs2026-ree:
    title: Mineral Commodity Summaries 2026, Rare Earths
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit-2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  webelements-physics:
    title: 'WebElements, Samarium: physical properties'
    id: WebElements Samarium - 62 Sm
    url: https://www.webelements.com/samarium/physics.html
    year: 2026
    kind: web
    license: WebElements copyright (cited, not reproduced)
  webelements-main:
    title: 'WebElements, Samarium: key properties and abundances'
    id: WebElements Samarium - 62 Sm
    url: https://www.webelements.com/samarium/
    year: 2026
    kind: web
    license: WebElements copyright (cited, not reproduced)
  nist-atomic-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements
    id: NIST Physical Measurement Laboratory, samarium row (Z = 62)
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Sm&all=all&ascii=html
    year: 2026
    kind: database
    license: public domain (NIST)
  unt-sm-neutron:
    title: A Preliminary Evaluation of Neutron Capture Cross Sections for Sm and Pm Isotopes (D. C. Gardner and M. A. Gardner, LLNL)
    id: DE86 008148, February 13, 1986
    url: https://digital.library.unt.edu/ark:/67531/metadc1097317/m2/1/high_res_d/5872583.pdf
    year: 1986
    kind: report
    license: US Government report, public domain
  ntrs-smco-wheel-1985:
    title: Magnetically Suspended Reaction Wheel Assembly (George Stocking, Sperry Flight Systems)
    id: NASA NTRS 19850005561
    url: https://ntrs.nasa.gov/citations/19850005561
    year: 1985
    kind: report
    license: public domain (NASA)
  ntrs-smco-tp3119:
    title: 'NASA Technical Paper 3119: 23 to 300 °C Demagnetization Resistance of Samarium-Cobalt Permanent Magnets (Niedra and Overton)'
    id: NASA TP-3119, N92-11252; NTRS 19920002034
    url: https://ntrs.nasa.gov/citations/19920002034
    year: 1991
    kind: report
    license: public domain (NASA)
  wikipedia-sm:
    title: Samarium, Wikipedia (history and naming only)
    id: Wikipedia article Samarium
    url: https://en.wikipedia.org/wiki/Samarium
    year: 2026
    kind: web
    license: CC BY-SA 4.0
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 1
  caveats: 2
  note: Written by an AI assistant on 2026-10-26 from pages fetched in this run. The LANL periodic-table page could not be reached. Values from WebElements and PubChem are kept as printed, and the two density values differ (7353 kg/m3 and 7.52 g/cm3); the boiling point differs by 9 °C between PubChem and WebElements.
story:
  recipe:
    line: Samarium is a single element, Sm. It is made by reducing samarium oxide with barium or lanthanum (PubChem, Methods of Manufacturing, from HSDB). Natural samarium is a mix of seven isotopes (NIST).
    parts:
      - name: Samarium
        symbol: Sm
        atoms: 1
        atomic_weight: 150.36
        role: The whole metal. The standard atomic weight of natural samarium is 150.36 (2), as NIST prints it.
  risk_groups:
    - title: For people
      level: 0
      verdict: Hazardous when handled as powder or chips
      lead: Solid samarium in bulk is much less hazardous than its powder. The main hazards are fire and the hydrogen released by water.
      points:
        - label: The powder
          line: PubChem's ECHA summary lists H228 (flammable solid) for 91% of reports and H261 (releases flammable gas with water) for 94.1%. Only 6 of 255 reports say the substance does not meet GHS hazard criteria.
        - label: Toxicity
          line: The HSDB record says the metal may be harmful if absorbed through the skin, swallowed or inhaled, but gives no quantitative toxicity values.
        - label: Fire
          line: Powder and chips ignite in air at 150 °C. Use dry sand or a class D extinguisher, never water.
    - title: If the metal reacts
      lead: These results come from fire and reactivity data, not from incidents.
      points:
        - label: Air
          line: Massive metal tarnishes in air. In moist air it corrodes quickly, and in dry air it reacts slowly at room temperature.
        - label: Water
          line: Powder reacts with water to form flammable and explosive hydrogen gas. Vapour and air mixtures are explosive at high temperatures.
    - title: Handling and storage
      points:
        - label: Storage
          line: Keep the container tightly closed, under inert gas and away from moisture. Store in a dry, well-ventilated place.
        - label: Spills
          line: Avoid dust. The HSDB text says to treat a spill as a radioactive spill, which was not verified and should be read as the supplier's instruction.
  why: Samarium is a rare-earth metal (element 62). Its relevance here comes from two properties. It captures thermal neutrons very strongly, and its alloy with cobalt makes permanent magnets that NASA tested up to 300 °C. The metal itself is reactive, so the uses listed here depend on keeping it dry and under inert gas.
  uses:
    - where: Mechanisms
      line: A 1976 to 1980 Air Force programme built a magnetically suspended reaction wheel with samarium-cobalt magnets, and the author reports that the magnets were shown to work in a space application. The programme was ground development, not a flight.
    - where: Reactor control
      line: Natural samarium and Sm-149 capture thermal neutrons strongly. Table 2 of a 1986 Livermore report gives 5670 barns for natural samarium and 40,140 barns for Sm-149.
    - where: High-temperature magnets
      line: NASA measured demagnetization resistance of samarium-cobalt magnets from 23 to 300 °C. It says temperatures above 250 °C are being studied for alternators on long space missions and that traveling wave tubes are another likely use.
  can_do:
    - label: Neutron capture
      benchmark: thermal_neutron_capture_cross_section
      line: Sm-149 has a thermal neutron capture cross section of 40,140 ± 600 barns. Natural samarium is 5670 ± 100 barns. Sm-150 is 104 ± 4 barns.
    - label: Density
      benchmark: density
      line: The solid density is 7.52 g/cm3 at 25 °C (PubChem), or 7353 kg/m3 (WebElements). The two figures differ by about 2%.
    - label: Melting point
      value: 1072 °C
      benchmark: melting_point
      line: Samarium melts at 1072 °C. PubChem and WebElements agree on this figure.
    - label: Stiffness
      benchmark: elastic_modulus
      line: Young's modulus is 50 GPa and the bulk modulus is 38 GPa (WebElements).
  compare: Samarium is a rare-earth metal with a density of about 7.5 g/cm3, so it is not a lightweight option. Its Young's modulus of 50 GPa is in the printed range for metals, and its melting point is 1072 °C. Its main value lies in neutron capture and in its alloys' magnetism, and reactivity with air and water limits how it can be handled. The table compares density, melting point and neutron capture for samarium alone; no other material's figures are used here.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Neutron capture (Sm-149)
      benchmark: thermal_neutron_capture_cross_section
  handling:
    - Store under inert gas and keep dry. Samarium is air and moisture sensitive.
    - Use dry sand or a class D extinguisher on a fire. Do not use water.
    - Keep powder and chips away from heat, sparks and open flames, and avoid making dust.
    - The supplier SDS (through HSDB) says to treat a spill as radioactive, which was not checked.
  good_for:
    - Neutron capture. Sm-149 captures thermal neutrons at 40,140 barns, the basis for its use in reactor control.
    - High-temperature magnets. Samarium-cobalt magnets have been tested up to 300 °C in NASA work, though this is the alloy and not the metal.
  watch_out:
    - Reactivity. Powder ignites at 150 °C, and water releases hydrogen.
    - Supply. USGS does not break out samarium, and China produces about 69% of world rare-earth mine output.
    - Evidence. The space work found is 1976 to 1991 ground development, and no flight or radiation result was found.
  verdict: Samarium's strong points are neutron capture and its role in samarium-cobalt magnets. Its reactivity and concentrated supply are the limits, and the space evidence is ground development from 1976 to 1991.