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Introduction

Sulfur-35 is a commonly used radionuclide with a half-life of 87.4 days, emitting only beta particles with a maximum energy of 0.167 MeV and an average energy of 0.049 MeV. The beta particles from S-35 travel a maximum of 24 cm. in air.

The above properties are very similar to those of C-14.

Concerns

The major concern with using S-35 is that its presence cannot be monitored during its use, since most Geiger Counters will not be able to detect S-35. Special precautions are needed to keep the work environment clean. The regular use of wipe testing is the only way to insure that your work space is not contaminated. Contamination on the skin will not likely cause a significant dose to the dead layer of skin, however, it could lead to the internal absorption of S-35 if there are cuts in the skin. The maximum permissible body burden for S-35 set by the NRC for the whole body is 400 uCi.

Shielding

Glass and plastic are the best shields for beta particles from S-35.

Detection

A tiny drop of contamination from S-35 can be easily detected with a wipe test from a Liquid Scintillation Counter.

Equipment/Supplies

The following equipment and supplies must be available before handling S-35:

  • Liquid scintillation detector
  • disposable latex or plastic gloves
  • Full-length lab coat
  • Radioactive waste receptacle
  • Pipettes dedicated to the use of S-35
  • Commercial decontaminate

Safety Rules

If the following safety precautions are used when handling S-35, personnel radiation exposure will be as low as reasonably achievable.

  • Designate a specific area of the lab for S-35 handling
  • Wear a full-length lab coat
  • Wear two pairs of disposable gloves to protect your hands from becoming contaminated from spills
  • Never pipette S-35 by mouth.
  • Only use pipettes which have been dedicated to your specific use of S-35
    • Pipettes will easily become contaminated and therefore, should not be shared with others
  • If you have reason to believe that your gloves are contaminated, immediately dispose of them in the radioactive waste container

Post-Use Procedures

  • Conduct a wipe test on all work benches, floor, equipment, centrifuges, and water baths
  • Count the wipes in a Liquid Scintillation counter
  • If contamination is found:
    • Use a commercial radiation contamination remover with paper towels to clean up the equipment
    • Place the towels in the radioactive waste receptacle
    • If contamination cannot be removed, place a "radiation" label on the equipment indicating that it is S-35, maximum cpm found, and the date you measured the level
    • Inform your fellow lab workers if any unremovable contamination is found
  • Check the normal trash container to make sure no radioactive waste has been accidentally placed there
  • Store the waste temporarily in marked containers
  • Wash your hands thoroughly

Other Information

Physical Data

  • Beta energy: 167 keV (maximum)
  • 53 keV (average) (100% abundance)
  • Physical Half Life: 87.4 days
  • Biological Half Life: 623 days (unbound S-35)
  • Effective Half Life: 44-76 days (unbound S-35)
  • Specific Activity: 42,400 Ci/g
  • Maximum Beta Range in Air: 26.00 cm
  • Maximum Beta Range in Water or Tissue: 0.32 mm
  • Maximum Beta Range in Plexiglas or Lucite: 0.25 mm
  • Fraction of S-35 betas transmitted through dead layer of skin = 12%

Radiological Data

  • Critical organ: Testis
  • Routes of Intake: Ingestion, inhalation, puncture, wound, skin contamination (absorption)
  • External exposure (deep dose) from weak S-35 beta particles is not a radiological concern
  • Internal exposure and contamination are the primary radiological concerns
  • Committed dose equivalent (CDE): 10.00 mrem/uCi (ingested)
  • 0.352 millirem/uCi (puncture)
  • Committed Effective Dose Equivalent (CEDE): 2.6 mrem l/uCi (ingested)1
  • Annual Limit on Intake (ALI)2: 10 mCi (ingestion of inorganic S-35 compounds)
  • 6 mCi (Ingestion of elemental S-35
  • 8 mCi (ingestion of sulfides or sulfates/LLI)3
  • 10 mCi (inhalation of S-35)
  • 20 mCi (inhalation of sulfides or sulfates)
  • 2 mCi (inhalation of elemental S-35
  • Skin Contamination Dose Rate: 1,170 - 1,260 mrem/1.0 uCi/cm2 (7.0 mg/cm2 depth)
  • Beta Dose Rates for S-35: 14.94 rad/h (contact) in air per 1.0 mCi
  • 0.20 rad/h (6 inches) in air per 1.0 mCi

1(Assumes a 90 day biological half life) 21.0 ALI = 10 mCi (inhaled S-35 vapors) = 5000 mrem CEDE 31.0 ALI = 8 mCi (ingestion sulfides/sulfates LLI) = 50000 mrem CDE

Shielding

None required (3/4", 3 mm Plexiglas shields; shielding optional)

Survey Instrumentation

  • Can detect using a thin window G-M survey meter (pancake), however, probe MUST be at close range, recommend 1 cm distance
  • G-M survey meter has low efficiency, usually 4 - 6%
  • Liquid scintillation counter (wipes, smears) may be used for secondary, but will NOT detect non removable contamination!

Dosimetry

Not needed, but recommended; S-35 beta energy is low, and is not an external radiation hazard

General Radiological Safety Information

  • Urinalysis: Not required, but may be requested by Health Physics staff after a spill or personnel contamination involving S-35
  • Inherent volatility (STP): SIGNIFICANT for S-35 methionine and cysteine
  • Radiolysis of S-35 amino acids (cysteine and methionine) during storage and use may lead to the release of volatile impurities
  • Volatile impurities are small (less than 0.05%)
  • Metabolic behavior of organic compounds of sulfur (cysteine and methionine) differs considerably from the metabolic behavior of inorganic compounds
  • Organic compounds of sulfur (cysteine and methionine) become incorporated into various metabolites
  • Thus, sulfur entering the body as an organic compound is often tenaciously retained
  • The fractional absorption of sulfur from the gastrointestinal tract is typically greater than 60% for organic compounds of sulfur. Elemental sulfur is less well absorbed from the GI tract than are inorganic compounds of the element (80% for all inorganic compounds and 10% for sulfur in its elemental form)
  • Elemental sulfur is an NRC inhalation Class W (meaning it is retained for weeks in the body)
  • Inhalation of the gases SO2, COS, H2S, and CS2 must be considered
  • Sulfur entering the lungs in these forms is completely and instantaneously translocated to the transfer compartment; from there, its metabolism is the same as that of sulfur entering the transfer compartment following ingestion or inhalation of any other organic compound of sulfur
  • Contamination of internal surfaces of storage and reaction vessels may occur (rubber stoppers, gaskets or o rings)
  • Vials of S-35 labeled cysteine and methionine should be opened and used in ventilated enclosures (exhaust hoods)
  • The volatile components of S-35 labeled amino acids should be opened and used in ventilated enclosures (exhaust hoods)
  • The volatile components of S-35 labeled cysteine and methionine are presumed to be hydrogen sulfide (H2S) and methyl mercaptan (CH3SH), respectively
  • S-35 vapors may be released when opening vials containing labeled amino acids, during any incubating of culture or cells containing S-35, and the storage of S-35 contaminated wastes
  • Excessive contamination can be found on the inside surfaces and in water reservoirs of incubators used for S-35 work
  • Most notable surface contamination can be found on rubber seals of incubators and centrifuges
  • Radiolytic breakdown may occur during freezing processes, releasing as much as 1.0 uCi of S-35 per 8.0 mCi vial of S-35 amino acid during the thawing process
  • S-35 labeled amino acids work should be conducted in an exhaust hood designated for radiolytic work
  • Vent S-35 amino acid stock vials with an open-ended charcoal-filled disposable syringe
  • Activated charcoal has a high affinity for S-35 vapors
  • Place an activated carbon or charcoal canister, absorbent sheet, or tray (50-100 grams of granules evenly distributed in a tray or dish) into an incubator to passively absorb 35S vapors
  • Discard absorbers which exhibit survey meter readings above normal area background levels in the solid radioactive waste