PHYSICS 345 Introduction Radiation Safety The first experiment(s)

Radiation Safety Radiation safety is your responsibility! Guiding principle: ALARA As Low As Reasonably Achievable

Types of Radiation Photons (x-rays, gamma rays) causing ionization Beta (e -, e + ) Alpha particles (He nuclei) Other charged ions (e.g., protons) Neutrons

Radiation Characteristics Photons: –most penetrating –interaction mechanisms (all produce energetic electrons) - Photoelectric absorption Compton scattering Pair production –Electrons can produce subsequent ionizations –Photon sources are nearly always sealed.

Radiation Characteristics Betas (e.g., < 2 MeV): –Do not penetrate deeply into tissue –interaction mechanisms - Ionization of the medium Scattering may produce photons (e.g., bremsstrahlung) –Electrons can produce subsequent ionizations –Sources may be exposed; avoid contact with exposed source

Radiation Characteristics Alphas (e.g., < 10 MeV): –Do not penetrate dead skin cells on tissue surface –interaction mechanisms - Ionization of the medium - lose energy rapidly (dE/dx) –Electrons can produce subsequent ionizations –Small external hazard; very large internal hazard if radioactive material is inhaled or ingested. –Sources are usually exposed; avoid contact!

Radiation Characteristics Charged ions (e.g., > 10 MeV): –May penetrate deeply into tissue. –interaction mechanisms - Ionization of the medium - lose energy rapidly (dE/dx) –Electrons can produce subsequent ionizations –May be significant external hazard –Sources are usually accelerators. –(These are not present in this laboratory.)

Radiation Characteristics Neutrons: –May penetrate deeply into tissue. –interaction mechanisms - Nuclear interaction - only; very disruptive to material. Charged particles from interaction can produce considerable ionization of material. –One of the most serious external radiation hazards. –QF is a significant function of the neutron energy –(You should not be exposed to neutrons in this laboratory.)

Biological Consequences: Assume Chronic Exposure Ionization in biological cell - –Change DNA structure => Mutations Cancers –Alter cell activity => cell fails to perform intended biological function. –Cell dies; may be replaced by other cells –Cell repairs damage; no lasting consequences. Damage to cell nucleus is most severe

Radiation Safety Units: Exposure = ∆x R = Roentgen (unit for photons - only) 1R = 2.58 x coulombs/(kg of dry air) +V Dry Air Photon ion pairs created collected electrons

Radiation Safety Units: Absorbed Dose = ∆D Rad = a measure of energy deposited in any material by any radiation. 1 Rad = 100 erg/gm = 10 7 joules/kg 1 Rad ≈ 1 R -- –if radiation is photons –if material is mammalian tissue

Radiation Safety Units: Absorbed Dose Equivalent= ∆DE REM = ∆D QF 1 QF 2 QF 3 … 1 REM = 1 Rad QF 1 QF 2 QF 3 … QF 1 = 1 for photons, betas > 1 for alpha (absorbed) > 1 for high energy ions QF 2 = distribution factor, e.g., > 1 for eyes, bone marrow, gonads, … > 1 for internal absorption of material

Radiation Safety Units: Rates ∆x/∆t = exposure rate (R/hr) ∆D/∆t = absorbed dose rate (Rad/hr) ∆DE/∆t = absorbed dose equivalent rate (REM/hr) … and fractions thereof, e.g., –mR/hr, –mRad/hr, –mREM/hr, –etc...

Safety Guidelines U.S. N.R.C. For radiation workers (voluntary employees) e.g., hospital technicians, physicists, radio- chemists, etc., the recommended “safe” chronic doses are -- 5 REM/yr is maximum 1.25 REM/qtr (13 weeks - maximum average) 100 mREM/wk (maximum average) 2.5 mREM/hr (maximum average)

Guidelines... “Safe” => body will repair minimal damage => probability of consequential harm is small. For non-radiation workers, the limits are smaller, and especially so for - –Pregnant women, children (< 18 yrs), –students, general public

Chronic Exposures For chronic exposures, it is total absorbed dose (not the instantaneous absorbed dose rate) which is important. Example: The measured dose rate at a location is 20 mREM/hr. If you work at that location for 20 minutes, what is the total absorbed dose?

Averaging Dose Rates These dose rates are assumed not to be acute. (e.g., a dose rate of 10 R/hr is acute!) –Acute doses: radiation accidents, patients undergoing radiation therapy,... Dose Averaging (example): If you absorb 300 mREM in 1 week, you should remove yourself from exposure for at least 2 weeks to bring the average to no more than 100 mREM/wk.

Assignment Find “acceptable” absorbed dose limits for - –Students –General public –Source: Title 10 CFR Part 20 (Code of Federal Regulations) In library, and, Online: Read (scan) the posting in laboratory for your rights and responsibilities.

Reducing Exposure You can reduce your exposure to radiation from a source if you -- Increase your distance from the source Decrease your time of exposure to the source Increase the shielding between you and source … but you need to know what the exposure rate is...

Radiation Safety Measurements Select the correct instrument: type of radiation and range of dose rate. Measure at the location you will be working. Photons and betas -- –Geiger-Mueller (GM) counter Detects ions from photon interactions (e.g., photoelectric absorptions and/or Compton scatters on gas ions in GM tube)

Geiger-Mueller Tube Filled with a “counting gas” (e.g., argon- ethane mixture) - ion multiplication saturates +V G-M gas Photon ion pairs created collected electrons

Geiger-Mueller Counter Counter must be calibrated in mR/hr on all ranges on the meter (you can/should check the date of the last calibration). GM tube may detect any ionizing radiation which will penetrate tube enclosure. Calibration is for photons only. GM tube must be handled with care; tubes can (and do) break, and they cost $$$.

Neutron Detectors Must detect neutron nuclear interaction and produce ionization in detector. Counter must be calibrated in mREM/hr on all ranges on the meter (you can/should check the date of the last calibration) Calibration is for neutrons only. Instrument must be handled with care; they can (and do) break.

Personnel Monitoring Before you work in a radiation environment (near a source of radiation) you must take a radiation survey - and record it. Take and record a background reading first. Record reading where you will be working - not very near the source where you will not be working. Evaluate whether the environment is “safe” for you to continue. Ask for help if needed!!

Personnel Monitoring At all times while you work in the laboratory you must wear a radiation monitoring badge. Be sure to return your badge to the rack when leaving at the conclusion of laboratory work. You may check your radiation badge report. You should always sign-in upon entering the laboratory; sign-out when leaving. You must abide by the Rules and Regulations for the Nuclear Physics Laboratories - posted.

Complacency... Familiarity breeds carelessness!! Pay attention to all radiation warning signs. –Radioactive materials => potential hazard if materials are handled. –Radiation hazard => exercise caution, measure radiation exposures, ask for advice. You are responsible for your own safety!