PHYSICS 345

1. PHYSICS 345 Introduction Radiation Safety The first experiment(s)

2. Radiation Safety • Radiation safety is yourresponsibility! • Guiding principle: ALARA As Low As Reasonably Achievable

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

4. 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.

5. 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

6. 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!

7. 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.)

8. 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.)

9. 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

10. Radiation Safety Units:Exposure = ∆x • R = Roentgen (unit for photons - only) 1R = 2.58 x 10-4 coulombs/(kg of dry air) Photon Dry Air ion pairs created +V collected electrons

11. Radiation Safety Units:Absorbed Dose = ∆D • Rad = a measure of energy deposited in any material by any radiation. • 1 Rad = 100 erg/gm = 107 joules/kg • 1 Rad ≈ 1 R -- • if radiation is photons • if material is mammalian tissue

12. Radiation Safety Units:Absorbed Dose Equivalent= ∆DE • REM = ∆D • QF1 • QF2 • QF3 • … • 1 REM = 1 Rad • QF1 • QF2 • QF3 • … • QF1 = 1 for photons, betas > 1 for alpha (absorbed) > 1 for high energy ions • QF2 = distribution factor, e.g., > 1 for eyes, bone marrow, gonads, … > 1 for internal absorption of material

13. 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...

14. Safety GuidelinesU.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)

15. 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

16. 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?

17. 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.

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

19. 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 youneed to know what the exposure rate is...

20. 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)

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

22. 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 $$$.

23. 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.

24. 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!!

25. 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.

26. 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!