1. Workshop for radioactivity and experimental observations 1

2. DefinitionSI unitcgs unit (obsolete) Activity, A, Number of disintegrations per second 1 becquerel (Bq)  1 disintegrations s -1 1 curie (Ci)  37x10 9 disintegrations s -1 Conversion 1 Bq  2.7 x10 -11 Ci1 Ci  37x10 9 Bq Ionizing radiation exposure The amount of radiation required to generate unit charge in unit mass (SI unit) or unit volume (cgs unit) of dry air at STP 1 C kg -1 of air 1 roentgen (R)  1 esu cm -3 of air Conversion1 C kg -1 = 3876 R1 R = 2.58 x10 -4 C kg -1 Radiation (absorbed) dose, D Radiation energy absorbed / unit mass 1 gray (Gy)  1 J kg -1 1 rad (rad)  100 ergs g -1 Conversion1 Gy = 100 rad1 rad = 0.01 Gy Equivalent dose D  W R = H, where W R is the radiation type weight factor 1 sievert (Sv)  1 J kg -1 1 rem (rem)  100 ergs g -1 Conversion (for  - or  -radiation) 1 Sv = 100 rem1 rem = 0.01 Sv Effective dose Weighted average of equivalent dose = Σ i D i  W Ri  W Ti = Σ i H i  W Ti, where W Ti is the tissue/organ weighting factor in Svin rem Radioactivity units 2

3. Weighting factor Radiation typeTissue / organ Radiation type, W R  -ray (photons),  -ray (electrons), muons 1 Protons, charged pions2  -ray, fission fragments, heavy ions 20 Neutrons Function of neutron energy Tissue, W T Bone marrow (red, 髓 ), colon ( 結 腸 ), lung, stomach, breast, remainder tissues 0.12 (each) Total for a body = 1 Gonads ( 生殖腺 )0.08 (each) Bladder( 膀胱 ), liver, esophagus( 食管 ), thyroid( 甲狀腺 ) 0.04 (each) Skin, bone surface, salivary glands, skin 0.01 (each) weighting factors 3

4. Effective dose EventEffectsRemarks 20 Sv Sudden, accidental, unwanted exposure Central nervous system (CNS) damaged, death within hrs fatal 10 Sv Gastrointestinal ( 胃腸 ) tract (GI) damaged, death within days 5 Sv Bone marrow failure, death within weeks 1 SvBlood count depressionmay recover 0.1 Sv = 100 mSv per year Risks are very low for dose values below. No observable harmful effects on humans. 15-20 mSv per year Cigarette smoking (1 pack per day) 20 mSv per year Maximum annual effective dose for a person employed in radiation work 2-3 mSv per year Annual effective dose from background, including: 0.25-0.35 mSv (cosmic ray) 0.4 mSv (food) 2 mSv (radon in household) 1 mSv per year Maximum annual effective dose for a public member 0.4 mSvX-ray diagnosis 0.01 mSv1000 mile flight trip Safety 4

5. 5 CT scan

6. Example 1  -ray  100 ergs in 1 gram of issue gives 1 R. 1 rad of absorbed dose  100 ergs of radiation energy absorbed by 1 gram. 1 rad  1 R. Example 2 A survey meter gives reading in Roentgen (R). For 1 R of  -ray  1 rad Since W R = 1, equivalent dose = 1 rem 1 rem = 0.01 Sv Hence 1 R  0.01 Sv = 10 mSv 6

7. Example 3 Background radiation = 0.02 mR hr -1.  0.01  0.02 mSv hr -1 = 0.2  Sv hr -1 = 1.75 mSv per year  the average background of 2.65 - 2.75 mSv per year 7

8. Example 4 A lantern mantle shows radiation of 2.5 mR hr -1 The radiation dose = 0.01  2.5 mR hr -1 = 0.025 mSv hr -1 Maximum dose is 1 mSv, maximum time to contact it = 1 mSv / 0.025 mSv hr -1 = 40 hrs (for a pubic member); or 20 mSv / 0.025 mSv hr -1 = 800 hrs (for a related worker), Note: Mantle contains thorium dioxide powder ---- radioative. Never touch it with bare hands. Wash hands after using it.thorium dioxide 8

9. 9 Safety of Food – effective dose coefficient (Bq to Sv 有效剂量系数 ( 婴儿 ) 有效剂量系数 ( 成人 ) 碘 131 0.000140.000016 铯 137 0.0000210.000013 钚 239 0.00420.00025 Example 5 菠菜含有 10000 Bq/kg 碘 131 成人每天吃菠菜⒛克 一年的有效剂量 = 10000 Bq/kg  0.02 kg x 365 days x 0.000016 = 1.2 mSv / year

10. 10 CoWIN webpage

11. 11 Experiment 1 Inverse square law of radiation Net count rate  1/d 2 Position of GM tube Position of source d1/d 2 Background count rate Count rateNet count rate

12. 12 Experiment 2 Absorption of  -radiation in aluminum I(x) = I o e -  x ln (I o /I) =  x Thickness (x )Background count rate Count rateNet count rate ln(I o /I) Slope = 11.69 /cm

13. 13 Cloud chamber and artificial precipitation & Emulation of radioactivity experiment