Workshop for radioactivity and experimental observations 1 Radioactivity

Workshop for radioactivity and experimental observations 1

Radioactivity units Definition Activity, A , Number of disintegrations per second Conversion 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 SI unit 1 becquerel (Bq) 1 disintegrations s-1 1 Bq 2. 7 x 10 -11 Ci 1 C kg-1 of air cgs unit (obsolete) 1 curie (Ci) 37 x 109 disintegrations s-1 1 Ci 37 x 109 Bq 1 roentgen (R) 1 esu cm-3 of air Conversion Radiation (absorbed) dose, D Radiation energy absorbed / unit mass Conversion Equivalent dose D WR = H, where WR is the radiation type weight factor 1 C kg-1 = 3876 R 1 gray (Gy) 1 J kg-1 1 R = 2. 58 x 10 -4 C kg-1 1 rad (rad) 100 ergs g-1 1 Gy = 100 rad 1 sievert (Sv) 1 J kg-1 1 rad = 0. 01 Gy 1 rem (rem) 100 ergs g-1 Conversion (for -radiation) Effective dose Weighted average of equivalent dose = Σi. Di WRi WTi = Σi. Hi WTi, where WTi is the tissue/organ weighting factor 1 Sv = 100 rem in Sv 1 rem = 0. 01 Sv in rem 2

weighting factors Weighting Radiation type Tissue / organ factor Radiation type, -ray (photons) , -ray WR (electrons), muons Protons, charged pions -ray, fission fragments, heavy ions Neutrons Tissue, WT 1 2 20 Function of neutron energy Bone marrow (red, 髓), colon (結 0. 12 (each) Total for a body = 1 腸), lung, stomach, breast, remainder tissues Gonads (生殖腺) 0. 08 (each) Bladder(膀胱), liver, esophagus( 0. 04 (each) 食管), thyroid(甲狀腺) Skin, bone surface, salivary 0. 01 (each) glands, skin 3

Safety Effective dose 20 Sv Event Sudden, accidental, unwanted exposure 10 Sv 5 Sv 1 Sv 0. 1 Sv = 100 m. Sv per year 15 -20 m. Sv per year Cigarette smoking (1 pack per day) 2 -3 m. Sv per year Annual effective dose from background, including: 0. 25 -0. 35 m. Sv (cosmic ray) 0. 4 m. Sv (food) 2 m. Sv (radon in household) Maximum annual effective dose for a person employed in radiation work 1 m. Sv per year 0. 4 m. Sv 0. 01 m. Sv Effects Remarks Central nervous system (CNS) damaged, fatal death within hrs Gastrointestinal (胃腸) tract (GI) damaged, death within days Bone marrow failure, death within weeks Blood count depression may recover Risks are very low for dose values below. No observable harmful effects on humans. Maximum annual effective dose for a public member X-ray diagnosis 1000 mile flight trip 4

CT scan 5

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 WR = 1 , equivalent dose = 1 rem = 0. 01 Sv Hence 1 R 0. 01 Sv = 10 m. Sv 6

Example 3 Background radiation = 0. 02 m. R hr-1. 0. 01 0. 02 m. Sv hr-1 = 0. 2 Sv hr-1 = 1. 75 m. Sv per year the average background of 2. 65 - 2. 75 m. Sv per year 7

Example 4 A lantern mantle shows radiation of 2. 5 m. R hr-1 The radiation dose = 0. 01 2. 5 m. R hr-1 = 0. 025 m. Sv hr-1 Maximum dose is 1 m. Sv, maximum time to contact it = 1 m. Sv / 0. 025 m. Sv hr-1 = 40 hrs (for a pubic member); or 20 m. Sv / 0. 025 m. Sv 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. 8

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. 00014 0. 000016 铯 137 0. 000021 0. 000013 钚 239 0. 0042 0. 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 m. Sv / year 9

Co. WIN webpage 10

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

Experiment 2 Absorption of -radiation in aluminum I(x) = Io e - x ln (Io /I) = x Thickness (x ) Background count rate Count rate Net count rate ln(Io/I) Slope = 11. 69 /cm 12

Cloud chamber and artificial precipitation & Emulation of radioactivity experiment 13