Workshop for radioactivity and

experimental observations

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Definition SI unit cgs unit (obsolete)

Activity, A , Number of disintegrations per second

1 becquerel (Bq) 1 disintegrations s-1

1 curie (Ci) 37x109 disintegrations s-1

Conversion 1 Bq 2.7 x10-11 Ci 1 Ci 37x109 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

Conversion 1 C kg-1 = 3876 R 1 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

Conversion 1 Gy = 100 rad 1 rad = 0.01 Gy

Equivalent dose

DWR = H, where WR 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 rem 1 rem = 0.01 Sv

Effective doseWeighted average of equivalent dose =

ΣiDiWRiWTi = ΣiHiWTi, where WTi is the

tissue/organ weighting factor

in Sv in rem

Radioactivity units

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Weighting factor

Radiation type Tissue / organ

Radiation type,

WR

-ray (photons) , -ray (electrons), muons

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Protons, charged pions 2-ray, fission fragments, heavy ions

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Neutrons Function of neutron energy

Tissue, WT 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

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Effective dose Event Effects Remarks

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 Sv Blood count depression may recover0.1 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 mSv X-ray diagnosis 0.01 mSv 1000 mile flight trip

Safety

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CT scan

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 2A survey meter gives reading in Roentgen (R). For 1 R of -ray 1 rad Since WR = 1 , equivalent dose = 1 rem

1 rem = 0.01 SvHence 1 R 0.01 Sv = 10 mSv

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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

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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.

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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 mSv / year

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CoWIN webpage

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Experiment 1 Inverse square law of radiation

Net count rate 1/d2

Position of GM tube

Position of source

d 1/d2 Background count rate

Count rate Net count rate

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Experiment 2 Absorption of -radiation in aluminum

I(x) = Io e - x

ln (Io /I) = xThickness (x ) Background

count rateCount rate Net count

rateln(Io/I)

Slope = 11.69 /cm

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Cloud chamber and artificial precipitation

&

Emulation of radioactivity experiment