Apr. 11 2011

Hokkaido University Special Lecture
The Latest Information on theFukushima Nuclear Power Plant

Environmental Radioactive Substances:
Data from the School of Engineering

Ryoko FUJIYOSHI
Faculty of Engineering, Hokkaido University
E-mail: fuji@eng.hokudai.ac.jp

Contents
1. What is radioactive substances?
2. Radioactive substances in theenvironment?
3. What are measures of radioactivesubstance and radiation?
4. Data from the School of Engineering
5. Summary

What is a radioactive atom (radionuclide)?
Atom with unstable (high energy level) nucleuse¯Radiation (α, β,γ)Decaye¯
Identification of a radionuclide
Emitting radiation

Type (α, β, γ)
Energy (E)Emission ratio
Half life (T1/2)

What is radioactivity?
Number of radionuclides decaying in a unit time
Unit：Becquerel（Bq）

dN  N
dt
Radioactivity (A) (Bq = s-1)
N: Number of radionuclides at time tt: Time (s)λ: Decay constantHow to represent a radionuclide
For example,Radioactive potassium

40K(K-40, Potassium-40)

There are many radionuclides
in our environment!
Classification of radionuclides
1. Primordial radionuclides with long
half life (T1/2>108 y) (40K, 238U, 232Th)
2. Cosmic ray produced radionuclides(3H, 7Be, 14C etc.)

3. Anthropogenic radionuclides(60Co, 90Sr, 137Cs, 131I, 99mTc etc.)

Natural Radionuclides in three Decay series (238U, 232Th, 235U)

Natural Radiation
Cosmic ray(n)14N214C + p+14CO

Concrete block(226Ra, 40K)

2

222Rn

238U (226Ra), 232Th, 40K

What is radiation exposure?
As you know now,
You are continually
Exposed to naturalradiation

Radiation exposure
・External exposure ()・Internal exposure ()Radiation dose (Sv) ：Radioactive
Material

External dose+Internal dose
Sievert (Sv): A unit to measure the amount of radiation energy (J) per unit of mass (kg)considering the type and biological effects of radiation

What is Sv, really?
Since many organs and tissues
are exposed to various radiation,
it is better to use “effective dose”(E), which is included the effectsof radiation type and also biologicaleffects. The unit is “Sv”.
mSv = 0.001 Sv

Causes of radiation exposure
External exposure + Internal exposure
Radiation dose from natural sources (mSv/y)Mean dose value in the world:
2.4 mSv（External dose: 0.9 mSv）
Mean annual radiation dose in Japan

1.4 mSv (External dose: 0.7 mSv）** The value is varied to a great extent depending on the location.

Effective doses from natural andhuman sources
Annual radiationdose for people inJapan

3.75 mSv/y

Medical ( 60 %)Others

(<1 %)Natural(external)

Natural (radon)(18 %)(11 %)Natural (internal)

原子力安全協会（編）：生活環境放射線(1992) をもとに作成(11 %)

When an accident happens at anuclear power plant,
Different radioactive substances
released from the plant are to beobserved in the environment at various
places depending on distance from thesite and also on elapsed time after theaccident.

Typical radionuclides to be observedwith gamma ray measurements

131I
134, 137Cs

Identification of the radionuclides withGamma energy (MeV)
Half life (T1/2)
Emission ratio ( - )131I (T
1/2 = 8.04 d）

0.080(2.6), 0.284(6.1), 0.364(81),0.637(7.3), 0.723(1.8)
134Cs (T
1/2 = 2.06 y）
0.563(8.4), 0.569(15), 0.605(98), 0.796(85),0.802(8.7), 1.365(3)137Cs (T1/2 = 30.17 y）
0.662(90)Data from the School of Engineering(since Mar. 14 2011)
1. Radiation dose rate (μSv/h)
2. Detection of radionuclides indust samples collected daily
with a dust sampler

1. Radiation Dose Rate
Observation points:
1. School of Eng. Bld. A roof
1.3m from the floor (23.5 mfrom the ground) 1:30pm
2. School of Eng. LINAC
Border of the controlled area
1m from the ground 1:30pm
Instruments:
1. CsI Scintillation Counter(Horiba Radi PA-1000)
NaI Scintillaiton Survey meter(Aloka, TCS-161)
2. NaI Scintillaiton Survey meter(Aloka, TCS-161)

Time series data on radiation dose ratemeasured in the School of Engineering sinceMar. 14 2011
Radiation Dose rate (μSv/h)School of Engineering
Bld. A (NaI)(CsI)
LINAC (NaI)*Date*A series of data before the accident (Mar. 11 2011) has been reserved in the LINAC facility(http://www2.qe.eng.hokudai.ac.jp/nuclear‐accident/dose/dose.html)

2. Detection of Radionuclides in Dust
Observation point:
School of Eng. Bld. A roof at
1.3m from the floor (23.5 mfrom the ground)
Dust sampling:
Dust sampler (TH-D5101/HVA-1,Chiyoda Technol. Co.Ltd.), Filter(HE-40T, ADVANTEC), 24hrs(Mean flow rate:700L/min)
Gamma spectrometry*:
Dust sample (dried at 60˚ C for30min)
Gamma spectrometry (ORTEC
GEMX10P) 20hrs* Conditions for the measurements (http://www2.qe.eng.hokudai.ac.jp/nuclear‐accident /dose/dose.html)

Radionuclides in a dust sample collectedfrom Mar. 14 to 15 2011
131I
134Cs
137Cs

Counts for 24 hrs

Mar. 14‐15 2011

01000

2000

Channel No3000

4000

131I (Bq/m3)

Time series data on 131I activityconcentration in dust samples

Date

Limit in the air: 5Bq/m3

137Cs (Bq/m3)

Time series data on 137Cs activity
concentration in dust samples

First detected on Mar.26-27

Date

Limit in the air: 30 Bq/m3

134Time series data on Cs activity

134Cs (Bq/m3)

concentration in dust samples

Date

Limit in the air: 20 Bq/m3

Data before the accident
1. Radiation dose measured at
LINAC facility since 2006
2. Activity concentration of137Cs in soil on the campusof Hokkaido University in 2002

137
Depth profiles of Cs activityconcentrations in soil
137Cs (Bq/kg)
137

0010C s (B q /k g )
20

30

40

50

20

Sapporo (2002)30
C s 1 37 (P o i n t 1 )C s 1 37 (P o i n t 2 )40

Depth (cm)Depth (cm)10

Tomakomai (2010)

Findings:
1. Radiation dose rate:
0.03-0.04 μSv/h(Mar. 14-Apr. 10)
2. Detection of radionuclides in dust
Mar. 22-23: 131I
Mar. 26-27: 131I, 137Cs
131
137
134
I, Cs, Cs
Apr. 4-5 :Summary· There are various radioactive
substances in the environment.
· The unit of radioactivity: Bq· The unit of radiation dose: Sv· Data from the School of Engineering
Radiation dose rate: 0.03-0.04 μSv/hRadionuclides detected: 131I, 134Cs, 137Cs(The activity level is quite low)

· Monitoring has still been continued.

Examples of useful HP:
http://www2.qe.eng.hokudai.ac.jp/nuclear-accident/dose/dose.html (Data)
http://www.iaea.org/news/tsunamiupdate01.html (Daily report)
http://ec.europa.eu/energy/nuclear/radiation_protection/publications_en.htm(Basic knowledge on radiation)
http://www.nirs.go.jp/ENG/index.html (Radiation protection)and more...

Thank you for your attention!
Ryoko Fujiyoshi