Safe Handling of Radiation
X-ray Generators

ISBN978-4-905025-03-0
大学等放射線施設協議会

113-0032 東京都文京区弥生2-11-16
東京大学アイソトープ総合センター内
電話: 03-5841-3058 Fax: 03-5841-3050
E-mail: kyogikai@ric.u-tokyo.ac.jp

Contents• Basic Physical Aspects of X-rays• Radiation Protection

大学等放射線施設協議会

1. Basic Physical Aspects of X-rays
1.1 Generation of X-rays• Characteristic X-rays– de-excitation of atoms– inherent wave length ⇒ Elemental analysis• Bremsstrahlung– Light emitted by acceleration of charged-particles– continuous spectrum

大学等放射線施設協議会

KαRelative intensity

KβCharacteristic X-ray
Accelerating voltage

Continuous X-ray

Energy (keV)
M shell
L shell
Kα
K shellKβ

E = hc/λKα = WK − WL
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1.2 X-ray tube
1.Glass valve
2. W coil filament
3. Focus electrode (Fe, NI)
4. Stem (Lead thru)
5.Cathode sleeve (Fe, NI)
6. Focus point (X-ray source)
6’.Focus trace (ring)
HV

7. Target (Fe, W alloy etc)
9. Anode axis for rotation
10. Kobal ring (Fe alloy-glass)
11. Anode Rotor

X ray beam
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12. Bearing with lubricant

1.3 Interaction of X-rays with materials
1.3.1 Attenuation & Absorption

Incident flux I0 (cm-2・s-1), Transmitted flux I (cm-2・s-1)

dI  x  x, I  I 0 exp(x)  I 0 exp(  x) ,I
μ: linear attenuation coefficient (cm-1)
μ/ρ: mass attenuation coefficient (cm2/g)
state independent (Ex. Water vs. vapor)

X cm

I0(#cm-2s-1)

I (#cm-2s-1)

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1.3.2 Photoelectric effect1.3.3 Compton scattering
1.3.4 Electron-pair creation
PhotoelectriceffectComptonscattering

Electron-paircreation

description

(pht)

(com)

(ept)

product

electronelectron andphotona pair of e- and e+

energy

Ee=EX- Wn

Ee= 0 ~ Emax

2 x 0.511MeV

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X-ray Energy

1.4 X-ray intensity
X-ray intensity at x cm from the source:I [#cm  s
2#] S [ ]

s

14 d

2

 exp(   x )d: distance from the source F, [cm]x: thickness of absorber, [cm]μ: linear attenuation coefficient of absorber [cm-1 ]14
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91.5 X-ray survey meter

TypeAdvantages

DisadvantagesIonization Chamber
Effective Range
30 keV ～ 1.5 MeV

Accurate
Good energy response(Sv/D)

Low sensitivity for all
kinds of X rays (Lowdetectivity)

GM (Geiger-Mullar)
Proportional Counters
Effective Range
100 keV ～ 1.5 MeVHigh sensitivity
Gas Multiplication
Convenient for usual
leakage check

Long dead-time (~200μS)  Count loss andsuffocation
Low sensitivity for lowenergy

Scintillation Counter
Semiconductor Counter
Effective Range
100 keV ～ 1.5 MeVHigh sensitivity
Large  value(solid state)

Low sensitivity for
Low energy X or γ-rays

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2. Radiation protection
2.1 Basics of radiation protection• The principles of radiological protection (ICRP2007)– Justification– Optimization of Protection• individual doses should all be kept as low as reasonably achievable(ALARA)– Application of Dose Limits• The principles of protection from external exposure– Shorten working time
– Keep distance from radiation source– Use shielding
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2.2 Tips for safe handling of X-ray generators•Never put any parts of your body into X-ray beams•

Shut down the generator power when exchanging your sample•

When the above is impractical, confirm the shutter being closed•

Improve working process or equipment to make exposure timeshorter•

Make radiation shields effective•

Take care of scattering and leakage of X-rays

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2.3 Shielding of X-rays• You should enclose X-ray equipment– Using lead sheet, lead glass, transparent plastic sheet including
heavy metals depending on the produced X-ray energy.

• Thickness of shielding should be calculated– based on the highest energy from an X-ray generator.
– for example, X-rays from a 50 kV generator can be shielded by a 1mm thick lead sheet.

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2.4 Radiation controlled area

• Area where the effective dose from radiation
sources may exceed 1.3 mSv / 3 months.
• Effective dose for accessible area should be lessthan 1 mSv / week.
• Notification by a sign noting “Radiation ControlledArea”.
• Radiation is shielded by wall and screen.

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2.5 Personal dosimeters

TypeFilm badge

ThermoLuminescence

Detection
limit(H1cm)

100μSv

1 μSv

0.5 μSv

1μSv

0.01μSv

Measuring
range (Sv)100μ ~ 0.1

10μ ~ a few

10μ ~ 1010μ ~ 100.01 ~ 99.9μ
1.0 ~ 999 μ

Energydependency

StrongStrongMedium

StrongWeakFading

NoMedium

WeakNoNo

Remarks

Not usednow

Repeated
use

Repeated
Use

Repeatedread out

Real time
Electric noise

LuxelBadge

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Glass badge Electric SSD

Luxel badge (Nagase)

Glass badge (Chiyoda )For dosimetry in stationary work with small fluctuationof dose rate

MenWomen
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Electrical dosimeter

For dosimetry in ashort working
period with big
fluctuation of doserate