Investigation of Characteristics of Lowenergy X-ray Radiated from Crookes Tube
Used in Radiological Education
Do Duy KHIEM, Hirokazu ANDO, Hiroto MATSUURA,Masafumi AKIYOSHILABORATORY OF RADIATION SAFETY MANAGEMENT
In The DEPARTMENT OF QUANTUM AND RADIATION ENGINEERINGGRADUATE SCHOOL OF ENGINEERING, OSAKA PREFECTURE UNIVERSITY
December 09, 2020

1

A WARD2O UTLINES
Section 1

General introduction

Section 2

Characteristics of low-energy X-ray radiated from the Crookes
tube

Section 3

Dose distribution from thethermoluminescent dosimeter

Section 4CrookestubeusingConclusions

3

SECTION

1General Introduction❑ What is a Crookes tube?
❑ Current state of Crookes tube usage❑ Exposure to X-ray radiation from a Crookes tube

❑ Problems on estimate of a Crookes tube
❑ Crookes tube project4

WHAT IS A CROOKES TUBE?
New Crookes tubes❑ 1875, William Crookes invented the Crookes tube.
❑ 1895, Wilhelm Conrad Röntgen discovered X-rays.
❑ 1901, W. C. Röntgen got the first Nobel Prize in Physics.

Conventional Crookes tube

William Crookes

X-ray of Kölliker's
hand, made byRöntgen (1896)

Wilhelm ConradRöntgenMechanism of a Crookes tube
1
2Tube vacuum:0.005 - 0.1 Pa

3X-rays1

Cations in the evacuated tube areaccelerated and impact the cathode,which knock out secondary electrons.

2

These electrons are accelerated under theapplied HV.

3

Accelerated electrons collide the glass
wall to radiate bremsstrahlung X-rays.

HV
Several tens of kV

Induction coil5

CURRENT STATE OF CROOKES TUBE USAGE IN JAPAN

Many teachers aredemonstrating on
Crookes tube in ascience class.

❑ Teaching of science atjunior-high schools.
❑ Containing
information
about Crookes tubes in all
five science textbooks❑ Understanding the natureof the radiation associatedwiththevacuum
discharge (MEXT, 2017).

Teachers do notknow radiation
emissionfromthe Crookes tube.

Radiation protection
and safety guidelines
for Crookes tubes havenot been investigatedsufficiently
yetinJapan.

No fund for new
Crookes tube withno radiation.
Lack of radiation
education in schoolfor a long time.

Risk of radiation
hazards.
6

EXPOSURE TO X-RAY RADIATION FROM A CROOKES TUBE
Energy was approximately 20 keV.
Hp(10) was up to 143 mSv/h at 5 cm.

X-raysPROBLEMS ON ESTIMATE OF A CROOKES TUBE
❑ Low energy X-rays (approximately 20 keV): hardly measure by conventional meters (evenused HPGe, NaI detectors).
❑ The pulse-shaped voltage creates the heterogeneous radiation: produces pile-up effect,broadened energy spectrum.
❑ Instability of induction coil and applied voltage: affected by temperature, humidity.
❑ Difficulty in effective dose estimate:o dose distribution in horizontal plane is inhomogenous,
o cannot assume an aligned and expanded radiation field,o cannot use Hp(10) as an approximation of effective dose.

7

CROOKES TUBE PROJECT
http://bigbird.riast.osakafu-u.ac.jp/~akiyoshi/Works/CrookesTubeProject.htm❑ Assoc. Prof. Masafumi Akiyoshi is theChief of the project.
❑ "Crookes tube project" has beenlaunched nationwide in Japan byvolunteer scientists since May 2017.

How to take advantageof old apparatuses but
radiation safety must
be ensured?

❑ Aiming to establish and promulgate
the radiation safety management
guidelines on Crookes tube ateducational sites.

Task 1

Task 2

Task 3▪

▪

Investigating theactual conditions
at the educationalsites.

▪

▪

Examining theoperationalmethods▪

▪

Verifying ALARA
principle.

▪

Evaluating theelectric parameterssuch as voltage andcurrent.
Developing
measurement
methods for safety
management ateducational sites.

▪

Evaluating theeffective dose.
Assessing the eyelens dose.
Estimating thereference level ofdose.

Task 4▪

Proposingeducational content
that utilizes lowenergy X-rays.

▪

Providing dose
measurement
methods.

▪

Spreading guidelines
at educational sites.
8CROOKES TUBE PROJECT
http://bigbird.riast.osakafu-u.ac.jp/~akiyoshi/Works/CrookesTubeProject.htm❑ From 2019-2020, the Japan Health Physics Society (JHPS) established the"Specialized study group on radiation safety management for low energy X-rays".
❑ In 2021, the specialized study group aims to establish the academic standard that
contains the following contents:(a) Crooks tube operation manual,(b) Measurement methods of low energy X-rays,(c) Evaluation of radiation protection and technical procedures against lowenergy X-rays,(d) Target value management:• Explanation of items,• Question and answer (Q&A).

9

SECTION

2

Characteristics of Low-energy X-ray Radiated fromthe Crookes Tube
❑ X-ray energy spectrum❑ Correlation of operation factors to output X-rays❑ Transmission of X-rays❑ Leakage dose

Khiem, D. D., Ando, H., Matsuura, H. and Akiyoshi, M. (2019), Radiation Safety Management 18, 9-15.

10

X-RAY SPECTROMETER

Crookes tube
(3C-B, KenisLtd., Japan)

CZT Detector (XR100T-CZT, Amptek
Inc., USA)Power supply andAmplifier (PX2T,Amptek Inc., USA)

Pocket Multichannel(MCA8000D, AmptekInc., USA)

Collimator

DPPMCA Software(Amptek Inc., USA)0.5 mm
3 mmFixed distance (90 cm)
CZT detector

11

HIGH VOLTAGE APPLIED BY THE INDUCTION COIL
50
Impressed voltage

Impressed voltage (kV)

(1) Electrode distance
1mm  1kV(2) Output power

4035 kV

3020100-10-20Induction coil

02040

60

80

100120140160

Time (ms)

500 MΩ
100 kΩ

PC USB Oscilloscope(6000BD, Hantek Ltd.)The induction coil
▪ Producing an applied voltage inpulsed-shape,▪ Creating pulsed radiation withheterogeneous energy of X-rays.

Voltage divider circuit
12

EFFECT OF VOLTAGE ON OUTPUT X-RAYS
68101214161820222426283040600

PW0 (15.8 keV)
PW2 (17.0 keV)
PW4 (18.1 keV)
Gauss Fitting

355004002520

Shifted energy

15Frequency

Intensity

30

PW0 (16 kV)
PW2 (17 kV)
PW4 (18 kV)
Gauss Fitting of PW0
Gauss Fitting of PW2
Gauss Fitting of PW4300

200

10100

5006810 12 14 16 18 20 22 24 26 28 30

Energy (keV)

X-ray spectra radiated by the Crookes
tube acquired by the CZT detector

0510152025303540High voltage (kV)The distribution of the applied voltage
shows an increase in the output voltage

1345454040peak X-ray EnergyMaximum Voltage
Peak Voltage

353025353025Appr. 20 keV

20201515101055002468101214161820Voltage (kV)

X-ray energy (keV)

EFFECT OF VOLTAGE ON OUTPUT X-RAYS

022Output Power❑ X-ray energy and applied voltage kept stability when a spark occurred.
o effective energy of approximately 20 keV,o maximum voltage of roughly 40 kV, equal to nominal voltage at an electrode distance of 40 mm.
o peak energy of X-ray matched well peak of voltage distribution.
❑ Change in applied voltage (kV): affecting both amplitude and energy of X-ray.

o intensifying of photon intensity,o shifting X-ray energy to higher in the spectrum.

14

TRANSMISSION ESTIMATE▪ Using Lambert-Beer equation:
D = D0 𝑒 −µ𝑥
Ionization chamber

30 cm

ICS-1323, Hitachi Ltd., Japanµ: Al
coefficientlinearattenuation

D0: initial dose
D: transmitted dose𝑥 : Al thickness (0.5 – 6 mm)▪ Distance of 30 cm.

Al linear attention measurement setting▪ Interpolating the effectiveenergy from µ of Al using
data from the National
Institute of Standards andTechnology (NIST, USA).

15TRANSMISSION ESTIMATE
012345625

10000

H*(0.07) dose (mSv/h)

1000

100

1020Energy (keV)

PW0PW2PW4PW6PW8PW10PW12PW14

15

Aluminum attenuator
CZT detector

105
1012345600

Al thickness (mm)Transmission of X-rays with various output
applied voltages through Al.

2468Output Power

101214

X-ray energy with various output powers obtaining
by attenuation measurement and CZT detector.

❑ Dose increased with increasing output power.
❑ Dose kept stability when a spark occurred.
❑ Effective energy of 19 keV acquired by CZT detector and 20 keV
by attenuation measurement, average difference of 7.5%.
❑ Change in the filtration: hardening the X-ray beamo reducing the photons with low energy,o shifting energy to the higher region.

16

SECTION

3

Dose Distribution from the Crookes Tube Using
Thermoluminescent Dosimeter❑ Evaluating the spatial dose distribution of theCrookes tube.
❑ Indicating the aspects of the Crookes tube withhigh dose.
❑ Estimating Hp(0.07) as an experimental index
for effective dose estimate.

Khiem, D. D., Matsuura, H. and Akiyoshi, M. (2020), Radiation Measurements 134, 106312.

17

SPATIAL DISTRIBUTION OF DOSETLD

Front side

60

12

3

4

5

6

7

8

9

10

1112

13

14

40

0-20-40-60-80

160 cmY (cm)

201515 cm

16171920

21

22

23

24

25

26

27

28-40 -30 -20 -10

015 cm1810 20 30 40

X (cm)▪ Fitting 2-D human-body-shape with a junior-high school student.
▪ Distributing 28 TLDs (Panasonic UD-802PQ) on the 2-D human body shape.

▪ Placing at four sides of the tube.
▪ Irradiating at a distance of 1m for 1h to integrate dose.

18

SPATIAL DISTRIBUTION OF DOSE
Hp(0.07) (mSv/h)

Hp(0.07) (mSv/h)60a) Front side

40

0.46

60

0.43

40
20

0.34

00.11

-20

-20

-40

0.09

0.26

-60

0.08

0.23

-80

0.28

-60
-80
-30

-20

-10

0

1020X (cm)

0.07

-30

30

-20-1001020X (cm)c) Left side

0.23

60

0.21

40

0.19

200.160.40

0.32

Y (cm)

00.44d) Right side

0.36

200.1830

Hp(0.07) (mSv/h)

Hp(0.07) (mSv/h)40

Y (cm)

0.10

0.31

-40

60

0.12

Y (cm)Y (cm)

0.37

0.15
0.130.402000.16b) Back side

00.28

-20-20

0.24

0.14

-40

0.13

-60

0.11

-80

0.10

-30

-20

-100X (cm)102030

-40

0.20

-60

0.16
0.13

-80
-30

-20-100102030X (cm)▪ Highest dose on the aligned direction to the head of the Crookes tube
▪ Distributing highly in the central area and having spatially non-uniform.

19SPATIAL DISTRIBUTION OF DOSE

▪ The fluorescent green inside the tube pointed out
where the electrons strike the glass and emit X-rays.
▪ It validated the experimental results that the dose washigh at the top-rear and the head tube.
20

SECTION

4Conclusions

21

CONCLUSIONS❑ Investigating properties and characteristics of X-rays emitted by Crookes tube:o Emitting X-rays with soft energy of approximately 20 keV,o Producing applied voltage in pulsed-shape,o Creating inhomogeneous radiation,o Changing electric operation causes changing exposure and X-ray energy.
❑ Dose distributes spatially non-uniform with highest dose on the head tube.
❑ Recommendations and guidelines on radiation protection:o Strictly avoiding the position facing the front of the tube,o Setting output power as low as possible,
o Setting the electrode distance shorter than 20 mm, never remove them,o Taking distance as far as possible, upon 1 m as recommendation,o Keeping the demonstration time shorter than 10 min,22

Let’s fight off

CORONAVIRUS

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