RADIATION RESEARCH CENTER MEETINGOPU - 2018, November 27th

INVESTIGATION OF LOW ENERGY X-RAY RADIATED
FROM CROOKES TUBE USED IN RADIOLOGICALEDUCATIONAuthors: Do Duy Khiem, Hirokazu Ando, Masafumi Akiyoshi
Laboratory on Radiation Safety Management
Department of Quantum and Radiation Engineering
Graduate School of Engineering, Osaka Prefecture University
1

HOW IS A CROOKES TUBE USED FOR TEACHING OF SCIENCE?
2008

BACKGROUND

The radiological education guideline has been
added to the school’s curricula by MEXT*.

March, 2011
Fukushima nuclear accident occurred.

Oct.,
2011
MEXT accomplished the radiation educationmaterials.

2014
The supplemental reading documents
included the accidental information have been
published (MEXT).

Crookes tube has been used in the teaching ofscience at a junior and high school in Japan.
X-ray radiation is possible exposure to ateacher who conducts the demonstrations andexperiments as well as participated students.
It was reported in Japan that the X-ray
radiated from the Crookes tube had very low
energy (about 20 keV) but the dose was very
high (up to several hundred mSv/h)1) .
It is necessary to accomplish the radiation
protection and safety guideline that have notbeen evaluated sufficiently yet in Japan.

OBJECTIVES
Conducting an initial evaluation of the characteristics and properties of X-ray beam radiated from theCrookes tube used in the junior-high school for educational science.
Developing the system that actually can be used in measurement of low energy X-rays.
Submitting the results as the recommendation and guideline for radiation protection rules to prevent
unwanted harmful effects from radiation.
1.

Ohmori Giroh (1995). X-ray exposure in the teaching of science at junior and senior high schools. NIRS-M—105, Japan, 107-112. 2*Ministry of Education, Culture, Sports, Science, and Technology

WHAT IS A CROOKES TUBE?
Discharge distance

21Crookes tube
(3C-B, Kenis Ltd.,Japan)

X-ray

Discharge output

Induction coil(ID-10, Kenis Ltd., Japan)

HV

Induction coil:o The range of spark gap is 10 – 100 mm.
o The nominal dielectric breakdown voltage in the air is about 1 kV at 1 mm,
o The desired output voltage can be obtained by regulating the distance of the discharge
electrodes or discharge output (0 to 20) .
o In this experiment, the discharge distance was set at 40 mm, and variable applied voltages
were controlled by change of discharge output from 0 to 20 (denoted by PW0 to PW20) inscale.

3MATERIALS AND METHODS
X-ray Spectrometer

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

CZT Detector (XR100T-CZT, AmptekInc., USA)

Cylindrical Pb collimators of 3 mm
pinhole, and thin plate Pb collimatorsof 0.5 mm pinhole were used.

Power supply andAmplifier (PX2T,Amptek Inc., USA)

Pocket Multichannel(MCA8000D,Amptek Inc., USA)DPPMCA Software(Amptek Inc., USA)

X-ray spectrum measurement
0.5 mmCollimator

Fixed distance(90 cm)Transmission measurement

3 mm

CZT detector

HV distribution
PC USB Oscilloscope(6000BD, Hantek Ltd.)

30 cm

Aluminumlayers
0.5 ÷ 6 mm inthickness

Voltage divider
500 MΩ + 100
kΩ4

RESULTS ANDDISCUSSION

241Am gamma

60

Energy (keV)

1200

FWHM
590 eVFWHM
410 eV

800

Escape peaks
from the Cd and Te

403020400

1000010203040

Energy (keV)

Spectrum from themanufactory (Amptek)

y = 0.04114x - 0.04876
2R =150

spectrum

1600Counts

59.54 keV

2000

26.34 keV

13.81 keVCZT DETECTOR CALIBRATION

506070241Am Calibration curve

0200400600

800

1000

120014001600

MCA Channel

The spectrometer is good energy resolution and accurate, so it
adapted well to low energy X-ray measurement.
The standard calibration spectrum was established using a
241Am standard source with three main energies 13.81 keV,
26.34 keV, and 59.54 keV.
The X-ray energy (keV) was determined basing on the5calibration spectrum.

RESULTS ANDAPPLIED VOLTAGE MEASURMENTPC USB Oscilloscope(6000BD, Hantek Ltd.)

4030Applied voltage (kV)

Voltage divider circuit:* Reducing the magnitude of voltage during
measurement against damage to oscilloscope
voltage probes due to high pulse.
* The circuit consists of two resistors inseries, one of 500 MΩ glass resistor, andanother of 100 kΩ.

DISCUSSION (CONT.)

20100-100300

600

900

1200

1500

1800

Time (ms)Figure 1. The high voltage pulse was observedby the oscilloscope with a buffer length of 32K,
and a Time/DIV of 20 ms.

The output-signal was counted to show the distributionof applied voltage.
6RESULTS AND

X-RAY SPECTRUM AND
APPLIED VOLTAGE DISTRIBUTION
60040PW0 (15.8 keV)
PW2 (17.0 keV)
PW4 (18.1 keV)
Gauss Fitting of PW0
Gauss Fitting of PW2
Gauss Fitting of PW4353025

PW0 (16 kV)
PW2 (17 kV)
PW4 (18 kV)
Gauss Fitting of PW0
Gauss Fitting of PW2
Gauss Fitting of PW4500400Frequency

Intensity

DISCUSSION (CONT.)2015300
200

10100

506810121416182022242628

Energy (keV)

Figure 2. X-ray spectra radiated from Crookes tube
acquired by CZT detector. Each X-ray spectra
corresponds to output power of PW0, PW2, and PW4.

3000510152025303540High voltage (kV)

Figure 3. The distribution of applied voltage shows theincrease in the output voltage of PW0, PW2, and PW4.

Correlation between applied voltage and X-ray energy:
There was a good correlation in the distribution behavior between the X-ray
spectrum and applied voltage.
With the output voltages of PW0, PW2, PW4:The X-ray energies were 15.8 keV, 17.0 keV, and 18.1 keV, respectively.
The average voltages were 16 kV, 17 kV, and 18 kV, respectively.

7THE CORRELATION IN THE DISTRIBUTION
OF X-RAY SPECTRUM AND APPLIED
VOLTAGEDISCUSSION (CONT.)

4545
High voltage
X-ray energy

4035353030252520

20

15

15

10

1055

X-ray energy (keV)

40High voltage (kV)RESULTS AND

00024681012

14161820Output Power

Figure 4. The relevant graphic of the applied voltage
and spectral distribution corresponding to output
voltage from PW0 to PW20.

Correlation between applied voltage
and X-ray energy:
The output voltage distributed increasingly
in 23.5 ~ 38.9 kV along with increasing output
power.
A spark appeared at PW9 then the output
voltage kept relatively consistent.
The actual average operating voltage wasabout 40 kV that shows good agreement with
the nominal discharge voltage at 40 mm ofplate-needle distance.
The spectral distribution changed in 15.8 ~20.3 keV corresponding to the applied voltagechange.
With the consistency of applied voltage, theX-ray energy also showed saturation at PW9(applied voltage reaches 40kV) with anaverage energy of about 19.5 keV.

8

ESTIMATION OF THE
TRANSMISSION
01RESULTS ANDDISCUSSION (CONT.)
2345610000
PW0PW2PW4PW6PW8PW10PW12PW14Transmission of
X-ray through Al.
1000

H*(0.07) dose (µSv/h)

30 cm• Linear attention coefficient:= 0 -µxµ: Al linear attention coefficient
I0: Initial intensity
I: Transmitted intensity through Al layers
x: Al thickness• Monitoring with Al thickness range from 0.5mm to 6 mm, step of 0.5 mm.

1001010123456Al thickness (mm)The transmission curve was fitted with the linear
expression of ln(I) = -µx + ln(I0).
The slope of the graph is the Al linear attenuation
coefficient (µ) with the best fitting coefficients rather
than 0.98.
The effective energy of X-ray was determined fromthe linear attenuation coefficient of Al using data fromthe National Institute of Standards and Technology(NIST, USA) and X-COM program2).
92. National Institute of Standards and Technology. Available on http://physics.nist.gov/xcom (Tuesday, 25 September 2018).

RESULTS AND

ALUMINUM LINEAR ATTENUATION COEFFICIENTDISCUSSION (CONT.)

25Table 1. X-ray energy estimated from Al attenuator andCZT detector. The ambient dose equivalent H*(0.07)
measured at a distance 30 cm from the Crookes tube.

Energy (keV)

2015Aluminum attenuator
CZT detector

105002468Output Power101214

Figure 5. X-ray energies with various output powers
obtaining by attenuation measurement and CZT detector.

Output
power
PW0
PW2
PW4
PW6
PW8
PW10
PW12PW14H*(0.07)µ (cm-1)(µSv/h)2195572064
40864182
50705244
5838

14.58
11.70
9.128.94
8.62
7.66
8.22
8.32

Energy (keV)
Al attenuator CZT detector
17.1
15.8
18.5
17.0
20.1
18.1
20.3
19.0
20.5
19.3
21.4
19.9
20.9
19.7
20.8
19.7

µ: Aluminum linear attenuation
coefficient

Relevance of X-ray energy between CZT detector and transmission measurement:
The effective energy from the transmission measurement was relatively good
agreement with the spectra from CZT detector.
The average percent difference between the two measurements was 7.5%, andthe average energy was about 19.5 keV for CZT detector and about 20 keV for
attenuation measurement (Table 1).
Added filtration caused hardening the X-ray beam because it absorbed the lower
energy photons. As a result, it produced a shift in the effective energy of the X10ray beam.

SUMMARY
We estimated low energy X-ray from the Crookes tube with variable
voltages that considered hardly to perform. It was about 19.5 keV withthe discharge distance of 40 mm.
We estimated the correlation in distribution between applied voltage
and X-ray energy. The X-ray energy was shifted to higher region in thespectrum when increasing the applied voltage.
We used the attenuation measurement as an effective approach toyield information of low photon energy as well as reflected the change ofenergy along with the change of output power. It should be considered as
an alternative approach of CZT detector in the estimation of low X-ray
energy in the teaching of science at junior-high school.

NEXT PLAN
Estimating the conductance of Crookes tubes.
Estimating of an effective dose in the relevance to other electricalcomponents and X-ray energy.
Suppressing an applied voltage to a certain level and evaluate effective
dose to assure extremely safe for education.
1112