Do Duy KHIEM, Hirokazu ANDO, Hiroto MATSUURA, Masafumi AKIYOSHI

Graduate School of Engineering, Osaka Prefecture University
1-1 Gakuen-cho, Naka-ku, Sakai-shi, Osaka 599-8531, JapanBACKGROUND

X-RAY SPECTROMETER• In Japan, a Crookes tube, as a discharge tube, has been used in junior-highscience classes, and the primary purpose is to teach the characteristics ofelectrons and current.
• The X-rays emitted by the Crookes tube may cause exposure to teachers andparticipating students.
• A radiation safety guideline has not been evaluated sufficiently yet in Japan.

HVShielding material
Several tens of kV

SCOPES OF THE RESEARCH

HV• Investigating the characteristics and properties of X-rays emitted by aCrookes tube used in educational sites.
• Estimating the transmittance of transparent shielding materials to assureradiation safety and demonstration observation.
• Submitting the results as the recommendation and guideline for radiation
protection at junior-high school science class.

Experimental settings:
o The applied voltage was regulated by change of output power, anddischarge distance was set at 30 mm.
o The ambient dose equivalent H*(0.07) measured for 3 min at a distance
50 cm from the Crookes tube, and it was converted to a dose rate.
Peak nergy of X-ray (keV)

15105051015202530

X-ray energy (keV)

Figure 1. X-ray energy emitted by the Crookes
tube acquired by a CZT detector. The energy
peak shifted to a higher region of thespectrum as the output power increased.
H*(0.07) dose rate (mSv/h)

1.4
1.2
1.0
0.8

Initial Dose
Transmitted dose by Acrylic
Transmitted dose by Lead acrylica)

Aluminum (1 mm)

60o For each discharge distance, theoutput power was set at theposition which the spark justoccurred.

1510

 The percentage of transmission
was calculated as a ratio of initial
dose to transmitted dose (Fig. 4).

5

Transmitted dose by Acrylic
ExperimentCalculation

Acrylic (9.3 mm)

 The transmitted dose of acrylic ishigher than aluminum. It caused ahigher transmission for acrylic.

b)

0.6

 Lead acrylic exhibits a goodattenuation which the percentageof transmission is less than 2%.

0.4

Figure 4. Transmission of X-rays withvarious discharge distances applied on theCrookes tube attenuated by shielding
materials.

0.20.0Acrylic
Aluminum
Lead acrylic

0.40.224681012Output PowerFigure 3. The transmitted dose of acrylic
determined by experiment and calculation.

14

 The
acrylic
shieldingcaused024
681012
hardening of X-rays owing to absorbing
Output Powerphotons with lower energy. As a result, it
Figure 2. The relevant graphic of theproduced a difference in the energy of Xtransmitted dose of acrylic and lead acrylic vs.
rays, 7.5% (Fig. 3a).
output power.
 The calculation in Fig. 3b was
 The exposure increased with andetermined by the equation of I = I0 𝑒 −µ𝑥
increase in the output power, and it
where the I0 was the initial dose in Fig.
is stable from PW8 when a spark
2. The linear attenuation coefficient µ ofoccurs. It means that the dose will
acrylic for each energy was interpolatedchange if the spark does not occur
using data from the National Institute of(Fig. 2.).
Standards and Technology (NIST, USA).
0.0

 The energy for the calculation was the peak energy of unshielded X-rays
shown in Fig. 3a. The energy of X-rays has a broad distribution shown inFig. 1, but the calculated results matched to the experiment very well.
Output Peak energy Initial dose* Transmitted dose* (µSv)
Table 1. X-ray energy
Lead acrylic
Acrylic
Power of X-ray (keV)(µSv)
and its attenuation
016.4
3.31
0.04
1.10
by materials with the2
17.5
10.1
0.11
3.65
change of the output
418.1
30.4
0.34
13.8
power.
6
18.0
43.2
0.45
19.0
8
18.6
70.6
1.09
36.5
* The dose measured for 3 min
1018.6
69.2
0.89
34.9
at distance 50 cm from theCrookes tube.
1218.468.7
0.9237.3a)

50403020
1001.4
1.2

Initial doseTransmitted dose by Acrylic
Transmitted dose by AluminumTransmitted dose by Lead acrylicb)

1.0
0.8
0.6
0.4
0.2
0.0
15

20

0.60

Lead acrylic (8 mm)

CZT detectoro The applied voltage was regulated
by change of output power and waslimited by the discharge distance.

200.890 cm

Experimental settings:

0H*(0.07) dose rate (mSv/h)Intensity

2050 cmCORRELATION BETWEEN DISCHARGE DISTANCE AND EXPOSURE

2525

Estimation of transmission

 Shielding materials:
Crookes tube:o Aluminum.
o By applying a voltage of several tens of kV
o Lead acrylic: 0.3 mm lead equivalence,
between the cathode and the anode, theKyowaglas-XA H-8, KURARAY Co., LTD.
cations in the evacuated tube areo Acrylic: Amersham Pharmicia Biotech LTD.
accelerated and impact the cathode, whichknock out secondary electrons.
 The transmission of X-rays was estimated byo These electrons emitted by the cold cathode the ambient dose equivalent H*(0.07) using an
are accelerated to collide with a glass tube ionization chamber (ICS-1323, Hitachi Ltd.,Japan).
to create a bremsstrahlung X-ray.

CORRELATION BETWEEN OUTPUT POWER AND EXPOSURE

Acrylic Shielding
Unshielding

DPPMCA Software(Amptek Inc., USA)

Collimator

X-ray

Transmission (%)

X-ray

30

Induction coil:* High voltage power supply,
spark gap of 10 – 100 mm.
* Nominal dielectric breakdown
voltageintheair
isapproximately 1 kV at 1 mm.
* The desired output voltage canbe obtained by regulating thedistance of the dischargeelectrodes or the output power.

Shielding material:• To
attenuate
radiation intensity
significantly.
• Transparent
shieldingtoobserve
thebehaviorof
electron beam in a
Crookes tube.

Pocket Multichannel(MCA8000D, AmptekInc., USA)Power supply and Amplifier(PX2T, Amptek Inc., USA)CZT Detector (XR-100TCZT, Amptek Inc., USA)

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

H*(0.07) dose rate (mSv/h) Energy of approximately 20 keV.
 Hp(10) was up to 143 mSv/h at 5cm1).

PW0 (14.8 keV)
PW2 (15.5 keV)PW4 (16.5 keV)
Gauss Fitting

Lisbon, May 27th – 31st, 2019

MATERIALS AND METHODSINTRODUCTION35

The 3rd International Conference on Dosimetry
and Its Applications (ICDA-3)

2530

35404550

Discharge distance (mm)Table 2. Transmittance of shielding materials vs. discharge distance.
Discharge
InitialTransmitted dose* (µSv)
distance dose* (µSv) Lead
Acrylic Aluminum
acrylic(mm)
20
0.81
0.01
0.39
0.20
25
12.5
0.12
5.84
3.16
30
44.7
0.73
24.6
15.7
40
53.4
0.82
29.4
17.1
50
71.4
1.18
40.9
26.3

Transmission (%)
LeadAcrylic Aluminum
acrylic
1.23
48.2
24.7
0.96
46.7
25.3
1.63
55.0
35.1
1.54
55.1
32.0
1.65
57.3
36.8

SUMMARY The Crookes tube emitted X-rays with soft energy of approximately 19 keV.
 The exposure and X-ray energy changed with electrical settings such as output
power, and discharge distance.
 The lead acrylic attenuated significantly the exposure caused by X-rays radiatedfrom the Crookes tube with the transmission approximately 2%.
 According to ICRP 36, the dose limit recommended 0.05 mSv per each teaching
exercise. The lead acrylic is well-adapted to a radiation shielding for Crookes
tube, and its transparence assures to observe the behavior of electron beamduring demonstrations.
References:

1) Ohmori Giroh, X-ray exposure in the teaching of science at junior and senior high schools. NIRS-M—105,
Japan, 107-112 (1995) (in Japanese).
2) M. Akiyoshi, et al., Development of evaluation techniques for low energy X-rays from a Crookes tube, Radiation
chemistry, 106 (2018) 31-38 (in Japanese).
3) Do Duy KHIEM, et al., Investigation of Characteristics of Low-energy X-ray Radiated from the Crookes Tube
Used in Radiological Education, Radiation Safety Management, submitted.