Principal Research Results

Developments of Laser-driven Ion Sources using T-cubed Laser

BackgroundOur laboratory raised laser and optical technology in enrichment of uranium, and now is developing optical measurement
technologies such as high-precision laser radar and researching laser-driven energetic particle sources. In particular, it might be possible to apply a special laser called T-cubed laser (T3:Table Top Tera Watt Laser) to material evaluation and diagnoses of facilities andequipments. In addition, since ion sources generated by this laser can produce positron emission isomer, application to positron emission tomography (PET), which is promising for early detection of cancer, is also expected. In order to turn this new type of ion source
to practical use, we need grasp the conditions for more efficient acceleration.

Objectives
To seize the characteristic of laser-driven ion sources, to find the most suitable condition for ion acceleration, and further
clarify the possibility of new ion sources to apply to diagnoses of plants and to the medical field.

Principal Results
1. Production of protons with high energy level for fluorine 18 generation
Using our T-cubed laser and a very thin tape target, which is made of a low density compound of hydrogen and carbon, weobtained hydrogen ion (proton) with maximum energy of 3 MeV (Fig.2). This value is equivalent to three million volts in acceleration
voltage and is beyond the threshold of generation of fluorine 18(18F), which is most frequently used as a positron emission isomer inPET. Although, usually protons with energy more than 10 MeV are used for the isomer generation, we have prospects for increasing
proton energy by improvement of laser focusing in the near future.
2. Clarification of proton acceleration mechanism
Dependence of proton generation on laser pulse duration was investigated and the result was that the difference was small
when pulse duration was longer than 1 ps. Maximum proton energy was found to be estimated by a isothermal plasma expanding
model. From these results, we derived the feasibility of effective ion acceleration by Yb-YAG Laser, which is expected to be more efficient and more compact, and showed the direction of future developments in this field.

Future Developments
From results as described above, we obtained prospects for generation of positron emission isomer in PET using T-cubedlaser. As the next step, other parameters such as laser focus diameter will be investigated for the purpose of developing more efficient
ion source. We will also try to generate positrons through X-ray conversion because positron analysis is a powerful tool for estimationof material damage.
Main Researcher: Koshichi Nemoto, Ph. D.,
Senior Research Scientist, Applied High Energy Physics Sector, Electric Power Engineering Research Laboratory
ReferenceT. Nayuki, et al., 2003, “Thin tape target driver for laser ion accelerator”, Rev. Sci. Instrum. vol.74, 3293.

12210. Advanced Basic Technologies - Laser and plasma scienceFig.1 T-cubed Laser
In spite of small energy of 1J, ultra short pulse can lead
12ultra high peak power of 20 TW (1 TW=10 W). Using

this laser, we are studying high-energy particle
generation and developing new diagnoses of plants andequipments.

3 MeV
Fig.2 Dependence of proton energy on targetmaximum proton energy (keV)-15(1fs=1×10 seconds)

hickness and densityAs a target, thinner and lower density material is better forgeneration of higher energy protons. Thus far, ourlaboratory obtained maximum energy of 3 MeV, which isequivalent to three million volts in acceleration voltage.

Polyethylene
terephthalatetarget thickness×density (μm×g/cm3 )3 MeV

http://www.nndc.bnl.gov/exfor

1000
D(d,n)3He
12
C(d,n)13N
11
B(p,n)11C
10
B(d,n)11C
14
N(p,α)11C
16
O(p,α)13N
14
N(d,n)15O
15N(p,n)15O
20
Ne(d,α)18F
18O(p,n)18F

It is possible of our protons with energy of 3
MeV to generate fluorine 18, which is mostfrequently used in medical diagnosis.
1818O(p,n) F means production of a fluorine 18 and aneutron by a interaction between a energetic
proton and a oxygen 18 in a target.

Cross section (mb)Fig.3 Cross Section for Positron
Emission Isomer Generation
100

10
18O(p,n)18F

10.1

1Ion Energy (MeV)

12310