Nikokukan 2017/6/28 11:40-

Development of time-of-flight detector
for mass measurements with R3

University of Tsukuba
Shinji Suzuki••••ContentsRequirements for the time-of-flight detector
Working principle
Design of the present detector
Performance test with the heavy ion beam

Rare-RI Ring (R3)
Mass-measurement tool for short-lived nuclei (half life <1ms)
F0

Secondary beam

TOF(F3-S0) in transport <1μs→ β(v/c)

Big RIPS

F3

Relative mass-to-charge ratio
m1q1=m0q0Measure

T1
T0

2
11
1

T1T02
1T0, m0 q0: revolution time, mass, charge of reference nucleus
T1, m1 q1: revolution time, mass, charge of target nucleus

Prog. Theor. Exp. Phys., 2012 (2012) 03C009.

Time-of-flight(TOF) detector to measure
the β and the revolution time (T)stop signal

start signal

TOF in the ring ~1ms
→ Revolution time T2S0
Rare RI ring

Requirements for TOF detector
1.

Time resolution σ < 100 ps for Δ(m/q)/(m/q) ~ 1×10-6
TOF for injection line <1μs → Δβ/β ~ 1×10-42.

Detection efficiency should be 100%3.

Detector should be as thin as possible
Minimize change of velocity by energy loss

4.

Large acceptance
Expected beam size at focal plane is <Φ30mm
We are developing the TOF detector witch uses
secondary electrons emitted from thin foil

Secondary electron emission
dE/dx dependence ofSE yield per impinging ion
Production mechanism of electrons

Carbon target

Phys. Rev. A 51(1995)3066

Phys. Rev. A 41(1990)2521
NSE

dE

dx
dE/dx : stopping power [keV/(μg/cm2)]
Λ : constant of proportionality [(μg/cm2)/keV]TOF detector with secondary electrons
d=2 mEqB 2

Nucl. Inst. Meth. 148 (1978) 503

Performance of the former detector
ESR / CSReCarbon
Foil(10-19 μg/cm2)
Magnetic field [Gauss]~84
Electric field [V/mm]
160 - 180
Time resolution σ [ps]~30
Detection efficiency [%]70 - 83
Nucl. Inst. Meth. A 821 160 (2016)
Nucl. Inst. Meth. A 756(2014) 1
Nucl. Inst. Meth. A 624(2010) 109

Nucl. Inst. Meth. A 821 160 (2016)

Magnetic field : ~172 Gauss increase!
Electric field : ~712 V/mm increase!
Foil (1) : Polymer (30 μg/cm2) coatedon carbon (30 μg/cm2)
Foil (2) : Aluminum coated (~100 nm)
on 1μm mylar
Effective area of foil and MCP : ~Φ40 mm

VerticalTOF detector
FoilMCPB

ION
Horizontalweak B,E (slow collection)

B

400
B
Electrode

Foil

TOF

B

2 m

34
FoilqB80
Iron return yoke
Permanent magnet

strong B,E (rapid collection)→ detect more electrons

e-Ion

E
MCP

150

Experimental setup
Nse ~ 37 for carbon
Nse ~ 60 for aluminized Mylar

84Kr(36+) of 200 MeV/nucleon provided by HIMAC(Heavy Ion Medical Accelerator in Chiba) in NIRSTrigger Pla

TOF detector
chamberNaI detector

84Kr

200MeV/u
PPAC

PPAC
TOF
camac
MCP

CFD

TDC
QDC

Timing and efficiency performance
Aluminized Mylar

CarbonSigma = 33 ps
Det. Eff. = 100.0(0.8)%

Sigma = 43 ps
Det. Eff. = 99.2(1.2)%

Position dependence of efficiency
Aluminized Mylar

Almost 100% in the whole area

MCP

VerticalHorizontal

Foil

CarbonEfficiency at upper area was cheap→Electric field was not optimum…

Position dependence of TOF
MCP

VerticalAluminized Mylar

Horizontal

FoilCarbon

TOF=0(x,y=0)
TOF=0(x,y=0)∆TOF < 100 ps (-20 < y < 20)∆TOF ~ 200 ps (-20 < y < 20)Summary• We are developing the TOF detector for mass measurementwith R3. The TOF detector uses secondary electrons emitted
from a thin foil.

• With the strong magnetic field, sufficient detection efficiency(~100%) was obtained by both of aluminized Mylar and carbon.

• Timing resolution was achieved σ <100 ps.
• No serious position dependence of measured TOF.
• We will optimize the electric field in the case of carbon.

Corroborators
University of Tsukuba
A. Ozawa, T. Moriguchi,
M. Amano, D. Kamioka,
Y. Ichikawa,Y. Tajiri,K. Hiraishi, T. Matsumoto

Saitama University
T. Yamaguchi, S. Ohmika,
Z. Ge, N. Tadano,
K. Wakayama

RIKEN Nishina Center
D. Nagae,Y. Abe, S. Naimi

National Institute ofRadiological Sciences (NIRS)
A. Kitagawa, S. Sato