Title Heavy Particle Identification with a T.O.F. : Method ...and Norihiko IzuTsu* Received October 5, 1970 Particle identification system with a T. O. F. method is developed to accomodate

Title Heavy Particle Identification with a T.O.F. : Method in NuclearReactions

Author(s) Yasue, Masaharu; Fujiwara, Noboru; Ohsawa, Takao; Izutsu,Norihiko

Citation Bulletin of the Institute for Chemical Research, KyotoUniversity (1971), 48(6): 223-235

Issue Date 1971-03-24

URL http://hdl.handle.net/2433/76351

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

Bull. Inst. Chem. Res., Kyoto Univ., Vol. 48, No. 6, 1970

Heavy Particle Identification with a T. O. F.

Method in Nuclear Reactions

Masaharu YASUE, Noboru FUJIWARA, Takao OHSA\NA and Norihiko IzuTsu*

Received October 5, 1970

Particle identification system with a T. O. F. method is developed to accomodate the high repetition rate of the cyclotron beam of 13 MHz. Starting signals of the T. O. F. system are obtained

from a tantalum plate in the course of a bunched beam from the Kyoto University cyclotron. Stop and energy signals are obtained from a solid state detector. An experiment on the p-d scattering at Ep 7.3 MeV shows that protons and deuterons are identified clearly with each other. The time

resolution was estimated to be of 2.6 ns but finally was improved to be of 1.5 ns by adding a diode limiter circuit to the T. O. F. system.

I. INTRODUCTION

It has been proposed by many authers" that a 'Li and a 'Li nuclei have a-1-d and a t structures respectively. If so, the sLi and the 'Li neuclei are thought to be a kind of cluster carriers such as d, t, and a. Moreover, if one assumes the cluster

pick-up reaction mechanism, the heavy particle producing reactions such as (d, 'Li), (a, 'Li) and so on are useful tools to investigate the cluster structure of the target nuclei.

In our laboratory, alpha cluster structure of light nuclei has been investigated by using (a, 2a) and (p, pa) reactions.2> As a natural development of research, we are interested in the heavy particle production reactions.

In earlier experiments, protons, deuterons and alpha particles were the main objects of our detection system, and a dE-E counter telescope system worked well to identify these particles. However, if heavy particles should be detected, this system is no longer useful. The reasons are as follows.

1) Because the charge states of heavy particle have freedom of wide range, the

pulses from the LIE counter is multi-valued even if the energy is fixed. Then one could not identify easily the heavy particle.

2) Because the energy loss of a heavy particle is very large, a dE counter stops completely the heavy particles produced in the low energy reaction such as studied in our laboratory. Then we can not afford a relevant 4E-E telescope system.

These difficulties could be removed if one measures directly the velocity and energy of the particle. A T. O. F. method coupled with a total energy detection system, not a dE-E telescope system, is therefore suitable for the heavy particle identifi-cation. At present, the Kyoto University Cyclotron produces a bunched beam of 13 MHz

* ffI1Eiu, JJiJ J ,jef: Laboratory of Nuclear Reaction, Institute for Chemical Research, Kyoto University.

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M. YASUE, N. FUJIWARA, T. OHSAWA and N. IzUTSu

repetition, then one should modify the T. 0. F. method to accomodate such high repetition. Heavy particle identification system with the T. 0. F. method in conjunction with a total energy detection, has been proposed by several anthers') and successfully used in the pulsed beam experiments," but there are few studies to use this system in the ordinary cyclotron experiments. In this report, a heavy particle identification system suitable for the high repetition cyclotron experiments is described.

IL PRINCIPLE OF IDENTIFICATION OF HEAVY PARTICLES

Flight time t of a particle of energy E over a distance d is given by the next formula in the non-relativistie limit.

i = 0.723d(m/E)1/2 ,(1)

where t, d and E are in units of nsec, cm, and MeV respectively and m is the mass number of the particle. The product Et', for a given d, depends on mass of the product

particle only and therefore simultaneous measurement of E and t identifies the mass of the particle. If various reaction products of the same mass are produced, for instance 6He, 'Li etc., Qvalues are in most cases different and the kinematic condition can usually determine the particle; the pulses of particles can be selected when a two dimensional representation is made between E and t or E versus Et' with the aid of a multiplying circuit. From eq. (1)

dm/m = 4E1E+2 dt; t .(2)

4E1E is negligible for semiconductor detector, so that substituting t by Eq. (1), Eq. (2) gives,

PICK-UP---PRE-MffPHASE-INV.— DELAY —ATTEND_ AMP. — DISC--AMP—DIV(AT7ENU) DELAYSTART

AVV0.Sv lOns

0.2vP 1Dns

----(ATTEND)------ COINGATE

---------- 1.Ov 13Dns

STOP S. S. D — PRE-AMP— DIV----DELAY------ ATTENU— AMP. — DISC —NIPDIV—DIV-------- DELAY

\/„-UU 0.2vDEns

6D»=

1 PS

SCALAR'-----SCALAR

STRETCHDR------------------------------------------------------------------------

V1-Ta. A. IS64 x 64 1

Fig. I. Block diagram of the circuit system

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Heavy Particle Identification with a T. O. F. Method in Nuclear Reactions

dm/in = 2•(4t/0.723d)(E/m)1"2.(3)

Eq. (3) indicates that the resolution dm/m becomes better with the lower energy and heavier particles. Therefore T. 0. F. method is suitable to identify the heavy

particle of low energy.

III. ELECTRONIC CIRCUITS

The block diagram of electronic system is shown in Fig. 1. The circuit parameters were adjusted to accomodate the RF frequency of 13 MHz. The time walk at the

Pre-Amp (+type) --------------- 0±/2T

• -lzv oao5l~"330!;:;33.0K,3Z:.~020KK 3.3 k3.

6.06"'T. T0.,-.7 Tio Oot Output

Input'6 r , .„~.T3Tq. TrT6------- Ts-re.e~

r o.os !kYrtklk-------- ..-----j„-Fo.o„ —NW.

K3e i3033ou3

43µ7

1qqq---------(4,~r 1o,oS1.p.s-!oE3.'k 10T0.3klo-I-I 3,3kT

• tlzv

T, T TµTsT Ts. Tio; 2SA'O

Ti T6 T7 ; 2 S C .21

Fig. 2. Circuit diagram of the pre-amplifier

Delay L inche lay Line

. !I,.,,TD.ainrxt O.t51to11' 5100.05 51 51(1TD.0.05 Lo output

680&1µtlcdLa680 ca1jtH1~ .H 0.0710K-820

4.75T-:20330 47K

fl1K1 K0.1T,OK330 vwr 2Kp r

-6'J 300°0.1220-1-9V -5V300—0730059V.

7Ytl -12V777-12V I. 0. (681;A, 0.00) All transistors are 2SC288A

Fig. 3. Circuit diagram of the discriminator

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M. YASUE, N. FUJIWARA, T. OHSAWA and N. IZUTSu

discriminator due to the input pulse height variation was lessened by using fast rise time

pre-amplifier.

The pre-amplifier was built after the design of Papadoplos,5) of which the circuitry

is shown in Fig. 2. It has the gain of 200 and the rise-fall time of 3 ns and was connected

to the positive pulses from a pick up probe.

10

C

T 0

cu i v7

o5

0 o •

N.

000.51.0

Input Pulse Height (V)

Fig. 4. Time delay of output pulse of the discriminator as a function of the input pulse height.

0,01 -1zv ---if-o out 10K3.3K0021 3.3K10K

• -6 V

1K 55/`4-470

0.07001 • 1K

0.0050.0051K0.0050005 Start 62T3taOµH !I TDI!!..,r,,470s1

6

100.02002 10 60KT0021,10• 50 • TT68K 22K 2K0, , 15 -12Vd

1.551.5K

~~,~----------------------------------------------------------------------------------0+24

-

O Gale Input 1,— -r, ; 25A495 D,- D, ; SD16 T D,^-TD3 ; ( 6mA, 0.5V 1

Fig. 5. Circuit diagram of the time to pulse height converter (T. P. C.)

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The pre-amplifier of the negative pulses from the solid state detector has the gain of 100 and of 2 ns rise time, and the circuitry is shown in Fig. 3 of ref. (7).

The circuit diagram of a discriminator is shown in Fig. 3, where two sets of discrim-inators are connected in series in order to prevent the high input pulses to go through. The output pulse width is determined by the length of the delay line. The dead time is of 50 ns duration and less than the start pulse period of 77 ns. The characteristics

of the discriminator is shown in Fig. 4. The time to pulse height converter shown in Fig. 5 is the same type as that was

designed by Ophir.6' The time constant of LC circuit determines the linear range of T. P. C.. The period of the start pulse is of 77 ns. Therefore the values of L and C are set so that the linear range is of 80 ns. Pulse heights and widths of the start, stop and gate pulses are, 0.5 volt and 10 ns, 0.5 volut and 50 ns and 1.0 volt and

Linearity of T, P.C.

Channel Number

400 —•—•— Input Pulse 60c

350

300

250 Channel

Number

200100

15080

60 100 - Start 13Mc

Stop 0.1 Mc40

50• 20

00 0 10 20 30 40 50 60 70 80 90 Delay Time( ns )

—•—.—; measured with 60 Hz pulses --°--°--; measured with 13 MHz start and 0 .1 MHz stop pulses

Fig. 6. Linearity of the T. P. C.

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M. YASUE, N. FUJIWARA, T. OHSAWA and N. IzuTsu

Stability of T. P. C.

C 100

60ns

z

3

0 r; 50 30 ns

10 ns

0 0 2 4 6 8 10 12

Hours

Fig. 7. Stability of the T. P. C.. The figures 10 ns, 30 ns and 60 ns denote the delay time of the stop pulse to the start pulse. The

time scale is 0.9 ns/ch.

100 ns respectively. The linearity of T. P. C. is shown in Fig. 6. Analyzing the

output pulses from T. P. C. by a 1000 channel P. H. A., the resolution was estimated to

be of 0.2 ns. The stability is shown in Fig. 7 and it is estimated to be 1%.

By varying the pulse heights fed to the discriminator from 0.1 volt to 1.0 volt and

observing the shift of the pulse heights from the T. P. C., the time walk is estimated to be of 1.8 ns.

The coincidence circuit system was tested to have a coincidence efficiency of 100%

in the case of 13 MHz start and 0.1 MHz stop pulses.

Circuit diagrams of linear amplifier, coincidence and stretcher are shown in Figs. 5, 18, and 23 of ref. 7 respectively.

IV. EXPERIMENTAL RESULTS

7.3 MeV proton beam from the 105 cm ordinary cyclotron of Kyoto University

bombarded a self supporting foil of deuterated polyethylene (CD2) film of about 1 mg/

cm' thickness, which was set at the center of 45 cm diameter scattering chamber.

ORTEC 500A-thick surface barrier SSD was placed at a distance 56 cm apart from

the target and at the angle of 27.5° with respect to the beam axis. A slit of 5 mm diameter was set in front of the detector and the solid angle subtended by the detector

was 2.6 x 10-4 sr. A beam pick-up probe shown in Fig. 8 was set in the beam course

at a distance of 15 cm behind the target.

Output signals from the pre-amplifier of the beam pick-up probe is shown in

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Heavy Particle Identification with a T. 0. F. Method in Nuclear Reactions

CE.) 0 4cm

5cm

Mica lex

6

1 cm T

Tanta( Plate

Pick-up probe

Fig. 8. Schematic drawing of the beam pick-up probe.The beam is collected by a tantalum plate of 1 mm thick. The area of the plate

is 1 cm x 1 cm. The current signal is transmitted to the BNC con- nector through the copper wire. Copper box with a 1 cm diameter

hole shields the R. F. signals from the oscillator. The micalex in- sulates the probe from the grounded box.

Photos 1 and 2. The intensity of H2' ion beam is about 50 nA. The pulse height is of 150 mV and the width at half maximum is less than 10 ns (about 6 ns). High Energy group of Kyoto University') showed in their T. 0. F. experiment using the Kyoto University Cyclotron that the one bunch width of Hz' ion beam is of about 1 ns, therefore, the width of the one bunch beam could be less than the value obtained in this experiment. The height of RF signal is 20 mV and the S/N ratio (the ratio of beam signal to the RF signal) is found to be 7. Photo 2 shows beam modulations. Photo 3 indicates the proper operation of the discriminator. From the cable curve

(Fig. 9) the coincidence width is estimated to be of 65 ns (equals to the sum of the width

1, l

Photo. 1. H2 ion beam signal at the output of the pre-amplifier. Maximum height is 160 mV and the repetition period is 77 ns.

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M. YASUE, N. FUJIWARA, T. OHSAWA and N. IZUTSU

•

^ j1I(III 11 j 6.. .YiMS1~...:~.lf~1^.I : ..

Y

i^i3

Photo. 2. Modulation of H2ion beam intensity. 120 c/sec modulation is due to the ripple of arc voltage of the ion source and the 360 c/sec

modulation is due to the ripple of do power supply of RF accelerating voltage.

Photo. 3. Wave form of the start pulse at the input (upper side) and the output (lower side) of the discriminator.

of start and stop pulses, 10 ns and 50 ns respectively). The beam pick up efficiency,

defined by the ratio of coincident counts to stop signal counts, is estimated to be 95%.

As the experiment was carried out at a fixed angle, energy and time scales were obtained in terms of a variable attenuator and a variable delay line. These were 105 KeVich.

and 1.3 ns/ch. respectively.

Cable Curve

Set Point of S.SD. Delay Line

1.0 o ---O__ _~_a ^~ a----------- Ja----------------

0.51o ° I I 0•LIIIh -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100

S.S.D. Delay E——i Pick-up Delay (ns )

Fig. 9. The ratio of the coincidence counts to the stop pulse counts as a function of the relative delay time of the start and stop pulses.

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Energy Spectrum

P+ CDz

2000 - EP = 7.3 Mev a Olab=27.5 C(

P,P)C 1000 - d(RP)d ~\ I I ; t

ot£It C _

.. _ C(PC )A} (n f

100 - C(P,P)C` I P(PP)P 50-f

{

10 -------------------------------------------------- 0 10 20 30 40 50 60

Channel Number (E )

Fig. 10. Energy spectrum of products from the reaction p+CD2 Ep=7.3 MeV, 01ab=27.5°.

E - T Representation of Particles

10 -in the Reaction P +CD2 EP=7.3Mev Flight Interval 56.0cm

C (p, P) c Olab =27.5o od(pP)d

-P(P.P)Pd (P,d )P 215 d(0,P)Pn •

c (p, p') c;s, c(p ,c)p

0 0 5 10 15 20 25 30 35

Flight Time (ns ) Fig. 11. Calculated values of energy and flight time for the reaction of p+CD2.

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M YASOL, N FUJIWARA, T OHS 1wA and N IzuTsu

•

•

Photo 4 Isometric view of the spectrum obtained using the reaction

p+CD2 X-axis shows the flight time and the Y-axis shows the

energy of product particles

iz?s•

•

£•

S•. ::TiB:.

Photo 5 Display of Photo 4 in the 64 x 64 channel mode Each

peak corresponds to the figure in Fig11

The energy spectrum is plotted in a logarithmic scale in Fig 10 Photo 4 shows

the isometric representation of coincidences between energy and flight time pulses and

Photo 5 is its two dimensional spectrum in 64 X 64 channel mode

Each peak in Photo 5 can be identified by the kinematics shown in Fig. 11 The

peak of recoiled carbon is late by one period z e 77 ns

In order to estimate the time resolution, time spectra are plotted in Fig 12, re-

presenting the velocity distribution of respective energy particles The full width at half maximum of each peak is 2 channels or 2 6 ns In the case of carbon detection,

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Heavy ParticIe Identification with a T. O. F. Method in Nuclear Reactions

Time Spectra Time Scale

500 fwhm=26ns1.3 n~h.

C (p,p) C 200E=7.1 Mev

5000 10 2030 40 50 60 fwhm= 2.6 ns

d(p,p)d 200 E=6.1Mev

1000 10 2030 40 50 60 fwhm=2.6ns d(p,d)p

40E=4 .7Mev

0

50 0 10 20 30 40 50 60

p(p p) p r fwhm=2.6ns pI C(p,C)P

20E=5.7Mev.i I E=1.7Mev

•

0 10 20 30 40 50 60 Channel Number ( Time )

Fig. 12. Time spectra at the peaks in the energy spectrum of Fig. 10.

the width is 3.9 ns due to the overlap of the proton background and the carbon peak. Hence the time resolution is estimated to be 2.6 ns.

V. DISCUSSIONS

Following factors can be the cause of errors in the time resolution.

1. One bunch width of pulsed beam; ziti 1 ns 2. Time resolution of TPC;4t2 ^ 0.2 ns

3. Timing fluctuation of output pulses from the surface barrier S. S. D.; 4t3 l ns

4. Time walk in the discriminator due to the pulse height variation of the start signal;dt4

(It is reported that the surface barrier detectors have 1 ns or better timing resolution inherently9)).

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M. YASUE, N. FUJIWARA, T. OASAWA and N. IZUTSU

+12 V

430 -1-6V D'680

T147p it ps I47T3

Input 1.5K1-0 Output

0.1 4770 0.1 3,3 K

—12 V U1 ti D3; SU16 'I,1; 2SC288A I'3, 13; 2SA488A

Fig. 13. Circuit diagram of the limiter.

The experimental time resolution is 2.6 ns and then

(dt12+422-I-dt32+dt42)1/2 2.6 ns .

From this relation, the time walk due to the pulse height variation of the start signal is estimated to be 2.0 ns.

In order to improve the time resolution, time walks should be lessened in the first place to the value of about 1 ns. Next two methods were carried out and proved

to be useful. First, the use of a limiter which delays the high input pulses by the effect of saturation. By inserting the diode type limiter circuit, shown in Fig. 13, in front of

the start timing discriminator, time walk was reduced to 1 ns for the input pulse ranging from 0.1 to 0.5 volt. Second, the S/N ratio of the beam signal to the background should be improved. S/N ratio was improved to the value of 10 by replacing the beam pick up probe with a slit type one and setting it at the objective of the beam analyzing magnet. The beam intensity at that point is about ten times stronger than at the former point. In conclusion, the time resolution was improved to 1.5 ns which was ascertained with an experiment on p-d scattering.

From the Eq. 3, lower than 20 MeV Li ions can be distinguished from alpha par-ticles, deuterons and protons with the E-T two dimensional analysis if the flight path is of 20 cm length and if the time resolution is equal to or less than 1.5 ns. To shorten the flight path to the length of 20 cm, has the following two merits.

1) The angular distribution spectrum can be easily obtained with a detector set within the 45 cm diameter scattering chamber.

2) The short path length gives a larger solid angle. This large solid angle enables the study of the rare event reactions such as (a, 'Li) reactions.

ACKNOWLEDGMENTS

The authers would like to express their appreciations to Profs T. Yanabu, Y.

Uemura and S. Yamashita for valuable comments and suggestions. They also wish

to thank the members of Keage Laboratory of Nuclear Science for operating the

cyclotron.

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REFERENCES

( 1) Y. C. Tang et al.: Phys. Rev., 123, 548 (1961). K. Wildermuth et al.: Nucl. Phys., 32 504 (1962).

E. W. Schmid et al.: Phys. Lett., 7, 263 (1963). Y. A. Kudeyarov et al.: Soy. J. Nucl. Phys., 9, 283 (1969).

D. R. Thompson: Phys. Rev., 179, 971 (1969).

(2 ) T. Yanabu et al.: J. Phys. Soc. Japan, 20, 1303 (1965). T. Yanabu et al.: J. Phys. Soc. Japan, 24, 667 (1968). S. Yamashita et al.: J. Phys. Soc. Japan, 26, 1078 (1969).

( 3 ) E. Blignaut et al.: Nuclear Instrum., 51, 102 (1967). H. Briickmann et al.: Nuclear Instrum., 67, 29 (1969).

(4) D. Maydon: Nuclear Instrum., 34, 229 (1965). L. T. Denes et al.: Phys. Rev., 148, 1097 (1966).

(5) I.. Papadopolos: Nuclear Instrum., 41, 241 (1966). (6) D. Ophire: Nuclear Instrum., 28, 237 (1964). (7) K. Fukunaga et al.: Bull. Inst. Chem. Res. Kyoto Univ., 47, 83 (1969). (8) K. Miyake et al.: Private communication. (9) C. W. Williams et al.: Nuclear Instrum., 25, 370 (1964).

H. WahI: Nuclear Instrum., 25, 247 (1964).

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Documents

Title Heavy Particle Identification with a T.O.F. : Method ...and Norihiko IzuTsu* Received October 5, 1970 Particle identification system with a T. O. F. method is developed to accomodate