Statistical model of PIPS detector operating in a real-time mode.Yu.S.TsyganovYu.S.Tsyganov

FLNR, JINRFLNR, JINR Content

1) Introduction Synthesis of SHE at the Dubna

Gas-filled Recoil, PIPS detector, EVR-α(n)-SF correlations…technical systems..etc.

2) Active correlations technique – radical suppression of beam associated backgrounds

a) Idea; b) Algorithm for PIPS position

sensitive detector, realization ; c) Statistical analysis of the

candidate to event measured with the mentioned method

3) Summary

Yu.Tsyganov08 Sept. NEC’2009Varna, Bulgaria

Target wheel mounting

**

**. ..

Experiment

226Ra+48Ca270Hs+4nDGFRS, 2008

The Dubna Gas –Filled recoil Separator(JINR+LLNL since ~2001)

GSI, RIKEN

Radioactive target design ( six sectors), Foil – 1.5 mcm Ti.

DG

FR

S +

Det

ecti

on

mod

ule

DGFRS+ Backgrounds (a few words)• Maim advantage of Gas Field separators – transport efficiency• Everything else : drawbacks.eg. Separation high cyclotron vacuum and working volume of the separator, separation

working area of the separator and TOF module (vacuum or pentane..), is not easy to provide linear measurement of the beam dose (cross section?), high intensity beam stop is near 2-3 m with respect to detection module etc..etc)

(!) especially : there are backgrounds in the beam On phase imitating well α-decays, that is, creating no signal in TOF module

DETECTION in real-time mode a candidate to ER –α chain is suppress radically such a background and provide a minimum loss in the whole efficiency (units of prc -10%)

Main histogram – spectrum with Main histogram – spectrum with suppression both TOF and VETO suppression both TOF and VETO detector.detector.Right hand tail is evident.Right hand tail is evident.Whereas, right-upper corner Whereas, right-upper corner histogram is with real-time detection histogram is with real-time detection of ER-alpha chainsof ER-alpha chains

Real-time algorithm ( in brief. In details – my report at NEC-2007 +Nucl. Inst.&Meth. A513(2003), A558(2006), A 525(2004), A573(2007),

A477(2002), J.Phys. G. 25(1999)937)

last versions: PSD-7 conf. (Liverpool, UK(2005)sept., & 6 th Balkan Phys. Union Conf., Istanbul (2006) sept.)idea: Yu.S. Tsyganov (NEC’97 (Sept., VARNA, Bulgaria) +HPC’ASIA-97, Seoul Hilton, Seoul, rep. Korea (May, 1997)

staticstatic dynamicdynamic

Case of EVR – alpha,// in the case of ER-alpha || alpha-alpha both matrixes are static

If there will follow an event under interest in the beam Off pause in the same strip , it will be pause prolongation up to 10-30 min automatically

Real PIPS detector (12 strip)Real PIPS detector (12 strip) Image in PC Image in PC

Plus one explanation schematics

Flowchart of the process Principle of background suppression

*

* B.N.Gikal: private communication

Statistical significance of the event (main part)

• One of the key questions of a rare event detecting procedure is a probability of the candidate to the real event to be a random

• In principle there are two basic approaches: LDSC (K.-H. Schmidt et al., Z.Phys. A 316 (1984)19 ) and BSC (V.B. Zlokazov , Yad.Fiz. V.66, №9 (2003)1714)

• ..others.. Can be easily represent according to the basis these concepts

LDSC – formalize the concept of a Linked Decay Signal Combination sequence analyzed does fit in this concept or not. ( in brief: a-priori info “Yes”)

// key term – link between signals or between “starter” signal and following signal, depending on the scenario

BSC – formalize the concept of Background Signal Combination and test, whether the signal sequence analyzed does fit the concept or not (a-priori info “No”)

// key term – time interval between “start” and “finish”

LDSC, BSC (mnemonics)

K-H. Schmidt, LDSCK-H. Schmidt, LDSC V.B. Zlokazov, BSCV.B. Zlokazov, BSC

K.-H. Schmidt mnemonics (graphs)

Fixed Fixed OrderOrder

Partially freePartially free Order Order

timetime timetime

EVREVREVREVR

SFSF SFSF

a(i)a(i)

timetime

EVREVR

SFSF

SpontaneousSpontaneousFissionFission

Flexible orderFlexible order((Yu.Tsyganov, JINR comm. P7-2008-189Yu.Tsyganov, JINR comm. P7-2008-189))

Alpha-decaysAlpha-decays}{}{

1,1,1

0

1,

1 0

1,11 dt

dt

dpdt

dt

dpTn

N

Mi

tii

M

i

ti

b

iMi

1

11, 1

ij

tti

ii ji eedt

dp

In the manner, similar to K.-H. Schmidt :

T – effective time T=npixelsT (exp), M signals are attributed to “unknown” nuclides and N-M-2 – to “known”.N- total number, including one SF. NSF-total fission fragmentNumber, λ-appropriate rates of event per coordinate pixel.

N

Miii

M

ii

MNMERSFb ttNn 1,

2,1

1 ~

Or, in simplified form:

Active correlation method (EVR-α break points)

• Graph for this case will be as shown in the figure:

Small dead time ~10Small dead time ~102 μs

LDSC philosophy frame for active correlation method(approach similar to BSC is in my paper Phys. Of Part. & Nucl. Lett. Vol.6 (2009) 59-62 )

• Being considering in the described above process a definite order correlated pair recoil-alpha E1E2 as a starter signal Ê1(E1E2) for forthcoming sequences of “”-decays and following to the philosophy of [6] one can rewrite the equation (1) for

the given case in the form of: • Here the parameter denotes not any single signal rate per pixel, but a rate of

correlations/pauses generating by the detection system during a long term experiment. Therefore, if NSTOP is a total number of pauses measured in an experiment, to a first approximation :

•

})({ˆ1

2 0

1,21

1,2

K

i

t

ib

i

dtdtdpTn

1̂

TN STOP 1̂

})({1

2 0

1,2

1,2

K

i

t

iSTOPb

i

dtdtdpNn

K

ii

KSTOPb tNn

3,2

2 Simplifications (only alpha decays, &λi Δti << 1)

a mean counting rate value for alpha – decay signals measured in beam-OFF pauses by the focal plane detector.

PRS

EVR

t

t 2

dtdt

dNmEVRt

m

m

STOP )(

1

0

More common case of “starter” correlation signal )...(ˆ13211 mEEEEE

Note, that Nstop is a value measured in experiment!!!

Practical examples from SHE experiments…

• “advantage factor” (def) ξ = nb( KHS )/nb( present report),

• That is :

n

ii

n

ii

t

t

3,2

3,1

(see also Yu.Tsyganov JINR P13-2008-92, p.6)

Example #1 , Z=113 from the reaction 273Np+48Ca 282113+3n; [Yu.Oganessian et al. PRC v.76 (2007)011601® ]. t1=0 (EVR), t2=0.0889 s, t3=0.0951 s, t4= 0.568 s, t5= 88.548, t6=1993 s (SF).

ξ=9532.68/523.655 ≈ factor of 20 and nb ≤ 5∙10-14 (except of ~10-12 in the original paper)

Example#2 Z=118 from the reaction 249Cf+48Ca 294118+3n; [ Yu.Oganessian et al. PRC v.74(2006)p.044602].t1 = 0 (EVR), t2=0.000456, t3=0.001467, t4 = 0.012864 SF).

ξ≈ 2

Supplement #1 (math. vs phys., general phylosophy

// in the form of hyposthesis)

Idealization

nb << 1

Real casef (nb / pCONFIG)=ńb

ńb << 1

The simplest way ~ nb/pconf

examples

• Example #1 EVR – α – SF short chains (N=6 , geom. Eff. For α – about 85%, second nuclide branch to SF ~ 50%. Combination Nα=0 (real SHE experiments) ). One event has nb~0.3 .

• Having considering combination probability P(6, 0) – zero non-completed chains from six attempts,• t.i. xnxx

n ppCxnP )1(),( For our case p= 0.5*0.85=0.425, x( number of full event)=0, n=6.

Example #2

Registration of one multi chain event like EVR-α-α-α-SF (see. Yu. Oganessian et al. , Revista Mexicana de Fisica 46 Suplemento 1 (2000)35 ) All three alpha are with y-position and have full energy. Probability of this fact isp ~ (0.67) 3≈0.3. P(1,1) = p1∙(1-p)0=0.3( additionally, one can take into account that efficiency to detect both fragments is not 100%, but around 40% !)

V.B.Zlokazov Yad. Phys. V.66 N9 (2003) 1718. Nm~0.0004 (one pixel) => nb~200 Nm=0.08

So, ńb ~0.08/0.3 ≈0.3 (large enough!) => It’s difficult to say anything definite!!! (event or not event =to be or not to be!)

036.0575.0)1(!6!0

!6)0,6( 6060 ppP ńb=0.3/0.036 >>1 ! and this event should be excluded from the list

SUMMARY (only two conclusions can be drawn here)

1) Modification of LDSC method to estimate statistical significance of the multi-chain event measured with a position sensitive PIPS detector has been performed for the method of “active correlations” (case EVR-alpha )

2) As a reasonable scenario, it is proposed to use some additional knowledge about event property (a priori +a posteriori ..etc) to compare any calculated (LDSC or BSC…) statistic parameter with the real probability of the measured configuration of the candidate

// in the form of hypothesis

Yu.S.TsyganovNEC’2009Sept. 08, Varna

In memory of S.IlievOne of the best electronics

engineer in the field of super heavy elements research