通过脉冲形状分析提高基于BEGe的高纯锗光谱仪的灵敏度资源-CSDN文库

Open

Access

188 浏览量 2020-03-22 09:58:45 上传评论收藏 1.67MB PDF 举报

资源推荐

资源详情

资源评论

Eur. Phys. J. C (2018) 78:392

https://doi.org/10.1140/epjc/s10052-018-5852-7

Regular Article - Experimental Physics

Improving sensitivity of a BEGe-based high-purity germanium

spectrometer through pulse shape analysis

M. Misiaszek

, K. Panas

1,a

, M. Wojcik

, G. Zuzel

,M.Hult

M. Smoluchowski Institute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Kraków, Poland

European Commission, DG JRC, JRC-Geel, Retieseweg 111, 2440 Geel, Belgium

Received: 23 December 2017 / Accepted: 26 April 2018

Abstract We performed Pulse Shape Analysis to sepa-

rate single-scattered gamma energy deposition events from

multiple-scattered photons in a high-sensitivity γ -ray spec-

trometer. The spectrometer is based on a Broad Energy High

Purity Germanium detector and the developed technique uses

multivariate analysis by an application of the Multi-Layer

Perceptron Neural Network. A very good separation of the

single-site- and multi-site events was achieved leading to a

signiﬁcant reduction of the background level of the investi-

gated spectrometer – the double escape peak, rich in single-

site events, was reduced by 95%, while the full energy peaks

lost at most 25% of their counts. The peak to Compton ratio,

calculated for the 2614.5 keV gamma line from

208

Tl, was

improved by 114.3%.

1 Introduction

For germanium semiconductor detectors a single energy

deposition by γ -ray is often described as a single-site event

(SSE). Multi-site events (MSEs), like e.g. multiple Comp-

ton scatterings, have several interaction sites separated by a

distance of about 1 cm. The differences and discrimination

between SSEs and MSEs is of primary interest for exper-

iments like Gerda [1,2] looking for the neutrinoless dou-

ble beta (0νββ) decay with application of the High Purity

Germanium (HPGe) detectors. Events from the hypothetical

0νββ decay would ionize the detector’s active volume by

means of two electrons (with a range of less than 1 mm in

germanium) and therefore belong to the ﬁrst category. The

background due to external γ -rays is typically of multi-site

type, because γ -rays with energies in the range of ∼ 1MeV

deposit their energy mainly via multiple Compton scattering

with a mean free path of a few centimeters.

e-mail: krzysztof.panas@doctoral.uj.edu.pl

For applications in γ -ray spectrometry the situation is

reversed: SSEs should be rejected and MSEs preserved. The

SSEs are of background type, because they are mostly single

Compton scattered events with the scattered photon escap-

ing the crystal, while the full energy peaks (FEPs) regis-

tered by the detector (and used to evaluate the activities of

radionuclides) contain mainly MSEs.

The developed proce-

dure shall therefore make peaks more distinguished by reduc-

ing the ﬂat Compton continuum and make possible to eval-

uate peaks from radioisotopes, which would be otherwise

under spectrometer’s minimal detectable activity (sensitiv-

ity).

Discrimination between SSEs and MSEs for the Broad

Energy Germanium (BEGe) detectors was extensively stud-

iedintheframeofGerda experiment [3–7], also with respect

to applications in ultra-low background γ -ray spectrometry

[8]. The approach that was worked out was to look for a ratio

of the maximal current signal amplitude (A) to the corre-

sponding event energy (E) – the so-called A/E cut. This is

a one-parameter method, where the cut value is determined

according to the calibration data, obtained usually by irradi-

ating the spectrometer with a

228

Th source (due to the emitted

high energy γ -ray from the decay of

208

Tl – a more detailed

explanation can be found in Sect. 3.2). Measurements car-

ried out for various BEGe detectors demonstrated very good

performance of the A/E method, however, its applications to

the coaxial detectors did not provide satisfactory results.

The main goal of our work was to ﬁnd an alternative, efﬁ-

cient and stable Pulse Shape Analysis (PSA) procedure to

distinguish between MSEs and SSEs in BEGe type detectors.

As it will be shown, our method does not need any corrections

like e.g. the ones related to the dependence of the A/E classi-

For typical detectors used nowadays in γ -ray spectroscopy (crystal

volume of several hundreds of cm

), and for energies of some hundred

keV and higher, the full energy peaks contain mostly events, which were

caused by a few Compton scatterings followed by the photoelectric

effect.

123

392 Page 2 of 11 Eur. Phys. J. C (2018) 78:392

Fig. 1 Schematic drawing of the 50% relative efﬁciency BEGe detec-

tor applied in the Ge-5 spectrometer and used in the presented study

ﬁer on energy [5]. To achieve this we applied methods imple-

mented in the Toolkit for Multivariate Analysis (Tmva)[9].

Tmva provides a Root-integrated machine-learning envi-

ronment for the processing and parallel evaluation of multi-

variate classiﬁcation and regression techniques [10]. Tmva

includes classiﬁers like Projective Likelihood (PL), Multi-

Layer Perceptron Neural Network (MLP, see Sect. 4.1 for

more details), Boosted Decision Trees (BDT) and Support

Vector Machine (SVM). Each of the implemented methods

provides training, testing, performance evaluation algorithms

and visualization scripts. The training and testing is per-

formed with the use of user-supplied data sets in the form

of Root trees or text ﬁles.

2 Experimental setup

To study the new PSA technique we collected data using

the BEGe-based γ -ray spectrometer (Ge-5) operated by the

JRC-Geel (formerly Institute for Reference Materials and

Measurements) in the HADES underground laboratory. The

rock overburden of 500 m water equivalent provides attenua-

tion of the muon ﬂux by about four orders of magnitude [11].

The spectrometer is based on a 50% relative efﬁciency p-type

BEGe diode installed in a standard vacuum cryostat produced

by Canberra (model BE5030). A massive low-radioactivity

shield surrounds the detector in order to reduce the environ-

mental background and makes the spectrometer sensitive to

very weak radioactivity. A sketch of the Ge-5 crystal is shown

in Fig. 1.

To train the Tmva-based methods and to evaluate their

performance, apart from the energy information (as obtained

usually from the system based on multi channel analyzers),

the waveforms from the preampliﬁer have to also be regis-

tered. They were acquired with the Struck SIS3302, a 16-bit

100 MHz Flash Analog to Digital Converter (FADC) – the

total length of each waveform was 30 µs. Noise and events

with dubious quality (trigger position much more before/after

pre-trigger, pile-upped events with multiple slopes) were

excluded form further analysis. For pulses, which survived

Fig. 2 Energy resolution of the peaks in the

228

Th spectrum. The out-

lying peak at 2103 keV is a single escape peak from 2615 keV

208

line. Its abnormally high FWMH value is due to the Doppler broadening

[12]

the quality cuts, the ﬁrst step was to perform the energy recon-

struction. The energy value for each pulse was determined

using the trapezoidal ﬁlter described in [13], followed by

a calibration using a linear function. The energy resolution

values for the selected peaks from the

228

Th decay chain

spectrum are plotted in Fig. 2.

3 Pulse shape analysis

The data features that are used to train machine learning

models have a huge inﬂuence on the ﬁnal performance. In

our case of the PSA, employing neural networks procedure

to the

228

Th data, the task of feature selection was limited

to a vector of the sampled waveforms of the preampliﬁer

output voltage. After series of dedicated tests, we found that

considering only samples close to the point of the maximal

current as the input parameters give us substantial discrimi-

nation effect. The shape of the pulse in the range of limited

samples manifests the type of interaction in the detector due

to the differences in speed and possible ﬂuctuations of the

charge collection over time.

In the ﬁrst step, after initial data pre-processing and energy

reconstruction, we were performing pulse shape normaliza-

tion. The sampled amplitudes were divided by the corre-

sponding reconstructed energy values in order to remove

potential energy dependency of the signal. Next, normalized

input variables were extracted from each rising edge and the

pulses (edges) were digitally differentiated and smoothed in

order to ﬁnd the moment of the maximal values of the current

signals. 31 single amplitudes in total were chosen for each

pulse for the PSA: 15 before, 1 at and 15 after the moment

123

剩余10页未读，继续阅读

评论收藏

内容反馈

weixin_38734361

粉丝: 6
资源: 903

通过脉冲形状分析提高基于BEGe的高纯锗光谱仪的灵敏度

灵敏度分析

用于GERDA II期的30 $$ ^ {76} $$ 76 Ge富集宽能Ge探测器的表征

WordPress主题：Bege v1.3.8响应式WooCommerce主题2022年最新版.zip

typescript-file-uploader：TypeScript，带有文件上传器组件的React实现。 演示可在https：youtu.bege9IOvJVKWE获得

Qt 5实现串口调试助手 （源工程文件、0积分下载）

【SystemVerilog】路科验证V2学习笔记（全600页）.pdf

AutoSAR标准协议4.2.2

光伏-储能并网系统仿真.rar

XCP协议的规范文档

GD32替换STM32注意事项.pdf

NPPJSONViewer.zip

蓝牙BLE协议中文版.pdf

CANoe通过CAPL脚本实现自动测试

电路分析基础第二版PDF电子书免费下载

qt样式表一键生成（花狗Fdog）

Tangent免费.rar

CMSIS-DAP使用说明及驱动.rar

VS2015安装证书，JavaScript_ProjectSystem.msi，JavaScript_LanguageService.msi

BaiduOCR.zip

Elsevier期刊word模板.zip

rpa拆包工具（小白适用）

电气类的visio模版元件库

软件需求规格说明书模板(超详细).doc

数字设计和计算机体系结构第二版奇数答案.pdf.zip

EPLAN部件库（正泰）

最新资源

typescript-file-uploader：TypeScript，带有文件上传器组件的React实现。演示可在https：youtu.bege9IOvJVKWE获得

Qt 5实现串口调试助手（源工程文件、0积分下载）